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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 that may result from its use. no license is granted by implication or otherwise under any patent or patent rights of analog devices. a 10-bit 60 msps a/d converter ad9020 functional block diagram 1024 10 d e c o d e l o g i c r r r r r r r r analog in 512 384 c o m p a r a t o r l a t c h e s 257 256 129 128 2 1 msb invert lsbs invert overflow overflow d 9 (msb) d 8 d 7 d 6 d 5 d 4 d 3 d 2 d 1 d 0 (lsb) overflow 385 ground +v s ? s r/2 r/2 r/2 r/2 r/2 r/2 r/2 r/2 ? ref ? sense encode 1/4 ref 1/2 ref 3/4 ref +v sense +v ref ad9020 l a t c h features monolithic 10-bit/60 msps converter ttl outputs bipolar ( 1.75 v) analog input 56 db snr @ 2.3 mhz input low (45 pf) input capacitance mil-std-883-compliant versions available applications digital oscilloscopes medical imaging professional video radar warning/guidance systems infrared systems general description the ad9020 a/d converter is a 10-bit monolithic converter capable of word rates of 60 msps and above. innovative archi- tecture using 512 input comparators instead of the traditional 1024 required by other flash converters reduces input capaci- tance and improves linearity. encode and outputs are ttl-compatible, making the ad9020 an ideal candidate for use in low power systems. an over- flow bit is provided to indicate analog input signals greater than +v sense . voltage sense lines are provided to insure accurate driving of the v ref voltages applied to the units. quarter-point taps on the resistor ladder help optimize the integral linearity of the unit. either 68-pin ceramic leaded (gull wing) packages or ceramic lccs are available and are specifically designed for low thermal impedances. two performance grades for temperatures of both 0 c to 70 c and ?5 c to +125 c ranges are offered to allow the user to select the linearity best suited for each application. dynamic performance is fully characterized and production tested at 25 c. mil-std-883 units are available. the ad9020 a/d converter is available in versions compliant with mil-std-883. refer to the analog devices military prod- ucts databook or current ad9020/883b data sheet for detailed specifications. one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 781/329-4700 www.analog.com fax: 781/326-8703 ? analog devices, inc., 2001
rev. c C2C ad9020?pecifications electrical characteristics test ad9020je/jz ad9020ke/kz parameter (conditions) temp level min typ max min typ max unit resolution 10 10 bits dc accuracy 3 differential nonlinearity 25 c i 1.0 1.25 0.75 1.0 lsb full vi 1.5 1.25 lsb integral nonlinearity 25 c i 1.25 2.75 1.0 2.25 lsb full vi 3.0 2.50 lsb no missing codes full vi guaranteed analog input input bias current 4 25 c i 0.4 1.0 0.4 1.0 ma full vi 2.0 2.0 ma input resistance 25 c i 2.0 7.0 2.0 7.0 k ? input capacitance 4 25 c v 45 45 pf analog bandwidth 25 c v 175 175 mhz reference input reference ladder resistance 25 c i 22 37 56 22 37 56 ? full vi 14 66 14 66 ? ladder tempco full v 0.1 0.1 ? / c reference ladder offset top of ladder 25 c i 45 90 45 90 mv full vi 90 90 mv bottom of ladder 25 c i 45 90 45 90 mv full vi 90 90 mv offset drift coefficient full v 50 50 v/ c switching performance conversion rate 25 c i 60 60 msps aperture delay (t a )25 cv 1 1 ns aperture uncertainty (jitter) 25 c v 5 5 ps, rms output delay (t od ) 5 25 c i 6 10 13 6 10 13 ns output time skew 5 25 ci 35 35 ns dynamic performance transient response 25 c v 10 10 ns overvoltage recovery time 25 c v 10 10 ns effective number of bits (enob) f in = 2.3 mhz 25 c i 7.9 9.0 7.9 9.0 bits f in = 10.3 mhz 25 c iv 7.6 8.4 7.6 8.4 bits f in = 15.3 mhz 25 c iv 7.2 8.0 7.2 8.0 bits signal-to-noise ratio 6 f in = 2.3 mhz 25 c i 49.5 56 49.5 56 db f in = 10.3 mhz 25 c i 47.5 53 47.5 53 db f in = 15.3 mhz 25 c i 45.5 50 45.5 50 db signal-to-noise ratio 6 (without harmonics) f in = 2.3 mhz 25 c i 49.5 56 49.5 56 db f in = 10.3 mhz 25 c i 49.5 54 49.5 54 db f in = 15.3 mhz 25 c i 48 52 48 52 db ( v s = 5 v; v sense = 1.75 v; encode = 40 msps unless otherwise noted) absolute maximum ratings 1 +v s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +6 v ? s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 v analog in . . . . . . . . . . . . . . . . . . . . . . . . . . . ? v to +2 v +v ref , ? ref , 3/4 ref , 1/2 ref , 1/4 ref . . . . . . . . . . 2 v to +2 v +v ref to ? ref . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.0 v digital inputs . . . . . . . . . . . . . . . . . . . . . . .?.5 v to +v s 3/4 ref , 1/2 ref , 1/4 ref current . . . . . . . . . . . . . . . . . . . 10 ma digital output current . . . . . . . . . . . . . . . . . . . . . . . . . 20 ma operating temperature ad9020je/ke/jz/kz . . . . . . . . . . . . . . . . . . . . 0 c to 70 c storage temperature . . . . . . . . . . . . . . . . . . . ?5 c to +150 c maximum junction temperature 2 . . . . . . . . . . . . . . . . . 150 c lead soldering temp (10 sec) . . . . . . . . . . . . . . . . . . . . 300 c
