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lt6604-15 1 660415fb typical application description dual very low noise, differential ampli er and 15mhz lowpass filter the lt ? 6604-15 consists of two matched, fully differential ampli? ers, each with a 4th order, 15mhz lowpass ? lter. the ? xed frequency lowpass ? lter approximates a chebyshev response. by integrating a ? lter and a differential ampli- ? er, distortion and noise are made exceptionally low. at unity gain, the measured in band signal-to-noise ratio is an impressive 76db. at higher gains, the input referred noise decreases, allowing the part to process smaller input differential signals without signi? cantly degrading the signal-to-noise ratio. gain and phase are highly matched between the two chan- nels. gain for each channel is independently programmed using two external resistors. the lt6604-15 enables level shifting by providing an adjustable output common mode voltage, making it ideal for directly interfacing to adcs. the lt6604-15 is fully speci? ed for 3v operation. the differential design enables outstanding performance at a 2v p-p signal level for a single 3v supply. see the back page of this datasheet for a co mplete list of related single and dual differential ampli? ers with integrated 2.5mhz to 20mhz lowpass ? lters. channel to channel gain matching features applications n dual differential ampli? er with 15mhz lowpass filters 4th order filters approximates chebyshev response guaranteed phase and gain matching resistor-programmable differential gain n 76db signal-to-noise (3v supply, 2v p-p output) n low distortion, 2v p-p , 800 load, v s = 3v 1mhz: 86dbc 2nd, 90dbc 3rd 10mhz: 63dbc 2nd, 69dbc 3rd n speci? ed for operation with 3v, 5v and 5v supplies n fully differential inputs and outputs n adjustable output common mode voltage n small 4mm 7mm 0.75mm qfn package n dual differential adc driver plus filter n single-ended to differential converter n matched, dual, differential filter stage n common mode translation of differential signals n high speed adc antialiasing and dac smoothing in wireless infrastructure or networking applications n high speed test and measurement equipment n medical imaging l , lt, ltc and ltm are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. 536536 3v 3v + C + C 660415 ta01 + C dout ain lt6604-15 ltc22xx + C 536536 3v Couta +outa Coutb+outb +inav midb v mida +inb v ocma v ocmb CinaCinb v C + C + C + C dout ain + C 50 50 dual adc v + a v + b v + b 50 50 18pf 18pf 0.01f 0.01f C0.25 12 16 0.15 660415 ta01b 84 10 14 62 0 C0.2 C 0.1 C0.15 0.05 C0.05 0.1 0.2 0 0.25 gain match (db) 50 typical unitst a = 25c gain = 1f in = 15mhz downloaded from: http:///
lt6604-15 2 660415fb pin configuration absolute maximum ratings total supply voltage .................................................11v operating temperature range (note 6).... C40c to 85c speci? ed temperature range (note 7) .... C40c to 85c junction temperature ........................................... 150c storage temperature range ................... C65c to 150c input current +in, Cin, v ocm , v mid (note 8) .........................10ma lead temperature (soldering, 10 sec) .................. 300c parameter conditions min typ max units filter gain either channel, v s = 3v v in = 2v p-p , f in = dc to 260khz v in = 2v p-p , f in =1.5mhz (gain relative to 260khz) v in = 2v p-p , f in = 7.5mhz (gain relative to 260khz) v in = 2v p-p , f in = 12mhz (gain relative to 260khz) v in = 2v p-p , f in = 15mhz (gain relative to 260khz) v in = 2v p-p , f in = 45mhz (gain relative to 260khz) v in = 2v p-p , f in = 75mhz (gain relative to 260khz) ll l l l l C0.5C0.1 C0.3 C0.3 C0.7 0.1 00 0.2 0 C29C46 0.50.1 0.4 1.0 1.0 C25 dbdb db db db db db order information lead free finish tape and reel part marking* package description specified temperature range lt6604cuff-15#pbf lt6604cuff-15#trpbf 60415 34-lead (4mm 7mm) plastic qfn 0c to 70c lt6604iuff-15#pbf lt6604iuff-15#trpbf 60415 34-lead (4mm 7mm) plastic qfn C40c to 85c consult ltc marketing for parts speci? ed with wider operating temperature ranges. *the temperature grade is identi? ed by a label on the shipping container. consult ltc marketing for information on non-standard lead based ? nish parts. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel speci? cations, go to: http://www.linear.com/tapeandreel/ electrical characteristics the l denotes speci? cations that apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. unless otherwise speci? ed v s = 5v (v + = 5v, v C = 0v), r in = 536, and r load = 1k. 31 v C 32 v C 33 nc 34 v mida v + b 17 nc 16 nc 15 v ocmb 14 30 nc 29 Couta 28 nc 27 +outa 26 nc 25 v + a 24 v C 23 nc22 nc 21 Coutb 20 nc 19 +outb 18 nc nc 1 +ina 2 nc 3 Cina 4 nc 5 v ocma 6 v C 7 v midb 8 nc 9 +inb 10 nc 11 Cinb 12 nc 13 top view uff package 34-lead (4mm 7mm) plastic qfn 35 t jmax = 150c, ja = 34c/w, jc = 2.7c/w exposed pad (pin 35) is v C , must be soldered to pcb (note 1) downloaded from: http:///
