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a
FEATURES +5 V Power Supply 50 MHz Speed On-Chip SINE Look-Up Table On-Chip 10-Bit DAC Parallel Loading Power-Down Option 72 dB SFDR 250 mW Power Consumption 48-Pin TQFP APPLICATIONS DDS Tuning Digital Demodulation GENERAL DESCRIPTION
CMOS Complete DDS AD9830
This DDS device is a numerically controlled oscillator employing a phase accumulator, a sine look-up table and a 10-bit D/A converter integrated on a single CMOS chip. Modulation capabilities are provided for phase modulation and frequency modulation. Clock rates up to 50 MHz are supported. Frequency accuracy can be controlled to one part in 4 billion. Modulation is effected by loading registers through the parallel microprocessor interface. A power-down pin allows external control of a power-down mode. The part is available in a 48-pin TQFP package.
FUNCTIONAL BLOCK DIAGRAM
DVDD DGND AVDD AGND REFOUT FS ADJUST REFIN
MCLK FSELECT
ON-BOARD REFERENCE
FULL SCALE CONTROL
COMP
FREQ0 REG MUX FREQ1 REG
PHASE ACCUMULATOR (32-BIT)
12
SIN ROM
IOUT 10-BIT DAC IOUT
PHASE0 REG PHASE1 REG PHASE2 REG PHASE3 REG MUX
AD9830
SLEEP PARALLEL REGISTER TRANSFER CONTROL RESET MPU INTERFACE
D0
D15
WR
A0
A1
A2
PSEL0
PSEL1
REV. A
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 which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. (c) Analog Devices, Inc., 1996 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703
(V AD9830-SPECIFICATIONS1 R
Parameter SIGNAL DAC SPECIFICATIONS Resolution Update Rate (fMAX) IOUT Full Scale Output Compliance DC Accuracy Integral Nonlinearity Differential Nonlinearity DDS SPECIFICATIONS2 Dynamic Specifications Signal-to-Noise Ratio Total Harmonic Distortion Spurious Free Dynamic Range (SFDR)3 Narrow Band ( 50 kHz) ( 200 kHz) Wide Band ( 2 MHz) Clock Feedthrough Wake Up Time Power-Down Option VOLTAGE REFERENCE Internal Reference @ +25C TMIN to TMAX REFIN Input Impedance Reference TC REFOUT Impedance LOGIC INPUTS VINH, Input High Voltage VINL, Input Low Voltage IINH, Input Current CIN, Input Capacitance POWER SUPPLIES AVDD DVDD IAA IDD IAA + IDD4 Low Power Sleep Mode5
DD
SET
= +5 V 5%; AGND = DGND = 0 V; TA = TMIN to TMAX; REFIN = REFOUT; = 1 k ; RLOAD = 51 for IOUT and IOUT unless otherwise noted)
Units Bits MSPS max mA max V max LSB typ LSB typ Test Conditions/Comments
AD9830A 10 50 20 1 1 0.5
50 -53
dB min dBc max
fMCLK = fMAX , fOUT = 2 MHz fMCLK = fMAX , fOUT = 2 MHz fMCLK = 6.25 MHz, fOUT = 2.11 MHz
-72 -68 -50 -55 1 Yes 1.21 1.21 7% 10 100 300 VDD-0.9 0.9 10 10 4.75/5.25 4.75/5.25 25 6 + 0.5/MHz 60 0.25 1
dBc min dBc min dBc min dBc typ ms typ
Volts typ Volts min/max M typ ppm/C typ typ V min V max A max pF max fOUT = 2 MHz V min/V max V min/V max mA max mA typ mA max mA typ mA max
1 M Resistor Tied Between REFOUT and AGND
NOTES 1 Operating temperature range is as follows: A Version: -40C to +85C. 2 All dynamic specifications are measured using IOUT. 100% production tested. 3 fMCLK = 6.25 MHz, Frequency Word = 5671C71C HEX, f OUT = 2.11 MHz. 4 Measured with the digital inputs static and equal to 0 V or DVDD. 5 The Low Power Sleep Mode current is 2 mA typically when a 1 M resistor is not tied from REFOUT to AGND. The AD9830 is tested with a capacitive load of 50 pF. The part can be operated with higher capacitive loads, but the magnitude of the analog output will be attenuated. For example, a 10 MHz output signal will be attenuated by 3 dB when the load capacitance equals 250 pF. Specifications subject to change without notice.
