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international airport industrial park ? mailing address: po box 11400, tucson, az 85734 ? street address: 6730 s. tucson blvd., tucson, az 85706 ? tel: (520) 746-1111 ? twx: 910-952-1111 internet: http://www.burr-brown.com/ ? faxline: (800) 548-6133 (us/canada only) ? cable: bbrcorp ? telex: 066-6491 ? fax: (520) 889-1510 ? immediate product info: (800) 548-6132 ? 1996 burr-brown corporation li-476a printed in u.s.a. october, 1996 description the dem-ads8xxu/e evaluation fixtures are de- signed for ease of use when evaluating the high speed analog-to-digital converter of the ads8xx family. a separate demonstration board is available for each of the five different converter products (see ordering information). however, all boards provide similar fea- tures that allow the user to evaluate all functions of the converter. for example, two options to apply the analog input signal are available, one dc-coupled and one ac-coupled path. the converter can be operated with one out of the three clock modes; on-board crystal clock, external clock, or external sine wave. furthermore, a reference circuit is provided to evalu- ate the converter with reference voltages other than the internal voltage levels. the data outputs from the ads8xx converter are decoupled from the connector via ttl-buffer. features l provides fast and easy perfor- mance testing l ac-coupled and dc-coupled inputs l on-board clock l external references l optimized 4-layer pc board layout dem-ads8xxe dem-ads8xxu evaluation fixture
2 dem-ads8xx the information provided herein is believed to be reliable; however, burr-brown assumes no responsibility for inaccuracies or omissions. burr-brown assumes no responsibility for the use of this information, and all use of such information shall be entirely at the users own risk. prices and specifications are subject to change without notice. no patent rights or licenses to any of the circuits described herein are implied or granted to any third party. burr-brown does not authorize or warrant any burr-brown product for use in life support devices and/or systems. the transformer to the converter inputs. at the same time it is recommended that resistors r38 and r39 are taken out. the center tap of the secondary side of the transformer can be connected to the mid-reference of the ads8xx by closing solder switch cm. if necessary the center tap can also be driven by the buffer amplifier u10. to activate this buffer open solder switch cm and close the one labeled t1-ct. in addition, closing solder switch x2 located at the primary side of the rf-transformer will short out half of the primary winding and change the turns ratio to 1:2. this function is not available with the transformer type used on the board. dc-coupled for evaluating input frequencies down to dc, the second analog input should be used. it is available through connec- tor j3, labeled dc coupled input. this input is also terminated for a 50 w system. the first stage consists of amplifier u11, which is configured as a buffer amplifier. using appropriate values for r21 and r22 the amplifier can be set for gain. the ads8xx requires a differential input signal with a common-mode voltage of +2.25v. this is accomplished by amplifiers u8, u9, and u10 (refer to figure 1). the amplifier u8 is configured in a non-inverting mode with a dc gain of +3v/v. the voltage divider formed by r27 and r28 gives an overall gain of +2v/v. the complementary input amplifier u9 is set for an inverting gain of +2v/v. the common-mode voltage of +2.25v is buffered from the ads8xx by amplifier u10 and applied to each of the driving amplifiers. the opa642 was selected to provide a low noise and low distortion front-end. to avoid any additional distortion due to the required output swing of +3.25v a level shifting stage was added. it consists of a silicon diode in series with the output of each driving amplifier and a resistor to the supply for biasing. regardless of the configuration of the driving amplifiers, a series resistor (r38, r39) in combination with a small capacitor to ground at the inputs of the ads8xx can improve the ac- performance. the capacitors (c34 and c35) will help to reduce the current transients that are generated by the ads8xx during sampling. note that when using the dc-coupled input resistors r40 and r41 should be removed to avoid unnecessary loading of the driving op amps. clock on-board clock the ads8xx demo board is equipped with a crystal oscilla- tor and d-type flip-flops (u6 and u7), which allow differ- ent discrete divider ratios for the clock. the selection of the divider ratio can be done using the solder switches labeled div2, div4, div8, and div16. for this mode of operation make sure that solder switch eclk is closed and cclk is open. initial configuration and quick start the demo board dem-ads8xx comes in a default configu- ration that makes it easy for the user to start evaluation. the factory settings are as follows: ? the clock source is the on-board crystal with the appropri- ate divider ratio ( ? 2, ? 4, etc.) selected. ? the dc-coupled input is activated. ? the external reference is inactive; solder switches reft and refb are open. ? the output data format is straight offset binary with the solder switch msbi open. ? the data output is enabled with the solder switch oe\ open. ? the data read delays set to one delay, solder switch dly1 closed. ? note that the pwrdwn solder switch is without func- tion and should stay open. evaluation in this configuration requires a 5v supply. the negative supply is necessary to power the op amp driving circuit, therefore, power connectors p1 and p2 must be connected appropriately to the supply unit. re-configuring the demo board for ac-coupled input in combination with the crystal or external pulse clock, makes it possible to operate the demo board on a single +5v supply. inputs transformer coupled the demo board provides one analog input at connector j4, which is labeled ac coupled input. this input is termi- nated with 50 w and ties to the rf-transformer t1. the model used is the t1-1t (by mini-circuits), a 1:1 ratio transformer with bandpass characteristic. the C3db frequen- cies are at 50khz and 200mhz for the lower and upper corners of the transformer. the C1db insertion loss frequen- cies are listed with 0.2mhz and 80mhz, which might be used for choosing the input frequency without effecting the signal too much. if the ac-coupled input is used the two resistors, r40 and r41 (0 w) have to be inserted to connect model crystal eclk div 2 div4 div 8 b11 dly 1 ads800 80mhz x x x x ads801 50mhz x x x x ads802 80mhz x x x x ads820 80mhz x x x ads821 80mhz x x x table i. factory configuration table of solder switches for the five different converter products.
