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14-Bit, 105/125 MSPS, 1.8 V ADC Preliminary Technical Data FEATURES 1.8 V analog supply operation 1.8 V to 3.3 V output supply SNR = 71.8 dBc (72.3dBFS) to 70MHz input SFDR = 85 dBc to 70MHz input Low power: 395 mW Differential input with 650 MHz bandwidth On-chip reference and sample-and-hold DNL = 0.5 LSB Flexible analog input: 1 V p-p to 2 V p-p range Offset binary or twos complement data format Clock duty cycle stabilizer AVDD AD9246 FUNCTIONAL BLOCK DIAGRAM DRVDD AD9246 VIN+ VIN- SHA MDAC1 4 REFT REFB CORRECTION LOGIC 15 OUTPUT BUFFERS VREF SENSE DCO D13 (MSB) D0 (LSB) 0.5V REF SELECT CLOCK DUTY CYCLE STABILIZER MODE SELECT SPI SCLK/DFS SPI SDIO/DCS SPI CSB OTR A/D 8-STAGE 1 1/2-BIT PIPELINE 8 A/D 3 APPLICATIONS Ultrasound equipment IF sampling in communications receivers: IS-95, CDMA-One, IMT-2000 Battery-powered instruments Hand-held scopemeters Low cost digital oscilloscopes AGND CLK+ CLK- PWDN DrGND Figure 1. GENERAL DESCRIPTION The AD9246 is a monolithic, single 1.8 V analog supply, 14-bit, 125 MSPS analog-to-digital converter (ADC), featuring a high performance sample-and-hold amplifier (SHA) and voltage reference. The AD9246 uses a multistage differential pipelined architecture with output error correction logic to provide 14-bit accuracy at 125 MSPS data rates and guarantees no missing codes over the full operating temperature range. The wide bandwidth, truly differential SHA allows a variety of user-selectable input ranges and offsets including single-ended applications. It is suitable for multiplexed systems that switch full-scale voltage levels in successive channels and for sampling single-channel inputs at frequencies well beyond the Nyquist rate. Combined with power and cost savings over previously available ADCs, the AD9246 is suitable for applications in communications, imaging, and medical ultrasound. A differential clock input is used to control all internal conversion cycles. A duty cycle stabilizer (DCS) compensates for wide variations in the clock duty cycle while maintaining excellent overall ADC performance. The digital output data is presented in straight binary or twos complement formats. A differential data output clock (DCO) is provided to ensure proper latch timing with receiving logic. Rev. PrH Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. Fabricated on an advanced CMOS process, the AD9246 is available in a 48- lead LFCSP and is specified over the industrial temperature range (-40C to +85C). PRODUCT DESCRIPTIONS 1. The AD9246 operates from a single analog 1.8 V power supply and features a separate digital output driver supply to accommodate 1.6 - 3.3 V logic families. The patented SHA input maintains excellent performance for input frequencies up to 180 MHz and can be configured for single-ended or differential operation. The clock DCS maintains overall ADC performance over a wide range of clock pulse widths. Standard serial port interface supports various product features and functions, such as data formatting (offset binary, 2's complement, or Gray coding), enabling a clock duty cycle stabilizer, power-down, and voltage reference mode. 2. 3. 4. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 (c)2005 Analog Devices, Inc. All rights reserved. AD9246 TABLE OF CONTENTS DC Specifications ............................................................................. 3 AC Specifications.............................................................................. 4 Digital Specifications........................................................................ 5 Switching Specifications .................................................................. 6 Explanation of Test Levels...... Error! Bookmark not defined. Absolute Maximum Ratings............................................................ 6 ESD Caution.................................................................................. 6 Terminology ...................................................................................... 7 Pin Configuration and Function Descriptions............................. 8 Theory of Operation ........................................................................ 9 Preliminary Technical Data Analog Input and Reference Overview ......................................9 Clock Input Considerations...................................................... 10 Power Dissipation and Standby Mode .................................... 11 Digital Outputs ........................................................................... 12 Timing ......................................................................................... 12 Voltage Reference ....................................................................... 13 Operational Mode Selection .. Error! Bookmark not defined. Evaluation Board ..................... Error! Bookmark not defined. Outline Dimensions ....................................................................... 19 Ordering Guide .......................................................................... 19 REVISION HISTORY 6/05--Revision PrG: Preliminary Version 9/05 - Revision PrH: corrected SNR on page 1 Rev. PrH | Page 2 of 19 Preliminary Technical Data DC SPECIFICATIONS AD9246 AVDD = 1.8 V, DRVDD = 3.3 V, sample rate = 125 MSPS, 2 V p-p differential input, 1.0 V internal reference, unless otherwise noted. Table 1. Parameter RESOLUTION ACCURACY No Missing Codes Offset Error Gain Error (External 1.0 V Reference) Gain Error Differential Nonlinearity (DNL)1 Integral Nonlinearity (INL)1 TEMPERATURE DRIFT Offset Error Gain Error Gain Error (External 1.0 V Reference) INTERNAL VOLTAGE REFERENCE Output Voltage Error (1 V Mode) Load Regulation @ 1.0 mA INPUT REFERRED NOISE VREF = 1.0 V ANALOG INPUT Input Span, VREF = 1.0 V Input Capacitance2 REFERENCE INPUT RESISTANCE POWER SUPPLIES Supply Voltage AVDD DRVDD Supply Current IAVDD1 IDRVDD1(3.3V) IDRVDD1 (1.8V PSRR POWER CONSUMPTION DC Input Sine Wave Input3 (DrVDD=1.8V) Sine Wave Input4 (DrVDD=3.3V) Standby Power Powerdown