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general description features ? monolithic ? 12-bit 20 msps converter ? 66 db snr @1 mhz input ? on-chip track/hold ? bipolar 2.0 v analog input ? low power (1.1 w typical) ? 5 pf input capacitance ? ttl outputs applications ? radar receivers ? professional video ? instrumentation ? medical imaging ? electronic warfare ? digital communications ? digital spectrum analyzers ? electro-optics signal processing technologies, inc. 4755 forge road, colorado springs, colorado 80907, usa phone: (719) 528-2300 fax: (719) 528-2370 spt7921 12-bit, 20 msps, ttl, a/d converter the spt7921 a/d converter is the industry's first 12-bit monolithic analog-to-digital converter capable of sample rates greater than 20 msps. on board input buffer and track/hold function assures excellent dynamic perfor- mance without the need for external components. drive requirement problems are minimized with an input ca- pacitance of only 5 pf. logic inputs and outputs are ttl. an overrange output signal is provided to indicate overflow conditions. output data 12 digital output 4 4-bit flash converter input buffer analog gain compression processor track-and-hold amplifiers asynchronous sar error correction, decoding and output ttl drivers 8 v in format is straight binary. power dissipation is very low at only 1.1 watts with power supply voltages of +5.0 and -5.2 volts. the spt7921 also provides a wide input voltage range of 2.0 volts. the spt7921 is available in 32-lead ceramic sidebrazed dip and 44-lead cerquad packages over the commercial tem- perature range. consult the factory for availability of die, military temperature and /883 versions. block diagram
spt 2 3/10/97 spt7921 electrical specifications t a =t min to t max , v cc =+5.0 v, v ee =-5.2 v, dv cc =+5.0 v, v in = 2.0 v, v sb =-2.0 v, v st =+2.0 v, f clk =20 mhz, 50% clock duty cycle, unless otherwise specified. test test spt7921 parameters conditions level min typ max units resolution 12 bits dc accuracy +25 c integral nonlinearity full scale v 2.0 lsb differential nonlinearity 100 khz sample rate v 0.8 lsb no missing codes vi guaranteed analog input f clk =1 mhz input voltage range vi 2.0 v input bias current t a =+25 c i 30 60 m a input resistance t a =+25 c, v in =0 v i 100 300 k w input capacitance v 5 pf input bandwidth 3 db small signal v 120 mhz +fs error v 5.0 lsb -fs error v 5.0 lsb reference input f clk =1 mhz reference ladder resistance vi 500 800 w reference ladder tempco v 0.8 w / c timing characteristics maximum conversion rate vi 20 mhz overvoltage recovery time v 20 ns pipeline delay (latency) iv 1 clock cycle output delay t a =+25 c v 14 18 ns aperture delay time t a =+25 cv 1 ns aperture jitter time t a =+25 c v 5 ps-rms dynamic performance effective number of bits f in =500 khz 10.2 bits f in =1.0 mhz 10.0 bits f in =3.58 mhz 9.5 bits signal-to-noise ratio (without harmonics) f in =500 khz t a =+25 c i 64 67 db t a =t min to t max iv 58 61 db f in =1 mhz t a =+25 c i 64 66 db t a =t min to t max iv 58 60 db f in =3.58 mhz t a =+25 c i 62 64 db t a =t min to t max iv 58 60 db absolute maximum ratings (beyond which damage may occur) 1 25 c supply voltages v cc ........................................................................... +6 v v ee ............................................................................ -6 v input voltages analog input ................................................ v fb v in v ft v ft , v fb . .................................................... +3.0 v, -3.0 v reference ladder current ..................................... 12 ma clk in ....................................................................... v cc output digital outputs .............................................. 0 to -30 ma temperature operating temperature ................................. 0 to +70 c junction temperature ......................................... +175 c lead temperature, (soldering 10 seconds) ........ +300 c storage temperature ................................ -65 to +150 c note: 1. operation at any absolute maximum rating is not implied. see electrical specifications for proper nominal applied conditions in typical applications.
