AD1674

a FEATURES Complete Monolithic 12-Bit 10 s Sampling ADC On-Board Sample-and-Hold Amplifier Industry Standard Pinout 8- and 16-Bit Microprocessor Interface AC and DC Specified and Tested Unipolar and Bipolar Inputs 5 V, 10 V, 0 V–10 V, 0 V–20 V Input Ranges Commercial, Industrial and Military Temperature Range Grades MIL-STD-883 and SMD Compliant Versions Available 12/8 CS A 0 CE R/C REF OUT 10V REF CLOCK 12-Bit 100 kSPS A/D Converter AD1674* FUNCTIONAL BLOCK DIAGRAM STS REGISTERS / 3-STATE OUTPUT BUFFERS CONTROL SAR 12 AGND 20k REF IN 5k BIP OFF 20V IN COMP 10k 10k IDAC 12 12 DB11 (MSB) DB0 (LSB) 5k 2.5k 2.5k SHA DAC 10VIN 5k AD1674 PRODUCT DESCRIPTION PRODUCT HIGHLIGHTS The AD1674 is a complete, multipurpose, 12-bit analog-todigital converter, consisting of a user-transparent onboard sample-and-hold amplifier (SHA), 10 volt reference, clock and three-state output buffers for microprocessor interface. The AD1674 is pin compatible with the industry standard AD574A and AD674A, but includes a sampling function while delivering a faster conversion rate. The on-chip SHA has a wide input bandwidth supporting 12-bit accuracy over the full Nyquist bandwidth of the converter. The AD1674 is fully specified for ac parameters (such as S/(N+D) ratio, THD, and IMD) and dc parameters (offset, full-scale error, etc.). With both ac and dc specifications, the AD1674 is ideal for use in signal processing and traditional dc measurement applications. The AD1674 design is implemented using Analog Devices’ BiMOS II process allowing high performance bipolar analog circuitry to be combined on the same die with digital CMOS logic. Five different temperature grades are available. The AD1674J and K grades are specified for operation over the 0°C to +70°C temperature range. The A and B grades are specified from –40°C to +85°C; the AD1674T grade is specified from –55°C to +125°C. The J and K grades are available in both 28-lead plastic DIP and SOIC. The A and B grade devices are available in 28-lead hermetically sealed ceramic DIP and 28-lead SOIC. The T grade is available in 28-lead hermetically sealed ceramic DIP. *Protected by U. S. Patent Nos. 4,962,325; 4,250,445; 4,808,908; RE30586 . 1. Industry Standard Pinout: The AD1674 utilizes the pinout established by the industry standard AD574A and AD674A. 2. Integrated SHA: The AD1674 has an integrated SHA which supports the full Nyquist bandwidth of the converter. The SHA function is transparent to the user; no wait-states are needed for SHA acquisition. 3. DC and AC Specified: In addition to traditional dc specifications, the AD1674 is also fully specified for frequency domain ac parameters such as total harmonic distortion, signal-to-noise ratio and input bandwidth. These parameters can be tested and guaranteed as a result of the onboard SHA. 4. Analog Operation: The precision, laser-trimmed scaling and bipolar offset resistors provide four calibrated ranges: 0 V to +10 V and 0 V to +20 V unipolar, –5 V to +5 V and –10 V to +10 V bipolar. The AD1674 operates on +5 V and ± 12 V or ± 15 V power supplies. 5. Flexible Digital Interface: On-chip multiple-mode three-state output buffers and interface logic allow direct connection to most microprocessors. REV. C 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. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703 AD1674–SPECIFICATIONS DC SPECIFICATIONS –12 V Parameter RESOLUTION INTEGRAL NONLINEARITY (INL) DIFFERENTIAL NONLINEARITY (DNL) (No Missing Codes) UNIPOLAR OFFSET 1 @ +25°C BIPOLAR OFFSET1 @ +25°C FULL-SCALE ERROR1, 2 @ +25°C (with Fixed 50 Ω Resistor from REF OUT to REF IN) TEMPERATURE RANGE TEMPERATURE DRIFT 3 Unipolar Offset2 Bipolar Offset2 Full-Scale Error2 POWER SUPPLY REJECTION VCC = 15 V ± 1.5 V or 12 V ± 0.6 V VLOGIC = 5 V ± 0.5 V VEE = –15 V ± 1.5 V or –12 V ± 0.6 V ANALOG INPUT Input Ranges Bipolar Unipolar Input Impedance 10 Volt Span 20 Volt Span POWER SUPPLIES Operating Voltages VLOGIC VCC VEE Operating Current ILOGIC ICC IEE POWER DISSIPATION INTERNAL REFERENCE VOLTAGE Output Current (Available for External Loads) 4 (External Load Should Not Change During Conversion NOTES 1 Adjustable to zero. 2 Includes internal voltage reference error. 