Power5 1 2 3 Temp Full Full Full 25C Full Full 25C Full 25C Full Full Full Full Full 25C Full Full Full AD9246BCPZ-105 Min Typ Max 14 Guaranteed 0.25 0.2 0.3 TBD 0.5 2 Min 14 AD9246BCPZ-125 Typ Max Unit Bits Guaranteed 0.25 0.2 0.3 0.5 TBD 2 TBD TBD TBD TBD TBD TBD 2 8 TBD % FSR % FSR % FSR LSB LSB LSB LSB ppm/C ppm/C ppm/C mV mV LSB rms V p-p pF k TBD TBD TBD TBD TBD TBD 2 8 TBD Full Full Full Full Full Full Full Full Full Full Full 1.7 1.6 1.8 3.3 219 19 10 0.01 395 412 457 40 1.8 1.9 3.6 1.7 1.6 1.8 3.3 219 19 10 0.01 395 412 457 40 1.8 1.9 3.6 V V mA mA mA % FSR mW mW mW mW mW Measured at the maximum clock rate, fIN = 2.4 MHz, full-scale sine wave, with approximately 5 pF loading on each output bit. Input capacitance refers to the effective capacitance between one differential input pin and AGND. Refer to Figure 2 for the equivalent analog input structure. Measured at ac specification conditions with approximately 5 pF loading on each output bit. 4 Measured at ac specification conditions with approximately 5 pF loading on each output bit. 5 Standby power is measured with a dc input, the CLK pin inactive (that is, set to AVDD or AGND). Rev. PrH | Page 3 of 19 AD9246 AC SPECIFICATIONS Preliminary Technical Data AVDD = 1.8 V, DRVDD = 3.3 V, sample rate = 125 MSPS, 2 V p-p differential input, 1.0 V internal reference, AIN = -0.5 dBFS, DCS on, unless otherwise noted. Table 2. Parameter SIGNAL-TO-NOISE-RATIO (SNR) fIN = 2.4 MHz fIN = 70 MHz fIN = 100 MHz fIN = 180 MHz SIGNAL-TO-NOISE-AND DISTORTION (SINAD) fIN = 2.4 MHz fIN = 70 MHz fIN = 100 MHz fIN = 180 MHz EFFECTIVE NUMBER OF BITS (ENOB) fIN = 2.4 MHz fIN = 70 MHz fIN = 100 MHz fIN = 180 MHz WORST SECOND OR THIRD HARMONIC fIN = 2.4 MHz fIN = 70 MHz fIN = 100 MHz fIN = 180 MHz SPURIOUS-FREE DYNAMIC RANGE (SFDR) fIN = 2.4 MHz fIN = 70 MHz fIN = 100 MHz fIN = 180 MHz TWO TONE SFDR fIN = 70 MHz, 71 MHz (-7 dBFS Each Tone) fIN = 70 MHz, 71 MHz (-7 dBFS Each Tone) ANALOG INPUT BANDWIDTH Temp 25C Full 25C Full 25C 25C 25C Full 25C Full 25C 25C 25C 25C 25C 25C 25C Full 25C Full 25C 25C 25C Full 25C Full 25C 25C 25C Full 25C AD9246BCPZ-105 Min Typ Max 72.0 70.8 71.8 70.5 71.5 69.0 AD9246BCPZ-125 Min Typ Max 72.0 70.8 71.8 70.5 71.5 69.0 Unit dB dB dB dB dB dB dB dB dB dB dB dB Bits Bits Bits Bits dBc dBc dBc dBc dBc dBc dBc dBc dBc dBc dBc dBc dBFS dBFS MHz 71.2 70.5 70.7 70.0 70.5 68.0 11.6 11.5 11.4 11.0 88 82 85 82 83 80 88 82 85 82 83 80 71.2 70.5 70.7 70.0 70.5 68.0 11.6 11.5 11.4 11.0 88 82 85 82 83 80 88 82 85 82 83 80 650 650 Rev. PrH | Page 4 of 19 Preliminary Technical Data DIGITAL SPECIFICATIONS AVDD1 = 1.8V V, DRVDD = 3.3 V Unless otherwise noted Table 3. Parameter CMOS LOGIC INPUTS (SPI CSB , SPI SDIO / DFS, SPI SCLK / DCS, CLKIN+, PWDN) High Level Input Voltage Low Level Input Voltage High Level Input Current Low Level Input Current Input Capacitance DIFFERENTIAL CLOCK INPUTS Internal Common-Mode Bias Differential Input (CLKIN+ - CLKIN-) Input Voltage Range Input Common-Mode Range Input Capacitance Input Resistance DIGITAL OUTPUTS DRVDD = 3.3 V High Level Output Voltage (IOH = 50 A) High Level Output Voltage (IOH = 0.5 mA) Low Level Output Voltage (IOH = 1.6 mA) Low Level Output Voltage (IOH = 50 A) DRVDD = 1.8 V High Level Output Voltage (IOH = 50 A) High Level Output Voltage (IOH = 0.5 mA) Low Level Output Voltage (IOH = 1.6 mA) Low Level Output Voltage (IOH = 50 A) Temp Min AD9246BCPZ-105 Typ Max AD9246BCPZ-125 Min Typ Max AD9246 Unit Full Full Full Full Full Full Full Full Full Full Full 2.0 0.8 -10 -10 2 +10 +10 2.0 -10 -10 2 1.2 6 AVDD+1.5 AVDD 10 12 0.2 AVDD-0.3 1.1V 8 10 6 AVDD+1.5 AVDD 12 0.8 +10 +10 V V A A pF V Vp-p V V pF 1.2 0.2 AVDD-0.3 1.1V 8 Full Full Full Full 3.29 3.25 0.2 0.05 3.29 3.25 0.2 0.05 V V V V Full Full Full Full 1.79 1.75 0.2 0.05 1.79 1.75 0.2 0.05 V V V V Rev. PrH | Page 5 of 19 AD9246 Table 4. Parameter CLOCK INPUT PARAMETERS Maximum Conversion Rate Minimum Conversion Rate CLK Period CLK Pulse Width High1 CLK Pulse Width Low1 DATA OUTPUT PARAMETERS Output Propagation Delay (tPD)2 Pipeline Delay (Latency) Aperture Delay (tA) Aperture Uncertainty (Jitter, tJ) Wake-Up Time3 OUT-OF-RANGE RECOVERY TIME 1 2 3 Preliminary Technical Data SWITCHING SPECIFICATIONS AVDD = 3 V, DRVDD = 2.5 V, UNLESS OTHERWISE NOTED. Temp AD9246BCPZ-105 Min Typ Max 105 10 9.5 TBD TBD 3.6 12 TBD 0.1 TBD TBD 8 TBD TBD 3.6 12 TBD 0.1 TBD TBD AD9246BCPZ-125 Min Typ Max 125 10 Unit Full Full Full Full Full Full Full Full Full Full Full MSPS MSPS ns ns ns ns Cycles ns ps rms ms Cycles With duty cycle stabilizer (DCS) enabled. Output propagation delay is measured from CLK 50% transition to DATA 50% transition, with 5 pF load. Wake-up time is dependant on the value of the decoupling capacitors, typical values shown with 0.1 F and 10 F capacitors on REFT and REFB. ABSOLUTE MAXIMUM RATINGS Table 5. Parameter With Respect to Min Max Unit ELECTRICAL AVDD AGND DRVDD DGND AGND DGND AVDD DRVDD D0 to D13 DGND CLK AGND VIN+, VIN- AGND VREF AGND SENSE AGND REFT, REFB AGND AGND PDWN, SPI CSB, SPI SDIO, SPI SCLK ENVIRONMENTAL Storage Temperature Operating Temperature Range Lead Temperature Range (Soldering 10 sec) Junction Temperature V V V V V V V V V V V Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other condition s above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Thermal Resistance JA is specified for the worst-case conditions on a 4-layer board in still air, in accordance with EIA/JESD51-1. Table 6. Thermal Resistance Package Type CP-48 JA 32.5 JC TBD Unit C/W -65 -40 +125 +85 +300 +150 C C C C Airflow increases heat dissipation effectively reducing JA. Also, more metal directly in contact with the package leads from metal traces, through holes, ground, and power planes reduce the JA. It is recommended that the exposed paddle be soldered to the ground plane for the LFCSP package. There is an increased reliability of the solder joints, and maximum thermal capability of the package is achieved with the exposed paddle soldered to the customer board. ESD CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. Rev. PrH | Page 6 of 19 Preliminary Technical Data TERMINOLOGY Analog Bandwidth (Full Power Bandwidth) The analog input frequency at which the spectral power of the fundamental frequency (as determined by the FFT analysis) is reduced by 3 dB. Aperture Delay (tA) The delay between the 50% point of the rising edge of the clock and the instant at which the analog input is sampled. Aperture Uncertainty (Jitter, tJ) The sample-to-sample variation in aperture delay. Integral Nonlinearity (INL) The deviation of each individual code from a line drawn from negative full scale through positive full scale. The point used as negative full scale occurs 1/2 LSB before the first code transition. Positive full scale is defined as a level 11/2 LSB beyond the last code transition. The deviation is measured from the middle of each particular code to the true straight line. Differential Nonlinearity (DNL, No Missing Codes) An ideal ADC exhibits code transitions that are exactly 1 LSB apart. DNL is the deviation from this ideal value. Guaranteed no missing codes to 14-bit resolution indicates that all 16,384 codes must be present over all operating ranges. Offset Error The major carry transition should occur for an analog value 1/2 LSB below VIN+ = VIN-. Offset error is defined as the deviation of the actual transition from that point. Gain Error The first code transition should occur at an analog value 1/2 LSB above negative full scale. The last transition should occur at an analog value 11/2 LSB below the positive full scale. Gain error is the deviation of the actual difference between first and last code transitions and the ideal difference between first and last code transitions. Temperature Drift The temperature drift for offset error and gain error specifies the maximum change from the initial (25C) value to the value at TMIN or TMAX. Power Supply Rejection Ratio The change in full scale from the value with the supply at the minimum limit to the value with the supply at its maximum limit. AD9246 Signal to Noise and Distortion (SINAD)Error! Bookmark not defined. The ratio of the rms input signal amplitude to the rms value of the sum of all other spectral components below the Nyquist frequency, including harmonics but excluding dc. Effective Number of Bits (ENOB) The effective number of bits for a sine wave input at a given input frequency can be calculated directly from its measured SINAD by ENOB = (SINAD - 1.76 ) 6.02 Signal to Noise Ratio (SNR)Error! Bookmark not defined. The ratio of the rms input signal amplitude to the rms value of the sum of all other spectral components below the Nyquist frequency, excluding the first six harmonics and dc. Spurious-Free Dynamic Range (SFDR)Error! Bookmark not defined. The difference in dB between the rms input signal amplitude and the peak spurious signal. The peak spurious component may or may not be a harmonic. Two Tone SFDRError! Bookmark not defined. The ratio of the rms value of either input tone to the rms value of the peak spurious component. The peak spurious component may or may not be an IMD product. Clock Pulse Width and Duty Cycle Pulse width high is the minimum amount of time that the clock pulse should be left in the Logic 1 state to achieve rated performance. Pulse width low is the minimum time the clock pulse should be left in the low state. At a given clock rate, these specifications define an acceptable clock duty cycle. Minimum Conversion Rate The clock rate at which the SNR of the lowest analog signal frequency drops by no more than 3 dB below the guaranteed limit. Maximum Conversion Rate The clock rate at which parametric testing is performed. Output Propagation Delay (tPD) The delay between the clock rising edge and the time when all bits are within valid logic levels. Out-of-Range Recovery Time The time it takes for the ADC to reacquire the analog input after a transition from 10% above positive full scale to 10% above negative full scale, or from 10% below negative full scale to 10% below positive full scale Rev. PrH | Page 7 of 19 AD9246 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS 48 47 46 45 44 43 42 41 40 39 38 37 DRVDD DRGND D1 D0 (LSB) DCO OE AVDD AGND AVDD CLKIN- CLKIN+ AGND Preliminary Technical Data D2 D3 1 2 PIN 1 INDICATOR D4 3 D5 4 D6 5 D7 6 DRGND 7 DRVDD 8 D8 9 D9 10 D10 11 D11 12 AD9246 TOP VIEW (Not to Scale) Pin 0 (Exposed Paddle):AGND 36 35 34 33 32 31 30 29 28 27 26 25 PWDN RBIAS CML AVDD AGND VIN- VIN+ AGND REFT REFB VREF SENSE D12 D13 (MSB) OR DRGND DRVDD SPI SDIO/DCS SPI SCLK/DFS SPI CSB AGND AVDD AGND AVDD 13 14 15 16 17 18 19 20 21 22 23 24 Figure 2. 48-Lead LFCSP Note that the pin configuration is subject to change. Contact applications engineering for more information. Table 7. Pin Function Description--48-Lead LFCSP Pin No. 1 to 6, 9 to 14, 45, 46 7, 16, 47 8, 17, 48 15 18 19 20 0, 21, 23, 29, 32, 37, 41 22, 24, 33, 40, 42 25 26 27 28 30 31 34 35 36 38 39 43 44 Mnemonic D0 (LSB) to D13 (MSB) DRGND DRVDD OR SPI SDIO/DCS SPI SCLK/DFS SPI CSB AGND AVDD SENSE VREF REFB REFT VIN+ VIN- CML RBIAS PDWN CLKIN+ CLKIN- OE DCO Description Data Output Bits. Digital Output Ground. Digital Output Driver Supply (1.8 V to 3.3 V). Out-of-Range Indicator. Serial Port Interface Data Input/Output in Serial Port Mode; Duty Cycle Stabilizer Select Pin in External Pin Mode. Serial Port Interface Clock in Serial Port Mode; Data Format Select Pin in External Pin Mode. Serial Port Interface Chip Select (Active Low). Analog Ground. (Pin 0 is the exposed thermal pad on bottom of package.) Analog Power Supply (Nominally 1.8 V). Reference Mode Selection (See Table 9 ). Voltage Reference Input/Output. Differential Reference (-). Differential Reference (+). Analog Input Pin (+). Analog Input Pin (-). Common-Mode Level Bias Output for Analog Inputs. External Bias Resister Connection. A TBD k resister should be connected between this pin and analog ground (GND). Power-Down Function Select. Clock Input--True. Clock Input--Complement. Output Enable (Active Low). Data Clock Output. Rev. PrH | Page 8 of 19 05491-002 Preliminary Technical Data THEORY OF OPERATION The AD9246 architecture consists of a front-end sample and hold amplifier (SHA) followed by a pipelined switched capacitor ADC. The quantized outputs from each stage are combined into a final 14-bit result in the digital correction logic. The pipelined architecture permits the first stage to operate on a new input sample, while the remaining stages operate on preceding samples. Sampling occurs on the rising edge of the clock. Each stage of the pipeline, excluding the last, consists of a low resolution flash ADC connected to a switched capacitor DAC and interstage residue amplifier (MDAC). The residue amplifier magnifies the difference between the reconstructed DAC output and the flash input for the next stage in the pipeline. One bit of redundancy is used in each stage to facilitate digital correction of flash errors. The last stage simply consists of a flash ADC. The input stage contains a differential SHA that can be ac- or dc-coupled in differential or single-ended modes. The outputstaging block aligns the data, carries out the error correction, and passes the data to the output buffers. The output buffers are powered from a separate supply, allowing adjustment of the output voltage swing. During power-down, the output buffers go into a high impedance state. AD9246 Figure 3.Switched-Capacitor SHA Input For best dynamic performance, the source impedances driving VIN+ and VIN- should be matched such that common-mode settling errors are symmetrical. These errors are reduced by the common-mode rejection of the ADC. An internal differential reference buffer creates positive and negative reference voltages, REFT and REFB, that define the span of the ADC core. The output common mode of the reference buffer is set to VCMREF (~1.6V), and the REFT and REFB voltages and span are defined as: REFT = VCMREF+1/2 VREF) REFB = VCMREF-1/2 VREF Span = 2 x (REFT - REFB) = 2 x VREF It can be seen from the equations above that the REFT and REFB voltages are symmetrical about the VCMREF voltage and, by definition, the input span is twice the value of the VREF voltage. ANALOG INPUT AND REFERENCE OVERVIEW The analog input to the AD9246 is a differential switched capacitor SHA that has been designed for optimum performance while processing a differential input signal. An on-board common-mode voltage reference is included in the design and is available from the CML pin. Optimum performance is achieved when the common-mode voltage of the analog input is set by the CML pin voltage (~0.55 x AVDD). In Figure 3, the clock signal alternatively switches the SHA between sample mode and hold mode. When the SHA is switched into sample mode, the signal source must be capable of charging the sample capacitors and settling within one-half of a clock cycle. A small resistor in series with each input can help reduce the peak transient current required from the output stage of the driving source. Also, a small shunt capacitor can be placed across the inputs to provide dynamic charging currents. This passive network creates a low-pass filter at the ADC's input; therefore, the precise values are dependant upon the application. In IF undersampling applications, any shunt capacitors should be reduced or removed. In combination with the driving source impedance, they would limit the input bandwidth. Differential Input Configurations Optimum performance is achieved while driving the AD9246 in a differential input configuration. For baseband applications, the AD8138 differential driver provides excellent performance and a flexible interface to the ADC. The output common-mode voltage of the AD8138 is easily set to AVDD/2, and the driver can be configured in a Sallen-Key filter topology to provide band limiting of the input signal. 1V p-p 49.9 499 499 33 AVDD VIN+ AD8138 0.1F 523 499 20pF 33 AD9246 VIN - CML 05491-004 Figure 4. Differential Input Configuration Using the AD8138 Rev. PrH | Page 9 of 19 AD9246 At input frequencies in the second Nyquist zone and above, the performance of most amplifiers is not adequate to achieve the true performance of the AD9246. This is especially true in IF undersampling applications where frequencies in the 70 MHz to 100 MHz range are being sampled. For these applications, differential transformer coupling is the recommended input configuration. The value of the shunt capacitor is dependent on the input frequency and source impedance and should be reduced or removed. The CML voltage is connected to the center tap of the transformer's secondary winding to bias the analog input. An example is shown in Figure 5. VIN Preliminary Technical Data diodes across the transformer secondary limit clock excursions into the AD9246 to approximately 0.8 V p-p differential. This helps prevent the large voltage swings of the clock from feeding through to other portions of the AD9246 while preserving the fast rise and fall times of the signal, which are critical to a low jitter performance. CLK+ Clock Source CLK- AD9246 Figure X. Transformer Coupled Differential Clock 33 49.9 10pF 33 VIN+ 2V p-p AD9246 VIN- If a low jitter clock is available, another option is to ac-couple a differential PECL signal to the sample clock input pins as shown in Figure X. The AD9512 (or same family) from offers excellent jitter performance. 150 CML 0.1F CLK+ 05491-005 Figure 5. Differential Transformer-Coupled Configuration PECL AD9512 0.1uF AD9246 CLK- The signal characteristics must be considered when selecting a transformer. Most RF transformers saturate at frequencies below a few MHz, and excessive signal power can also cause core saturation, which leads to distortion. 