10nF
RSET 1k REFOUT REFIN FS ADJUST FULL-SCALE CONTROL COMP
AVDD 10nF
ON-BOARD REFERENCE
IOUT 12 SIN ROM 10-BIT DAC IOUT 51 51 50pF 50pF
Figure 1. Test Circuit with Which Specifications Are Tested
-2-
REV. A
AD9830 TIMING CHARACTERISTICS (V
Parameter t1 t2 t3 t4 1 t4A1 t5 t6 t7 t8 t9 1 t9A1 t10 Limit at TMIN to TMAX (A Version) 20 8 8 8 8 8 t1 5 3 8 8 t1
DD =
+5 V
5%; AGND = DGND = 0 V, unless otherwise noted)
Units ns min ns min ns min ns min ns min ns min ns min ns min ns min ns min ns min ns min
Test Conditions/Comments MCLK Period MCLK High Duration MCLK Low Duration WR Rising Edge Before MCLK Rising Edge WR Rising Edge After MCLK Rising Edge WR Pulse Width Duration Between Consecutive WR Pulses Data/Address Setup Time Data/Address Hold Time FSELECT, PSEL0, PSEL1 Setup Time Before MCLK Rising Edge FSELECT, PSEL0, PSEL1 Setup Time After MCLK Rising Edge RESET Pulse Duration
NOTES 1 See Pin Description section. Guaranteed by design, but not production tested.
t1
MCLK
t2
t3 t5
t4
WR
t4A t6
Figure 2. WR-MCLK Relationship
t6 t5
WR
t8 t7
A0, A1, A2 DATA
VALID DATA
VALID DATA
Figure 3. Writing to a Phase/Frequency Register
MCLK
t9
FSELECT PSEL0, PSEL1 VALID DATA VALID DATA
t9A
VALID DATA
RESET
t10
Figure 4. Control Timing
REV. A
-3-
AD9830
ABSOLUTE MAXIMUM RATINGS*
(TA = +25C unless otherwise noted) AVDD to AGND . . . . . . . . . . . . . . . . . . . . . . . -0.3 V to +7 V DVDD to DGND . . . . . . . . . . . . . . . . . . . . . . -0.3 V to +7 V AVDD to DVDD . . . . . . . . . . . . . . . . . . . . . . -0.3 V to +0.3 V AGND to DGND . . . . . . . . . . . . . . . . . . . . . -0.3 V to +0.3 V Digital I/O Voltage to DGND . . . . . -0.3 V to DVDD + 0.3 V Analog I/O Voltage to AGND . . . . . -0.3 V to AVDD + 0.3 V Operating Temperature Range Industrial (A Version) . . . . . . . . . . . . . . . . -40C to +85C Storage Temperature Range . . . . . . . . . . . . -65C to +150C
Maximum Junction Temperature . . . . . . . . . . . . . . . . TQFP JA Thermal Impedance . . . . . . . . . . . . . . . . . Lead Temperature, Soldering Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . .
+150C 75C/W +215C +220C
*Stresses above those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other conditions above those listed in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
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 device 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.
WARNING!
ESD SENSITIVE DEVICE
ORDERING GUIDE
Model AD9830AST
Temperature Range -40C to +85C
Package Option* ST-48
*ST = Thin Quad Flatpack (TQFP).
PIN CONFIGURATION
FS ADJUST
COMP
AGND IOUT
AGND
AGND
AVDD
IOUT
NC
AVDD
48 47 46 45 44 43 42 41 40 39 38 37
REFIN 1 REFOUT 2 SLEEP 3 DVDD 4 DVDD 5 DGND 6 MCLK 7 WR 8 DVDD 9 FSELECT 10 PSEL0 11 PSEL1 12
13 14 15 16 17 18 19 20 21 22 23 24 PIN 1 IDENTIFIER
NC
NC
36 35 34 33
AGND RESET A0 A1 A2 DB0 DB1 DGND DB2 DB3 DB4 DVDD
AD9830
TOP VIEW (Not to Scale)
32 31 30 29 28 27 26 25
DB15
DB14
DB13
DGND
DB12
DB11
DB10
DB6
NC = NO CONNECT
-4-
DB9
DB8
DB7
DB5
REV. A
AD9830
PIN DESCRIPTION
Mnemonic
Function
POWER SUPPLY AVDD Positive power supply for the analog section. A 0.1 F capacitor should be connected between AVDD and AGND. AVDD has a value of +5 V 5%. AGND Analog Ground. DVDD Positive power supply for the digital section. A 0.1 F decoupling capacitor should be connected between DVDD and DGND. DVDD has a value of +5 V 5%. DGND Digital Ground. ANALOG SIGNAL AND REFERENCE IOUT, IOUT Current Output. This is a high impedance current source. A load resistor should be connected between IOUT and AGND. IOUT should be either tied directly to AGND or through an external load resistor to AGND. FS ADJUST Full-Scale Adjust Control. A resistor (RSET) is connected between this pin and AGND. This determines the magnitude of the full-scale DAC current. The relationship between RSET and the full-scale current is as follows: IOUTFULL-SCALE = 16 VREFIN/RSET VREFIN = 1.21 V nominal, RSET = 1 k typical REFIN Voltage Reference Input. The AD9830 can be used with either the on-board reference, which is available from pin REFOUT, or an external reference. The reference to be used is connected to the REFIN pin. The AD9830 accepts a reference of 1.21 V nominal. REFOUT Voltage Reference Output. The AD9830 has an on-board reference of value 1.21 V nominal. The reference is made available on the REFOUT pin. This reference is used as the reference to the DAC by connecting REFOUT to REFIN. REFOUT should be decoupled