3 Maximum change from 25 °C value to the value at T MIN or TMAX. 4 Reference should be buffered for ± 12 V operation. All min and max specifications are guaranteed. Specifications subject to change without notice. (TMIN to TMAX, VCC = +15 V 10% or +12 V 5% unless otherwise noted) Min 12 5%, VLOGIC = +5 V AD1674J Typ 10%, VEE = –15 V 10% or Max Min 12 AD1674K Typ Max Unit Bits ±1 ± 1/2 LSB 12 ±3 ±6 0.1 0 0.25 +70 ±2 ±2 ±6 ±2 ± 1/2 ±2 12 ±2 ±4 0.1 0 0.25 +70 ±1 ±1 ±3 ±1 ± 1/2 ±1 Bits LSB LSB % of FSR °C LSB LSB LSB LSB LSB LSB –5 –10 0 0 3 6 5 10 +5 +10 +10 +20 7 14 –5 –10 0 0 3 6 5 10 +5 +10 +10 +20 7 14 Volts Volts Volts Volts kΩ kΩ +4.5 +11.4 –16.5 5 10 14 385 9.9 10.0 +5.5 +16.5 –11.4 8 14 18 575 10.1 2.0 +4.5 +11.4 –16.5 5 10 14 385 9.9 10.0 +5.5 +16.5 –11.4 8 14 18 575 10.1 2.0 Volts Volts Volts mA mA mA mW Volts mA –2– REV. C AD1674 AD1674A Typ Max AD1674B Typ Max AD1674T Typ Max Parameter RESOLUTION INTEGRAL NONLINEARITY (INL) DIFFERENTIAL NONLINEARITY (DNL) (No Missing Codes) UNIPOLAR OFFSET 1 @ +25°C BIPOLAR OFFSET @ +25°C 1 Min 12 Min 12 Min 12 Unit Bits ±1 ±1 12 ±2 ±6 0.1 –40 0.25 +85 ±2 ±2 ±8 ±2 ± 1/2 ±2 –40 0.1 12 ± 1/2 ± 1/2 12 ±2 ±3 0.125 +85 ±1 ±1 ±5 ±1 ± 1/2 ±1 –55 0.1 ± 1/2 ±1 LSB LSB Bits ±2 ±3 0.125 +125 ±1 ±2 ±7 ±1 ± 1/2 ±1 LSB LSB % of FSR °C LSB LSB LSB LSB LSB LSB FULL-SCALE ERROR1, 2 @ +25°C (with Fixed 50 Ω Resistor from REF OUT to REF IN) TEMPERATURE RANGE TEMPERATURE DRIFT 3 Unipolar Offset2 Bipolar Offset2 Full-Scale Error2 POWER SUPPLY REJECTION VCC = 15 V ± 1.5 V or 12 V ± 0.6 V VLOGIC = 5 V ± 0.5 V VEE = –15 V ± 1.5 V or –12 V ± 0.6 V ANALOG INPUT Input Ranges Bipolar Unipolar Input Impedance 10 Volt Span 20 Volt Span POWER SUPPLIES Operating Voltages VLOGIC VCC VEE Operating Current ILOGIC ICC IEE POWER DISSIPATION INTERNAL REFERENCE VOLTAGE Output Current (Available for External Loads) 4 (External Load Should Not Change During Conversion 9.9 –5 –10 0 0 3 6 5 10 +5 +10 +10 +20 7 14 –5 –10 0 0 3 6 5 10 +5 +10 +10 +20 7 14 –5 –10 0 0 3 6 5 10 +5 +10 +10 +20 7 14 Volts Volts Volts Volts kΩ kΩ +4.5 +11.4 –16.5 5 10 14 385 10.0 +5.5 +4.5 +16.5 +11.4 –11.4 –16.5 8 14 18 575 10.1 2.0 9.9 5 10 14 385 10.0 +5.5 +4.5 +16.5 +11.4 –11.4 –16.5 8 14 18 575 10.1 2.0 9.9 5 10 14 385 10.0 +5.5 +16.5 –11.4 8 14 18 575 10.1 2.0 Volts Volts Volts mA mA mA mW Volts mA REV. C –3– AD1674–SPECIFICATIONS AC SPECIFICATIONS Parameter Signal to Noise and Distortion (S/N+D) Ratio2, 3 Total Harmonic Distortion (THD) 4 (TMIN to TMAX, with VCC = +15 V 10% or +12 V 5%, VLOGIC = +5 V 10%, VEE = –15 V 10% or –12 V 5%, fSAMPLE = 100 kSPS, fIN = 10 kHz, stand-alone mode unless otherwise noted)1 Min 69 AD1674J/A Typ Max 70 –90 –92 1 500 –90 –90 50 250 1 –80 –80 –82 0.008 –82 1 500 –90 –90 50 250 1 –80 –80 Min 70 AD1674K/B/T Typ Max 71 –90 –92 –82 0.008 –82 Units dB dB % dB MHz kHz dB dB ns ps µs Peak Spurious or Peak Harmonic Component Full Power Bandwidth Full Linear Bandwidth Intermodulation Distortion (IMD)5 Second Order Products Third Order Products SHA (Specifications are Included in Overall Timing Specifications) Aperture Delay Aperture Jitter Acquisition Time DIGITAL SPECIFICATIONS V Parameter (for all grades TMIN to TMAX, with VCC = +15 V 10% or –12 V 5%) EE = –15 V Test Conditions 10% or +12 V Min +2.0 –0.5 –10 –10 5%, VLOGIC = +5 V Max VLOGIC +0.5 V +0.8 +10 +10 10 10%, Units V V µA µA pF V V µA pF LOGIC INPUTS VIH High Level Input Voltage VIL Low Level Input Voltage IIH High Level Input Current (VIN = 5 V) IIL Low Level Input Current (VIN = 0 V) CIN Input Capacitance LOGIC OUTPUTS VOH High Level Output Voltage VOL Low Level Output Voltage IOZ High-Z Leakage Current COZ High-Z Output Capacitance VIN = VLOGIC VIN = 0 V IOH = 0.5 mA IOL = 1.6 mA VIN = 0 to VLOGIC +2.4 –10 +0.4 +10 10 NOTES 1 fIN amplitude = –0.5 dB (9.44 V p-p) 10 V bipolar mode unless otherwise noted. All measurements referred to –0 dB (9.997 V p-p) input signal unless otherwise noted. 2 Specified at worst case temperatures and supplies after one minute warm-up. 3 See Figures 12 and 13 for other input frequencies and amplitudes. 4 See Figure 11. 5 fa = 9.08 kHz, fb = 9.58 kHz with f SAMPLE = 100 kHz. See Definition of Specifications section and Figure 15. All min and max specifications are guaranteed. Specifications subject to change without notice. –4– REV. C AD1674 SWITCHING SPECIFICATIONS CONVERTER START TIMING (Figure 1) Parameter Conversion Time 8-Bit Cycle 12-Bit Cycle STS Delay from CE CE Pulse Width CS to CE Setup CS Low During CE High R/C to CE Setup R/C Low During CE High A0 to CE Setup A0 Valid During CE High J, K, A, B, Grades T Grade Symbol Min Typ Max Min Typ Max Units tC tC tDSC tHEC tSSC tHSC tSRC tHRC tSAC tHAC 7 9 50 50 50 50 50 0 50 8 10 200 50 50 50 50 50 0 50 7 9 8 µs 10 µs 225 ns ns ns ns ns ns ns ns tHEC tHSC tSSC tSRC tHRC (for all grades TMIN to TMAX with VCC = +15 V 10% or +12 V 5%, VLOGIC = +5 V 10%, VEE = –15 V 10% or –12 V 5%; VIL = 0.4 V, VIH = 2.4 V unless otherwise noted) CE __ CS _ R/C A0 tSAC tHAC tC STS DB11 – DB0 tDSC READ TIMING—FULL CONTROL MODE (Figure 2) Parameter Access Time Data Valid After CE Low Output Float Delay CS to CE Setup R/C to CE Setup A0 to CE Setup CS Valid After CE Low R/C High After CE Low A0 Valid After CE Low J, K, A, B, Grades T Grade Symbol Min Typ Max Min Typ Max Units tDD1 tHD tHL5 tSSR tSRR tSAR tHSR tHRR tHAR 75 252 203 150 50 0 50 0 0 50 50 0 50 0 0 50 150 252 154 75 150 ns ns ns 150 ns ns ns ns ns ns ns HIGH IMPEDANCE Figure 1. Converter Start Timing