test ad9020je/jz ad9020ke/kz parameter (conditions) temp level min typ max min typ max unit dynamic performance (continued) harmonic distortion f in = 2.3 mhz 25 c i 54.5 67 54.5 67 dbc f in = 10.3 mhz 25 c i 48.5 59 48.5 59 dbc f in = 15.3 mhz 25 c i 46.5 53 46.5 53 dbc two-tone intermodulation distortion rejection 7 25 c v 70 70 dbc differential phase 25 c v 0.5 0.5 degree differential gain 25 cv 1 1 % encode input logic ??voltage full vi 2.0 2.0 v logic ??voltage full vi 0.8 0.8 v logic ??current full vi 500 500 a logic ??current full vi 800 800 a input capacitance 25 cv 5 5 pf pulsewidth (high) 25 ci66ns pulsewidth (low) 25 ci66ns digital outputs logic ??voltage (i oh = 2 ma) full vi 2.4 2.4 v logic ??voltage (i ol = 6 ma) full vi 0.4 v power supply +v s supply current 25 c i 440 530 440 530 ma full vi 542 542 ma ? s supply current 25 c i 140 170 140 170 ma full vi 177 177 ma power dissipation 25 c i 2.8 3.3 2.8 3.3 w full vi 3.4 3.4 w power supply rejection ratio (psrr) 8 full vi 6 10 6 10 mv/v notes 1 absolute maximum ratings are limiting values to be applied individually, and beyond which the service ability of the circuit ma y be impaired. functional operability is not necessarily implied. exposure to absolute maximum rating conditions for an extended period of time may affect device reliab ility. 2 typical thermal impedances (part soldered onto board): 68-pin leaded ceramic chip carrier: jc = 1 c/w; ja = 17 c/w (no air flow); ja = 15 c/w (air flow = 500 lfm). 68-pin ceramic lcc: jc = 2.6 c/w; ja = 15 c/w (no air flow); ja = 13 c/w (air flow = 500 lfm). 3 3/4 ref , 1/2 ref , and 1/4 ref reference ladder taps are driven from dc sources at +0.875 v, 0 v, and ?.875 v, respectively. accuracy of the overflow compar ator is not tested and not included in linearity specifications. 4 measured with analog in = +v sense . 5 output delay measured as worst-case time from 50% point of the rising edge of encode to 50% point of the slowest rising or fall ing edge of d 0 ? 9 . output skew measured as worst-case difference in output delay among d 0 ? 9 . 6 rms signal to rms noise with analog input signal 1 db below full scale at specified frequency. 7 intermodulation measured with analog input frequencies of 2.3 mhz and 3.0 mhz at 7 db below full scale. 8 measured as the ratio of the worst-case change in transition voltage of a single comparator for a 5% change in +v s or ? s . specifications subject to change without notice. rev. c C3C ad9020
ad9020 C4C rev. c ordering guide temperature package device range description option * ad9020jz 0 c to 70 c 68-lead leaded ceramic z-68 ad9020je 0 c to 70 c 68-terminal ceramic lcc e-68a ad9020kz 0 c to 70 c 68-lead leaded ceramic z-68 ad9020ke 0 c to 70 c 68-terminal ceramic lcc e-68a ad9020sz/883 ?5 c to +125 c 68-lead leaded ceramic z-68 ad9020se/883 ?5 c to +125 c 68-terminal ceramic lcc e-68a ad9020tz/883 ?5 c to +125 c 68-lead leaded ceramic z-68 ad9020te/883 ?5 c to +125 c 68-terminal ceramic lcc e-68a ad9020/pcb 0 c to 70 c evaluation board * e = ceramic leadless chip carrier; z = ceramic leaded chip carrier. die layout and mechanical information die dimensions . . . . . . . . . . . . . . . 