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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
3-V, 10-Bit, 40-MSPS CMOS ANALOG-TO-DIGITAL CONVERTER
FEATURES
D D D D D D D D D D D D D D D
Analog Supply 3 V Digital Supply 3 V Configurable Input Functions: - Single Ended - Differential Differential Nonlinearity: 0.45 LSB Signal-to-Noise: 60 dB Typ at 4.8 MHz Spurious Free Dynamic Range: 72 dB Adjustable Internal Voltage Reference On-Chip Voltage Reference Generator Unsigned Binary Data Output Out-of-Range Indicator Power-Down Mode
bypassed to use an external reference to suit the dc accuracy and temperature drift requirements of the application. The out-of-range output indicates any out-of-range condition in THS1040's input signal. The speed, resolution, and single-supply operation of the THS1040 are suited to applications in set-top-box (STB), video, multimedia, imaging, high-speed acquisition, and communications. The speed and resolution ideally suit charge-couple device (CCD) input systems such as color scanners, digital copiers, digital cameras, and camcorders. A wide input voltage range allows the THS1040 to be applied in both imaging and communications systems. The THS1040C is characterized for operation from 0C to 70C, while the THS1040I is characterized for operation from -40C to 85C.
APPLICATIONS
Video/CCD Imaging Communications Set-Top Box Medical
28-PIN TSSOP/SOIC PACKAGE (TOP VIEW)
DESCRIPTION
The THS1040 is a CMOS, low power, 10-bit, 40-MSPS analog-to-digital converter (ADC) that operates from a single 3-V supply. The THS1040 has been designed to give circuit developers flexibility. The analog input to the THS1040 can be either single-ended or differential. The THS1040 provides a wide selection of voltage references to match the user's design requirements. For more design flexibility, the internal reference can be
AGND DVDD D0 D1 D2 D3 D4 D5 D6 D7 D8 D9 OVR DGND
1 2 3 4 5 6 7 8 9 10 11 12 13 14
28 27 26 25 24 23 22 21 20 19 18 17 16 15
AVDD AIN+ VREF AIN- REFB MODE REFT BIASREF TEST AGND REFSENSE STBY OE CLK
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters.
Copyright 2002, Texas Instruments Incorporated
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
AVAILABLE OPTIONS TA 0C to 70C - 40C to 85C PACKAGED DEVICES 28-TSSOP (PW) THS1040CPW THS1040IPW 28-SOIC (DW) THS1040CDW THS1040IDW
functional block diagram
Digital Control BIASREF
STBY
AIN+ SHA AIN-
10-Bit ADC
3-State Output Buffers
D (0-9) OVR OE
MODE
Mode Detection
ADC Reference Resistor
DVDD DGND Timing Circuit CLK
VREF A2 AVDD AGND REFB NOTE: A1 - Internal bandgap reference A2 - Internal ADC reference generator REFT VREF A1
+ 0.5 V -
REFSENSE
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
Terminal Functions
TERMINAL NAME AGND AIN+ AIN- AVDD BIASREF CLK DGND DVDD D0 D1 D2 D3 D4 D5 D6 D7 D8 D9 MODE OE OVR REFB REFSENSE REFT STBY TEST VREF NO. 1, 19 27 25 28 21 15 14 2 3 4 5 6 7 8 9 10 11 12 23 16 13 24 18 22 17 20 26 I/O I I I I O I I I Analog ground Positive analog input Negative analog input Analog supply When the MODE pin is at AVDD, a buffered AVDD/2 is present at this pin that can be used by external input biasing circuits. The output is high impedance when MODE is AGND or AVDD/2. Clock input Digital ground Digital supply Digital data bit 0 (LSB) Digital data bit 1 Digital data bit 2 Digital data bit 3 Digital data bit 4 Digital data bit 5 Digital data bit 6 Digital data bit 7 Digital data bit 8 Digital data bit 9 (MSB) Operating mode select (AGND, AVDD/2, or AVDD) High to 3-state the data bus, low to enable the data bus Out-of-range indicator Bottom ADC reference voltage VREF mode control Top ADC reference voltage Drive high to power-down the THS1040 Production test pin. Tie to DVDD or DGND Internal or external reference DESCRIPTION
O
I I O I/O I I/O I I I/O
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
absolute maximum ratings over operating free-air temperature (unless otherwise noted)
Supply voltage range: AVDD to AGND, DVDD to DGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 0.3 V to 4 V AGND to DGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 0.3 V to 0.3 V AVDD to DVDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 4 V to 4 V MODE input voltage range, MODE to AGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 0.3 V to AVDD + 0.3 V Reference voltage input range, REFT, REFB, to AGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 0.3 V to AVDD + 0.3 V Analog input voltage range, AIN to AGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 0.3 V to AVDD + 0.3 V Reference input voltage range, VREF to AGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 0.3 V to AVDD + 0.3 V Reference output voltage range, VREF to AGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 0.3 V to AVDD + 0.3 V Clock input voltage range, CLK to AGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 0.3 V to AVDD + 0.3 V Digital input voltage range, digital input to DGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 0.3 V to DVDD + 0.3 V Digital output voltage range, digital output to DGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 0.3 V to DVDD + 0.3 V Operating junction temperature range, TJ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0C to 150C Storage temperature range, Tstg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 65C to 150C Lead temperature 1,6 mm (1/16 in) from case for 10 seconds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300C
Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under "recommended operating conditions" is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
recommended operating conditions
MIN Supply voltage, AVDD, DVDD High-level digital input, VIH Low-level digital input, VIL Minimum digital output load resistance, RL Maximum digital output load capacitance, CL Clock frequency, fclk Clock duty cycle THS1040C Operating free air temperature free-air THS1040I 5 45% 0 -40 50% 25 25 3 DVDD DGND 100 10 40 55% 70 85 C NOM 3 MAX 3.6 DVDD DGND UNIT V V V k pF MHz
electrical characteristics over recommended operating conditions, AVDD = 3 V, DVDD = 3 V, fs = 40 MSPS/50% duty cycle, MODE = AVDD (internal reference), differential input range = 1 VPP and 2 VPP, TA = Tmin to Tmax (unless otherwise noted)
dc accuracy
PARAMETER Resolution INL DNL Integral nonlinearity (see definitions) Differential nonlinearity (see definitions) Zero error (see definitions) Full-scale error (see definitions) Missing code MIN TYP 10 0.75 0.45 0.7 2.2 1.5 0.9 1.5 3 MAX UNIT Bits LSB LSB %FSR %FSR
No missing code assured
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
electrical characteristics over recommended operating conditions, AVDD = 3 V, DVDD = 3 V, fs = 40 MSPS/50% duty cycle, MODE = AVDD (internal reference), differential input range = 1 VPP and 2 VPP, TA = Tmin to Tmax (unless otherwise noted) (continued)
power supply
PARAMETER AVDD DVDD ICC PD PD(STBY) Supply voltage Operating supply current Power dissipation Standby power All circuits active All circuits active TEST CONDITIONS MIN 3 3 33 100 75 TYP MAX 3.6 3.6 40 120 UNIT V mA mW W
Power up time for all references from standby, t(PU) 770 s t(WU) Wake-up time See Note 1 45 s NOTE 1: Wake-up time is from the power-down state to accurate ADC samples being taken and is specified for MODE = AGND with external reference sources applied to the device at the time of release of power-down, and an applied 40-MHz clock. Circuits that need to power up are the bandgap, bias generator, ADC, and SHA.
analog inputs
MIN Differential analog input voltage, VI(AIN) = AIN+ - AIN- (see Note 2) -1 NOM MAX 1 UNIT V
Reference input voltage, VI(VREF) 0.5 1 V NOTE 2: Any input common mode voltage is acceptable provided that the voltages at pins AIN+ and AIN- stay between AGND and AVDD at all times.
REFT, REFB external ADC reference voltages inputs (MODE = AGND)
PARAMETER Reference input voltage (REFT-REFB) Reference common mode voltage (REFT + REFB)/2 Input resistance between REFT and REFB AVDD = 3 TEST CONDITIONS MIN 0.5 1.5 1.9 NOM MAX 1 UNIT V V k
REFT, REFB internal ADC reference voltages outputs (MODE = AVDD or AVDD/2)
PARAMETER Reference voltage top, REFT top Reference voltage bottom, REFB bottom VREF = 0.5 V VREF = 1 V VREF = 0.5 V VREF = 1 V TEST CONDITIONS AVDD = 3 V AVDD = 3 V MIN TYP 1.75 2 1.25 1 MAX UNIT V V
VREF (on-chip voltage reference generator)
PARAMETER Internal 0.5-V reference voltage (REFSENSE = VREF) Internal 1-V reference voltage (REFSENSE = AGND) External reference voltage (REFSENSE = AVDD) Reference input resistance (REFSENSE = AVDD, MODE = AVDD/2 or AVDD) MIN 0.45 0.95 0.5 14 TYP 0.5 1 MAX 0.55 1.05 1 UNIT V V V k
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
electrical characteristics over recommended operating conditions, AVDD = 3 V, DVDD = 3 V, fs = 40 MSPS/50% duty cycle, MODE = AVDD (internal reference), differential input range = 1 VP-P and 2 VP-P, TA = Tmin to Tmax (unless otherwise noted) (continued)
dynamic performance (ADC)
PARAMETER ENOB SFDR THD SNR SINAD BW Effective number of bits Spurious free dynamic range Total harmonic distortion Signal-to-noise Signal to noise ratio Signal to noise and distortion Signal-to-noise Full power bandwidth (-3 dB) TEST CONDITIONS f = 4.8 MHz, -0.5 dBFS f = 20 MHz, -0.5 dBFS f = 4.8 MHz, -0.5 dBFS f = 20 MHz, -0.5 dBFS f = 4.8 MHz, -0.5 dBFS f = 20 MHz, -0.5 dBFS f = 4.8 MHz, -0.5 dBFS f = 20 MHz, -0.5 dBFS f = 4.8 MHz, -0.5 dBFS f = 20 MHz, -0.5 dBFS 55.6 55.7 60.5 MIN 8.8 TYP 9.6 9.5 72 70 - 72.5 - 71.6 60 57 59.7 59.6 900 - 61.3 MAX UNIT Bits dB dB dB dB MHz
digital specifications
PARMETER Digital Inputs VIH VIL IIH IIL Ci VOH VOL High-level High level input voltage Low-level Low level input voltage High-level input current Low-level input current Input capacitance Iload = 50 A Iload = -50 A 5 Clock input All other inputs Clock input All other inputs 0.8 x AVDD 0.8 x AVDD 0.2 x AVDD 0.2 x DVDD 1 |-1| V V A A pF MIN NOM MAX UNIT
Digital Outputs High-level output voltage Low-level output voltage High-impedance output current Rise/fall time Clock Input tc tw(CKH) tw(CKL) td(o) td(AP) Clock cycle time Pulse duration, clock high Pulse duration, clock low Clock duty cycle Clock to data valid, delay time Pipeline latency Aperture delay time Aperture uncertainty (jitter) 25 11.25 11.25 45% 50% 9.5 4 0.1 1 200 110 110 55% 16 ns Cycles ns ps ns ns ns Cload = 15 pF 3.5 DVDD-0.4 0.4 1 V V A ns
timing
PARAMETER td(DZ) td(DEN) Output disable to Hi-Z output, delay time Output enable to output valid, delay time MIN 0 0 TYP MAX 10 10 UNIT ns ns
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
PARAMETER MEASUREMENT INFORMATION
Sample 2 Sample 1 Analog Input tc tw(CKL) Sample 3 Sample 4 Sample 5 Sample 6 Sample 7
tw(CKH) Input Clock See Note A
Pipeline Latency Digital Output td(DEN) OE
td(o) (I/O Pad Delay or Propagation Delay) Sample 1 Sample 2 td(DZ)
NOTE A: All timing measurements are based on 50% of edge transition.