CE __ CS tSSR _ R/C tHSR tSSR tHRR A0 tSAR tHS NOTES 1 tDD is measured with the load circuit of Figure 3 and is defined as the time required for an output to cross 0.4 V or 2.4 V. 2 0°C to TMAX. 3 At –40°C. 4 At –55°C. 5 tHL is defined as the time required for the data lines to change 0.5 V when loaded with the circuit of Figure 3. All min and max specifications are guaranteed. Specifications subject to change without notice. tHAR STS tHD DB11 – DB0 HIGH IMPEDANCE DATA VALID HIGH IMP. tDD tHL Figure 2. Read Timing Test Access Time High Z to Logic Low Float Time Logic High to High Z Access Time High Z to Logic High Float Time Logic Low to High Z VCP 5V 0V 0V 5V COUT 100 pF 10 pF 100 pF 10 pF DOUT COUT IOL VCP IOH Figure 3. Load Circuit for Bus Timing Specifications REV. C –5– AD1674 TIMING—STAND-ALONE MODE (Figures 4a and 4b) Parameter Data Access Time Low R/C Pulse Width STS Delay from R/C Data Valid After R/C Low STS Delay After Data Valid High R/C Pulse Width Symbol tDDR tHRL tDS tHDR tHS tHRH Min 50 J, K, A, B Grades Typ Max 150 Min 50 T Grade Typ Max 150 225 Units ns ns ns ns µs ns 200 25 0.6 150 0.8 1.2 25 0.6 150 0.8 1.2 NOTE All min and max specifications are guaranteed. Specifications subject to change without notice. tHRL _ R/C _ R/C tHRH tDS STS STS tDS tC tHDR DB11 – DB0 DATA VALID HIGH-Z DATA VALID tDDR tHS DB11 – DB0 HIGH-Z tHDR DATA VALID tC HIGH-Z tHL Figure 4a. Stand-Alone Mode Timing Low Pulse for R/C ABSOLUTE MAXIMUM RATINGS* Figure 4b. Stand-Alone Mode Timing High Pulse for R/C VCC to Digital Common . . . . . . . . . . . . . . . . . . . 0 to + 16.5 V VEE to Digital Common . . . . . . . . . . . . . . . . . . . . . 0 to –16.5 V VLOGIC to Digital Common . . . . . . . . . . . . . . . . . . 0 V to +7 V Analog Common to Digital Common . . . . . . . . . . . . . . . ± 1 V Digital Inputs to Digital Common . . . –0.5 V to VLOGIC +0.5 V Analog Inputs to Analog Common . . . . . . . . . . . . VEE to VCC 20 VIN to Analog Common . . . . . . . . . . . . . . . . . VEE to +24 V REF OUT . . . . . . . . . . . . . . . . . Indefinite Short to Common . . . . . . . . . . . . . . . . . . . . . . . . . . . Momentary Short to VCC Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . +175°C Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 825 mW Lead Temperature, Soldering (10 sec) . . . . . . . +300°C, 10 sec Storage Temperature . . . . . . . . . . . . . . . . . . . –65°C to +150°C *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 indicated in the operational section 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 the AD1674 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. ORDERING GUIDE WARNING! ESD SENSITIVE DEVICE Model1 AD1674JN AD1674KN AD1674JR AD1674KR AD1674AR AD1674BR AD1674AD AD1674BD AD1674TD Temperature Range 0°C to +70°C 0°C to +70°C 0°C to +70°C 0°C to +70°C –40°C to +85°C –40°C to +85°C –40°C to +85°C –40°C to +85°C –55°C to +125°C INL (TMIN to TMAX) ± 1 LSB ± 1/2 LSB ± 1 LSB ± 1/2 LSB ± 1 LSB ± 1/2 LSB ± 1 LSB ± 1/2 LSB ± 1 LSB S/(N+D) (TMIN to TMAX) 69 dB 70 dB 69 dB 70 dB 69 dB 70 dB 69 dB 70 dB 70 dB Package Description Plastic DIP Plastic DIP Plastic SOIC Plastic SOIC Plastic SOIC Plastic SOIC Ceramic DIP Ceramic DIP Ceramic DIP Package Option2 N-28 N-28 R-28 R-28 R-28 R-28 D-28 D-28 D-28 NOTES 1 For details on grade and package offerings screened in accordance with MIL-STD-883, refer to the Analog Devices Military Products Databook or current AD1674/883B data sheet. SMD is also available. 2 N = Plastic DIP; D = Hermetic Ceramic DIP; R = Plastic SOIC. –6– REV. C AD1674 PIN DESCRIPTION Symbol AGND A0 Pin No. Type 9 4 P DI Name and Function Analog Ground (Common). Byte Address/Short Cycle. If a conversion is started with A0 Active LOW, a full 12-bit conversion cycle is initiated. If A0 is Active HIGH during a convert start, a shorter 8-bit conversion cycle results. During Read (R/C = 1) with 12/8 LOW, A0 = LOW enables the 8 most significant bits (DB4–DB11), and A0 = HIGH enables DB3–DB0 and sets DB7–DB4 = 0. Bipolar Offset. Connect through a 50 Ω resistor to REF OUT for bipolar operation or to Analog Common for unipolar operation. Chip Enable. Chip Enable is Active HIGH and is used to initiate a convert or read operation. Chip Select. Chip Select is Active LOW. Data Bits 11 through 8. In the 12-bit format (see 12/8 and A0 pins), these pins provide the upper 4 bits of data. In the 8-bit format, they provide the upper 4 bits when A0 is LOW and are disabled when A0 is HIGH. Data Bits 7 through 4. In the 12-bit format these pins provide the middle 4 bits of data. In the 8-bit format they provide the middle 4 bits when Ao is LOW and all zeroes when A0 is HIGH. Data Bits 3 through 0. In the 12-bit format these pins provide the lower 4 bits of data. In the 8-bit format these pins provide the lower 4 bits of data when A0 is HIGH, they are disabled when A0 is LOW. Digital Ground (Common). +10 V Reference Output. Read/Convert. In the full control mode R/C is Active HIGH for a read operation and Active LOW for a convert operation. In the stand-alone mode, the falling edge of R/C initiates a conversion. Reference Input is connected through a 50 Ω resistor to +10 V Reference for normal operation. Status is Active HIGH when a conversion is in progress and goes LOW when the conversion is completed. +12 V/+15 V Analog Supply. –12 V/–15 V Analog Supply. +5 V Logic Supply. 