206 140 15 ( 2) mils pad dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4 mils metalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . gold backing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . none substrate potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v s passivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . nitride analog in msb invert lsbs invert overflow d 9 (msb) d 8 d 7 d 6 d 5 d 4 d 3 d 2 d 1 d 0 (lsb) ground +v s v s v ref v sense encode 1/4 ref 1/2 ref 3/4 ref +v sense +v ref analog in ground +v s +v s ground ground +v s v s nc ground v s v s +v s ground ground +v s +v s v s ground +v s ground ground +v s v s v s ground +v s +v s ground v s +v s ground +v s ground v s +v s +v s 46 51 ad9020 12 56 14 analog in msb invert lsbs invert d 0 d 4 ground +v s v s v ref encode +v ref 3,6,15,18,25,30,33,34, 37,40,45,52,55,65,68 2,16,28,29,35, 41,42,54,64 4,5,13,17, 27,31,32, 36,38,39, 43,53,66,67 d 5 d 9 510 510 510 100 +2v 2v ad2 ad1 5.0v 5.2v 0.1 f 0.1 f static: ad1 = 2v; ad2 = +2.4v dynamic: ad1 = 2v triangle wave ad2 = ttl pulse train 61 59 19 23 8 9 figure 1. burn-in circuit explanation of test levels test level i 100% production tested. ii 100% production tested at 25 c, and sample tested at specified temperatures. iii sample tested only. iv parameter is guaranteed by design and characterization testing. v parameter is a typical value only. vi all devices are 100% production tested at 25 c. 100% production tested at temperature extremes for extended temperature devices; sample tested at temperature e xtremes for commercial/industrial devices.
ad9020 C5C rev. c pin function descriptions pin no. name function 1 1/2 ref midpoint of internal reference ladder. 2, 16, 28, 29, 35, 41, 42, ? s negative supply voltage; nominally ?.0 v 5%. 54, 64 3, 6, 15, 18, 25, 30, 33, 34, +v s positive supply voltage; nominally 5 v 5%. 37, 40, 45, 52, 55, 65, 68 4, 5, 13, 17, 27, 31, 32, ground all ground pins should be connected together and to low impedance ground 36, 38, 39, 43, 53, 66, 67 plane. 7 3/4 ref three-quarter point of internal reference ladder. 8, 9 analog in analog input; nominally between 1.75 v. 11 +v sense voltage sense line to most positive point on internal resistor ladder. normally 1.75 v. 12 +v ref voltage force connection for top of internal reference ladder. normally driven to provide 1.75 v at +v sense . 14 encode ttl-compatible convert command used to begin digitizing process. 19?3, 46?0 d 0 ? 4 , d 5 ? 9 ttl-compatible digital output data. 51 overflow ttl-compatible output indicating analog in > +v sense . 56 ? ref voltage force connection for bottom of internal reference ladder. normally driven to provide ?.75 v at ? sense . 57 ? sense voltage sense line to most negative point on internal resistor ladder. normally ?.75 v. 59 lsbs invert normally grounded. when connected to +v s , lower order bits (d 0 ? 8 ) are inverted. 61 msb invert normally grounded. when connected to +v s , most significant bit (msb; d 9 ) is inverted. 63 1/4 ref one-quarter point of internal reference ladder. pin configuration analog in msb invert +v s v s 1/4 ref 1/2 ref 3/4 ref analog in +v s +v s +v s v s gnd gnd gnd gnd nc lsbs invert overflow d 9 (msb) d 8 d 7 d 6 d 5 v ref v sense +v s v s +v s +v s nc nc nc gnd d 4 d 3 d 2 d 1 (lsb) d 0 +v s +v s +v sense +v ref gnd nc encode +v s v s gnd nc nc gnd v s v s +v s +v s +v s v s +v s +v s v s v s gnd gnd gnd gnd gnd gnd nc = no connect ad9020 top view (not to scale) 9 61 60 10 26 27 43 44
ad9020 C6C rev. c theory of operation refer to the ad9020 block diagram. as shown, the ad9020 uses a modified ?lash,?or parallel, a/d architecture. the analog input range is determined by an external voltage refer- ence (+v ref and ? ref ), nominally 1.75 v. an internal resistor ladder divides this reference into 512 steps, each rep- resenting two quantization levels. taps along the resistor ladder (1/4 ref , 1/2 ref and 3/4 ref ) are provided to optimize linearity. rated performance is achieved by driving these points at 1/4, 1/2, and 3/4, respectively, of the voltage reference range. the a/d conversion for the nine most significant bits (msbs) is performed by 512 comparators. the value of the least sig- nificant bit (lsb) is determined by a unique interpolation scheme between adjacent comparators. the decoding logic processes the comparator outputs and provides a 10-bit code to the output stage of the converter. flash architecture has an advantage over other a/d architec- tures because conversion occurs in one step. this means the performance of the converter is primarily limited by the speed and matching of the individual comparators. in the ad9020, an innovative interpolation scheme takes advantage of flash architecture but minimizes the input capacitance, power and device count usually associated with that method of conversion. these advantages occur by using only half the normal num- ber of input