Figure 1. Digital Output Timing Diagram
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
TYPICAL CHARACTERISTICS
DIFFERENTIAL NONLINEARITY vs INPUT CODE
1.00 AVDD = 3 V DVDD = 3 V fs = 40 MSPS Vref = 1 V
DNL - Differential Nonlinearity - LSB
0.50
0.00
-0.50
-1 0 128 256 384 512 Input Code 640 768 896 1024
Figure 2
INTEGRAL NONLINEARITY vs INPUT CODE
INL - Integral Nonlinearity - LSB
1.00
0.50
0.00 AVDD = 3 V DVDD = 3 V fs = 40 MSPS Vref = 1 V 0 128 256 384 512 Input Code 640 768 896 1024
-0.50
-1.00
Figure 3
INTEGRAL NONLINEARITY vs INPUT CODE
INL - Integral Nonlinearity - LSB 1.00 AVDD = 3 V DVDD = 3 V fs = 40 MSPS Vref = 0.5 V
0.50
0.00
-0.50
-1.00 0 128 256 384 512 Input Code 640 768 896 1024
Figure 4
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
TYPICAL CHARACTERISTICS
TOTAL HARMONIC DISTORTION vs INPUT FREQUENCY
-80 1-V FS Differential Input Range THD - Total Harmonic Distortion - dB THD - Total Harmonic Distortion - dB -75 -70 -65 -60 -55 -50 -45 See Note -40 0 10 20 30 40 50 60 70 80 90 100 110 120 fi - Input Frequency - MHz -40 0 -20 dB -6 dB -0.5 dB -80 -75 -70 -65 -60 -55 -50 -45 See Note 10 20 30 40 50 60 70 80 90 100 110 120 fi - Input Frequency - MHz -20 dB -0.5 dB -85 2-V FS Differential Input Range
TOTAL HARMONIC DISTORTION vs INPUT FREQUENCY
-6 dB
Figure 5
SIGNAL-TO-NOISE RATIO vs INPUT FREQUENCY
61 59 SNR - Signal-to-Noise Ratio - dB SFDR - Spurious Free Dynamic Range - dB Diff Input = 2 V SE Input = 2 V 82
Figure 6
SPURIOUS FREE DYNAMIC RANGE vs INPUT FREQUENCY
Diff Input = 2 V 72 Diff Input = 1 V 62
57 55 53
Diff Input = 1 V
SE Input = 1 V 51
52
42 SE Input = 1 V See Note 32 0 10 SE Input = 2 V
49 See Note 47 0 10 20 30 40 50 60 70 80 90 100 110 120 fi - Input Frequency - MHz
20 30 40 50 60 70 80 90 100 110 120 fi - Input Frequency - MHz
Figure 7
Figure 8
NOTE: AVDD = DVDD = 3 V, CLK = 40 MSPS, 20-pF capacitors AIN+ to AGND and AIN- to AGND, Input series resistor = 25 , 2-V Input: Ext Ref, REFT = 2 V, REFB = 1 V, -0.5 dBFS 1-V Input: Ext Ref, REFT = 1.75 V, REFB = 1.25 V, -0.5 dBFS
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
TYPICAL CHARACTERISTICS
SIGNAL-TO-NOISE PLUS DISTORTION vs INPUT FREQUENCY
SINAD - Signal-to-Noise Plus Distortion - dB Diff Input = 2 V 57 THD - Total Harmonic Distortion - dB Diff Input = 1 V -82
TOTAL HARMONIC DISTORTION vs INPUT FREQUENCY
Diff Input = 2 V Diff Input = 1 V -72
52
47
-62
42
SE Input = 1 V
-52
37 See Note 32
SE Input = 2 V
-42 SE Input = 1 V SE Input = 2 V See Note -32 0 10 20 30 40 50 60 70 80 90 100 110 120 fi - Input Frequency - MHz
0 10 20 30 40 50 60 70 80 90 100 110 120 fi - Input Frequency - MHz
Figure 9
Figure 10
NOTE: AVDD = DVDD = 3 V, CLK = 40 MSPS, 20-pF capacitors AIN+ to AGND and AIN- to AGND, Input series resistor = 25 , 2-V Input: Ext Ref, REFT = 2 V, REFB = 1 V, -0.5 dBFS 1-V Input: Ext Ref, REFT = 1.75 V, REFB = 1.25 V, -0.5 dBFS
TOTAL HARMONIC DISTORTION vs SAMPLE RATE
-75 THD - Total Harmonic Distortion - dB 75
SIGNAL-TO-NOISE RATIO vs SAMPLE RATE
-65
SNR - Signal-To-Noise Ratio - dB
-70
70 65
-60 -55
60 55
-50 -45 -40 0 5 10 15 20
50 45 40
Diff Input = 2 V
fi = 20 MHz, -0.5 dBFS 25 30 35 40 45 50 55 Sample Rate - MSPS
Diff Input = 2 V
fi = 20 MHz, -0.5 dBFS 0 5 10 15 20 25 30 35 40 45 50 55
Sample Rate - MSPS
Figure 11
Figure 12
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