with a 10 nF capacitor to AGND. COMP Compensation pin. This is a compensation pin for the internal reference amplifier. A 10 nF decoupling ceramic capacitor should be connected between COMP and AVDD. DIGITAL INTERFACE AND CONTROL MCLK Digital Clock Input. DDS output frequencies are expressed as a binary fraction of the frequency of MCLK. The output frequency accuracy and phase noise are determined by this clock. FSELECT Frequency Select Input. FSELECT controls which frequency register, FREQ0 or FREQ1, is used in the phase accumulator. FSELECT is sampled on the rising MCLK edge. FSELECT needs to be in steady state when an MCLK rising edge occurs. If FSELECT changes value when an MCLK rising edge occurs, there is an uncertainty of one MCLK cycle as to when control is transferred to the other frequency register. To avoid any uncertainty, a change on FSELECT should not coincide with an MCLK rising edge. WR Write, Edge-Triggered Digital Input. The WR pin is used when writing data to the AD9830. The data is loaded into the AD9830 on the rising edge of the WR pulse. This data is then loaded into the destination register on the MCLK rising edge. The WR pulse rising edge should not coincide with the MCLK rising edge as there will be an uncertainty of one MCLK cycle regarding the loading of the destination register with the new data. The WR rising edge should occur before an MCLK rising edge. The data will then be transferred into the destination register on the MCLK rising edge. Alternatively, the WR rising edge can occur after the MCLK rising edge and the destination register will be loaded on the next MCLK rising edge. D0-D15 Data Bus, Digital Inputs for destination registers. A0-A2 Address Digital Inputs. These address bits are used to select the destination register to which the digital data is to be written. PSEL0, PSEL1 Phase Select Input. The AD9830 has four phase registers. These registers can be used to alter the value being input to the SIN ROM. The contents of the phase register can be added to the phase accumulator output, the inputs PSEL0 and PSEL1 selecting the phase register to be used. Like the FSELECT input, the AD9830 samples the PSEL0 and PSEL1 inputs on the MCLK rising edge. Therefore, these inputs should be in steady state at the MCLK rising edge or, there is an uncertainty of one MCLK cycle as to when control is transferred to the selected phase register. SLEEP Low Power Control, active low digital input. SLEEP puts the AD9830 into a low power mode. Internal clocks are disabled and the DAC's current sources and REFOUT are turned off. The AD9830 is re-enabled by taking SLEEP high. RESET Reset, active low digital input. RESET resets the phase accumulator to zero which corresponds to an analog output of midscale.
REV. A
-5-
AD9830
TERMINOLOGY
Integral Nonlinearity Output Compliance
This is the maximum deviation of any code from a straight line passing through the endpoints of the transfer function. The endpoints of the transfer function are zero scale, a point 0.5 LSB below the first code transition (000 . . . 00 to 000 . . . 01) and full scale, a point 0.5 LSB above the last code transition (111 . . . 10 to 111 . . . 11). The error is expressed in LSBs.
Differential Nonlinearity
The output compliance refers to the maximum voltage which can be generated at the output of the DAC to meet the specifications. When voltages greater than that specified for the output compliance are generated, the AD9830 may not meet the specifications listed in the data sheet. For the AD9830, the maximum voltage which can be generated by the DAC is 1V.
Spurious Free Dynamic Range
This is the difference between the measured and the ideal 1 LSB change between two adjacent codes in the DAC.
Signal to (Noise + Distortion)
Signal to (Noise + Distortion) is measured signal to noise at the output of the DAC. The signal is the rms magnitude of the fundamental. Noise is the rms sum of all the nonfundamental signals up to half the sampling frequency (fMCLK/2) but excluding the dc component. Signal to (Noise + Distortion) is dependent on the number of quantization levels used in the digitization process; the more levels, the smaller the quantization noise. The theoretical Signal to (Noise + Distortion) ratio for a sine wave input is given by Signal to (Noise + Distortion) = (6.02 N + 1.76) dB where N is the number of bits. Thus, for an ideal 10-bit converter, Signal to (Noise + Distortion) = 61.96 dB.