lt6604-15 3 660415fb electrical characteristics the l denotes speci? cations that apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. unless otherwise speci? ed v s = 5v (v + = 5v, v C = 0v), r in = 536, and r load = 1k. parameter conditions min typ max units matching of filter gain, v s = 3v v in = 2v p-p , f in = dc to 260khz v in = 2v p-p , f in = 1.5mhz (gain relative to 260khz) v in = 2v p-p , f in = 7.5mhz (gain relative to 260khz) v in = 2v p-p , f in = 12mhz (gain relative to 260khz) v in = 2v p-p , f in = 15mhz (gain relative to 260khz) v in = 2v p-p , f in = 45mhz (gain relative to 260khz) v in = 2v p-p , f in = 75mhz (gain relative to 260khz) ll l l l l 0.050.01 0.02 0.03 0.06 0.13 0.15 0.50.1 0.3 0.4 0.6 1.5 2.8 dbdb db db db db db matching of filter phase, v s = 3v v in = 2v p-p , f in = 1.5mhz v in = 2v p-p , f in = 7.5mhz v in = 2v p-p , f in = 12mhz ll l 0.60.8 0.9 13 4 degdeg deg filter gain either channel, v s = 5v v in = 2v p-p , f in = dc to 260khz v in = 2v p-p , f in =1.5mhz (gain relative to 260khz) v in = 2v p-p , f in = 7.5mhz (gain relative to 260khz) v in = 2v p-p , f in = 12mhz (gain relative to 260khz) v in = 2v p-p , f in = 15mhz (gain relative to 260khz) v in = 2v p-p , f in = 45mhz (gain relative to 260khz) v in = 2v p-p , f in = 75mhz (gain relative to 260khz) ll l l l l C0.5C0.1 C0.4 C0.4 C0.8 00 0 0.1 0 C29C46 0.50.1 0.3 0.9 0.9 C25 dbdb db db db db db matching of filter gain, v s = 5v v in = 2v p-p , f in = dc to 260khz v in = 2v p-p , f in =1.5mhz (gain relative to 260khz) v in = 2v p-p , f in = 7.5mhz (gain relative to 260khz) v in = 2v p-p , f in = 12mhz (gain relative to 260khz) v in = 2v p-p , f in = 15mhz (gain relative to 260khz) v in = 2v p-p , f in = 45mhz (gain relative to 260khz) v in = 2v p-p , f in = 75mhz (gain relative to 260khz) ll l l l l 0.050.01 0.02 0.03 0.06 0.13 0.15 0.50.1 0.3 0.4 0.6 1.5 2.8 dbdb db db db db db matching of filter phase, v s = 5v v in = 2v p-p , f in = 1.5mhz v in = 2v p-p , f in = 7.5mhz v in = 2v p-p , f in = 12mhz ll l 0.60.8 0.9 13 4 degdeg deg filter gain either channel, v s = 5v v in = 2v p-p , f in = dc to 260khz C0.6 C0.1 0.4 db filter gain, r in = 133 v in = 0.5v p-p , f in = dc to 260khz v s = 3v v s = 5v v s = 5v 11.511.5 11.4 12.012.0 11.9 12.512.5 12.4 dbdb db filter gain temperature coef? cient (note 2) f in = 250khz, v in = 2v p-p 780 ppm/c noise noise bw = 10khz to 15mhz, r in = 536 109 v rms distortion (note 4) 1mhz, 2v p-p , r l = 800, v s = 3v 2nd harmonic 3rd harmonic 8690 dbcdbc 10mhz, 2v p-p , r l = 800, v s = 3v 2nd harmonic 3rd harmonic 6369 dbcdbc channel separation (note 9) 1mhz, 2v p-p , r l = 800 C117 db 10mhz, 2v p-p , r l = 800 C102 db differential output swing measured between +out and Cout, v ocm shorted to v mid v s = 5v v s = 3v ll 3.803.75 4.754.50 v p-p_diff v p-p_diff input bias current average of in + and in C l C90 C35 a input referred differential offset r in = 536 v s = 3v v s = 5v v s = 5v ll l 5 1010 2530 35 mvmv mv r in = 133 v s = 3v v s = 5v v s = 5v ll l 55 5 1517 20 mvmv mv downloaded from: http:///
lt6604-15 4 660415fb parameter conditions min typ max units differential offset drift 10 v/c input common mode voltage (note 3) differential input = 500mv p-p, r in = 133 v s = 3v v s = 5v v s = 5v ll l 00 C2.5 1.5 31 vv v output common mode voltage (note 5) differential output = 2v p-p, v mid = open, common mode voltage at v ocm v s = 3v v s = 5v v s = 5v ll l 1 1.5 C1 1.5 32 vv v output common mode offset (with respect to v ocm ) v s = 3v v s = 5v v s = 5v ll l C35C40 C55 55 C10 4040 35 mvmv mv common mode rejection ratio 64 db voltage at v mid v s = 3v v s = 5v l 2.45 2.50 1.5 2.56 v v v mid input resistance l 4.3 5.7 7.7 k v ocm bias current v ocm = v mid = v s /2 v s = 3v v s = 5v ll C10C10 C2C2 aa power supply current (per channel) v s = 3v, v s = 5v v s = 3v v s = 5v v s = 5v ll l 3534 38 3944 45 48 mama ma ma power supply voltage l 31 1 v electrical characteristics the l denotes speci? cations that apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. unless otherwise speci? ed v s = 5v (v + = 5v, v C = 0v), r in = 536, and r load = 