3 dem-ads8xx external clock in addition to the on-board clock the demo board allows for two other clock configurations using external clock sources. the first alternative requires an external pulse generator, preferably with fast rise and fall times ( 2ns) and low jitter. this source can be directly connected to the board using the sma connector j2. the input is terminated for 50 w systems. operation in this mode requires to close solder switch cclk and open eclk. if a low jitter sine wave generator is the only signal source available the second external clock input might be used. the ecl to ttl translator ic (u5) will transform the sine wave input into a logic signal with 50% duty cycle. different divider ratios can be selected. the solder switch xclk and eclk should be closed in this mode and solder switch cclk should be open. external reference each of the converter inputs operates with a 2vp-p input signal swing set between +1.25v and +3.25v. the input structure of the ads8xx is differential making the comple- mentary input of the ads8xx 180 out of phase. this allows for an effective full scale input range of 4vp-p. the +1.25v and the +3.25v are set by the internal reference voltages of the converter. these reference voltages may be adjusted with external references in order to reduce the full scale range. the demo board provides a circuit for this mainly consisting of the reference ic u13 and the op amps u12 and u14. to activate this circuit the solder switches labeled reft and refb should be closed. the top reference voltage can be adjusted with potentiometer rv1 between +3.25v and +2.25v. potentiometer rv2 adjusts the bottom reference between +1.25v and +2.25v. note that those reference voltages can vary slightly. also, reducing the references too much will degrade the signal-to-noise ratio. data output the output data is provided at cmos logic levels. the standard output coding is straight offset binary where the full scale input signal corresponds to all 1 for the data output. this is with solder switch msbi open. closing this solder switch will invert the msb (see the individual data sheet for details). to account for different data read timing up to four propagation delay cycles can be selected using the solder switches dly1 through dly4. the minimum propa- gation delay for the used buffer is 1.5ns with a maximum of 8ns. pc-board layout the ads8xx demo board is a four layer pc-board. to achieve the highest level of performance surface mount components are used wherever possible. this reduces the trace length and minimizes the effects of parasitic capaci- tance and inductance. the analog-to-digital converter is treated like a pure analog component. therefore the demo board has only one consistent ground plane. this approach may or may not yield optimum performance results when designing the ads8xx into different individual applications. in any case, thoroughly bypassing the supply pins of the converter, like demonstrated on the demo board, is strongly recommended. a/d resolution f conv order number ads800 12-bit 40mhz dem-ads800u ads801 12-bit 25mhz dem-ads801u ads802 12-bit 10mhz dem-ads802u ads820 10-bit 20mhz dem-ads820u ads821 10-bit 40mhz dem-ads821u ads8xx 10/12-bit dem-ads8xxe note: the demo board dem-ads8xxe is designed to fit the ads8xx line of converters in the 28-pin ssop package. the board is offered as fully populated except for the individual a/d converter (u1), which can be obtained through a sample request. ordering information
4 dem-ads8xx figure 1a. dem-ads8xx circuit schematic. dc couple input j3 ac couple input j4 6 u11 7 4 5 8 2 3 opa642 +5v ?v r 24 100 w r 23 100 w 6 u8 7 4 5 8 2 3 opa642 d3 bas16 c 45 2.2? + 6 u9 7 4 5 8 2 3 opa642 r 29 604 w r 36 301 w d4 bas16 +5v 6 7 4 3 2 +5v mc34071d u10 t1 t1 - 1t t1 - ct cm r 39 49.9 w refb tp1 reft cm refb cm tp2 reft tp3 in in reft cm refb r 38 49.9 w r 33 49.9 w c 41 0.1 m f r 41 (1) r 34 2.49k w r 35 2.49k w r 40 (1) +5v ?v +5v ?v r 43 100 w r 42 100 w 1 x 2 2 3 6 5 4 r 22 24.9 w r 21 (1) c 44 0.1? r 32 301 w r 31 604 w + r 26 301 w r 27 604 w c 50 0.1? c 51 2.2? + c 56 0.1? c 57 0.1? r 30 301 w r 28 301 w r 25 604 w r 37 301 w +5v note: (1) part not assembled.