Total Harmonic Distortion
Along with the frequency of interest, harmonics of the fundamental frequency and images of the MCLK frequency will be present at the output of a DDS device. The spurious free dynamic range (SFDR) refers to the largest spur or harmonic which is present in the band of interest. The wideband SFDR gives the magnitude of the largest harmonic or spur relative to the magnitude of the fundamental frequency in the bandwidth 2 MHz about the fundamental frequency. The narrowband SFDR gives the attenuation of the largest spur or harmonic in a bandwidth of 200 kHz and 50 kHz about the fundamental frequency.
Clock Feedthrough
There will be feedthrough from the MCLK input to the analog output. The clock feedthrough refers to the magnitude of the MCLK signal relative to the fundamental frequency in the AD9830's output spectrum.
Total Harmonic Distortion (THD) is the ratio of the rms sum of harmonics to the rms value of the fundamental. For the AD9830, THD is defined as
THD = 20log (V 2 +V 3 +V 4 +V 5 +V 6 V1
2 2 2 2 2
where V1 is the rms amplitude of the fundamental and V2, V3, V4, V5 and V6 are the rms amplitudes of the second through the sixth harmonic.
-6-
REV. A
Typical Performance Characteristics-AD9830
60 AVDD = DVDD = +5V TA = +25C fOUT = 200kHz
-35 50MHz -40
55 TOTAL CURRENT - mA
SFDR (0-MCLK/2) - dB
50
-45 30MHz -50 10MHz -55
45
40
35
-60 AVDD = DVDD = +5V
30 10
-65
20
30 40 MCLK FREQUENCY - MHz
50
0
0.05
0.1
0.15 0.2 fOUT/fMCLK
0.25
0.3
0.35
Figure 5. Typical Current Consumption vs. MCLK Frequency
Figure 8. WB SFDR vs. fOUT/fMCLK for Various MCLK Frequencies
-50 AVDD = DVDD = +5V fOUT/fMCLK = 1/3 -55
60 AVDD = DVDD = +5V fOUT = fMCLK/3 55
SFDR (200kHz) - dB
-60 SNR - dB
-65
50
-70 45 -75
-80 10 20 30 40 MCLK FREQUENCY - MHz 50
40 10
20
30 40 MCLK FREQUENCY - MHz
50
Figure 6. Narrow Band SFDR vs. MCLK Frequency
Figure 9. SNR vs. MCLK Frequency
-40 AVDD = DVDD = +5V fOUT/fMCLK = 1/3
60 AVDD = DVDD = +5V
-45 SFDR (2MHz) - dB
55 10MHz
SNR - dB
-50
30MHz 50 50MHz
-55
45
-60
-65 10
40
20 30 40 MCLK FREQUENCY - MHz 50
0
0.1
0.2 fOUT/fMCLK
0.3
0.4
Figure 7. Wide Band SFDR vs. MCLK Frequency
Figure 10. SNR vs. fOUT/fMCLK for Various MCLK Frequencies
REV. A
-7-
AD9830
0 -10 -20 -30 0 -10 -20 -30 10dB/DIV -40 -50 -60 -70 -80 -90 START 0Hz RBW 1kHz
10dB/DIV
-40 -50 -60 -70 -80 -90 START 0Hz RBW 1kHz
VBW 3kHz
STOP 25MHz ST 50 SEC
VBW 3kHz
STOP 25MHz ST 50 SEC
Figure 11. fMCLK = 50 MHz, fOUT = 2.1 MHz, Frequency Word = ACO8312
Figure 14. fMCLK = 50 MHz, fOUT = 9.1 MHz, Frequency Word = 2E978D50
0 -10 -20 -30
0 -10 -20 -30 10dB/DIV
STOP 25MHz ST 50 SEC
10dB/DIV
-40 -50 -60 -70 -80 -90 START 0Hz RBW 1kHz
-40 -50 -60 -70 -80 -90 START 0Hz RBW 1kHz
VBW 3kHz
VBW 3kHz
STOP 25MHz ST 50 SEC
Figure 12. fMCLK = 50 MHz, fOUT = 3.1 MHz, Frequency Word = FDF3B64
Figure 15. fMCLK = 50 MHz, fOUT = 11.1 MHz, Frequency Word = 38D4FDF4
0 -10 -20 -30 10dB/DIV -40 -50 -60 -70 -80 -90 START 0Hz RBW 1kHz 10dB/DIV STOP 25MHz ST 50 SEC
0 -10 -20 -30 -40 -50 -60 -70 -80 -90 START 0Hz RBW 1kHz
VBW 3kHz
VBW 3kHz
STOP 25MHz ST 50 SEC
Figure 13. fMCLK = 50 MHz, fOUT = 7.1 MHz, Frequency Word = 245A1CAC
Figure 16. fMCLK = 50 MHz, fOUT = 13.1 MHz, Frequency Word = 43126E98
-8-
REV. A
AD9830
0 -10 -20 -30 10dB/DIV -40 -50 -60 -70 -80 -90 START 0Hz RBW 1kHz
VBW 3kHz
STOP 25MHz ST 50 SEC
Figure 17. fMCLK = 50 MHz, fOUT = 16.5 MHz, Frequency Word = 547AE148
Register FREQ0 REG
Size 32 Bits