comparator cells to accomplish the conversion. in addition, a proprietary decoding scheme minimizes error codes. input control pins allow the user to select from among binary, inverted binary, two? complement and inverted two? complement coding (see table i). applications many of the specifications used to describe analog/digital converters have evolved from system performance require- ments in these applications. different systems emphasize particular specifications, depending on how the part is used. the following applications highlight some of the specifications and features that make the ad9020 attractive in these systems. wideband receivers radar and communication receivers (baseband and direct if digitization), ultrasound medical imaging, signal intelligence and spectral analysis all place stringent ac performance require- ments on analog-to-digital converters (adcs). frequency domain characterization of the ad9020 provides sig- nal-to-noise ratio (snr) and harmonic distortion data to simplify selection of the adc. receiver sensitivity is limited by the signal-to-noise ratio of the system. the snr for an adc is measured in the fre- quency domain and calculated with a fast fourier transform (fft). the snr equals the ratio of the fundamental compo- nent of the signal (rms amplitude) to the rms value of the noise. the noise is the sum of all other spectral components, including harmonic distortion, but excluding dc. good receiver design minimizes the level of spurious signals in the system. spurious signals developed in the adc are the result of imperfections (nonlinearities, delay mismatch, vary- ing input impedance, etc.) in the device transfer function. in the adc, these spurious signals appear as harmonic dis- tortion. harmonic distortion is also measured with an fft and is specified as the ratio of the fundamental component of the signal (rms amplitude) to the rms value of the worst-case harmonic (usually the 2nd or 3rd). two-tone intermodulation distortion (imd) is a frequently cited specification in receiver design. in narrow-band receiv- ers, third-order imd products result in spurious signals in the passband of the receiver. like mixers and amplifiers, the adc is characterized with two, equal-amplitude, pure input frequencies. the imd equals the ratio of the power of either of the two input signals to the power of the strongest third- order imd signal. unlike mixers and amplifiers, the imd does not always behave as it does in linear devices (reduced input levels do not result in predictable reductions in imd). performance graphs provide typical harmonic and snr data for the ad9020 for increasing analog input frequencies. in choosing an a/d converter, always look at the dynamic range for the analog input frequency of interest. the ad9020 specifications provide guaranteed minimum limits at three analog test frequencies. aperture delay is the delay between the rising edge of the encode command and the instant at which the analog input is sampled. many systems require simultaneous sampling of more than one analog input signal with multiple adcs. in these situations, timing is critical and the absolute value of the aperture delay is not as critical as the matching between devices. aperture uncertainty, or jitter, is the sample-to-sample variation in aperture delay. this is especially important when sampling high slew rate signals in wide bandwidth systems. aperture uncertainty is one of the factors that degrade dynamic performance as the ana- log input frequency is increased. digitizing oscilloscopes oscilloscopes provide amplitude information about an observed waveform with respect to time. digitizing oscilloscopes must accurately sample this signal, without distorting the information to be displayed. one figure of merit for the adc in these applications is effective number of bits (enobs). enob is calculated with a sine wave curve fit and equals: enob = n ?log 2 [ error ( measured ) /error (ideal )] n is the resolution (number of bits) of the adc. the measured error is the actual rms error calculated from the converter out- puts with a pure sine wave input. the analog bandwidth of the converter is the analog input fre- quency at which the spectral power of the fundamental signal is reduced 3 db from its low frequency value. the analog band- width is a good indicator of a converter? stewing capabilities.