10 V Span Input, 0 V to +10 V unipolar mode or –5 V to +5 V bipolar mode. When using the AD1674 in the 20 V Span 10 VIN should not be connected. 20 V Span Input, 0 V to +20 V unipolar mode or –10 V to +10 V bipolar mode. When using the AD1674 in the 10 V Span 20 VIN should not be connected. The 12/8 pin determines whether the digital output data is to be organized as two 8-bit words (12/8 LOW) or a single 12-bit word (12/8 HIGH). FUNCTIONAL BLOCK DIAGRAM 12/8 CS A 0 CE R/C REF OUT 10V REF CLOCK SAR 12 BIP OFF CE CS DB11–DB8 12 6 3 27–24 AI DI DI DO DB7–DB4 DB3–DB0 23–20 19–16 DO DO DGND REF OUT R/C REF IN STS VCC VEE VLOGIC 10 VIN 20 VIN 12/8 TYPE: AI AO DI DO P = = = = = 15 8 5 10 28 7 11 1 13 14 2 P AO DI AI DO P P P AI AI DI Analog Input Analog Output Digital Input Digital Output Power PIN CONFIGURATION VLOGIC 1 2 3 4 5 6 7 8 9 10 28 27 STS DB11(MSB) STS REGISTERS / 3-STATE OUTPUT BUFFERS CONTROL 12/8 CS A0 R/C CE VCC REF OUT 26 DB10 25 24 23 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0(LSB) DGND AD1674 TOP VIEW (Not to Scale) 22 21 20 19 18 17 16 15 AGND 20k REF IN 5k BIP OFF 20V IN COMP 10k 10k IDAC 12 12 DB11 (MSB) DB0 (LSB) AGND REF IN VEE 11 BIP OFF 10VIN 20VIN 12 13 14 5k 2.5k 2.5k SHA DAC 10VIN 5k AD1674 REV. C –7– AD1674 DEFINITION OF SPECIFICATIONS INTEGRAL NONLINEARITY (INL) are present in a sample sequence. The result, called Prime Coherent Sampling, is a highly accurate and repeatable measure of the actual frequency-domain response of the converter. NYQUIST FREQUENCY The ideal transfer function for an ADC is a straight line drawn between “zero” and “full scale.” The point used as “zero” occurs 1/2 LSB before the first code transition. “Full scale” is defined as a level 1 1/2 LSB beyond the last code transition. Integral nonlinearity is the worst-case deviation of a code from the straight line. The deviation of each code is measured from the middle of that code. DIFFERENTIAL NONLINEARITY (DNL) An implication of the Nyquist sampling theorem, the “Nyquist Frequency” of a converter is that input frequency which is onehalf the sampling frequency of the converter. SIGNAL-TO-NOISE AND DISTORTION (S/N+D) RATIO A specification which guarantees no missing codes requires that every code combination appear in a monotonic increasing sequence as the analog input level is increased. Thus every code must have a finite width. The AD1674 guarantees no missing codes to 12-bit resolution; all 4096 codes are present over the entire operating range. UNIPOLAR OFFSET S/(N+D) is the ratio of the rms value of the measured input signal to the rms sum of all other spectral components below the Nyquist frequency, including harmonics but excluding dc. The value for S/(N+D) is expressed in decibels. TOTAL HARMONIC DISTORTION (THD) The first transition should occur at a level 1/2 LSB above analog common. Unipolar offset is defined as the deviation of the actual transition from that point at 25° C. This offset can be adjusted as shown in Figure 11. BIPOLAR OFFSET THD is the ratio of the rms sum of the first six harmonic components to the rms value of a full-scale input signal and is expressed as a percentage or in decibels. For input signals or harmonics that are above the Nyquist frequency, the aliased component is used. INTERMODULATION DISTORTION (IMD) In the bipolar mode the major carry transition (0111 1111 1111 to 1000 0000 0000) should occur for an analog value 1/2 LSB below analog common. The bipolar offset error specifies the deviation of the actual transition from that point at 25°C. This offset can be adjusted as shown in Figure 12. FULL-SCALE ERROR The last transition (from 1111 1111 1110 to 1111 1111 1111) should occur for an analog value 1 1/2 LSB below the nominal full scale (9.9963 volts for 10 volts full scale). The full-scale error is the deviation of the actual level of the last transition from the ideal level at 25°C. The full-scale error can be adjusted to zero as shown in Figures 11 and 12. TEMPERATURE DRIFT With inputs consisting of sine waves at two frequencies, fa and fb, any device with nonlinearities will create distortion products, of order (m+n), at sum and difference frequencies of mfa ± nfb, where m, n = 0, 1, 2, 3. . . . Intermodulation terms are those for which m or n is not equal to zero. For example, the second order