Description Frequency Register 0. This defines the output frequency, when FSELECT = 0, as a fraction of the MCLK frequency. Frequency Register 1. This defines the output frequency, when FSELECT = 1, as a fraction of the MCLK frequency. Phase Offset Register 0. When PSEL0 = PSEL1 = 0, the contents of this register are added to the output of the phase accumulator. Phase Offset Register 1. When PSEL0 = 1 and PSEL1 = 0, the contents of this register are added to the output of the phase accumulator. Phase Offset Register 2. When PSEL0 = 0 and PSEL1 = 1, the contents of this register are added to the output of the phase accumulator. Phase Offset Register 3. When PSEL0 = PSEL1 = 1, the contents of this register are added to the output of the phase accumulator.
A2 0 0 0 0 1 1 1 1
A1 0 0 1 1 0 0 1 1
A0 0 1 0 1 0 1 0 1
Destination Register FREQ0 REG 16 LSBs FREQ0 REG 16 MSBs FREQ1 REG 16 LSBs FREQ1 REG 16 MSBs PHASE0 REG PHASE1 REG PHASE2 REG PHASE3 REG
FREQ1 REG
32 Bits
PHASE0 REG
12 Bits
Figure 19. Addressing the Control Registers
PHASE1 REG
12 Bits
D15 MSB
Figure 20. Frequency Register Bits
D0 LSB
PHASE2 REG
12 Bits
D15 D14 D13 D12 D11 X X X X MSB
D0 LSB
PHASE3 REG
12 Bits
X = Don't Care
Figure 21. Phase Register Bits
Figure 18. AD9830 Control Registers
REV. A
-9-
AD9830
CIRCUIT DESCRIPTION Numerical Controlled Oscillator + Phase Modulator
The AD9830 provides an exciting new level of integration for the RF/Communications system designer. The AD9830 combines the Numerical Controlled Oscillator (NCO), SINE Look-Up table, Frequency and Phase Modulators, and a Digital-to-Analog Converter on a single integrated circuit. The internal circuitry of the AD9830 consists of three main sections. These are: Numerical Controlled Oscillator (NCO) + Phase Modulator SINE Look-Up Table Digital-to-Analog Converter The AD9830 is a fully integrated Direct Digital Synthesis (DDS) chip. The chip requires one reference clock, two low precision resistors and eight decoupling capacitors to provide digitally created sine waves up to 25 MHz. In addition to the generation of this RF signal, the chip is fully capable of a broad range of simple and complex modulation schemes. These modulation schemes are fully implemented in the digital domain allowing accurate and simple realization of complex modulation algorithms using DSP techniques.
THEORY OF OPERATION
This consists of two frequency select registers, a phase accumulator and four phase offset registers. The main component of the NCO is a 32-bit phase accumulator which assembles the phase component of the output signal. Continuous time signals have a phase range of 0 to 2. Outside this range of numbers, the sinusoid functions repeat themselves in a periodic manner. The digital implementation is no different. The accumulator simply scales the range of phase numbers into a multibit digital word. The phase accumulator in the AD9830 is implemented with 32 bits. Therefore, in the AD9830, 2 = 232. Likewise, the Phase term is scaled into this range of numbers 0 < Phase < 232 -1. Making these substitutions into the equation above f = Phase x fMCLK/232 where 0 < Phase < 232 With a clock signal of 50 MHz and a phase word of 051EB852 hex f = 51EB852 x 50 MHz/232 = 1.000000000931 MHz The input to the phase accumulator (i.e., the phase step) can be selected either from the FREQ0 Register or FREQ1 Register and this is controlled by the FSELECT pin. NCOs inherently generate continuous phase signals, thus avoiding any output discontinuity when switching between frequencies. More complex frequency modulation schemes can be implemented by updating the contents of these registers. This facilitates complex frequency modulation schemes, such as GMSK. Following the NCO, a phase offset can be added to perform phase modulation using the 12-bit PHASE Registers. The contents of this register are added to the most significant bits of the NCO. The AD9830 has four PHASE registers. The resolution of the phase registers equals 2/4096.