TYPICAL CHARACTERISTICS
POWER DISSIPATION vs SAMPLE RATE
AVDD = 3 V, Vref = 1 V PD - Power Dissipation - mW I DD - Total Current - mA 110 Int. Ref TA = 25C Ext. Ref TA = 25C 36
TOTAL CURRENT vs CLOCK FREQUENCY
AVDD = 3 V Vref = 1 V
34 Int. Ref TA = 25C
32
30
90
28 Ext. Ref TA = 25C
26 70 4 8 12 16 20 24 28 32 36 fs - Sample Rate - MSPS 40 44 24 0 5 10 15 20
25
30
35
40
45
fclk - Clock Frequency - MHz
Figure 13
INPUT BANDWIDTH
4 AVDD = 3 V DVDD = 3 V fs = 40 MSPS
Figure 14
2
Amplitude - dB
0
-2
-4
-6 See Note -8 10 100 300 500 700 900 fi - Input Frequency - MHz 1100
Figure 15
NOTE: No series resistors and no bypass capacitors at AIN+ and AIN- inputs.
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
TYPICAL CHARACTERISTICS
POWER-UP TIME FOR INTERNAL REFERENCE VOLTAGE FROM STANDBY
2.4 125 Vref = 1 V, Reft = 10 F, Refb = 10 F, AVDD = 3 V 120 MODE = AGND, Clock = 40 MHz, Ext. REF = 1 V and 2 V, AVDD = 3 V
ADC CODES vs WAKE-UP SETTLING TIME
Reft, Refb Reference Voltage - V
2 Vreft ADC Codes 1.6 115 110 105 100
1.2
Vrefb
0.8
0.4
95 See Note 90 -10
0
90
0
1080
180
270
360
450
540
630
720
810
900
990
1170
5
20
35
50
65
80
95
110
Power-Up Time - s
Wake-Up Settling Time - s
Figure 16
Figure 17
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
TYPICAL CHARACTERISTICS
FFT
20 0 Amplitude - dB -20 -40 -60 -80 -100 -120 -140 0 5 10 f - Frequency - MHz 15 20 fi= 10 MHz, -0.5 dBFS CLK = 40 MSPS, Diff Input = 2 V
Figure 18
20 0 Amplitude - dB -20 -40 -60 -80 -100 -120 -140 0 5 10 f - Frequency - MHz 15 20 fi = 4.5 MHz, -0.5 dBFS CLK = 40 MSPS, Diff Inpt = 2 V
FFT
Figure 19
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
PRINCIPLES OF OPERATION functional overview
See the functional block diagram. A single-ended, sample rate clock is required at pin CLK for device operation. Analog inputs AIN+ and AIN- are sampled on each rising edge of CLK in a switched capacitor sample and hold unit, the output of which feeds the ADC core, where analog-to-digital conversion is performed against the ADC reference voltages REFT and REFB. Internal or external ADC reference voltage configurations are selected by connecting the MODE pin appropriately. When MODE = AGND, the user must provide external sources at pins REFB and REFT. When MODE = AVDD or MODE = AVDD/2, an internal ADC references generator (A2) is enabled which drives the REFT and REFB pins using the voltage at pin VREF as its input. The user can choose to drive VREF from the internal bandgap reference, or disable A1 and provide their own reference voltage at pin VREF. On the fourth rising CLK edge following the edge that sampled AIN+ and AIN-, the conversion result is output via data pins D0 to D9. The output buffers can be disabled by pulling pin OE high. The following sections explain further:
D D D
How signals flow from AIN+ and AIN- to the ADC core, and how the reference voltages at REFT and REFB set the ADC input range and hence the input range at AIN+ and AIN-. How to set the ADC references REFT and REFB using external sources or the internal reference buffer (A2) to match the device input range to the input signal. How to set the output of the internal bandgap reference (A1) if required.
signal processing chain (sample and hold, ADC)
Figure 20 shows the signal flow through the sample and hold unit to the ADC core.