5 dem-ads8xx figure 1b. dem-ads8xx circuit schematic. reft 3.75 - 2.25v refb 1.25 - 2.25v refb cm reft r 11 2.49k w 6 7 4 2 3 2.10 - 2.30v +5 c 11 0.1? c 19 (1) 2.2? + c 24 (1) 0.1? c 16 (1) 2.2? + c 23 (1) 0.1? rv 1 2k w r 12 21.0k w os adj c 12 0.1? 6 7 4 2 3 +5 c 13 0.1? rv 2 5k w fs adj r 15 13.7k w r 16 2.49k w r 14 6.19k w u12 mc34071d c 14 2.2? + 8 7 6 5 1 2 3 4 u13 ref1004-2.5 +5v u14 mc34071d r 10 0 w c 15 0.1? r 18 2.49k w r 13 2k w r 17 0 w r 19 2.49k w r 20 2.49k w note: (1) part not assembled.
6 dem-ads8xx figure 1c. dem-ads8xx circuit schematic. 28 27 26 25 24 23 22 21 20 19 18 17 16 15 gnd in in gnd +v s reft cm refb +v s msb invert oe +v s clk +v s 1 2 3 4 5 6 7 8 9 10 11 12 13 14 gnd b1 (msb) b2 b3 b4 b5 b6 b7 b8 b9 b10 b11 b12 (lsb)/nc gnd u1 ads8xxu/e 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 p3 digital output 19 1 9 8 7 6 5 4 3 2 oeb (1) oea (1) d7 d6 d5 d4 d3 d2 d1 d0 11 12 13 14 15 16 17 18 07 06 05 04 03 02 01 00 u2 idt74fct541t 19 1 9 8 7 6 5 4 3 2 oeb (1) oea (1) d7 d6 d5 d4 d3 d2 d1 d0 11 12 13 14 15 16 17 18 07 06 05 04 03 02 01 00 u2 idt74fct541t r 4 100k w r 5 100k w b11 pwrdwn r 6 1k w r 7 49.9 w r 3 0 w dly1 dly2 dly3 dly4 dv msbi +5 +5 oe cclk eclk c 21 2.2? + c 25 0.1? in c 17 2.2? + c 18 0.1? c 20 2.2? + c 22 0.1? c 35 22pf c 34 22pf convert clock input j2 r 9 49.9 w +5 +5 +5 +5 in cm reft refb clock +5v gnd ? p1 +5 + p2 +5v ? +v 1 2 3 2 1 c 7 0.1? +5v c 26 0.1? +5v +5v c 27 0.1? c 28 0.1? +5v c 29 0.1? c 6 (1) c 10 (1) +5v c 8 0.1? +5v c 9 100? +5v c 36 100? +5v c 5 100? +5v c 30 2.2? +5v c 31 0.1? +5v c 37 2.2? +5v +5v c 38 0.1? c 49 2.2? +5v c 48 0.1? +5v c 32 2.2? ?v c 33 0.1? ?v ?v c 39 2.2? c 40 0.1? ?v c 46 2.2? ?v c 47 0.1? ?v c 52 2.2? ++++ +5v +5v c 53 2.2? c 54 2.2? +5v c 55 2.2? +5v c 42 100? +v + c 43 100? ? gnd r 8 (1) r 2 1k w +++ +++ +++ note: (1) part not assembled.
7 dem-ads8xx figure 1d. dem-ads8xx circuit schematic. +5 ?v +5v 14 13 12 11 10 9 8 1clk 1d 1clr v cc 2clr 2d 2clk 1 2 3 4 5 6 7 1 pre 1q 1q gnd 2q 2q 2 pre u6 74ac11074 nc gnd +v out 4 3 1 2 u4 crystal oscillator +5 +5 +5 14 13 12 11 10 9 8 1clk 1d 1clr v cc 2clr 2d 2clk 1 2 3 4 5 6 7 1 pre 1q 1q gnd 2q 2q 2 pre u7 74ac11074 +5 +5 7 xclk 8 5 4 1 3 2 c 1 0.1? c 3 0.1? c 4 0.1? u5 mc100elt25 ext clock input j1 +5v c 2 0.1? r 1 49.9 w div2 clock div4 div8 div16
8 dem-ads8xx figure 2. top-layer (component side) with silk-screen; dem-ads8xxu. figure 3. power plane; dem-ads8xxu.