Sine Look-Up Table (LUT)
Sine waves are typically thought of in terms of their magnitude form a (t) = sin (t). However, these are nonlinear and not easy to generate except through piece wise construction. On the other hand, the angular information is linear in nature. That is, the phase angle rotates through a fixed angle for each unit of time. The angular rate depends on the frequency of the signal by the traditional rate of = 2f
MAGNITUDE +1
0
-1 PHASE 2
0
To make the output useful, the signal must be converted from phase information into a sinusoidal value. Since phase information maps directly into amplitude, a ROM LUT converts the phase information into amplitude. To do this, the digital phase information is used to address a sine ROM LUT. Although the NCO contains a 32-bit phase accumulator, the output of the NCO is truncated to 12 bits. Using the full resolution of the phase accumulator is impractical and unnecessary as this would require a look-up table of 232 entries. It is necessary only to have sufficient phase resolution in the LUTs such that the dc error of the output waveform is dominated by the quantization error in the DAC. This requires the look-up table to have two more bits of phase resolution than the 10-bit DAC.
Digital-to-Analog Converter
Figure 22. Sine Wave
Knowing that the phase of a sine wave is linear and given a reference interval (clock period), the phase rotation for that period can be determined. Phase = t Solving for = Phase/t = 2f Solving for f and substituting the reference clock frequency for the reference period (1/fMCLK = t) f = Phase x fMCLK/2 The AD9830 builds the output based on this simple equation. A simple DDS chip can implement this equation with three major subcircuits.
The AD9830 includes a high impedance current source 10-bit DAC, capable of driving a wide range of loads at different speeds. Full-scale output current can be adjusted, for optimum power and external load requirements, through the use of a single external resistor (RSET). The DAC can be configured for single or differential ended operation. IOUT can be tied directly to AGND for single ended operation or through a load resistor to develop an output voltage. The load resistor can be any value required, as long as the
-10-
REV. A
AD9830
full-scale voltage developed across it does not exceed the voltage compliance range. Since full-scale current is controlled by RSET, adjustments to RSET can balance changes made to the load resistor. However, if the DAC full-scale output current is significantly less than 20 mA, the linearity of the DAC may degrade.
DSP and MPU Interfacing
The AD9830 has a parallel interface, with 16 bits of data being loaded during each write cycle. The frequency or phase registers are loaded by asserting the WR signal. The destination register for the 16-bit data is selected using the address inputs A0, A1 and A2. The phase registers are 12 bits wide so, only the 12 LSBs need to be valid--the 4 MSBs of the 16 bit word do not have to contain valid data. Data is loaded into the AD9830 by pulsing WR low, the data being latched into the AD9830 on the rising edge of WR. The values of inputs A0, A1 and A2 are also latched into the AD9830 on the WR rising edge. The appropriate register is updated on the next MCLK rising edge. To ensure that the AD9830 contains valid data at the rising edge of MCLK, the rising edge of the WR pulse should not coincide with the rising MCLK edge. The WR pulse must occur several nanoseconds before the MCLK rising edge. If the WR rising edge occurs at the MCLK rising edge, there is an uncertainty of one MCLK cycle regarding the loading of the destination register--the destination register may be loaded with the new data immediately or the destination register may be updated on the next MCLK rising edge. To avoid any uncertainty, the times listed in the specifications should be complied with.
RESET
FSELECT, PSEL0 and PSEL1 are sampled on the MCLK rising edge. Again, these inputs should be valid when an MCLK rising edge occurs as there will be an uncertainty of one MCLK cycle introduced otherwise. When these inputs change value, there will be a pipeline delay before control is transferred to the selected register--there will be a pipeline delay before the analog output is controlled by the selected register. Similarly, there is a delay when a new word is written to a register. PSEL0, PSEL1, FSELECT and WR have latencies of six MCLK cycles. The flow chart in Figure 23 shows the operating routine for the AD9830. When the AD9830 is powered up, the part should be reset using RESET. This will reset the phase accumulator to zero so that the analog output is at midscale. RESET does not reset the phase and frequency registers. These registers will contain invalid data and, therefore, should be set to zero by the user. The registers to be used should be loaded, the analog output being fMCLK/232 x FREG where FREG is the value contained in the selected frequency register. This signal will be phase shifted by an amount 2/4096 x PHASEREG where PHASEREG is the value contained in the selected phase register. When FSELECT, PSEL0 and PSEL1 are programmed, there will be a pipeline delay of approximately 6 MCLK cycles before the analog output reacts to the change on these inputs.