0.1uF 150 CLOCK INPUT CONSIDERATIONS For optimum performance, the AD9246 the sample clock inputs (CLK+ and CLK-) should be clocked with a differential signal. This signal is typically ac ac-coupled into the CLK+ and CLKpins via a transformer or capacitors. These pins are biased internally and require no additional bias (See Figure X). AVDD Figure X. Differential PECL Sample Clock In some applications it may acceptable to drive the sample clock inputs with a single ended CMOS signal. In such applications, CLK+ should be directly driven from a CMOS gate, while the CLK- pin should be bypassed to ground with a 0.1uF capacitor (see figure X). CLK+ may be directly driven from a CMOS gate. While the CLK+ input circuit supply is AVDD (1.8V), this input is designed to withstand input voltages up to 3.6V, making the selection of the drive logic voltage very flexible. 1.2V CLK+ 2pF CLK2pF CLK0.1uF CMOS CLK+ AD9246 Figure .Equivalent Clock Input Circuit Figure X shows one preferred method for clocking the AD9246. The clock source (low jitter) is converted from single-ended to differential using an RF transformer. The back-to-back Schottky Rev. PrH | Page 10 of 19 Figure X. Differential PECL Sample Clock Preliminary Technical Data Clock Input Considerations Typical high speed ADCs use both clock edges to generate a variety of internal timing signals, and as a result may be sensitive to clock duty cycle. Commonly, a 5% tolerance is required on the clock duty cycle to maintain dynamic performance characteristics. The AD9246 contains a DCS (duty cycle stabilizer) that retimes the nonsampling edge, providing an internal clock signal with a nominal 50% duty cycle. This allows a wide range of clock input duty cycles without affecting the performance of the AD9246. Noise and distortion performance are nearly flat for a wide range duty cycles with the DCS on. The DCS The duty cycle stabilizer uses a delay-locked loop (DLL) to create the nonsampling edge. As a result, any changes to the sampling frequency require approximately TBD clock cycles to allow the DLL to acquire and lock to the new rate. AD9246 AD9246. Power supplies for clock drivers should be separated from the ADC output driver supplies to avoid modulating the clock signal with digital noise. Low jitter, crystal-controlled oscillators make the best clock sources. If the clock is generated from another type of source (by gating, dividing, or other methods), it should be retimed by the original clock at the last step. POWER DISSIPATION AND STANDBY MODE As shown in Figure 7, the power dissipated by the AD9246 is proportional to its sample rate. The digital power dissipation is determined primarily by the strength of the digital drivers and the load on each output bit. The maximum DRVDD current (IDRVDD) can be calculated as I DRVDD = VDRVDD x C LOAD x f CLK x N Jitter Considerations High speed, high resolution ADCs are sensitive to the quality of the clock input. The degradation in SNR at a given input frequency (fINPUT) due only to aperture jitter (tJ) can be calculated by SNR = 20 log f INPUT x t J 2 where N is the number of output bits, 14 in the case of the AD9246. This maximum current occurs when every output bit switches on every clock cycle, that is, a full-scale square wave at the Nyquist frequency, fCLK/2. In practice, the DRVDD current is established by the average number of output bits switching, which is determined by the sample rate and the characteristics of the analog input signal. Reducing the capacitive load presented to the output drivers can minimize digital power consumption. The data in Figure 7 was taken with the same operating conditions as the Typical Performance Characteristics and a 5 pF load on each output driver. By asserting the PDWN pin high, the AD9246 is placed in standby mode. In this state, the ADC typically dissipates 1 mW if the CLK and analog inputs are static. During standby, the output drivers are placed in a high impedance state. Reasserting the PDWN pin low returns the AD9246 into its normal operational mode. In the equation, the rms aperture jitter represents the root-mean square of all jitter sources, which include the clock input, analog input signal, and ADC aperture jitter specification. IF undersampling applications are particularly sensitive to jitter, see Figure 6. 75 70 65 0.5ps SNR (dBc) 60 55 50 45 40 0.2ps 425 ANALOG CURRENT 140 120 400 1.0ps Total Power (mW) TOTAL POWER 375 100 Current (mA) 80 60 40 1.5ps 2.0ps 2.5ps 3.0ps 350 325 20 1 10 100 INPUT FREQUENCY (MHz) 1000 300 10 20 30 DIGITAL CURRENT 40 50 60 70 SAMPLE RATE (MSPS) 80 90 0 100 Figure 6. SNR vs. Input Frequency and Jitter The clock input should be treated as an analog signal in cases where aperture jitter may affect the dynamic range of the Rev. PrH | Page 11 of 19 Figure 7. Power and Current vs. Sample Rate @ 2.5 MHz AD9246 Low power dissipation in standby mode is achieved by shutting down the reference, reference buffer, and biasing networks. The decoupling capacitors on REFT and REFB are discharged when entering standby mode and then must be recharged when returning to normal operation. As a result, the wake-up time is related to the time spent in standby mode and shorter standby cycles result in proportionally shorter wake-up times. With the recommended 0.1 F and 10 F decoupling capacitors on REFT and REFB, it takes approximately 1 sec to fully discharge the reference buffer decoupling capacitors and 3 ms to restore full operation. Preliminary Technical Data that is updated along with the data output corresponding to the particular sampled input voltage. Thus, OTR has the same pipeline latency as the digital data. OTR is low when the analog input voltage is within the analog input range and high when the analog input voltage exceeds the input range as shown in Figure 8. OTR will remain high until the analog input returns to within the input range and another conversion is completed. By logically AND-ing OTR with the MSB and its complement, overrange high or underrange low conditions can be detected. DIGITAL OUTPUTS The AD9246 output drivers can be configured to interface with 1.8 V to 3.3 V logic families by matching DRVDD to the digital supply of the interfaced logic. The output drivers are sized to provide sufficient output current to drive a wide variety of logic families. However, large drive currents tend to cause current glitches on the supplies that