terms are (fa + fb) and (fa – fb) and the third order terms are (2fa + fb), (2fa – fb), (fa + 2fb) and (fa – 2fb). The IMD products are expressed as the decibel ratio of the rms sum of the measured input signals to the rms sum of the distortion terms. The two signals are of equal amplitude and the peak value of their sums is –0.5 dB from full scale. The IMD products are normalized to a 0 dB input signal. FULL-POWER BANDWIDTH The full-power bandwidth is that input frequency at which the amplitude of the reconstructed fundamental is reduced by 3 dB for a full-scale input. FULL-LINEAR BANDWIDTH The temperature drifts for full-scale error, unipolar offset and bipolar offset specify the maximum change from the initial (25°C) value to the value at TMIN or TMAX. POWER SUPPLY REJECTION The effect of power supply error on the performance of the device will be a small change in full scale. The specifications show the maximum full-scale change from the initial value with the supplies at various limits. FREQUENCY-DOMAIN TESTING The full-linear bandwidth is the input frequency at which the slew rate limit of the sample-hold-amplifier (SHA) is reached. At this point, the amplitude of the reconstructed fundamental has degraded by less than –0.1 dB. Beyond this frequency, distortion of the sampled input signal increases significantly. APERTURE DELAY Aperture delay is a measure of the SHA’s performance and is measured from the falling edge of Read/Convert (R/C) to when the input signal is held for conversion. APERTURE JITTER The AD1674 is tested dynamically using a sine wave input and a 2048 point Fast Fourier Transform (FFT) to analyze the resulting output. Coherent sampling is used, wherein the ADC sampling frequency and the analog input frequency are related to each other by a ratio of integers. This ensures that an integral multiple of input cycles is captured, allowing direct FFT processing without windowing or digital filtering which could mask some of the dynamic characteristics of the device. In addition, the frequencies are chosen to he “relatively prime” (no common factors) to maximize the number of different ADC codes that Aperture jitter is the variation in aperture delay for successive samples and is manifested as noise on the input to the A/D. –8– REV. C Typical Dynamic Performance–AD1674 80 fSAMPLE = 100kSPS FULL-SCALE = +10V 0 S/(N+D) – dB 70 60 0dB INPUT –20dB INPUT –20 AMPLITUDE – dB THD –40 –60 –80 –100 –120 1 10 100 1000 10000 INPUT FREQUENCY – kHz 3RD HARMONIC 2NDHARMONIC 50 40 30 20 –60dB INPUT 10 0 1 10 100 1000 10000 INPUT FREQUENCY – kHz Figure 5. Harmonic Distortion vs. Input Frequency 0 –20 Figure 6. S/(N+D) vs. Input Frequency and Amplitude 0 –10 –20 –30 –40 –50 –60 –70 –80 –90 –100 –110 –120 –130 0 5 10 15 Figure 7. S/(N+D) vs. Input Amplitude AMPLITUDE – dB –40 –60 –80 –100 –120 –140 0 5 10 15 20 25 30 35 40 45 50 FREQUENCY – kHz AMPLITUDE – dB Figure 8. Nonaveraged 2048 Point FFT at 100 kSPS, fIN = 25.049 kHz GENERAL CIRCUIT OPERATION 30 20 25 FREQUENCY – kHz 35 40 45 50 Figure 9. IMD Plot for fIN = 9.08 kHz (fa), 9.58 kHz (fb) The AD1674 is a complete 12-bit, 10 µs sampling analog-todigital converter. A block diagram of the AD1674 is shown on page 7. When the control section is commanded to initiate a conversion (as described later), it places the sample-and-hold amplifier (SHA) in the hold mode, enables the clock, and resets the successive approximation register (SAR). Once a conversion cycle has begun, it cannot be stopped or restarted and data is not available from the output buffers. The SAR, timed by the internal clock, will sequence through the conversion cycle and return an end-of-convert flag to the control section when the conversion has been completed. The control section will then disable the clock, switch the SHA to sample mode, and delay the STS LOW going edge to allow for acquisition to 12-bit accuracy. The control section will allow data read functions by external command anytime during the SHA acquisition interval. During the conversion cycle, the internal 12-bit, 1 mA full-scale current output DAC is sequenced by the SAR from the most significant bit (MSB) to the least significant bit (LSB) to provide an output that accurately balances the current through the 5 kΩ resistor from the input signal voltage held by the SHA. The SHA’s input scaling resistors divide the input voltage by 2 for the 10 V input span and by 4 V for the 20 V input span, maintaining a 1 mA full-scale output current through the 5 kΩ resistor for both ranges. The comparator determines whether the addition of each successively weighted bit current causes the REV. C –9– DAC current sum to be greater than or less than the input current. If the sum is less, the bit is left on; if more, the bit is turned off. After testing all the bits, the SAR contains a 12-bit binary