REFT VQ+ AIN+ AIN- X1 X-1 Sample and Hold VQ- REFB ADC Core
Figure 20. Analog Input Signal Flow
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
PRINCIPLES OF OPERATION sample-and-hold
Differential input signal sources can be connected directly to the AIN+ and AIN- pins using either dc- or ac-coupling. For single-ended sources, the signal can be dc- or ac-coupled to one of AIN+ or AIN-, and a suitable reference voltage (usually the midscale voltage, see operating configuration examples) must be applied to the other pin. Note that connecting the signal to AIN- results in it being inverted during sampling. The sample and hold differential output voltage VQ = (VQ+) - (VQ-) is given by: VQ = (AIN+) - (AIN-) (1)
analog-to-digital converter
VQ is digitized by the ADC, using the voltages at pins REFT and REFB to set the ADC zero-scale (code 0) and full-scale (code 1023) input voltages. VQ(ZS)
+ * (REFT * REFB) VQ(FS) + (REFT * REFB)
(2) (3)
Any inputs at AIN+ and AIN- that give VQ voltages less than VQ(ZS) or greater than VQ(FS) lie outside the ADC's conversion range and attempts to convert such voltages are signalled by driving pin OVR high when the conversion result is output. VQ voltages less than VQ(ZS) digitize to give ADC output code 0 and VQ voltages greater than VQ(FS) give ADC output code 1023. complete system and system input range Combining the above equations to find the input voltages [(AIN+) - (AIN-)] that correspond to the limits of the ADC's valid input range gives: (REFB
* REFT) v [(AIN)) * (AIN*)] v (REFT * REFB)
(4)
For both single-ended and differential inputs, the ADC can thus handle signals with a peak-to-peak input range [(AIN+) - (AIN-)] of: [(AIN+) - (AIN-)] pk-pk input range = 2 x (REFT - REFB) (5)
The REFT and REFB voltage difference and the gain sets the device input range. The next sections describe in detail the various methods available for setting voltages REFT and REFB to obtain the desired input span and device performance.
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
PRINCIPLES OF OPERATION ADC reference generation
The THS1040 ADC references REFT and REFB can be driven from external (off-chip) sources or from the internal (on-chip) reference buffer A2. The voltage at the MODE pin determines the ADC references source. Connecting MODE to AGND enables external ADC references mode. In this mode the internal buffer A2 is powered down and the user must provide the REFT and REFB voltages by connecting external sources directly to these pins. This mode is useful where several THS1040 devices must share common references for best matching of their ADC input ranges, or when the application requires better accuracy and temperature stability than the on-chip reference source can provide. Connecting MODE to AVDD or AVDD/2 enables internal ADC references mode. In this mode the buffer A2 is powered up and drives the REFT and REFB pins. External reference sources should not be connected in this mode. Using internal ADC references mode when possible helps to reduce the component count and hence the system cost. When MODE is connected to AVDD, a buffered AVDD/2 voltage is available at the BIASREF pin. This voltage can be used as a dc bias level for any ac-coupling networks connecting the input signal sources to the AIN+ and AIN- pins.
MODE PIN AGND AVDD/2 AVDD REFERENCE SELECTION External Internal Internal BIASREF PIN FUNCTION High impedance High impedance AVDD/2 for AIN bias
external reference mode (MODE = AGND)
AIN+ AIN-
X1 X-1
Sample and Hold
ADC Core
VREF
Internal Reference Buffer
REFT REFB
Figure 21. ADC Reference Generation, MODE = AGND Connecting pin MODE to AGND powers down the internal references buffer A2 and disconnects its outputs from the REFT and REFB pins. The user must connect REFT and REFB to external sources to provide the ADC reference voltages required to match the THS1040 input range to their application requirements. The common-mode reference voltage must be AVDD/2 for correct THS1040 operation: (REFT
) REFB) + AVDD
2 2
(6)
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
PRINCIPLES OF OPERATION internal reference mode (MODE = AVDD or AVDD/2)
AVDD + VREF 2
AIN+ AIN-
X1 X-1
Sample and Hold
ADC Core
VREF AGND
Internal Reference Buffer
AVDD - VREF 2
Figure 22. ADC Reference Generation, MODE = AVDD/2 Connecting MODE to AVDD or AVDD/2 enables the internal ADC references buffer A2. The outputs of A2 are connected to the REFT and REFB pins and its inputs are connected to pins VREF and AGND. The resulting voltages at REFT and REFB are: REFT
+ +
AV
DD
) VREF
2
(7)
AV
REFB
DD
* VREF
2
(8)
Depending on the connection of the REFSENSE pin, the voltage on VREF may be driven by an off-chip source or by the internal bandgap reference A1 (see onboard reference generator) to match the THS1040 input range to their application requirements. When MODE = AVDD the BIASREF pin provides a buffered, stabilized AVDD/2 output voltage that can be used as a bias reference for ac coupling networks connecting the signal sources to the AIN+ or AIN- inputs. This removes the need for the user to provide a stabilized external bias reference.