may affect converter performance. Applications requiring the ADC to drive large capacitive loads or large fan-outs may require external buffers or latches. As detailed in Interfacing to ADC SPI Error! Reference source not found., the data format can be selected for either offset binary or twos complement, or Gray code (SPI access only). Figure 8. OTR Relation to Input Voltage and Output Data TIMING The AD9246 provides latched data outputs with a pipeline delay of twelve clock cycles. Data outputs are available one propagation delay (tPD) after the rising edge of the clock signal. Out-of-Range (OTR) An out-of-range condition exists when the analog input voltage is beyond the input range of the ADC. OTR is a digital output Table 8. Table III. Output Data Format Input (V) VIN+ - VIN- VIN+ - VIN- VIN+ - VIN- VIN+ - VIN- VIN+ - VIN- Condition (V) < -VREF - 0.5 LSB = -VREF =0 = +VREF - 1.0 LSB > +VREF - 0.5 LSB Binary Output Mode 00 0000 0000 0000 00 0000 0000 0000 10 0000 0000 0000 11 1111 1111 1111 11 1111 1111 1111 Twos Complement Mode 10 0000 0000 0000 10 0000 0000 0000 00 0000 0000 0000 01 1111 1111 1111 01 1111 1111 1111 OTR 1 0 0 0 1 Table 9. Reference Configuration Summary Selected Mode External Reference Internal Fixed Reference Programmable Reference Internal Fixed Reference SENSE Voltage AVDD VREF 0.2 V to VREF AGND to 0.2 V Internal Switch Position N/A SENSE SENSE Internal Divider Resulting VREF (V) N/A 0.5 R 2 (See Figure 10) 0 .5 x 1 + R1 Resulting Differential Span (V p-p) 2 x External Reference 1.0 2 x VREF 2.0 1.0 Rev. PrH | Page 12 of 19 Preliminary Technical Data The length of the output data lines and loads placed on them should be minimized to reduce transients within the AD9246. These transients can degrade the converter's dynamic performance. The AD9246 also provides data clock output (DCO) intended for capturing the data in an external register. The data outputs are valid on the rising edge of DCO. The lowest typical conversion rate of the AD9246 is 10 MSPS. At clock rates below 1 MSPS, dynamic performance can degrade. AD9246 ence by the other converters must be considered. Figure 11 depicts how the internal reference voltage is affected by loading. VIN+ VIN- REFT ADC CORE REFB VREF 1.0 uF 0.1 uF 0.1 uF Digital Output Enable Function (OEB) The AD9246 has three-state ability. If the OEB pin is low, the output data drivers are enabled. If the OEB pin is high, the output data drivers are placed in a high impedance state. It is not intended for rapid access to the data bus. Note that OEB is referenced to the digital supplies (DRVDD) and should not exceed that supply voltage. SELECT LOGIC SENSE 0.5V AD9246 Figure 9. Internal Reference Configuration VOLTAGE REFERENCE A stable and accurate 0.5 V voltage reference is built into the AD9246. The input range can be adjusted by varying the reference voltage applied to the AD9246, using either the internal reference or an externally applied reference voltage. The input span of the ADC tracks reference voltage changes linearly. The various reference modes are summarized in in the next few sections. VIN+ VIN- REFT ADC CORE 0.1 uF REFB Internal Reference Connection A comparator within the AD9246 detects the potential at the SENSE pin and configures the reference into four possible states, which are summarized in Table X. If SENSE is grounded, the reference amplifier switch is connected to the internal resistor divider (see Figure 9), setting VREF to 1 V. Connecting the SENSE pin to VREF switches the reference amplifier output to the SENSE pin, completing the loop and providing a 0.5 V reference output. If a resistor divider is connected as shown in Figure 10, the switch again sets to the SENSE pin. This puts the reference amplifier in a noninverting mode with the VREF output defined as R2 VREF = 0.5 x 1+ R1 1.0 uF 0.1 uF VREF SELECT LOGIC R2 SENSE R1 0.5V AD9246 Figure 10. Programmable Reference Configuration External Reference Operation The use of an external reference may be necessary to enhance the gain accuracy of the ADC or improve thermal drift characteristics. When multiple ADCs track one another, a single reference (internal or external) may be necessary to reduce gain matching errors to an acceptable level. Figure 12 shows the typical drift characteristics of the internal reference in both 1 V and 0.5 V modes. When the SENSE pin is tied to AVDD, the internal reference is disabled, allowing the use of an external reference. An internal reference buffer loads the external reference with an equivalent TBD k load. The internal buffer still generates the positive and negative full-scale references, REFT and REFB, for the ADC core. The input span is always twice the value of the reference The VREF pin should be externally decoupled to ground with a low ESR 1.0uF capacitor in parallel with a 0.1uF cap. In all reference configurations, REFT and REFB drive the A/D converter core and establish its input span. AN external 0.1uF capacitor should be placed across REFT / REFB to stabilize this reference. The input range of the ADC always equals twice the voltage at the reference pin for either an internal or an external reference. If the internal reference of the AD9246 is used to drive multiple converters to improve gain matching, the loading of the refer- Rev. PrH | Page 13 of 19 AD9246 voltage; therefore, the external reference must be limited to a maximum of 1 V. 0.05 Preliminary Technical Data There are three pins that define the serial port interface or SPI to this particular ADC. They are the SPI SCLK / DFS, SPI SDIO / DCS, and CSB pins. The SCLK/DFS (serial clock) is used to synchronize the read and write data presented the ADC.. The SDIO / DCS (serial data input/output) is a dual purpose pin that allows data to be sent and read from the internal ADC memory map registers. The CSB or chip select bar is an active low control that enables or disables the read and write cycles. See Table X. Table X. Serial Port Pins 1V ERROR (%) 0 -0.05 Error (%) 0.5V ERROR (%) -0.10 -0.15 Pin SCLK SDIO -0.20 -0.25 