spt 3 3/10/97 spt7921 electrical specifications t a =t min to t max , v cc =+5.0 v, v ee =-5.2 v, dv cc =+5.0 v, v in = 2.0 v, v sb =-2.0 v, v st =+2.0 v, f clk =20 mhz, 50% clock duty cycle, unless otherwise specified. test test spt7921 parameters conditions level min typ max units dynamic performance harmonic distortion f in =500 khz t a =+25 c i 63 66 db t a =t min to t max iv 59 62 db f in =1.0 mhz t a =+25 c i 63 65 db t a =t min to t max iv 59 61 db f in =3.58 mhz t a =+25 c i 59 61 db t a =t min to t max iv 57 59 db signal-to-noise and distortion f in =500 khz t a =+25 c i 60 63 db t a =t min to t max iv 55 58 db f in =1.0 mhz t a =+25 c i 60 62 db t a =t min to t max iv 55 57 db f in =3.58 mhz t a =+25 c i 57 59 db t a =t min to t max iv 54 56 db spurious free dynamic range 1 t a =+25 c v 74 db differential phase 2 t a =+25 c v 0.2 degree differential gain 2 t a =+25 c v 0.7 % digital inputs f clk =1 mhz logic 1 voltage t a =+25 c i 2.4 4.5 v logic 0 voltage t a =+25 c i 0.8 v maximum input current low t a =+25 c i 0 +5 +20 m a maximum input current high t a =+25 c i 0 +5 +20 m a pulse width low (clk) iv 20 ns pulse width high (clk) iv 20 300 ns digital outputs f clk =1 mhz logic 1 voltage t a =+25 c i 2.4 v logic 0 voltage t a =+25 c i 0.6 v power supply requirements voltages v cc iv 4.75 5.0 5.25 v dv cc iv 4.75 5.0 5.25 v -v ee iv -4.95 -5.2 -5.45 v currents i cc t a =+25 c i 135 150 ma di cc t a =+25 c i 40 55 ma -i ee t a =+25 c i 45 70 ma power dissipation vi 1.1 1.3 w power supply rejection 5 v 0.25 v, -5.2 0.25 v v 1.0 lsb typical thermal impedances (unsoldered, in free air): 32l sidebrazed dip: q ja = +50 c/w 44l cerquad: q ja = +78 c/w q ja at 1 m/s airflow = +58 c/w q jc = +3.3 c/w 1 f in = 1 mhz. 2 f in = 3.58 and 4.35 mhz.
spt 4 3/10/97 spt7921 test level codes all electrical characteristics are subject to the following conditions: all parameters having min/max specifications are guaranteed. the test level column indi- cates the specific device testing actually per- formed during production and quality assur- ance inspection. any blank section in the data column indicates that the specification is not tested at the specified condition. test procedure 100% production tested at the specified temperature. 100% production tested at t a = +25 c, and sample tested at the specified temperatures. qa sample tested only at the specified temperatures. parameter is guaranteed (but not tested) by design and characterization data. parameter is a typical value for information purposes only. 100% production tested at t a = +25 c. parameter is guaranteed over specified temperature range. test level i ii iii iv v vi parameters description min typ max units t d clk to data valid prop delay - 14 18 ns t pwh clk high pulse width 20 - 300 ns t pwl clk low pulse width 20 - - ns figure 1a: timing diagram table i - timing parameters figure 1b: single event clock a a a clk a a output data t d tt pwh pwl data valid n+1 a a a a a a a a a a a a a n n+1 n+2 data valid n n-2 n-1 data valid clk output data t d
spt 5 3/10/97 spt7921 specification definitions aperture delay aperture delay represents the point in time, relative to the rising edge of the clock input, that the analog input is sampled. aperture jitter the variations in aperture delay for successive samples. differential gain (dg) a signal consisting of a sine wave superimposed on various dc levels is applied to the input. differential gain is the maximum variation in the sampled sine wave amplitudes at these dc levels. differential phase (dp) a signal consisting of a sine wave superimposed on various dc levels that is applied to the input. differential phase is the maximum variation in the sampled sine wave phases at these dc levels. effective number of bits (enob) sinad = 6.02n + 1.76, where n is equal to the effective number of bits. n = sinad-1.76 6.02 +/- full-scale error (gain error) difference between measured full scale response [(+fs) - (-fs)] and the theoretical response (+4 v -2 lsbs) where the +fs (full scale) input voltage is defined as the output transition between 1-10 and 1-11 and the -fs input voltage is defined as the output transition between 0-00 and 0-01. input bandwidth small signal (50 mv) bandwidth (3 db) of analog input stage. differential nonlinearity (dnl) error in the width of each code from its theoretical value. (theoretical = v fs /2 n ) integral nonlinearity (inl) linearity error refers to the deviation of each individual code (normalized) from a straight line drawn from -fs through +fs. the deviation is measured from the edge of each particular code to the true straight line. output delay time between the clock's triggering edge and output data valid. overvoltage recovery time the time required for the adc to recover to full accuracy after an analog input signal 125% of full scale is reduced to 50% of the full-scale value. signal-to-noise ratio (snr) the ratio of the fundamental sinusoid power to the total noise power. harmonics are excluded. signal-to-noise and distortion (sinad) the ratio of the fundamental sinusoid power to the total noise and distortion power. total harmonic distortion (thd) the ratio of the total power of the first 64 harmonics to the power of the measured sinusoidal signal. spurious free dynamic range (sfdr) the ratio of the fundamental sinusoidal amplitude to the single largest harmonic or spurious signal.