ad9020 C7C rev. c the maximum conversion rate is defined as the encode rate at which the snr for the lowest analog signal test frequency tested drops by no more than 3 db below the guaranteed limit. imaging both visible and infrared imaging systems require similar char- acteristics from adcs. the signal input (from a ccd camera, or multiplexer) is a time division multiplexed signal consisting of a series of pulses whose amplitude varies in direct proportion to the intensity of the radiation detected at the sensor. these vary- ing levels are then digitized by applying encode commands at the correct times, as shown in figure 2. ad9020 encode +fs fs a in figure 2. imaging application using ad9020 the actual resolution of the converter is limited by the thermal and quantization noise of the adc. the low frequency test for snr or enob is a good measure of the noise of the ad9020. at this frequency, the static errors in the adc determine the useful dynamic range of the adc. although the signal being sampled does not have a significant slew rate, this does not imply dynamic performance is not impor- tant. the transient response and overvoltage recovery time specifications ensure that the adc can track full-scale changes in the analog input sufficiently fast to capture a valid sample. transient response is the time required for the ad9020 to achieve full accuracy when a step function is applied. overvoltage recovery time is the time required for the ad9020 to recover to full accuracy after an analog input signal 150% of full scale is reduced to the full-scale range of the converter. professional video digital signal processing (dsp) is now common in television production. modern studios rely on digitized video to create state-of-the-art special effects. video instrumentation also requires high resolution adcs for studio quality measurement and frame storage. the ad9020 provides sufficient resolution for these demanding applications. conversion speed, dynamic performance and ana- log bandwidth are suitable for digitizing both composite and rgb video sources. using the ad9020 voltage references the ad9020 requires that the user provide two voltage references: +v ref and ? ref . these two voltages are applied across an internal resistor ladder (nominally 37 ? ) and set the analog input voltage range of the converter. the voltage references should be driven from a stable, low impedance source. in addition to these two references, three evenly spaced taps on the resistor ladder (1/4 ref , 1/2 ref , 3/4 ref ) are available. providing a reference to these quarter points on the resistor ladder wil improve the integral linearity of the converter and improve ac performance. (ac and dc specifications are tested while driving the quarter points at the indicated levels.) figure 3 is not intended to show the transfer function of the adc, but illustrates how the linearity of the device is affected by reference voltages applied to the ladder. v in 0000000000 output code taps driven taps floating ideal linearity (not to scale) 1/4 ref 1/2 ref 3/4 ref v sense +v sense 0100000000 1000000000 1100000000 1111111111 figure 3. effect of reference taps on linearity resistance between the reference connections and the taps of the first and last comparators causes offset errors. these errors, called ?op and bottom of the ladder offsets,?can be nulled by using the voltage sense lines, +v sense and ? sense , to adjust the reference voltages. current through the sense lines should be limited to less than 100 a. excessive current drawn through the voltage sense lines will affect the accuracy of the sense line voltage.