DATA WRITE FREG<0, 1> = 0 PHASEREG<0, 1, 2, 3> = 0
DATA WRITE FREG<0> = fOUT0/fMCLK*232 FREG<1> = fOUT1/fMCLK*232 PHASEREG<3:0> = DELTA PHASE<0, 1, 2, 3>
SELECT DATA SOURCES SET FSELECT SET PSEL0, PSEL1
WAIT 6 MCLK CYCLES
DAC OUTPUT VOUT = VREFIN*8*ROUT/RSET*(1 + SIN(2(FREG*fMCLK*t/232 + PHASEREG/212)))
CHANGE PHASE? NO NO CHANGE FOUT? YES CHANGE FREG? YES
YES
NO CHANGE PHASEREG? YES CHANGE PSEL0, PSEL1
NO CHANGE FSELECT
Figure 23. Flow Chart for AD9830 Initialization and Operation
REV. A
-11-
AD9830
APPLICATIONS
The AD9830 contains functions which make it suitable for modulation applications. The part can be used to perform simple modulation such as FSK. More complex modulation schemes such as GMSK and QPSK can also be implemented using the AD9830. In a FSK application, the two frequency registers of the AD9830 are loaded with different values, one frequency will represent the space frequency while the other will represent the mark frequency. The digital data stream is fed to the FSELECT pin which will cause the AD9830 to modulate the carrier frequency between the two values. The AD9830 has four phase registers which enable the part to perform PSK. With phase shift keying, the carrier frequency is phase shifted, the phase being altered by an amount which is
related to the bit stream being input to the modulator. The presence of four shift registers eases the interaction needed between the DSP and the AD9830. The frequency and phase registers can be written to continuously, if required. The maximum update rate equals the frequency of the MCLK. However, if a selected register is loaded with a new word, there will be a delay of 6 MCLK cycles before the analog output will change accordingly. The AD9830 is also suitable for signal generator applications. With its low current consumption, the part is suitable for mobile applications in which it can be used as a local oscillator. Figure 24 shows the interface between the AD9830 and AD6459 which is a down converter used on the receive side of mobile phones or basestations.
AD9830
10 BITS RSET 1k
FILTER 51 51 LOIP 0.1F
AD6459
RFHI MXOP ANTENNA RFLO MXOM BANDPASS FILTER IFIM MIDPOINT BIAS GENERATOR GAIN TC COMPENSATION VPS1 VPS2 PRUP BIAS CIRCUIT IFIP 0 PLL 90
IRxP IRxN FREF FLTR
QRxP QRxN
GAIN GREF
COM1
COM2
Figure 24. AD9830 and AD6459 Receiver Circuit
-12-
REV. A
AD9830
Grounding and Layout AD9830 Evaluation Board
The printed circuit board that houses the AD9830 should be designed so that the analog and digital sections are separated and confined to certain areas of the board. This facilitates the use of ground planes which can be separated easily. A minimum etch technique is generally best for ground planes as it gives the best shielding. Digital and analog ground planes should only be joined in one place. If the AD9830 is the only device requiring an AGND to DGND connection, then the ground planes should be connected at the AGND and DGND pins of the AD9830. If the AD9830 is in a system where multiple devices require AGND to DGND connections, the connection should be made at one point only, a star ground point that should be established as close as possible to the AD9830. Avoid running digital lines under the device as these will couple noise onto the die. The analog ground plane should be allowed to run under the AD9830 to avoid noise coupling. The power supply lines to the AD9830 should use as large a track as is possible to provide low impedance paths and reduce the effects of glitches on the power supply line. Fast switching signals like clocks should be shielded with digital ground to avoid radiating noise to other sections of the board. Avoid crossover of digital and analog signals. Traces on opposite sides of the board should run at right angles to each other. This will reduce the effects of feedthrough through the board. A microstrip technique is by far the best but is not always possible with a double-sided board. In this technique, the component side of the board is dedicated to ground planes while signals are placed on the other side. Good decoupling is important. The analog and digital supplies to the AD9830 are independent and separately pinned out to minimize coupling between analog and digital sections of the device. All analog and digital supplies should be decoupled to AGND and DGND respectively with 0.1 F ceramic capacitors in parallel with 10 F tantalum capacitors. To achieve the best from the decoupling capacitors, they should be placed as close as possible to the device, ideally right up against the device. In systems where a common supply is used to drive both the AVDD and DVDD of the AD9830, it is recommended that the system's AVDD supply be used. This supply should have the recommended analog supply decoupling between the AVDD pins of the AD9830 and AGND and the recommended digital supply decoupling capacitors between the DVDD pins and DGND.