1k. note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. note 2: this is the temperature coef? cient of the internal feedback resistors assuming a temperature independent external resistor (r in ). note 3: the input common mode voltage is the average of the voltages applied to the external resistors (r in ). speci? cation guaranteed for r in 100. note 4: distortion is measured differentially using a differential stimulus. the input common mode voltage, the voltage at v ocm , and the voltage at v mid are equal to one half of the total power supply voltage. note 5: output common mode voltage is the average of the +out and Cout voltages. the output common mode voltage is equal to v ocm . note 6: the lt6604c-15 is guaranteed functional over the operating temperature range C40c to 85c. note 7: the lt6604c-15 is guaranteed to meet 0c to 70c speci? cations and is designed, characterized and expected to meet the extended temperature limits, but is not tested at C40c and 85c. the lt6604i-15 is guaranteed to meet speci? ed performance from C40c to 85c. note 8: input pins (+in, Cin, v ocm and v mid ) are protected by steering diodes to either supply. if the inputs should exceed either supply voltage, the input current should be limited to less than 10ma. in addition, the inputs +in, Cin are protected by a pair of back-to-back diodes. if the differential input voltage exceeds 1.4v, the input current should be limited to less than 10ma. note 9: channel separation (the inverse of crosstalk) is measured by driving a signal into one input, while terminating the other input. channel separation is the ratio of the resulting output signal at the driven channel to the output at the channel that is not driven. downloaded from: http:///
lt6604-15 5 660415fb typical performance characteristics output impedance common mode rejection ratio power supply rejection ratio distortion vs frequency distortion vs signal level amplitude response passband gain and phase passband gain and delay frequency (mhz) 0.1 C20 gain (db) C10 0 10 1 10 100 660415 g01 C30C40 C50 C60 v s = 5v gain = 1t a = 25c frequency (mhz) 0 gain (db) phase (deg) C3 C1 1 20 660415 g02 C5C7 C4 C2 0 C6C8 C9 45 135 225C45 C135 0 90 180C90 C180 C225 5 10 15 25 v s = 5v gain = 1t a = 25c gain phase frequency (mhz) 0 gain (db) delay ( ns ) 6 10 14 20 660415 g04 2 C2 4 8 12 0 C4C6 30 40 5020 10 25 35 4515 5 0 5 10 15 25 v s = 5v gain = 4t a = 25c gain delay frequency (mhz) 1 output impedance () 10 0.1 10 100 660415 g05 0.1 1 100 v s = 5v gain = 1t a = 25c frequency (mhz) 0.1 cmrr (db) 60 70 80 1 10 100 660415 g06 5040 30 65 7555 45 35 v in = 1v p-p v s = 5v gain = 1t a = 25c frequency (mhz) 0.1 50 psrr (db) 60 70 80 1 10 100 660415 g07 4030 20 10 0 v s = 3v v in = 200mv p-p t a = 25c v + to diffout frequency (mhz) 0.1 C100C110 distortion (dbc) C60 C50 1 10 100 660415 g08 C70C80 C90 differential input, 2nd harmonicdifferential input, 3rd harmonic single-ended input, 2nd harmonic single-ended input, 3rd harmonic v in = 2v p-p v s = 3v r l = 800 at each outputgain = 1 t a = 25c input level (v p-p ) 0 C60 C50 C40 4 660415 g09 C70C80 123 5 C90 C100C110 distortion (dbc) v s = 3v r l = 800 at each outputgain = 1 t a = 25c 2nd harmonic 10mhz input 2nd harmonic 1mhz input 3rd harmonic 10mhz input 3rdharmonic 1mhz input passband gain and delay frequency (mhz) 0 gain (db) delay (ns) C3 C1 1 20 660415 g03 C5C7 C4 C2 0 C6C8 C9 30 40 5020 10 25 35 4515 5 0 5 10 15 25 v s = 5v gain = 1t a = 25c gain delay downloaded from: http:///
lt6604-15 6 660415fb typical performance characteristics distortion vs output common mode level single channel supply current vs total supply voltage transient response, channel separation vs frequency (note 9) distortion vs signal level distortion vs input common mode level distortion vs input common mode level input level (v p-p ) 0 C60 C50 C40 4 660415 g10 C70C80 123 5 C90 C100C110 distortion (dbc) v s = 5v r l = 800 at each output gain = 1 t a = 25c 2nd harmonic, 10mhz input 3rd harmonic, 10mhz input 2nd harmonic, 1mhz input 3rd harmonic,1mhz input input common mode votlage relative to v mid (v) C3 C110 C100 distortion component (dbc) C90 C80 C70 C60 C50 C40 C2 C1 0 1 2 660415 g11 3 2nd harmonic,v s = 3v 3rd harmonic,v s = 3v 2nd harmonic,v s = 5v 3rd harmonic,v s = 5v gain = 1 r l = 800 at each outputt a = 25c 2v p-p 1mhz input input common mode votlage relative to v mid (v) C3 C100 distortion component (dbc) C90 C80 C70 C60 C50 C40 C2 C1 0 1 2 660415 g12 3 gain = 4, r l = 800 at each output t a = 25c, 500mv p-p 1mhz input 2nd harmonic,v s = 3v 3rd