ad9020 C8C rev. c figure 5 shows a reference circuit that nulls out the offset errors using two op amps, and provides appropriate voltage references to the quarter-point taps. feedback from the sense lines causes the op amps to compensate for the offset errors. the two tran- sistors limit the amount of current drawn directly from the op amps; resistors at the base connections stabilize their operation. the 10 k ? resistors (r1?4) between the voltage sense lines form an external resistor ladder; the quarter point voltages are taken off this external ladder and buffered by an op amp. the actual values of resistors r1?4 are not critical, but they should match well and be large enough ( 10 k ? ) to limit the amount of current drawn from the voltage sense lines. the select resistors (r s ) shown in the schematic (each pair can be a potentiometer) are chosen to adjust the quarter-point voltage references, but are not necessary if r1?4 match within 0.05%. an alternative approach for defining the quarter-point references of the resistor ladder is to evaluate the integral linearity error of an individual device, and adjust the voltage at the quarter-points to minimize this error. this may improve the low frequency ac performance of the converter. performance of the ad9020 has been optimized with an analog input voltage of 1.75 v (as measured at v sense ). if the analog input range is reduced below these values, relatively larger differ- ential nonlinearity errors may result because of comparator mismatches. as shown in figure 4, performance of the converter is a function of v sense . v sense volts 0.4 signal-to-noise (snr) db 32 38 44 50 56 62 0.6 0.8 1.0 1.2 1.4 1.8 2.0 1.6 5.0 6.0 7.0 8.0 9.0 10.0 effective number of bits (enob) figure 4. snr and enob vs. reference voltage applying a voltage greater than 4 v across the internal resistor ladder will cause current densities to exceed rated values, and may cause permanent damage to the ad9020. the design of the reference circuit should limit the voltage available to the references. analog input signal the signal applied to analog in drives the inputs of 512 parallel comparator cells (see figure 6). this connection typi- cally has an input resistance of 7 k ? , and input capacitance of 45 pf. the input capacitance is nearly constant over the ana- log input voltage range, as shown in the graph that illustrates that characteristic. the analog input signal should be driven from a low-distortion, low-noise amplifier. a good choice is the ad9617, a wide bandwidth, monolithic operational amplifier with excellent ac and dc performance. the input capacitance should be isolated by a small series resistor (24 ? for the ad9617) to improve the ac performance of the amplifier (see figure 14).
ad9020 C9C rev. c analog input v sense 1/4 ref 1/2 ref 3/4 ref +v sense figure 6. equivalent analog input digital bits and overflow +v s '
- 6 5 encode 5.0v 13k figure 8. equivalent encode circuit = wiring r r r r r r r r/2 r/2 r/2 v ref v sense 1/4 ref 1/2 ref 3/4 ref +v sense +v ref r/2 r/2 r/2 r resistance = < 5 ad9020 r/2 to comparators ad580 1/2 ad708 0.1 f r2 10k r1 10k r s r s r s r s r3 10k r4 10k +1.75v 150 150 +2.5v 1.75v 0v +5v 1.75v 0.875v +0.875v 150 5v 20k 20k r/2 1/2 ad708 0.1 f 1/2 ad708 0.1 f 1/2 ad708 0.1 f 0.1 f 1/2 ad708 356 figure 5. reference circuit
ad9020 C10C rev. c analog input n encode data output n + 1 n + 1 data for n data for n + 1 t a t od t a aperture delay t od output delay n n figure 9. timing diagram timing in the ad9020, the rising edge of the encode signal triggers the a/d conversion by latching the comparators. (see figure 9.) the encode is ttl/cmos-compatible and should be driven from a low jitter (phase noise) source. jitter on the en code signal will raise the noise floor of the converter. fast, clean edges will reduce the jitter in the signal and allow optimum ac perfor- mance. locking the system clock to a crystal oscillator also helps reduce jitter. the ad9020 is designed to operate with a 50% duty cycle; small (10%) variations in duty cycle should not degrade performance. data format the format of the output data (d 0 ? 9 ) is controlled by the msb invert and lsbs invert pins. t hese inputs are dc control inputs, and should be connected to ground or +v s . table i gives information to choose from among binary, inverted binary, two? complement and inverted two? complement coding. the overflow output is an indication that the analog input signal has exceeded the voltage at +v sense . the accuracy of the overflow transition voltage and output delay are not tested or included in the data sheet limits. performance of the overflow indicator is dependent on circuit layout and slew rate of the encode signal. the operation of this function does not affect the other data bits (d 0 ? 9 ). it is not recommended for applications requiring a critical measure of the analog input voltage. layout and power supplies proper layout of high speed circuits is always critical but par- ticularly important when both analog and digital signals are involved. analog signal paths should be kept as short as possible and be properly terminated to avoid reflections. the analog input volt- age and the voltage references should be kept away from digital signal paths; this reduces the amount of digital switching noise that is capacitively coupled into the analog section of the circuit. digital signal paths should also be kept short, and run lengths should be matched to avoid propagation delay mismatch. in high-speed circuits, layout of the ground circuit is a critical fac- tor. a single, low impedance ground plane, on the component side of the board, will reduce noise on the circuit ground. power supplies should be capacitively coupled to the ground plane to reduce noise in the circuit. multilayer boards allow designers to lay out signal traces without interrupting the ground plane and provide low impedance power planes. it is especially important to maintain the continuity of the ground plane under and around the ad9020. in systems with dedicated digital and analog grounds, all grounds of the ad9020 should be connected to the analog ground plane. the power supplies (+v s and ? s ) of the ad9020 should be iso- lated from the supplies used for external devices; this further reduces the amount of noise coupled into the a/d converter. sockets limit the dynamic performance and should be used only for prototypes or evaluation?ck elastomerics part # ccs-68-55 is recommended for the lcc package. an evaluation board is available to aid designers and provide a suggested layout.