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
PRINCIPLES OF OPERATION internal reference mode (MODE = AVDD or AVDD/2) (continued)
AVDD or +FS AIN+ -FS +FS AIN- -FS AIN- REFSENSE 0.1 F AIN+ MODE AVDD 2
REFT 10 F 0.1 F REFB
VREF
1 V (Output) VMID if MODE = AVDD High-Impedance if MODE = AVDD 2
0.1 F
BIASREF
Figure 23. Internal Reference Mode, 1-V Reference Span
AVDD 2 AIN+ MODE or AVDD
+FS VM -FS
DC SOURCE = VM VM 0.1 F
+ _
AIN-
REFT 10 F 0.1 F REFB
VREF
0.5 V (Output)
0.1 F
REFSENSE
Figure 24. Internal Reference Mode, 0.5-V Reference Span, Single-Ended Input
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
PRINCIPLES OF OPERATION onboard reference generator configuration
The internal bandgap reference A1 can provide a supply-voltage-independent and temperature-independent voltage on pin VREF. External connections to REFSENSE control A1's output to the VREF pin as shown in Table 1. Table 1. Effect of REFSENSE Connection on VREF Value
REFSENSE CONNECTION VREF pin AGND External divider junction AVDD A1 OUTPUT TO VREF 0.5 V 1V (1 + Ra/Rb)/2 V Open circuit SEE: Figure 25 Figure 26 Figure 27 Figure 28
REFSENSE = AVDD powers the internal bandgap reference A1 down, saving power when A1 is not required. If MODE is connected to AVDD or AVDD/2, then the voltage at VREF determines the ADC reference voltages: REFT
+ AV2DD ) VREF 2
(9) (10)
+ AV2DD * VREF 2 REFT-REFB + VREF
REFB
ADC References Buffer A2 MODE = AVDD or AVDD 2 VREF = 0.5 V 0.1 F REFSENSE 1 F
(11)
VBG
+ _
+ _
AGND
Figure 25. 0.5-V VREF Using the Internal Bandgap Reference A1
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
PRINCIPLES OF OPERATION onboard reference generator configuration (continued)
ADC References Buffer A2 MODE = AVDD or AV DD 2 VREF = 1 V 10 k REFSENSE 10 k 0.1 F 1 F
VBG
+ _
+ _
AGND
Figure 26. 1-V VREF Using the Internal Bandgap Reference A1
ADC References Buffer A2 MODE = AVDD or AVDD 2
VBG
+ _
+ _
VREF = (1 + Ra/Rb)/2 Ra REFSENSE Rb 0.1 F 1 F
AGND
Figure 27. External Divider Mode
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
PRINCIPLES OF OPERATION onboard reference generator configuration (continued)
ADC References Buffer A2 MODE = AVDD or AVDD 2
VBG
+ _
+ _
VREF = External
REFSENSE AVDD AGND
Figure 28. Drive VREF Mode
operating configuration examples
Figure 29 shows a configuration using the internal ADC references for digitizing a single-ended signal with span 0 V to 2 V. Tying REFSENSE to ground gives 1 V at pin VREF. Tying MODE to AVDD/2 then sets the REFT and REFB voltages via the internal reference generator for a 2-Vp-p ADC input range. The VREF pin provides the 1-V mid-scale bias voltage required at AIN-. VREF should be well decoupled to AGND to prevent sample-and-hold switching at AIN- from corrupting the VREF voltage.
2V 1V 0V 20 20 pF 20 20 pF AIN- AVDD/2 AIN+ MODE
10 F 0.1 F
VREF = 1 V
REFT 10 F 0.1 F 0.1 F REFB REFSENSE
Figure 29. Operating Configuration: 2-V Single-Ended Input, Internal ADC References
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
PRINCIPLES OF OPERATION operating configuration examples (continued)
Figure 30 shows a configuration using the internal ADC references for digitizing a dc-coupled differential input with 1.5-Vp-p span and 1.5-V common-mode voltage. External resistors are used to set the internal bandgap reference output at VREF to 0.75 V. Tying MODE to AVDD then sets the REFT and REFB voltages via the internal reference generator for a 1.5-Vp-p ADC input range. If a transformer is used to generate the differential ADC input from a single-ended signal, then the BIASREF pin provides a suitable bias voltage for the secondary windings center tap when MODE = AVDD.
1.875 V 1.5 V 1.125 V 1.875 V 1.5 V 1.125 V 20 20 20 pF AIN- 20 pF VREF = 0.75 V 5 k 0.1 F REFT 10 F 0.1 F 0.1 F REFB REFSENSE 10 k 10 F AVDD AIN+ MODE
Figure 30. Operating Configuration: 1.5-V Differential Input, Internal ADC References Figure 31 shows a configuration using the internal ADC references and an external VREF source for digitizing a dc-coupled single-ended input with span 0.5 V to 2 V. A 1.25-V external source provides the bias voltage for the AIN- pin and also, via a buffered potential divider, the 0.75 VREF voltage required to set the input range to 1.5 Vp-p MODE is tied to AVDD to set internal ADC references configuration.
2V 1.25 V 0.5 V AVDD 20 20 pF AIN+ MODE
1.25 Source 10 k 10 F (0.75 V) 15 k
20
20 pF AIN- _ VREF + REFB REFT 0.1 F
0.1 F
10 F 0.1 F
REFSENSE
AVDD
Figure 31. Operating Configuration: 1.5-V Single-Ended Input, External VREF Source
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
PRINCIPLES OF OPERATION power management
In power-sensitive applications (such as battery-powered systems) where the THS1040 is not required to convert continuously, power can be saved between conversion intervals by placing the THS1040 into power-down mode. This is achieved by pulling the STBY pin high. In power-down mode, the device typically consumes less than 0.1 mW of power. If the internal VREF generator (A1) is not required, it can be powered down by tying pin REFSENSE to AVDD, saving approximately 1.2 mA of supply current. If the BIASREF function is not required when using internal references then tying MODE to AVDD/2 powers the BIASREF buffer down, saving approximately 1.2 mA.
digital I/O
While the OE pin is held low, ADC conversion results are output at pins D0 (LSB) to D9 (MSB). The ADC input over-range indicator is output at pin OVR. OVR is also disabled when OE is held high. The only ADC output data format supported is unsigned binary (output codes 0 to 1023). Twos complement output (output codes -512 to 511) can be obtained by using an external inverter to invert the D9 output.