harmonic,v s = 3v 2nd harmonic,v s = 5v 3rd harmonic,v s = 5v (v ocm C v mid ) voltage (v) distortion component (dbc) C70 C60 C50 0.5 1 1.5 660415 g13 C80C90 C1.5 C1 C0.5 0 2 2.5 C100C110 C40 2v p-p 1mhz input gain = 1,r l = 800 at each output t a = 25c 2nd harmonic,v s = 3v 3rd harmonic,v s = 3v 2nd harmonic,v s = 5v 3rd harmonic,v s = 5v 2nd harmonic,v s = 5v 3rd harmonic,v s = 5v total supply voltage (v) 20 supply current (ma) 30 40 5025 35 45 2468 660415 g14 10 12 t a = C40c t a = 25c t a = 85c out C 200mv/div in + 500mv/div in C 100ns/div differential gain = 1single-ended input differental output 660415 g15 out + 200mv/div frequency (mhz) 0.1 C50C60 channel separation (db) C40 1 10 100 660415 g16 C70C80 C100 C90 C120C130 C110 v in = 2v p-p v s = 5v r l = 800 at each outputgain = 1 downloaded from: http:///
lt6604-15 7 660415fb pin functions +ina and Cina (pins 2, 4): channel a input pins. signals can be applied to either or both input pins through identi- cal external resistors, r in . the dc gain from differential inputs to the differential outputs is 536/r in . v ocma (pin 6): dc common mode reference voltage for the 2nd filter stage in channel a. its value programs the common mode voltage of the differential output of the ? lter. pin 6 is a high impedance input, which can be driven from an external voltage reference, or pin 6 can be tied to pin 34 on the pc board. pin 6 should be bypassed with a 0.01f ceramic capacitor unless it is connected to a ground plane. v C (pins 7, 24, 31, 32, 35): negative power supply pin (can be ground). v midb (pin 8): the v midb pin is internally biased at mid- supply, see block diagram. for single supply operation the v midb pin should be bypassed with a quality 0.01f ceramic capacitor to ground. for dual supply operation, pin 8 can be bypassed or connected to a high quality dc ground. a ground plane should be used. a poor ground will increase noise and distortion. pin 8 sets the output common mode voltage of the 1st filter stage in channel b. it has a 5.5k impedance, and it can be overridden with an external low impedance voltage source. +inb and Cinb (pins 10, 12): channel b input pins. signals can be applied to either or both input pins through identi- cal external resistors, r in . the dc gain from differential inputs to the differential outputs is 536/r in . v ocmb (pin 14): is the dc common mode reference voltage for the 2nd filter stage in channel b. its value programs the common mode voltage of the differential output of the ? lter. pin 14 is a high impedance input, which can be driven from an external voltage reference, or pin 14 can be tied to pin 8 on the pc board. pin 14 should be bypassed with a 0.01f ceramic capacitor unless it is connected to a ground plane. v + a and v + b (pins 25, 17): positive power supply pins for channels a and b. for a single 3.3v or 5v supply (pins 7, 24, 31, 32 and 35 grounded) a quality 0.1f ceramic bypass capacitor is required from the positive supply pin (pins 25, 17) to the negative supply pin (pins 7, 24, 31, 32 and 35). the bypass should be as close as possible to the ic. for dual supply applications, bypass the negative supply pins to ground and pins 25 and 17 to ground with a quality 0.1f ceramic capacitor. +outb and Coutb (pins 19, 21): o u t p u t p i n s . p i n s 19 a n d 21 are the ? lter differential outputs for channel b. with a typical short-circuit current limit greater than 40ma each pin can drive a 100 and/or 50pf load to ac ground. +outa and Couta (pins 27, 29): output pins. pins 27 and 29 are the ? lter differential outputs for channel a. with a typical short-circuit current limit greater than 40ma each pin can drive a 100 and/or 50pf load to ac ground. v mida (pin 34) : the v mida pin is internally biased at mid- supply, see block diagram. for single supply operation the v mida pin should be bypassed with a quality 0.01f ceramic capacitor to ground. for dual supply operation, pin 34 can be bypassed or connected to a high quality dc ground. a ground plane should be used. a poor ground will increase noise and distortion. pin 34 sets the output common mode voltage of the 1st stage ? lter stage in chan- nel a. it has a 5.5k impedance, and it can be overridden with an external low impedance voltage source. exposed pad (pin 35): v C . the exposed pad must be soldered to the pcb. downloaded from: http:///