ad9020 C11C rev. c input frequency mhz 1 signal-to-noise (snr) db effective number of bits (enob) 10 100 20 26 32 38 44 56 62 4.0 5.0 6.0 7.0 8.0 9.0 50 10.0 encode rate = 40msps 25 c 55 c & 125 c 200 figure 10. snr and enob vs. input frequency input frequency mhz 1 harmonics dbc 10 100 70 65 60 55 50 40 35 45 25 c 55 c 30 125 c figure 11. harmonics vs. input frequency table i. truth table offset binary two? complement range true inverted true inverted 0 = ?.75 v msb inv = ? msb inv = ? msb inv = ? msb inv = ? step fs = +1.75 v lsbs inv = ? lsbs inv = ? lsbs inv = ? lsbs inv = ? 1024 > +1.7500 (1)1111111111 (1)0000000000 (1)0111111111 (1)1000000000 1023 +1.7466 1111111111 0000000000 0111111111 1000000000 1022 +1.7432 1111111110 0000000001 0111111110 1000000001 512 +0.0034 1000000000 0111111111 0000000000 1111111111 511 0.000 0111111111 1000000000 1111111111 0000000000 510 ?.0034 0111111110 1000000001 1111111110 0000000001 02 ?.7432 0000000010 1111111101 1000000010 0111111101 01 ?.7466 0000000001 1111111110 1000000001 0111111110 00 ($ 7
ad9020 C12C rev. c c00548bC0C7/01(c) printed in u.s.a. ad9020/pcb evaluation board the ad9020/pcb evaluation board is available from the factory and is shown here in block diagram form. the board includes a reference circuit that allows the user to adjust both references and the quarter-point voltages. the ad9617 is included as the drive amplifier, and the user can configure the gain from ? to ?5. on-board reconstruction of the digital data is provided through the ad9713, a 12-bit monolithic dac. the analog and recon- structed waveforms can be summed on the board to allow the user to observe the linearity of the ad9020 and the effects of the quarterpoint voltages. the digital data and an adjustable data ready signal are available through a 37-pin edge connector. q analog input msb invert lsbs invert +5v overflow buffered analog input d 9 (msb) d 8 d 7 d 6 d 5 d 4 d 3 d 2 d 1 d 0 (lsb) gnd +v s v s v ref v sense encode 1/4 ref 1/2 ref 3/4 ref +v sense +v ref ad9713 dac ad9020 dut u5 ad9617 to error waveform circuit dut analog input dac out to error waveform circuit output data collector data ready timing circuit ttl latches reference circuit ttl clk clk i out d d d d d d d d d d d +5v 5v 50 j2 24 400 200 50 d figure 14. ad9020/pcb evaluation board block diagram outline dimensions dimensions shown in inches and (mm). 68-leaded ceramic chip carrier (z-68) 68-terminal leadless chip carrier (lcc) (e-68a) 10 61 60 27 26 43 9 44 pin 1 top view 0.050 (1.27) typ 0.950 0.010 sq (24.13 0.254) 0.700 0.005 sq (17.78 0.127) 0.850 0.009 ( 21.59 0.229 ) 0.018 0.002 (0.457 0.05) 0.130 (3.301) typ 1.210 0.010 (30.73 0.254) 0.025 (0.625) min 0.040 (1.016) min 0.025 (0.625) min 0.105 0.013 (2.667 0.330) 0.075 0.008 (1.905 0.203) 0.030 (0.762) typ 0.105 0.013 (2.667 0.330) 10 61 60 27 26 9 44 pin 1 top view 43 0.050 (1.27) typ 0.950 0.010 sq (24.13 0.254) 0.700 0.005 sq (17.78 0.127) 0.850 0.009 ( 21.59 0.229 ) 0.036 0.003 (0.965 0.076) 0.050 0.008 (1.27 0.076) ad9020?evision history location page data sheet changed from rev. b to rev. c. edit to absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

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