The AD9830 Evaluation Board allows designers to evaluate the high performance AD9830 DDS Modulator with a minimum of effort. To prove that this device will meet the user's waveform synthesis requirements, the user only requires a +5 V power supply, an IBM-compatible PC and a spectrum analyzer along with the evaluation board. The evaluation setup is shown below. The DDS Evaluation kit includes a populated, tested AD9830 printed circuit board along with software which controls the AD9830 in a Windows environment.
IBM COMPATIBLE PC PARALLEL PORT CENTRONICS PRINTER CABLE AD9830 EVALUATION BOARD
AD9830.EXE
Figure 25. AD9830 Evaluation Board Setup
Using the AD9830 Evaluation Board
The AD9830 Evaluation kit is a test system designed to simplify the evaluation of the AD9830. Provisions to control the AD9830 from the printer port of an IBM-compatible PC are included along with the necessary software. An application note is also available with the evaluation board which gives information on operating the evaluation board.
Prototyping Area
An area is available on the evaluation board where the user can add additional circuits to the evaluation test set. Users may want to build custom analog filters for the outputs or add buffers and operational amplifiers which are to be used in the final application.
XO vs. External Clock
The AD9830 can operate with master clocks up to 50 MHz. A 50 MHz oscillator is included on the evaluation board. However, this oscillator can be removed and an external CMOS clock connected to the part, if required.
Power Supply
Power to the AD9830 evaluation board must be provided externally through the pin connections. The power leads should be twisted to reduce ground loops.
REV. A
-13-
AD9830
DVDD 0.1F C1, C2, C3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 DVDD LATCH D0 D1 D2 D3 D4 D5 D6 D7 0.1F C13 AVDD 0.1F C4, C5 DVDD 4, 5, 9, 25 D15 D8 AVDD 38, 43 COMP REFIN AVDD 10nF C6 SMB5 1 LK5
U2
VDD 74HC574 CK 14 21
48
J1
PC INTERFACE WR RESET LATCH LOAD D7 D0 LOAD DVDD 0.1F C14
U3
VDD 74HC574 CK 22 31 32 34 D7 D0 A2
REFOUT
2 10nF C7 DVDD
J2
0.1F C8
J3
0.1F C10
AVDD 10F C11
AD9830
U1
FSADJUST 47
RESET
LATCH
10F C9
A0 WR RESET PSEL1 IOUT PSEL0 FSELECT MCLK SLEEP DGND AGND IOUT 45 51 R7
R1 10k SMB1 SMB2 SMB3
R2 10k
R3 10k LK1 LK2 LK3
WR RESET
8 35 12 11 10
1k R5
SMB6 44 51 R6 SMB7
MCLK
7 3
LOAD SW DVDD
DVDD
6,13, 29
36, 39, 41, 46
SMB4 WR R4 50 DVDD C12 0.1F
LK4
U4
DVDD OUT XTAL1 DGND
Figure 26. Evaluation Board Layout
COMPONENT LIST Integrated Circuits
Links
U1 U2, U3 XTAL1
Capacitors
AD9830 (48-Pin TQFP) 74HC574 Latches OSC XTAL 50 MHz 10 F Tantalum Capacitor 0.1 F Ceramic Capacitor 0.1 F Ceramic Chip Capacitor 10 nF Ceramic Capacitor 1 k Resistor 51 Resistor 50 Resistor 10 k Resistor
LK5 LK1, LK2, LK3, LK4
Switch
Two Pin Link Three Pin Link End Stackable Switch (SDC Double Throw) Sub-Miniature BNC Connector PCB Mounting Terminal Block 36-Pin Edge Connector
SW
Sockets
C9, C11 C8, C10, C12-C14 C1-C5 C6, C7
Resistors
SMB1-SMB7
Connectors
R5 R6, R7 R4 R1-R3
J2, J3 J1
-14-
REV. A
AD9830
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
48-Lead TQFP (ST-48)
0.063 (1.60) MAX 0.030 (0.75) 0.018 (0.45) 0.030 (0.75) 0.057 (1.45) 0.018 (0.45) 0.053 (1.35)
48 1
0.354 (9.00) BSC 0.276 (7.0) BSC
37 36
SEATING PLANE TOP VIEW
(PINS DOWN)
0.006 (0.15) 0.002 (0.05) 0 - 7
0 MIN 0.007 (0.18) 0.004 (0.09)
12 13
25 24
0.019 (0.5) BSC
0.011 (0.27) 0.006 (0.17)
REV. A
-15-
0.354 (9.00) BSC
0.276 (7.0) BSC
-16-
C2142a-10-9/96
PRINTED IN U.S.A.

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