lt6604-15 8 660415fb block diagram C + C + v ocm C C + + v ocm 536 536 200 200 200 200 v + a v + b v C 11k11k op amp proprietary lowpass filter stage v in C b v in + b v in + a v in C a r in r in r in r in 660415 bd v ocmb nc nc v + b nc +outa Couta nc ncv + a nc v C ncnc +outb nc Coutb v C v C v mida v ocma v midb v C nc nc 1 23 4 5 6 7 8 9 nc nc nc +inaCina +inb Cinb ncnc C + C + v ocm C C + + v ocm 536 536 200 200 200 200 v C 11k11k op amp proprietary lowpass filter stage 10 11 1213 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 downloaded from: http:///
lt6604-15 9 660415fb applications information interfacing to the lt6604-15 note: the lt6604-15 contains two identical ? lters. the following applications information only refers to one ? lter. the two ? lters are independent except that they share the same negative supply voltage v C . the two ? lters can be used simultaneously by replicating the example circuits. the referenced pin numbers correspond to the a channel ? lter the lt6604-15 channel requires two equal external re- sistors, r in , to set the differential gain to 536/r in . the inputs to the ? lter are the voltages v in + and v in C presented to these external components, figure 1. the difference between v in + and v in C is the differential input voltage. the average of v in + and v in C i s t h e c o m m o n m o d e i n p u t v o l t a g e . similarly, the voltages v out + and v out C appearing at pins 27 and 29 of the lt6604-15 are the ? lter outputs. the dif- ference between v out + and v out C is the differential output voltage. the average of v out + and v out C is the common mode output voltage. figure 1 illustrates the lt6604-15 operating with a single 3.3v supply and unity passband gain; the input signal is dc coupled. the common mode input voltage is 0.5v, and the differential input voltage is 2v p-p . the common mode output voltage is 1.65v, and the differential output voltage is 2v p-p for frequencies below 15mhz. the common mode output voltage is determined by the voltage at v ocm . since v ocm is shorted to v mid , the output common mode is the mid-supply voltage. in addition, the common mode input voltage can be equal to the mid-supply voltage of v mid . figure 2 shows how to ac couple signals into the lt6604-15. in this instance, the input is a single-ended signal. ac cou- pling allows the processing of single-ended or dif ferentia l signals with arbitrary common mode levels. the 0.1f coupling capacitor and the 536 gain setting resistor form a high pass ? lter, attenuating signals below 3khz. larger values of coupling capacitors will proportionally reduce this highpass 3db frequency. C + 536 536 0.01f 0.1f 3.3v C + v in C v in + 25 27 4 34 62 29 7 660415 f01 v out + v out C v t 32 1 v in + v in C v t 32 1 v out + lt6604-15 v out C 0 0 1/2 C + 536 536 0.01f 0.1f 0.1f 0.1f 3.3v C + v in + 25 1/2 27 4 34 62 29 7 660415 f02 v out + v out C v 32 2 1 v t 10 0 C1 v in + lt6604-15 v out + v out C figure 1figure 2 downloaded from: http:///
lt6604-15 10 660415fb applications information in figure 3 the lt6604-15 is providing 12db of gain. the gain resistor has an optional 62pf in parallel to improve the passband ? atness near 15mhz. the common mode output voltage is set to 2v. use figure 4 to determine the interface between the lt6604-15 and a current output dac. the gain, or tran- simpedance, is de? ned as a = v out /i in . to compute the transimpedance, use the following equation: a = 536 ? r1 (r1 + r2) ( ) by setting r1 + r2 = 536, the gain equation reduces to a = r1 (). the voltage at the pins of the dac is determined by r1, r2, the voltage on v mid and the dac output current. consider figure 4 with r1 = 49.9 and r2 = 487. the voltage at v mid , for v s = 3.3v, is 1.65v. the voltage at the dac pins is given by: v dac = v mid ? r1 r1 + r2 + 536 + i in ? r1? r2 r1 + r2 = 77mv + i in ? 45.3 i in is i in + or i in C . the transimpedance in this example is 49.8. evaluating the lt6604-15 the low impedance levels and high frequency operation of the lt6604-15 require some attention to the matching networks between the lt6604-15 and other devices. the p r e v i o u s e x a m p l e s a s s u m e a n i d e a l (0 ) s o u r c e i m p e d a n c e and a large (1k) load resistance. among practical examples C + 133 133 0.1f 0.01f 5v C + v in C v in + 25 27 4 34 62 29 7 660415 f03 v out + v out C 62pf62pf + C 2v v t 32 1 0 v in + v in C v t 32 1 0 v out + v out C lt6604-15 500mv p-p (diff) 1/2 C + 0.1f 0.01f 3.3v C + lt6604-15 25 27 v out + i in + i in C v out C 4 1/2 34 62 29 7 660415 f04 current output dac r1 r1 r2 r2 = v out + C v out C i in + C i in C 536 ? r1 r1 + r2 figure 3 figure 4 C + 0.1f 0.1f 2.5v C2.5v C + lt6604-15 25 27 4 34 62 29 7 660415 f05 402 402 network analyzer input 50 coilcraft ttwb-16a 4:1 network analyzer source coilcraft ttwb-1010 1:1 50 52.3 523 523 1/2 figure 5 downloaded from: http:///