spt 6 3/10/97 spt7921 performance characteristics 50 20 30 40 60 70 80 10 -1 10 0 10 1 thd vs input frequency input frequency (mhz) total harmonic distortion (db) fs = 20 msps input frequency (mhz) signal-to-noise ratio (db) snr vs input frequency 10 -1 10 0 10 1 30 40 50 60 70 20 80 fs = 20 msps signal-to-noise and distortion (db) 20 30 40 50 60 70 80 10 -1 10 0 10 1 sinad vs input frequency input frequency (mhz) fs =20 msps 10 0 a a a a a a a a 20 30 40 50 60 70 80 10 1 10 2 snr, thd, sinad vs sample rate sample rate (msps) snr, thd, sinad (db) snr, thd sinad f in = 1 mhz spt7921 spectral response -120 db -90 db -60 db -30 db 0 db amplitude (db) frequency (mhz) 012345 f s = 20 msps f in = 1 mhz snr, thd, sinad vs temperature temperature (c) snr, thd, sinad (db) 55 60 65 70 75 50 f s = 20 msps f in = 1 mhz sinad thd snr -25 0 +25 +50 +75
spt 7 3/10/97 spt7921 typical interface circuit the spt7921 requires few external components to achieve the stated operation and performance. figure 2 shows the typical interface requirements when using the spt7921 in normal circuit operation. the following section provides a description of the pin functions and outlines critical perfor- mance criteria to consider for achieving the optimal device performance. power supplies and grounding the spt7921 requires -5.2 v and +5 v analog supply voltages. the +5 v supply is common to analog v cc and digital dv cc . a ferrite bead in series with each supply line is intended to reduce the transient noise injected into the analog v cc . these beads should be connected as closely as possible to the device. the connection between the beads and the spt7921 should not be shared with any other device. each power supply pin should be bypassed as closely as possible to the device. use 0.1 m f for v ee and v cc , and 0.01 m f for dv cc (chip caps are preferred). agnd and dgnd are the two grounds available on the spt7921. these two internal grounds are isolated on the device. the use of ground planes is recommended to achieve optimum device performance. dgnd is needed for the dv cc return path (40 ma typical) and for the return path for all digital output logic interfaces. agnd and dgnd should be separated from each other and connected together only at the device through a ferrite bead. a schottky or hot carrier diode connected between agnd and v ee is required. the use of separate power supplies between v cc and dv cc is not recommended due to poten- tial power supply sequencing latch-up conditions. using the recommended interface circuit shown in figure 2 will provide optimum device performance for the spt7921. voltage reference the spt7921 requires the use of two voltage references: v ft and v fb . v ft is the force for the top of the voltage reference ladder (+2.5 v typ), v fb (-2.5 v typ) is the force for the bottom of the voltage reference ladder. both voltages are applied across an internal reference ladder resistance of 800 ohms. the +2.5 v voltage source for reference v ft must be current limited to 20 ma maximum if a different driving circuit is used in place of the recommended reference circuit shown in figures 2 and 3. in addition, there are five reference ladder taps (vst, vrt1, v rt2, v rt3, and v sb ). v st is the sense for the top of the reference ladder (+2.0 v), v rt2 is the midpoint of the ladder (0.0 v typ) and v sb is the sense for the bottom of the reference ladder (-2.0 v). v rt1 and v rt3 are quarter point ladder taps (+1.0 and -1.0 v typical, respectively). the voltages seen at v st and v sb are the true full scale input voltages of the device when v ft and v fb are driven to the recommended voltages (+2.5 v and -2.5 v typical respec- tively). v st and v sb should be used to monitor the actual full scale input voltage of the device. v rt1, v rt2 and v rt3 should not be driven to the expected ideal values as is commonly done with standard flash converters. when not being used, a decoupling capacitor of .01 m f connected to agnd from each tap is recommended to minimize high frequency noise injection. - 5.2 v coarse a/d analog prescaler successive interpolation stage # 1 successive interpolation stage # n d e c o d i n g n e t w o r k 4 d11 d10 d9 d8 d7 d6 d5 d4 d3 d2 d1 d0 d12 d i g i t a l o u t p u t s ic1 (ref-03) 6 5 2 4 + 5 v + v out tr i m gnd v in 1 f c1 .01 f + - 10 k w 1 32 4 8 7 6 10 k w 30 k w 30 k w c19 1 f + +5 v c18 .01 f c17 .01 f clk v in v ft v st v rt3 v rt2 v rt1 v sb v fb r 2r 2r 2r 2r r + c16 1 f clk v in ic2 op-07 v ee v cc dv cc v ee v cc dv cc agnd dgnd dgnd agnd c15 10 f c14 10 f + d1 c12 .01 f + (ttl) (2 v) +2.5 v -2.5 v fb +5 v agnd dgnd -5.2 v (analog) (analog) fb fb 17 24 21 22 23 25 26 27 28 18 31 19 30 20 29 16 32 1 15 (overrange) (msb) (lsb) 14 13 12 11 10 9 8 7 6 5 4 3 2 c13 .01 f r1 100 w 2.5 v max c2 .01 f c3 .01 f c4 .01 f c5 .01 f c6 .01 f c7 .01 f c8 .1 f c9 .1 f c10 c11 notes to prevent latch-up due to power sequencing: 1) d1 = schottky or hot carrier diode, p/n in5817. 2) fb = ferrite bead, fair rite p/n 2743001111 to be mounted as close to the device as possible. the ferrite bead to the adc connection should not be shared with any other device. 3) c1-c13 = chip cap (recommended) mounted as close to the device's pin as possible. 4) use of a separate supply for v cc and dv cc is not recommended. 5) r1 provides current limiting to 45 ma. 6) c8, c9, c10 and c11 should be ten times larger than c12 and c13. 7) c10 = c11 = 0.1 f cap in parallel with a 4.7 f cap. figure 2 - typical interface circuit