9 dem-ads8xx figure 4. ground plane; dem-ads8xxu. figure 5. bottom layer with silk-screen; dem-ads8xxu.
10 dem-ads8xx figure 6. top-layer with silk-screen; dem-ads8xxe. figure 7. bottom-layer with silk-screen; dem-ads8xxe.
11 dem-ads8xx c1, c2, c3, c4, c7, c8, c11-13, c15, 28 08055c104kat 0.1 m f 50v x7r 0805 ceramic capacitor avx c18, c22, c25-29, c31, c33, c38, c40, c41, c44, c47, c48, c50, c56, c57 c14, c16, c17, c19-c21, c30, 14 tajr225006 2.2 m f 10v 3216 tantalum capacitor avx c32, c37, c39, c45, c46, c49, c51 c34, c35 2 08055c220kat 22pf 50v npo 0805 ceramic capacitor avx c6, c10 2 08055c100kat 10pf 50v npo 0805 ceramic capacitor avx c5, c36, c42, c43 4 ece-v1aa101p 100 m f 16v surface-mount aluminum capacitor panasonic c9 1 ece-v1cv100sr 10 m f 16v surface-mount aluminum capacitor panasonic d1, d2 2 bas16 signal diode sot-23 philips j1-4 4 142-0701-201 straight sma pcb connector ef johnson p1 1 ed555/3ds 3-pin term block on-shore technology p2 1 ed555/2ds 2-pin term block on-shore technology p3 1 idh-40lp-s3-tg 20 x 2 dual-row shrouded header robinson-nugent r1, r7, r9, r33, r38, r39 6 crcw080549r9f 49.9 w 1/10w 1% mf 0805 chip resistor dale r26, r28, r30, r32, r36, r37 6 crcw08053010f 301 w 1/10w 1% mf 0805 chip resistor dale r11, r16, r18-20, r34, r35 7 crcw08052491f 2.49k w 1/10w 1% mf 0805 chip resistor dale r12 1 crcw08056040f 20k w 1/10w 5% mf 0805 chip resistor dale r13 1 crcw08052001f 2k w 1/10w 1% mf 0805 chip resistor dale r14 1 crcw08056191f 6.19k w 1/10w 1% mf 0805 chip resistor dale r15 1 crcw08051372f 13.7k w 1/10w 1% mf 0805 chip resistor dale r2, r6 2 crcw08051001f 1k w 1/10w 1% mf 0805 chip resistor dale r22 1 crcw080524r9f 24.9 w 1/10w 1% mf 0805 chip resistor dale r23, r24, r42, r43 4 crcw12061000f 100 w 1/10w 1% mf 1206 chip resistor dale r25, r27, r29, r31 4 crcw08056040f 604 w 1/10w 1% mf 0805 chip resistor dale r3, r10, r17 3 crcw0805zerof 0 w 1/10w 1% mf 0805 chip resistor dale r4, r5 2 crcw08051003f 100k w 1/10w 1% mf 0805 chip resistor dale rv1 1 rj26fw-202 2k w 1/4" 10-turn pot bourns rv2 1 rj26fw-502 5k w 1/4" 10-turn pot bourns t1 1 t1-1t-kk81 rf transformer mini-circuits refb, reft, cm 3 151-205 test point mouser tp4, tp5 2 10-216-2-01 turret terminal, brass, silver plated concord u10, u12, u14 3 mc34071d single op-amp so-8 motorola u13 1 ref1004c-2.5 2.5v voltage reference so-8 burr-brown u2, u3 2 idt74fct 541t octal bi-directional buffers so-20 idt u3 1 ads8xxu monolithic high-speed adc so-28 burr-brown u4a (1) 1 f3000 80.000mhz 80mhz dip crystal oscillator fox u4b (2) 1 f3000 50.000mhz 50mhz dip crystal oscillator fox u5 1 mc100elt25 ecl to ttl translator so-8 motorola u6, u7 2 74ac11074 dual d-type flip-flop so-14 t.i. u8, u9, u11 3 opa642u single high-speed op-amp so-8 burr-brown 1 a039a pcb 4 sj5003-0-n rubber feet, black, 0.44 x 0.2 digi-key notes: (1) used on the dem-ads800u, dem-ads802u, dem-ads820u, and dem-ads821u. (2) used on the dem-ads801u. component list reference qty part number description manufacturer

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