lt6604-15 11 660415fb applications information where impedance must be considered is the evaluation of the lt6604-15 with a network analyzer. figure 5 is a laboratory setup that can be used to char- acterize the lt6604-15 using single-ended instruments with 50 source impedance and 50 input impedance. for a unity gain con? guration the lt6604-15 requires an 536 source resistance yet the network analyzer output is calibrated for a 50 load resistance. the 1:1 transformer, 52.3 and 523 resistors satisfy the two constraints above. the transformer converts the single- ended source into a differential stimulus. similarly, the output of the lt6604-15 will have lower distortion with larger load resistance yet the analyzer input is typically 50. the 4:1 turns (16:1 impedance) transformer and the two 402 resistors of figure 5, present the output of the lt6604-15 with a 1600 differential load, or the equiva- lent of 800 to ground at each output. the impedance seen by the network analyzer input is still 50, reducing re? ections in the cabling between the transformer and analyzer input. differential and common mode voltage ranges the differential ampli? ers inside the lt6604-15 contain circuitry to limit the maximum peak-to-peak differential voltage through the ? lter. this limiting function prevents excessive power dissipation in the internal circuitry and provides output short-circuit protection. the limiting function begins to take effect at output signal levels above 2v p-p and it becomes noticeable above 3.5v p-p . this is illustrated in figure 6; the lt6604-15 channel was con? gured with unity passband gain and the input of the ? lter was driven with a 1mhz signal. because this voltage limiting takes place well before the output stage of the ? lter reaches the supply rails, the input/output behavior of the ic shown in figure 6 is relatively independent of the power supply voltage. the two ampli? ers inside the lt6604-15 channel have independent control of their output common mode voltage (see the block diagram section). the following guidelines will optimize the performance of the ? lter. v mid can be allowed to ? oat, but it must be bypassed to an ac ground with a 0.01f capacitor or some instability may be observed. v mid can be driven from a low impedance source, provided it remains at least 1.5v above v C and at least 1.5v below v + . an internal resistor divider sets the voltage of v mid . while the internal 11k resistors are well matched, their absolute value can vary by 20%. this should be taken into consideration when connecting an external resistor network to alter the voltage of v mid . v ocm can be shorted to v mid for simplicity. if a different common mode output voltage is required, connect v ocm to a voltage source or resistor network. for 3v and 3.3v supplies the voltage at v ocm must be less than or equal to the mid supply level. for example, voltage (v ocm ) 1.65v on a single 3.3v supply. for power supply voltages higher than 3.3v the voltage at v ocm can be set above mid supply. the voltage on v ocm should not be more than 1v below the voltage on v mid . the voltage on v ocm should not be more than 2v above the voltage on v mid . v ocm is a high impedance input. the lt6604-15 was designed to process a variety of input signals including signals centered on the mid-supply volt- age and signals that swing between ground and a positive voltage in a single supply system (figure 1). the range of allowable input common mode voltage (the average of v in + and v in C in figure 1) is determined by the power supply level and gain setting (see distortion vs input common mode level in the typical performance characteristics). 1mhz input level (v p-p ) 0 20 0 C20C40 C60 C80 C100 35 660415 f06 12 46 7 output level (dbv) 3rd harmonic 85c 1db compression points 25c 85c 3rd harmonic 25c 2nd harmonic, 25c 2nd harmonic 85c figure 6. output level vs input level, differential 1mhz input, gain = 1 downloaded from: http:///