code which accurately represents the input signal to within ± 1/2 LSB. CONTROL LOGIC The AD1674 may be operated in one of two modes, the fullcontrol mode and the stand-alone mode. The full-control mode utilizes all the AD1674 control signals and is useful in systems that address decode multiple devices on a single data bus. The stand-alone mode is useful in systems with dedicated input ports available and thus not requiring full bus interface capability. Table I is a truth table for the AD1674, and Figure 10 illustrates the internal logic circuitry. Table I. AD1674A Truth Table CE CS 0 X 1 1 1 1 1 X 1 0 0 0 0 0 R/C X X 0 0 1 1 1 12/8 A0 Operation X X X X 1 0 0 X X 0 1 X 0 1 None None Initiate 12-Bit Conversion Initiate 8-Bit Conversion Enable 12-Bit Parallel Output Enable 8 Most Significant Bits Enable 4 LSBs +4 Trailing Zeroes AD1674 VALUE OF A AT LAST 0 CONVERT COMMAND D Q EN D Q QB EN EOC 12 EOC 8 R S S Q R QB CE 1µs DELAY-HOLD SETTLING CLK ENABLE CS STATUS R/C 1µs DELAY-ACQUISITION A0 12/8 READ NYBBLE A NYBBLE B NYBBLE C NYBBLE B = 0 TO OUTPUT BUFFERS HOLD/SAMPLE Q SAR RESET Figure 10. Equivalent Internal Logic Circuitry FULL-CONTROL MODE Chip Enable (CE), Chip Select (CS) and Read/ Convert (R/C) are used to control Convert or Read modes of operation. Either CE or CS may be used to initiate a conversion. The state of R/C when CE and CS are both asserted determines whether a data Read (R/C = 1) or a Convert (R/C = 0) is in progress. R/C should be LOW before both CE and CS are asserted; if R/C is HIGH, a Read operation will momentarily occur, possibly resulting in system bus contention. STAND-ALONE MODE The register control inputs, A0 and 12/8, control conversion length and data format. If a conversion is started with A0 LOW, a full 12-bit conversion cycle is initiated. If A0 is HIGH during a convert start, a shorter 8-bit conversion cycle results. During data read operations, A0 determines whether the threestate buffers containing the 8 MSBs of the conversion result (A0 = 0) or the 4 LSBs (A0 = 1) are enabled. The 12/8 pin determines whether the output data is to be organized as two 8-bit words (12/8 tied LOW) or a single 12-bit word (12/8 tied HIGH). In the 8-bit mode, the byte addressed when A0 is high contains the 4 LSBs from the conversion followed by four trailing zeroes. This organization allows the data lines to be overlapped for direct interface to 8-bit buses without the need for external three-state buffers. INPUT CONNECTIONS AND CALIBRATION The AD1674 can be used in a “stand-alone” mode, which is useful in systems with dedicated input ports available and thus not requiring full bus interface capability. Stand-alone mode applications are generally able to issue conversion start commands more precisely than full-control mode. This improves ac performance by reducing the amount of control-induced aperture jitter. In stand-alone mode, the control interface for the AD1674 and AD674A are identical. CE and 12/8 are wired HIGH, CS and A0 are wired LOW, and conversion is controlled by R/C. The three-state buffers are enabled when R/C is HIGH and a conversion starts when R/C goes LOW. This gives rise to two possible control signals—a high pulse or a low pulse. Operation with a low pulse is shown in Figure 4a. In this case, the outputs are forced into the high impedance state in response to the falling edge of R/C and return to valid logic levels after the conversion cycle is completed. The STS line goes HIGH 200 ns after R/C goes LOW and returns low 1 µs after data is valid. If conversion is initiated by a high pulse as shown in Figure 4b, the data lines are enabled during the time when R/C is HIGH. The falling edge of R/C starts the next conversion and the data lines return to three-state (and remain three-state) until the next high pulse of R/C. CONVERSION TIMING The 10 V p-p and 20 V p-p full-scale input ranges of the AD1674 accept the majority of signal voltages without the need for external voltage divider networks which could deteriorate the accuracy of the ADC. The AD1674 is factory trimmed to minimize offset, linearity, and full-scale errors. In many applications, no calibration trimming will be required and the AD1674 will exhibit the accuracy limits listed in the specification tables. In some applications, offset and full-scale errors need to be trimmed out completely. The following sections describe the correct procedure for these various situations. UNIPOLAR RANGE INPUTS Once a conversion is started, the STS line goes HIGH. Convert start commands will be ignored until the conversion cycle is complete. The output data buffers will be enabled a minimum of 0.6 µs prior to STS going LOW. The STS line will return LOW at the end of the conversion cycle. Figure 11 illustrates the external connections for the AD1674 in unipolar-input mode. The first output-code