spt 8 3/10/97 spt7921 figure 3 - analog equivalent input circuit the drive requirements for the analog inputs are minimal when compared to conventional flash converters due to the spt7921s extremely low input capacitance of only 5 pf and very high input impedance of 300 k w . for example, for an input signal of 2 v p-p with an input frequency of 10 mhz, the peak output current required for the driving circuit is only 628 m a. clock input the spt7921 is driven from a single-ended ttl input (clk). for optimal noise performance, the clock input slew rate should be a minimum of 6 ns. because of this, the use of fast logic is recommended. the clock input duty cycle should be 50% where possible, but performance will not be degraded if kept within the range of 40-60%. however, in any case the clock pulse width (tpwh) must be kept at 300 ns maximum to ensure proper operation of the internal track and hold ampli- fier (see timing diagram). the analog input signal is latched on the rising edge of the clk. the clock input must be driven from fast ttl logic (v ih 4.5 v, t rise <6 ns). in the event the clock is driven from a high current source, use a 100 w resistor in series to current limit to approximately 45 ma. digital outputs the format of the output data (d0-d11) is straight binary. (see table ii.) the outputs are latched on the rising edge of clk with a propagation delay of 14 ns (typ). there is a one clock cycle latency between clk and the valid output data. (see timing diagram.) table ii - output data information analog input overrange output code d12 d11-do >+2.0 v + 1/2 lsb 1 1111 1111 1111 +2.0 v -1 lsb o 1111 1111 111? 0.0 v o ???? ???? ???? -2.0 v +1 lsb o oooo oooo ooo? <-2.0 v o oooo oooo oooo (? indicates the flickering bit between logic 0 and 1). the rise times and fall times of the digital outputs are not symmetrical. the propagation delay of the rise time is typi- cally 14 ns and the fall time is typically 6 ns. (see figure 4.) the nonsymmetrical rise and fall times create approximately 8 ns of invalid data. the analog input range will scale proportionally with respect to the reference voltage if a different input range is required. the maximum scaling factor for device operation is 20% of the recommended reference voltages of v ft and v fb . how- ever, because the device is laser trimmed to optimize perfor- mance with 2.5 v references, the accuracy of the device will degrade if operated beyond a 2% range. an example of a recommended reference driver circuit is shown in figure 2. ic1 is ref-03, the +2.5 v reference with a tolerance of 0.6% or +/- 0.015 v. the potentiometer r1 is 10 k w and supports a minimum adjustable range of up to 150 mv. ic2 is recommended to be an op-07 or equivalent device. r2 and r3 must be matched to within 0.1% with good tc tracking to maintain a 0.3 lsb matching between v ft and v fb . if 0.1% matching is not met, then potentiometer r4 can be used to adjust the v fb voltage to the desired level. r1 and r4 should be adjusted such that v st and v sb are exactly +2.0 v and -2.0 v respectively. the following errors are defined: +fs error = top of ladder offset voltage = d (+fs -v st ) -fs error = bottom of ladder offset voltage = d (-fs -v sb ) where the +fs (full scale) input voltage is defined as the output 1 lsb above the transition of 110 and 111 and the -fs input voltage is defined as the output 1 lsb below the transition of 000 and 001. analog input v in is the analog input. the full scale input range will be 80% of the reference voltage or 2 volts with v fb =-2.5 v and v ft =+2.5 v. vcc vee v ft vin a a a a a a a a analog prescaler
spt 9 3/10/97 spt7921 figure 4 - digital output characteristics evaluation board the eb7921 evaluation board is available to aid designers in demonstrating the full performance of the spt7921. this board includes a reference circuit, clock driver circuit, output data latches and an on-board reconstruction of the digital data. an application note (an7921) describing the operation of this board as well as information on the testing of the spt7921 is also available. contact the factory for price and availability. overrange output the overrange output (d12) is an indication that the analog input signal has exceeded the full scale input voltage by 1 lsb. when this condition occurs, the outputs will switch to logic 1s. all other data outputs are unaffected by this opera- tion. this feature makes it possible to include the spt7921 into higher resolution systems. n+1 rise time 6 ns 2.4 v n clk in 2.4 v invalid data 6 ns typ. (n-2) (n-1) (n) data out (actual) 3.5 v 0.8 v 0.5 v invalid data data out (equivalent) invalid data (n-1) (n-2) (n-1) invalid data t pd1 (14 ns typ.)