lt6604-15 12 660415fb common mode dc currents in applications like figure 1 and figure 3 where the lt6604-15 not only provides lowpass ? ltering but also level shifts the common mode voltage of the input signal, dc currents will be generated through the dc path between input and output terminals. minimize these currents to decrease power dissipation and distortion. consider the application in f igur e 3. v mid s e t s t he ou t pu t c ommon mode vol t age o f the 1st differential ampli? er inside the lt6604-15 channel (see the block diagram section) at 2.5v. since the input common mode voltage is near 0v, there will be approxi- mately a total of 2.5v drop across the series combination of the internal 536 feedback resistor and the external 133 input resistor. the resulting 3.7ma common mode dc current in each input path, must be absorbed by the sources v in + and v in C . v ocm sets the common mode output voltage of the 2nd differential ampli? er inside the lt6604-15 channel, and therefore sets the common mode output voltage of the ? lter. since, in the example of figure 3, v ocm differs from v mid by 0.5v, an additional 2.5ma (1.25ma per side) of dc current will ? ow in the resistors coupling the 1st differential ampli? er output stage to the ? lter output. thus, a total of 9.9ma per channel is used to translate the common mode voltages. a simple modi? cation to figure 3 will reduce the dc com- mon mode currents by 40%. if v mid is shorted to v ocm the common mode output voltage of both op amp stages will be 2v and the resulting dc current will be 6ma per channel. of course, by ac coupling the inputs of figure 3, the common mode dc current can be reduced to 2.5ma per channel. noise the noise performance of the lt6604-15 channel can be evaluated with the circuit of figure 6. given the low noise output of the lt6604-15 and the 6db attenuation of the transformer coupling network, it will be necessary to measure the noise ? oor of the spectrum analyzer and subtract the instrument noise from the ? lter noise mea- surement. example: with the ic removed and the 25 resistors grounded, figure 6, measure the total integrated noise (e s ) of the spectrum analyzer from 10khz to 15mhz. with the ic inserted, the signal source (v in ) disconnected, and the input resistors grounded, measure the total integrated noise out of the ? lter (e o ). w i t h t h e s i g n a l s o u r c e c o n n e c t e d , set the frequency to 1 mhz and adjust the amplitude until v in measures 100mv p-p . measure the output amplitude, v out , and compute the passband gain a = v out /v in . now compute the input referred integrated noise (e in ) as: e in = (e o ) 2 ?(e s ) 2 a table 1 lists the typical input referred integrated noise for various values of r in . table 1. noise performance passband gain r in input referred integrated noise 10khz to 15mhz input referred integrated noise 10khz to 30mhz 41 3 3 3 6 v rms 51v rms 22 6 7 6 2 v rms 92v rms 15 3 6 1 0 9 v rms 169v rms applications information downloaded from: http:///
lt6604-15 13 660415fb figure 8 is plot of the noise spectral density as a function of frequency for an lt6604-15 with r in = 536 using the ? xture of figure 7 (the instrument noise has been subtracted from the results). the noise at each output is comprised of a differential component and a common mode component. using a transformer or combiner to convert the differential outputs to single-ended signal rejects the common mode noise and gives a true measure of the s/n achievable in the system. conversely, if each output is measured individually and the noise power added together, the resulting calculated noise level will be higher than the true differential noise. power dissipation the lt6604-15 ampli? ers combine high speed with large signal currents in a small package. there is a need to en- sure that the dies junction temperature does not exceed 150c. the lt6604-15 has an exposed pad (pin 35) which is connected to the lower supply (v C ). connecting the pad to a ground plane helps to dissipate the heat generated by the chip. metal trace and plated through-holes can be used to spread the heat generated by the device to the backside of the pc board. junction temperature, t j , is calculated from the ambient temperature, t a , and power dissipation, p d . the power dissipation is the product of supply voltage, v s , and supply current, i s . therefore, the junction temperature is given by: t j = t a + (p d ? ja ) = t a + (v s ? i s ? ja ) where the supply current, i s , is a function of signal level, load impedance, temperature and common mode voltages. for a given supply voltage, the worst-case power dissipation occurs when the dif ferential input signal is ma ximum, the common mode currents are maximum (see applications information regarding common mode dc currents), the load impedance is small and the ambient temperature is maximum. to compute the junction temperature, measure the supply current under these worstcase conditions, use 34c/w as the package thermal resistance, then apply the equation for tj. for example, using the circuit in figure 3 with dc differential input voltage of 250mv, a differential output voltage of 1v, no load resistance and an ambient temperature of 85c, the supply current (current into v + ) measures 50ma the resulting junction temperature is: t j = t a + (p d ? ja ) = 85 + (5 ? 