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
APPLICATION INFORMATION driving the THS1040 analog inputs
driving the clock input Obtaining good performance from the THS1040 requires care when driving the clock input. Different sections of the sample-and-hold and ADC operate while the clock is low or high. The user should ensure that the clock duty cycle remains near 50% to ensure that all internal circuits have as much time as possible in which to operate. The CLK pin should also be driven from a low jitter source for best dynamic performance. To maintain low jitter at the CLK input, any clock buffers external to the THS1040 should have fast rising edges. Use a fast logic family such as AC or ACT to drive the CLK pin, and consider powering any clock buffers separately from any other logic on the PCB to prevent digital supply noise appearing on the buffered clock edges as jitter. As the CLK input threshold is nominally around AVDD/2, any clock buffers need to have an appropriate supply voltage to drive above and below this level. driving the sample and hold inputs driving the AIN+ and AIN- pins Figure 32 shows an equivalent circuit for the THS1040 AIN+ and AIN- pins. The load presented to the system at the AIN pins comprises the switched input sampling capacitor, CSample, and various stray capacitances, C1 and C2.
AVDD CLK 1.2 pF AIN C1 8 pF AGND + _ CLK VCM = AIN+/AIN- Common Mode Voltage CSample C2 1.2 pF
Figure 32. Equivalent Circuit for Analog Input Pins AIN+ and AIN- The input current pulses required to charge CSample and C2 can be time averaged and the switched capacitor circuit modelled as an equivalent resistor: R IN2
+C
1 S f CLK
(12)
where CS is the sum of CSample and C2. This model can be used to approximate the input loading versus source resistance for high impedance sources.
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
APPLICATION INFORMATION
AVDD R2 = 1/CS fCLK AIN C1 8 pF AGND IIN + _ VCM = AIN+/AIN- Common Mode Voltage
Figure 33. Equivalent Circuit for the AIN Switched Capacitor Input AIN input damping The charging current pulses into AIN+ and AIN- can make the signal sources jump or ring, especially if the sources are slightly inductive at high frequencies. Inserting a small series resistor of 20 or less and a small capacitor to ground of 20 pF or less in the input path can damp source ringing (see Figure 34). The resistor and capacitor values can be made larger than 20 and 20 pF if reduced input bandwidth and a slight gain error (due to potential division between the external resistors and the AIN equivalent resistors) are acceptable. Note that the capacitors should be soldered to a clean analog ground with a common ground point to prevent any voltage drops in the ground plane appearing as a differential voltage at the ADC inputs.
R < 20 AIN VS
C < 20 pF
Figure 34. Damping Source Ringing Using a Small Resistor and Capacitor driving the VREF pin Figure 35 shows the equivalent load on the VREF pin when driving the ADC internal references buffer via this pin (MODE = AVDD/2 or AVDD and REFSENSE = AVDD).
AVDD
RIN VREF 10 k MODE = AVDD AGND + _ (AVDD + VREF) /4 REFSENSE = AVDD, MODE = AVDD/2 or AVDD
Figure 35. Equivalent Circuit of VREF The nominal input current IREF is given by: I
+ 3 VREF * AVDD REF 4R
IN
(13)
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
APPLICATION INFORMATION
driving the VREF pin (continued) Note that the maximum current may be up to 30% higher. The user should ensure that VREF is driven from a low noise, low drift source, well decoupled to analog ground and capable of driving the maximum IREF. driving REFT and REFB (external ADC references, MODE = AGND)
AVDD
REFT
To ADC Core
AGND AVDD
2 k
REFB
To ADC Core
AGND
Figure 36. Equivalent Circuit of REFT and REFB Inputs reference decoupling VREF pin When the on-chip reference generator is enabled, the VREF pin should be decoupled to the circuit board's analog ground plane close to the THS1040 AGND pin via a 1-F capacitor and a 0.1-F ceramic capacitor. REFT and REFB pins In any mode of operation, the REFT and REFB pins should be decoupled as shown in Figure 37. Use short board traces between the THS1040 and the capacitors to minimize parasitic inductance.
0.1 F REFT THS1040
10 F
0.1 F
REFB 0.1 F
Figure 37. Recommended Decoupling for the ADC Reference Pins REFT and REFB BIASREF pin When using the on-chip BIASREF source, the BIASREF pin should be decoupled to the circuit board's analog ground plane close to the THS1040 AGND pin via a 1-F capacitor and a 0.1-F ceramic capacitor.