transition (from 0000 0000 0000 to 0000 0000 0001) should nominally occur for an input level of +1/2 LSB (1.22 mV above ground for a 10 V range; 2.44 mV for a 20 V range). To trim unipolar offset to this nominal value, apply a +1/2 LSB signal between Pin 13 and ground (10 V range) or Pin 14 and ground (20 V range) and adjust R1 until the first transition is located. If the offset trim is not required, Pin 12 can be connected directly to Pin 9; the two resistors and trimmer for Pin 12 are then not needed. –10– REV. C AD1674 R1 100k –15V +15V R2 100Ω 2 3 4 5 6 10 8 12 12/8 CS A 0 STS 28 HIGH BITS 24-27 MIDDLE BITS 20-23 LOW BITS 16-19 REFERENCE DECOUPLING 100k 100Ω R/C CE REF IN REF OUT BIP OFF It is recommended that a 10 µF tantalum capacitor be connected between REF IN (Pin 10) and ground. This has the effect of improving the S/(N+D) ratio through filtering possible broad-band noise contributions from the voltage reference. BOARD LAYOUT 0 TO +10V ANALOG INPUTS 0 TO +20V AD1674 13 10VIN 14 20VIN 9 ANA COM +5V 1 +15V 7 –15V 11 DIG COM 15 Figure 11. Unipolar Input Connections with Gain and Offset Trims The full-scale trim is done by applying a signal 1 1/2 LSB below the nominal full scale (9.9963 V for a 10 V range) and adjusting R2 until the last transition is located (1111 1111 1110 to 1111 1111 1111). If full-scale adjustment is not required, R2 should be replaced with a fixed 50 Ω ± 1% metal film resistor. If REF OUT is connected directly to REF IN, the additional full-scale error will be approximately 1%. BIPOLAR RANGE INPUTS Designing with high resolution data converters requires careful attention to board layout. Trace impedance is a significant issue. At the 12-bit level, a 5 mA current through a 0.5 Ω trace will develop a voltage drop of 2.5 mV, which is 1 LSB for a 10 V full-scale range. In addition to ground drops, inductive and capacitive coupling need to be considered, especially when high accuracy analog signals share the same board with digital signals. Finally, power supplies should be decoupled in order to filter out ac noise. The AD1674 has a wide bandwidth sampling front end. This means that the AD1674 will “see” high frequency noise at the input, which nonsampling (or limited-bandwidth sampling) ADCs would ignore. Therefore, it’s important to make an effort to eliminate such high frequency noise through decoupling or by using an anti-aliasing filter at the analog input of the AD1674. Analog and digital signals should not share a common path. Each signal should have an appropriate analog or digital return routed close to it. Using this approach, signal loops enclose a small area, minimizing the inductive coupling of noise. Wide PC tracks, large gauge wire, and ground planes are highly recommended to provide low impedance signal paths. Separate analog and digital ground planes are also desirable, with a single interconnection point to minimize ground loops. Analog signals should be routed as far as possible from digital signals and should cross them (if necessary) only at right angles. The AD1674 incorporates several features to help the user’s layout. Analog pins are adjacent to help isolate analog from digital signals. Ground currents have been minimized by careful circuit architecture. Current through AGND is 2.2 mA, with little code-dependent variation. The current through DGND is dominated by the return current for DB11–DB0. SUPPLY DECOUPLING The connections for the bipolar-input mode are shown in Figure 12. Either or both of the trimming potentiometers can be replaced with 50 Ω ± 1% fixed resistors if the specified AD1674 accuracy limits are sufficient for the application. If the pins are shorted together, the additional offset and gain errors will be approximately 1%. To trim bipolar offset to its nominal value, apply a signal 1/2 LSB below midrange (–1.22 mV for a ± 5 V range) and adjust R1 until the major carry transition is located (0111 1111 1111 to 1000 0000 0000). To trim the full-scale error, apply a signal 1 1/2 LSB below full scale (+4.9963 V for a ± 5 V range) and adjust R2 to give the last positive transition (1111 1111 1110 to 1111 1111 1111). These trims are interactive so several iterations may be necessary for convergence. A single-pass calibration can be done by substituting a negative full-scale trim for the bipolar offset trim (error at midscale), using the same circuit. First, apply a signal 1/2 LSB above minus full scale (–4.9988 V for a ± 5 V range) and adjust R1 until the minus full-scale transition is located (0000 0000 0001 to 0000 0000 0000). Then perform the gain error trim as outlined above. 