0 0.5 1.0 1.5 LOAD (mA) 2.0 2.5 3.0 CSB Function SCLK (Serial Clock) is the serial shift clock in. SCLK is used to synchronize serial interface reads and writes. SDIO (Serial Data Input/Output) is a dual purpose pin. The typical role for this pin is an input and output depending on the instruction being sent and the relative position in the timing frame. CSB (Chip Select Bar) is active low controls that gates the read and write cycles. Figure 11. VREF Accuracy vs. Load 1.0 0.9 0.8 0.7 VREF ERROR(%) 0.6 0.5 0.4 0.3 0.2 0.1 0 -40 -30 -20 -10 0 VREF = 0.5V 10 20 30 40 50 60 70 80 The falling edge of the CSB in conjunction with the rising edge of the SCLK determines the start of the framing. An example of the serial timing and its definitions can be found in Figure X and Table X. Table X. SPI Timing Diagram specifications Spec Name tDS tDH tCLK VREF = 1V Meaning Setup time between data and rising edge of SCLK Hold time between data and rising edge of SCLK Period of the clock Setup time between CSB and SCLK Hold time between CSB and SCLK Minimum period that SCLK should be in a logic high state Minimum period that SCLK should be in a logic low state tS tH tHI tLO Figure 12. Typical VREF Drift RBIAS The AD9246 requires the user to place a 10K resistor between the RBIAS pin and ground. This resister should have a 1% tolerance, and is used to set the master current reference of the ADC core. AD9246 CONFIGURATION USING THE SPI The AD9246 serial port interface allows the user to configure the converter for specific functions or operations through a structured register space inside the ADC. This gives the user added flexibility to customize device opertation depending on the application. Addresses are accessed (programmed or read back) serially in one-byte words. Each byte may be further divided down into fields which are documented in the Memory Map Section below. Rev. PrH | Page 14 of 19 During an instruction phase a 16bit instruction is transmitted. Data then follows the instruction phase and is determined by the W0 and W1 bits which is 1 or more bytes of data. All data is composed of 8bit words. The first bit of each individual byte of serial data indicates whether this is a read or write command. This allows the serial data input/output (SDIO) pin to change direction from an input to an output. Data may be sent in MSB or in LSB first mode. MSB first is default on power up and may be changed by changing the configuration register. For more information about this feature and others see SPI Doc at www.analog.com. Preliminary Technical Data HARDWARE INTERFACE The pins described in Table X comprise the physical interface between the user's programming device and the serial port of the AD9246. All serial pins are inputs, which is an open-drain output and should be tied to an external pull-up or pull-down resistor (suggested value 10 k). This interface is flexible enough to be controlled by either PROMS or PIC mirocontrollers as well. This provides the user to use an alternate method to program the ADC other than a SPI controller. If the user chooses to not use the SPI interface, some pins serve a dual function and are associated with a specific function when strapped externally to AVDD or ground during device power on. The section below describes the strappable functions supported on the AD9246. AD9246 AD9246 configuration register map (Address 0x00 to Address 0x02), device index and transfer register map (Address 0x04 to Address 0x05, and Address 0xFF), global ADC function register map (Address 0x08 to Address 0x09), and flexible ADC functions register map (Address 0x0B to Address 0x25). The flexible ADC functions register map is product specific. Starting from the right hand column, the memory map register in Table Xdocuments the default hex value for each hex address shown. The column with the heading Byte 7 (MSB) is the start of the default hex value giving. For example, hex address 0x14, flex_output_phase has a hex default value of 00h. This means Bit 3 = 0, Bit 2 = 0, Bit 1 = 1, and Bit 0 = 1 or 0011 in binary. This setting is the default output clock or DCO phase adjust option. The default value adjusts the DCO phase 90deg relative to the Nominal DCO edge and 180deg relative to the data edge. For more information on this function and others consult the SPI Doc at www.analog.com. CONFIGURATION WITHOUT THE SPI In applications that do not interface to the SPI control registers, the SPI SDIO / DCS and SPI SCLK / DFS pins can alternately serve as stand alone CMOS compatible control pins When the device is powered up, it is assumed that the user intends to use the pins as static control lines for the duty cycle stabilizer. In this mode the SPI CSB chip select should be connected to ground, which will disable the serial port interface. Table 10. Mode Selection Pin SPI SDIO / DCS SPI SCLK / DFS External Voltage AVDD AGND AVDD AGND Configuration Duty Cycle Stabilizer Enabled Duty Cycle Stabilizer Disabled 2's Complement Enabled Offset Binary Enabled OPEN LOCATIONS All locations marked as "open" are currently not supported for this particular device. When required, these locations should be written with 0s. Writing to these locations is required only when part of an address location is open (for example, Address 0x14). If the whole address location is open (for example, Address 0x13), then this address location does not need to be written. DEFAULT VALUES Coming out of reset, some of the address locations (but not all) are loaded with default values. The default values for the registers are given in the Table X. LOGIC LEVELS An explanation of various registers, "bit is set" is synonymous with "bit is set to Logic 1" or "writing Logic 1 for the bit." Similarly "clear a bit" is synonymous with "bit is set to Logic 0" or "writing Logic 0 for the bit." READING THE MEMORY MAP TABLE Each row in the memory map table has eight address locations. The memory map is roughly divided into four sections: chip Figure X. Serial Port Interface Timing Diagram Rev. PrH | Page 15 of 19 