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
APPLICATION INFORMATION
supply decoupling The analog (AVDD, AGND) and digital (DVDD, DGND) power supplies to the THS1040 must be separately decoupled for best performance. Each supply needs at least a 10-F electrolytic or tantalum capacitor (as a charge reservoir) and a 100-nF ceramic type capacitor placed as close as possible to the respective pins (to suppress spikes and supply noise). digital output loading and circuit board layout The THS1040 outputs are capable of driving rail-to-rail with up to 10 pF of load per pin at 40-MHz clock frequency and 3-V digital supply. Minimizing the load on the outputs improves THS1040 signal-to-noise performance by reducing the switching noise coupling from the THS1040 output buffers to the internal analog circuits. The output load capacitance can be minimized by buffering the THS1040 digital outputs with a low input capacitance buffer placed as close to the output pins as physically possible, and by using the shortest possible tracks between the THS1040 and this buffer. Inserting small resistors in the range 100 to 300 between the THS1040 I/O outputs and their loads can help minimize the output-related noise in noise-critical applications. Noise levels at the output buffers, which may affect the analog circuits within THS1040, increase with the digital supply voltage. Where possible, consider using the lowest DVDD that the application can tolerate. Use good layout practices when designing the application PCB to ensure that any off-chip return currents from the THS1040 digital outputs (and any other digital circuits on the PCB) do not return via the supplies to any sensitive analog circuits. The THS1040 should be soldered directly to the PCB for best performance. Socketing the device degrades performance by adding parasitic socket inductance and capacitance to all pins. user tips for obtaining best performance from the THS1040
D D D D D
Choose differential input mode for best distortion performance. Choose a 2-V ADC input span for best noise performance. Choose a 1-V ADC input span for best distortion performance. Drive the clock input CLK from a low-jitter, fast logic stage, with a well-decoupled power supply and short PCB traces. Use a small RC filter (typically 20 and 20 pF) between the signal source(s) the AIN+ (and AIN-) input(s) when the systems bandwidth requirements allow this.
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
APPLICATION INFORMATION definitions
D D
Integral nonlinearity (INL)--Integral nonlinearity refers to the deviation of each individual code from a line drawn from zero to full scale. The point used as zero occurs 1/2 LSB before the first code transition. The full-scale point is defined as a level 1/2 LSB beyond the last code transition. The deviation is measured from the center of each particular code to the true straight line between these two endpoints. Differential nonlinearity (DNL)--An ideal ADC exhibits code transitions that are exactly 1 LSB apart. DNL is the deviation from this ideal value. Therefore this measure indicates how uniform the transfer function step sizes are. The ideal step size is defined here as the step size for the device under test (i.e., (last transition level - first transition level) / (2n - 2)). Using this definition for DNL separates the effects of gain and offset error. A minimum DNL better than -1 LSB ensures no missing codes. Zero-error--Zero-error is defined as the difference in analog input voltage--between the ideal voltage and the actual voltage--that switches the ADC output from code 0 to code 1. The ideal voltage level is determined by adding the voltage corresponding to 1/2 LSB to the bottom reference level. The voltage corresponding to 1 LSB is found from the difference of top and bottom references divided by the number of ADC output levels (1024). Full-scale error--Full-scale error is defined as the difference in analog input voltage--between the ideal voltage and the actual voltage--that switches the ADC output from code 1022 to code 1023. The ideal voltage level is determined by subtracting the voltage corresponding to 1.5 LSB from the top reference level. The voltage corresponding to 1 LSB is found from the difference of top and bottom references divided by the number of ADC output levels (1024). Wake-up time--Wake-up time is from the power-down state to accurate ADC samples being taken and is specified for MODE = AGND with external reference sources applied to the device at the time of release of power-down, and an applied 40-MHz clock. Circuits that need to power up are the bandgap, bias generator, ADC, and SHA. Power-up time--Power-up time is from the power-down state to accurate ADC samples being taken and is specified for MODE = AVDD/2 or AVDD and an applied 40-MHz clock. Circuits that need to power up include VREF reference generation (A1), bias generator, ADC, the SHA, and the on-chip ADC reference generator (A2). Aperture delay--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)--The sample-to-sample variation in aperture delay.
D
D
D D D D
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
MECHANICAL DATA
DW (R-PDSO-G**)
16 PINS SHOWN 0.050 (1,27) 16 0.020 (0,51) 0.014 (0,35) 9
PLASTIC SMALL-OUTLINE
0.010 (0,25) M
0.419 (10,65) 0.400 (10,15) 0.299 (7,59) 0.293 (7,45) 0.010 (0,25) NOM
Gage Plane 0.010 (0,25) 1 A 8 0- 8 0.050 (1,27) 0.016 (0,40)
Seating Plane 0.104 (2,65) MAX 0.012 (0,30) 0.004 (0,10) PINS ** DIM A MAX 0.004 (0,10)
16 0.410 (10,41) 0.400 (10,16)
20 0.510 (12,95) 0.500 (12,70)
24 0.610 (15,49) 0.600 (15,24)
28 0.710 (18,03) 0.700 (17,78) 4040000 / C 07/96
A MIN
NOTES: A. B. C. D.
All linear dimensions are in inches (millimeters). This drawing is subject to change without notice. Body dimensions do not include mold flash or protrusion not to exceed 0.006 (0,15). Falls within JEDEC MS-013
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THS1040
SLAS290B - OCTOBER 2001 - REVISED MARCH 2002
MECHANICAL DATA
PW (R-PDSO-G**)
14 PINS SHOWN
PLASTIC SMALL-OUTLINE
0,65 14 8
0,30 0,19
0,10 M
0,15 NOM 4,50 4,30 6,60 6,20 Gage Plane 0,25 1 A 7 0- 8 0,75 0,50
Seating Plane 1,20 MAX 0,15 0,05 0,10
PINS ** DIM A MAX
8
14
16
20
24
28
3,10
5,10
5,10
6,60
7,90
9,80
A MIN
2,90
4,90
4,90
6,40
7,70
9,60
4040064/F 01/97 NOTES: A. B. C. D. All linear dimensions are in millimeters. This drawing is subject to change without notice. Body dimensions do not include mold flash or protrusion not to exceed 0,15. Falls within JEDEC MO-153
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