2 3 4 5 6 10 8 12 12/8 CS A0 R/C CE REF IN REF OUT BIP OFF STS 28 HIGH BITS 24-27 MIDDLE BITS 20-23 LOW BITS 16-19 +5V 1 +15V 7 –15V 11 DIG COM 15 The AD1674 power supplies should be well filtered, well regulated, and free from high frequency noise. Switching power supplies are not recommended due to their tendency to generate spikes which can induce noise in the analog system. Decoupling capacitors should be used in very close layout proximity between all power supply pins and ground. A 10 µF tantalum capacitor in parallel with a 0.1 µF disc ceramic capacitor provides adequate decoupling over a wide range of frequencies. An effort should be made to minimize the trace length between the capacitor leads and the respective converter power supply and common pins. The circuit layout should attempt to locate the AD1674, associated analog input circuitry, and interconnections as far as possible from logic circuitry. A solid analog ground plane around the AD1674 will isolate large switching ground currents. For these reasons, the use of wire-wrap circuit construction is not recommended; careful printed-circuit construction is preferred. R2 100Ω ±5V ANALOG INPUTS ±10V R1 100Ω AD1674 13 10V IN 14 20VIN 9 ANA COM Figure 12. Bipolar Input Connections with Gain and Offset Trims REV. C –11– AD1674 GROUNDING PACKAGE INFORMATION Dimensions shown in inches and (mm). 0.505 (12.83) 28 15 0.59 ±0.01 (14.98 ±0.254) 1 14 1.42 (36.07) 1.40 (35.56) 0.145 ±0.02 (3.68 ±0.51) 0.125 (3.17) MIN 0.017 ±0.003 (0.43 ±0.076) 0.1 (2.54) 0.047 ±0.007 (1.19 ±0.178) 0.085 (2.16) SEATING PLANE 0.010 ±0.002 (0.254 ±0.05) 0.6 (15.24) 0.050 ±0.010 (1.27 ±0.254) 0.095 (2.41) PIN 1 GENERAL MICROPROCESSOR INTERFACE CONSIDERATIONS A typical A/D converter interface routine involves several operations. First, a write to the ADC address initiates a conversion. The processor must then wait for the conversion cycle to complete, since most ADCs take longer than one instruction cycle to complete a conversion. Valid data can, of course, only be read after the conversion is complete. The AD1674 provides an output signal (STS) which indicates when a conversion is in progress. This signal can be polled by the processor by reading it through an external three-state buffer (or other input port). The STS signal can also be used to generate an interrupt upon completion of a conversion, if the system timing requirements are critical (bear in mind that the maximum conversion time of the AD1674 is only 10 microseconds) and the processor has other tasks to perform during the ADC conversion cycle. Another possible time-out method is to assume that the ADC will take 10 microseconds to convert, and insert a sufficient number of “no-op” instructions to ensure that 10 microseconds of processor time is consumed. Once it is established that the conversion is finished, the data can be read. In the case of an ADC of 8-bit resolution (or less), a single data read operation is sufficient. In the case of converters with more data bits than are available on the bus, a choice of data formats is required, and multiple read operations are needed. The AD1674 includes internal logic to permit direct interface to 8-bit or 16-bit data buses, selected by the 12/8 input. In 16-bit bus applications (12/8 HIGH) the data lines (DB11 through DB0) may be connected to either the 12 most significant or 12 least significant hits of the data bus. The remaining four bits should be masked in software. The interface to an 8-bit data bus (12/8 LOW) contains the 8 MSBs (DB11 through DB4). The odd address (A0 HIGH) contains the 4 LSBs (DB3 through DB0) in the upper half of the byte, followed by four trailing zeroes, thus eliminating bit masking instructions. 28-Lead Plastic DIP Package (N-28) 28 15 0.550 (13.97) 0.530 (13.462) PIN 1 1 1.450 (38.83) 1.440 (35.576) 0.200 (5.080) MAX 14 0.160 (4.06) 0.140 (3.56) 0.606 (15.39) 0.594 (15.09) 0.175 (4.45) 0.120 (3.05) 0.020 (0.508) 0.015 (0.381) 0.105 (2.67) 0.095 (2.41) 0.065 (1.65) 0.045 (1.14) SEATING PLANE 15° 0° 0.012 (0.305) 0.008 (0.203) 28-Lead Wide-Body SO Package (R-28) 28 15 0.2992 (7.60) 0.2914 (7.40) PIN 1 1 14 0.4193 (10.65) 0.3937 (10.00) 0.0291 (0.74) x 45° 0.0098 (0.25) 0.0118 (0.30) 0.0040 (0.10) 0.0500 (1.27) BSC 0.0192 (0.49) 0.0138 (0.35) 0.0125 (0.32) 0.0091 (0.23) 8° 0° 0.0500 (1.27) 0.0157 (0.40) AD1674 Data Format for 8-Bit Bus –12– REV. C PRINTED IN U.S.A. 0.7125 (18.10) 0.6969 (17.70) 0.1043 (2.65) 0.0926 (2.35) C1425b–10–3/94 If a single AD1674 is used with separate analog and digital ground planes, connect the analog ground plane to AGND and the digital ground plane to DGND keeping lead lengths as short as possible. Then connect AGND and DGND together at the AD1674. If multiple AD1674s are used or the AD1674 shares analog supplies with other components, connect the analog and digital returns together once at the power supplies rather than at each chip. This prevents large ground loops which inductively couple noise and allow digital currents to flow through the analog system. 28-Pin Ceramic DIP Package (D-28)