AD9246 Table X. AD9246 Device Configuration Register Memory Map Addr (Hex) Preliminary Technical Data Parameter Name Bit 7 (MSB) Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 (LSB) Def. Value (Hex) Default Notes and comments Chip Configuration Registers 00 chip_port_config OPEN LSB First Soft Reset OPEN OPEN Soft Reset LSB First OPEN 18h The nibbles should be mirrored by the user so that LSB or MSB first mode will register correctly regardless of shift mode. Unique chip ID 01 chip_id 8-bit Chip ID bits 7:0 AD9246 - 00h Read only OPEN Read only 02 chip_grade OPEN Child ID 125MS -00h 105MS - 08h Device Index and Transfer Registers Read only. Child ID used to differentiate speed grades. FF device_update OPEN SW Transfer 00h Synchronously transfers data from the master shift register to the slave Global ADC Functions 08 global_modes OPEN PWDN Function 0 - Full Power Down 1Standb y OPEN Internal Power Down Mode 0 - normal (power up) 1 - full power down 2 - standby 3 - normal (power up) Note: External PWDN pin overrides internal power down mode setting OPEN Duty Cycle Stabilizer 0disabled 1Enabled 01h 00h Determines various generic modes of chip operation. 09 global_clock Flexible ADC Functions Rev. PrH | Page 16 of 19 Preliminary Technical Data Addr (Hex) AD9246 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 (LSB) Def. Value (Hex) Default Notes and comments Parameter Name Bit 7 (MSB) Bit 6 10 Digital Offset Adjust 10h<5:0> Offset in LSBs 011111 +31 011110 +30 011101 +29 . . . 000010 000001 000000 111111 111110 111101 . . 100001 100000 -31 -32 Global Output Test Options 0 - off 1 - midscale short 2 - +FS short 3 - -FS short 4 - checker board output 5 - PN 23 sequence 6 - PN 9 7 - one/zero word toggle OPEN Output Data Invert 1=inver t Data Format Select 0 - offset binary 1 - 2's complement 3 - Gray 4 - offset binary +2 +1 0 1 -2 -3 00h 0D flex_test_io PN23 0= normal 1=reset PN9 0= normal 1=reset Output Disable 1- Ouputs disabled 0 - Ouputs Enabled Note External OE/ pin over mist be HIGH 00h When set, the test data is placed on the output pins in place of normal data 14 flex_output_mode OPEN 00h Configures the outputs and the format of the data. 16 flex_output_phase Output Clock Polarity 1=inver ted 0=Nor mal OPEN 00h 17 flex_output_drive RESERVED 0 Output Driver Configuration 1000 for DrVDD =3.3V 1000 for DrVDD = V 1110 for DrVDD=1.8V Reserved 000 70h Rev. PrH | Page 17 of 19 AD9246 Addr (Hex) Preliminary Technical Data Bit 7 (MSB) Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 (LSB) Def. Value (Hex) Default Notes and comments Parameter Name 18 flex_vref Internal Reference Resistor Divider 00 - VREF=1.25V 01 - VREF=1.5V 10 - VREF=1.75V 11 - VREF=2.00V Open 0Ch Power and Ground Recommendations When connecting power to the AD9246, it is recommended that two separate supplies be used: one for analog (AVDD, 1.8V nominal) and one for digital (DRVDD, 1.8-3.3V nominal). If only a single 1.8V supply is available, then it should be routed to the AVDD first and tapped off and isolated with a ferrite bead or filter choke with decoupling capacitors proceeding its connection to DrVDD. The user can employ several different decoupling capacitors to cover both high and low frequencies. These should be located close to the point of entry at the PC board level and close to the parts with minimal trace length. A single PC board ground plane should be sufficient when using the AD9246. With proper decoupling and smart partitioning of the PC board's analog, digital, and clock sections, optimum performance is easily achieved. resistive thermal path for heat dissipation to flow through the bottom of the PCB. These vias should be solder filled or plugged. To maximize the coverage and adhesion between the ADC and PCB, overlay a silkscreen to partition the continuous plane on the PCB into several uniform sections. This provides several tie points between the two during the reflow process. Using one continuous plane with no partitions only guarantees one tie point between the ADC and PCB. See Figure for a PCB layout example. For detailed information on packaging and the PCB layout of chip scale packages, go to www.analog.com. SILKSCREEN PARTITION PIN 1 INDICATOR Exposed Paddle Thermal Heat Slug Recommendations It is mandatory that the exposed paddle on the underside of the ADC is connected to analog ground (AGND) to achieve the best electrical and thermal performance of the AD9228. A continuous exposed (no solder mask) copper plane on the PCB should mate to the AD9246 exposed paddle, Pin 0. The copper plane should have several vias to achieve the lowest possible 04418-052 Figure 6. Typical PCB Layout Rev. PrH | Page 18 of 19 Preliminary Technical Data OUTLINE DIMENSIONS 7.00 BSC SQ 0.60 MAX 0.60 MAX 37 36 AD9246 0.30 0.23 0.18 48 1 PIN 1 INDICATOR PIN 1 INDICATOR TOP VIEW 6.75 BSC SQ EXPOSED PAD (BOTTOM VIEW) 5.25 5.10 SQ 4.95 0.50 0.40 0.30 25 24 12 13 0.25 MIN 5.50 REF 1.00 0.85 0.80 12 MAX 0.80 MAX 0.65 TYP 0.05 MAX 0.02 NOM 0.50 BSC SEATING PLANE 0.20 REF COPLANARITY 0.08 COMPLIANT TO JEDEC STANDARDS MO-220-VKKD-2 Figure 13. 48-Lead Frame Chip Scale Package [LFCSP_VQ] 7 mm x 7 mm Body, Very Thin Quad (CP-48-1) Dimensions shown in millimeters ORDERING GUIDE Model AD9246BCPZ-1251 AD9246BCPZRL7-1251 AD9246BCPZ-1051 AD9246BCPZRL7-1051 AD9246BCPZ-125EB1 1 Temperature Package -40C to +85C -40C to +85C -40C to +85C -40C to +85C Package Description 48-Lead Lead Frame Chip Scale Package 48-Lead Lead Frame Chip Scale Package 48-Lead Lead Frame Chip Scale Package 48-Lead Lead Frame Chip Scale Package Evaluation Board Package Outline CP-48-1 CP-48-1 CP-48-1 CP-48-1 It is recommended that the exposed paddle be soldered to the ground plane for the LFCSP package. There is an increased reliability of the solder joints, and the maximum thermal capability of the package is achieved with the exposed paddle soldered to the customer board. (c)2005 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. (PrG) Rev. PrG | Page 19 of 19 |
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