2 ? 0.05 ? 34) = 102c. the thermal resistance can be affected by the amount of copper on the pcb that is connected to v C . the thermal resistance of the circuit can increase if the exposed pad is not connected to a large ground plane with a number of vias. applications information C + 0.1f 0.1f 2.5v C2.5v C + lt6604-15 25 27 4 34 62 29 7 r in r in 25 25 660415 f07 spectrum analyzer input 50 v in coilcraft ttwb-1010 1:1 1/2 frequency (mhz) 10 noise density (nv rms /hz) integrated noise (v) 20 25 35 4540 0.01 1 10 100 660415 f08 0 0.1 3015 5 40 80 100 140 180160 0 12060 20 noise density, gain = 1x noise density, gain = 4x integrated noise, gain = 1x integrated noise, gain = 4x figure 7 figure 8. input referred noise, gain = 1 downloaded from: http:///
lt6604-15 14 660415fb typical application C + r in 536 r in 536 i q 1/2 0.1f 0.1f 3v C + 25 27 4 34 62 29 25 25 7 lt6604-15 660415 ta02 2.2f 5.6pf v cmb v cma 5.6pf5.6pf C + r in 536 r in 536 gain = 536/r in 1/2 0.1f 0.1f 3v C + 17 19 12 8 1410 21 25 25 24 lt6604-15 2.2f 5.6pf 5.6pf5.6pf inainb ltc2299 0.1f 3v dual matched i and q lowpass filter and adc (typical phase matching 1 degree) downloaded from: http:///
lt6604-15 15 660415fb information furnished by linear technology corpor ation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technolo gy corporation makes no representa- t i o n t h a t t h e i n t e r c o n n e c t i o n o f i t s c i r c u i t s a s d e s c r i b e d h e r e i n w i l l n o t i n f r i n g e o n e x i s t i n g p a t e n t r i g h t s . package description 4.00 0.10 1.50 ref 7.00 0.10 note:1. drawing i s not a jedec package outline 2. drawing not to s cale 3. all dimen s ion s are in millimeter s 4. dimen s ion s of expo s ed pad on bottom of package do not include mold fla s h. mold fla s h, if pre s ent, s hall not exceed 0.20mm on any s ide 5. expo s ed pad s hall be s older plated 6. s haded area i s only a reference for pin 1 location on the top and bottom of package pin 1top mark (note 6) 0.40 0.10 34 33 12 bottom view?expo s ed pad 6.00 ref 0.75 0.05 r = 0.125 typ r = 0.10 typ pin 1 notch r = 0.30 or 0.25 45 chamfer 0.25 0.05 0.50 b s c 0.200 ref 0.00 ? 0.05 (uff34) qfn 0807 rev ? recommended s older pad pitch and dimen s ion s apply s older ma s k to area s that are not s oldered 0.70 0.05 0.25 0.05 0.50 b s c 1.50 ref 6.00 ref 6.10 0.05 7.50 0.05 3.10 0.05 4.50 0.05 package outline 2.64 0.10 1.47 0.10 1.90 0.10 1.83 0.10 1.90 0.10 0.99 0.10 2.64 0.05 1.47 0.05 1.90 0.05 1.90 0.05 1.29 0.05 1.83 0.05 uff package 34-lead plastic qfn (4mm 7mm) (reference ltc dwg # 05-08-1758 rev ?) downloaded from: http:///
lt6604-15 16 660415fb linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 2008 lt 0409 rev b printed in usa related parts part number description comments integrated filters ltc1562-2 very low noise, 8 th order filter building block lowpass and bandpass filters up to 300khz ltc1565-31 650khz linear phase lowpass filter continuous time, 7 th order, differential ltc1566-1 low noise, 2.3mhz lowpass filter continuous time, 7 th order, differential lt1568 very low noise, 4 th order filter building block lowpass and bandpass filters up to 10mhz ltc1569-7 linear phase, tunable 10 th order lowpass filter single-resistor programmable cut-off to 300khz lt6600-2.5 very low noise differential 2.5mhz lowpass filter snr = 86db at 3v supply, 4 th order filter lt6600-5 very low noise differential 5mhz lowpass filter snr = 82db at 3v supply, 4 th order filter lt6600-10 very low noise differential 10mhz lowpass filter snr = 82db at 3v supply, 4 th order filter lt6600-15 very low noise differential 15mhz lowpass filter snr = 76db at 3v supply, 4 th order filter lt6600-20 very low noise differential 20mhz lowpass filter snr = 76db at 3v supply, 4 th order filter lt6604-2.5 dual very low noise, differential ampli? er and 2.5mhz lowpass filter snr = 86db at 3v supply, 4 th order filter lt6604-5 dual very low noise, differential ampli? er and 5mhz lowpass filter snr = 82db at 3v supply, 4 th order filter lt6604-10 dual very low noise, differential ampli? er and 10mhz lowpass filter snr = 82db at 3v supply, 4 th order filter downloaded from: http:///

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