spt 10 3/10/97 spt7921 package outlines 32-lead sidebrazed a b c d e f g 1 32 i h j inches millimeters symbol min max min max a 0.081 0.099 2.06 2.51 b 0.016 0.020 0.41 0.51 c 0.095 0.105 2.41 2.67 d .050 typ 1.27 e 0.040 1.02 f 0.175 0.225 4.45 5.72 g 1.580 1.620 40.13 41.15 h 0.585 0.605 14.86 15.37 i 0.009 0.012 0.23 0.30 j 0.600 0.620 15.24 15.75 44-lead cerquad c d a b a b 0 - 5 e f g h inches millimeters symbol min max min max a 0.550 typ 13.97 typ b 0.685 0.709 17.40 18.00 c 0.037 0.041 0.94 1.04 d 0.016 typ 0.41 typ e 0.008 typ 0.20 typ f 0.027 0.051 0.69 1.30 g 0.006 typ 0.15 typ h 0.080 0.150 2.03 3.81
spt 11 3/10/97 spt7921 pin assignments pin functions name function dgnd digital ground agnd analog ground d0-d11 ttl outputs (d0=lsb) d12 ttl output overrange clk clock input v ee -5.2 v supply v cc +5.0 v supply v rt1 -v rt3 voltage reference taps v in analog input dv cc digital +5.0 v supply (ttl outputs) v ft force for top of reference ladder v st sense for top of reference ladder v fb force for bottom of reference ladder v sb sense for bottom of reference ladder 17 clk 21 v ft 20 v cc 18 v ee 25 v rt2 24 v in 27 v sb 26 v rt1 22 v st agnd 30 v ee 31 32 28 v fb 29 v cc dv cc dgnd d0 d1 d2 d3 d4 d5 d6 d7 d8 d9 d10 dgnd d12 dv cc 1 2 3 4 5 6 7 8 9 10 11 12 15 14 16 13 d11 23 v rt3 19 agnd ordering information part number temperature range package SPT7921SCJ 0 to +70 c 32l sidebrazed dip spt7921scq 0 to +70 c 44l cerquad n/c v fb v sb v rt1 v rt2 v in v rt3 v st v ft n/c v cc d1 d n/c dgnd dv cc v ee n/c agnd n/c v cc n/c n/c d12 dgnd dv cc n/c clk n/c v ee n/c agnd n/c d2 d3 d4 d5 d6 d7 d8 d9 d10 d11 n/c 1 2 3 4 5 6 7 8 9 10 11 33 32 31 30 29 28 27 26 25 24 23 12 13 14 15 16 17 18 19 20 21 22 44 43 42 41 40 39 38 37 36 35 34 32l sidebrazed 44l cerquad signal processing technologies, inc. reserves the right to change products and specifications without notice. permission is hereby expressly granted to copy this literature for informational purposes only. copying this material for any other use is strictly prohibited. warning - life support applications policy - spt products should not be used within life support systems without the specific written consent of spt. a life support system is a product or system intended to support or sustain life which, if it fails, can be reasonably expected to result in significant personal injury or death. signal processing technologies believes that ultrasonic cleaning of its products may damage the wire bonding, leading to device failure. it is therefore not recommended, and exposure of a device to such a process will void the product warranty.

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