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ltc6401-20 1 640120f typical application features applications description 1.3ghz low noise, low distortion differential adc driver for 140mhz if the ltc ? 6401-20 is a high-speed differential ampli? er targeted at processing signals from dc to 140mhz. the part has been speci? cally designed to drive 12-, 14- and 16-bit adcs with low noise and low distortion, but can also be used as a general-purpose broadband gain block. the ltc6401-20 is easy to use, with minimal support circuitry required. the output common mode voltage is set using an external pin, independent of the inputs, which eliminates the need for transformers or ac-coupling ca- pacitors in many applications. the gain is internally ? xed at 20db (10v/v). the ltc6401-20 saves space and power compared to alternative solutions using if gain blocks and transform- ers. the ltc6401-20 is packaged in a compact 16-lead 3mm 3mm qfn package and operates over the C40c to 85c temperature range. 1.3ghz C3db bandwidth fixed gain of 10v/v (20db) C93dbc imd 3 at 70mhz (equivalent oip 3 = 50.5dbm) C74dbc imd 3 at 140mhz (equivalent oip 3 = 41dbm) 1nv/ ? h ? z internal op amp noise 2.1nv/ ? h ? z total input noise 6.2db noise figure differential inputs and outputs 200 input impedance 2.85v to 3.5v supply voltage 50ma supply current (150mw) 1v to 1.6v output common mode voltage, adjustable dc- or ac-coupled operation max differential output swing 4.4v p-p small 16-lead 3mm 3mm 0.75mm qfn package differential adc driver differential driver/receiver single ended to differential conversion if sampling receivers saw filter interfacing , lt, ltc and ltm are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. 29 66.5 0.1 f 0.1 f 640120 ta01a ltc6401-20 v ocm enable ltc2208 10 0.1 f + 1000pf input 0.1 f ltc2208 130msps 16-bit adc 1.25v 3.3v 10 ain + ain v cm v dd 20db gain v + ?n +in 3.3v +out +outf ?utf ?ut v single-ended to differential adc driver equivalent output ip3 vs frequency frequency (mhz) 0 output ip3 (dbm) 70 (note 7) 60 50 40 30 20 10 0 100 50 150 640120 ta01b 200
ltc6401-20 2 640120f absolute maximum ratings supply voltage (v + ? v ? ) ..........................................3.6v input current (note 2) ..........................................10ma operating temperature range (note 3) ............................................... ?40c to 85c speci? ed temperature range (note 4) ............................................... ?40c to 85c storage temperature range ................... ?65c to 150c maximum junction temperature........................... 150c (note 1) 16 15 14 13 5 6 7 8 top view ud package 16-lead (3mm 3mm) plastic qfn 9 10 11 17 12 4 3 2 1 v + v ocm v + v e v e enable v + v e ein ein +in +in eout eoutf +outf +out t jmax = 150c, e ja = 68c/w, e jc = 4.2c/w exposed pad (pin 17) is v ? , must be soldered to pcb order information ltc6400 and ltc6401 selector guide part number gain (db) gain (v/v) z in (differential) (1) i cc (ma) ltc6400-20 20 10 200 90 ltc6401-20 20 10 200 50 in addition to the ltc6401 family of ampli? ers, a lower distortion ltc6400 family is available. the ltc6400 is pin compatible to the ltc6401, and has the same low noise performance. the low distortion of the ltc6400 comes at the expense of higher power consumption. please refer to the separate ltc6400 data sheets for complete details. other gain versions from 8db to 26db will follow. please check each datasheet for complete details. pin configuration lead free finish tape and reel part marking* package description temperature range ltc6401cud-20#pbf ltc6401cud-20#trpbf lcdb 16-lead (3mm 3mm) plastic qfn 0c to 70c ltc6401iud-20#pbf ltc6401iud-20#trpbf lcdb 16-lead (3mm 3mm) plastic qfn ?40c 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/
ltc6401-20 3 640120f dc electrical characteristics symbol parameter conditions min typ max units input/output characteristic g diff gain v in = 100mv differential 19.4 20 20.6 db g temp gain temperature drift v in = 100mv differential 1 mdb/c v swingmin output swing low each output, v in = 400mv differential 90 170 mv v swingmax output swing high each output, v in = 400mv differential 2.3 2.44 v v outdiffmax maximum differential output swing 1db compressed 4.4 v p-p i out output current drive single-ended 10 ma v os input offset voltage differential C2 2 mv tcv os input offset voltage drift differential 1.4 v/c i vrmin input common mode voltage range, min 1 v i vrmax input common mode voltage range, max 1.6 v r indiff input resistance differential 170 200 230 c indiff input capacitance differential, includes parasitic 1 pf r outdiff output resistance differential 18 25 32 r outfdiff filtered output resistance differential 85 100 115 c outfdiff filtered output capacitance differential, includes parasitic 2.7 pf cmrr common mode rejection ratio input common mode voltage 1.1v to 1.4v 45 66 db output common mode voltage control g cm common mode gain v ocm = 1v to 1.6v 1 v/v v ocmmin output common mode range, min 1 1.1 v v v ocmmax output common mode range, max 1.6 1.5 v v v oscm common mode offset voltage v ocm = 1.1v to 1.5v C15 15 mv tcv oscm common mode offset voltage drift 6 v/c iv ocm v ocm input current 515 a ? e ? n ? a ? b ? l ? e pin v il ? e ? n ? a ? b ? l ? e input low voltage 0.8 v v ih ? e ? n ? a ? b ? l ? e input high voltage 2.4 v i il ? e ? n ? a ? b ? l ? e input low current ? e ? n ? a ? b ? l ? e = 0.8v 0.5 a i ih ? e ? n ? a ? b ? l ? e input high current ? e ? n ? a ? b ? l ? e = 2.4v 1.2 3 a power supply v s operating supply range 2.85 3 3.5 v i s supply current ? e ? n ? a ? b ? l ? e = 0.8v 38 50 62 ma i shdn shutdown supply current ? e ? n ? a ? b ? l ? e = 2.4v 13 ma psrr power supply rejection ratio (differential outputs) 2.85v to 3.5v 55 84 db the denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. v + = 3v, v C = 0v, +in = Cin = v ocm = 1.25v, ? e ? n ? a ? b ? l ? e = 0v, no r l unless otherwise noted.
ltc6401-20 4 640120f ac electrical characteristics speci? cations are at t a = 25c. v + = 3v, v C = 0v, +in and Cin ? oating, v ocm = 1.25v, ? e ? n ? a ? b ? l ? e = 0v, no r l unless otherwise noted. symbol parameter conditions min typ max units C3dbbw C3db bandwidth 200mv p-p,out (note 6) 1.25 ghz 0.1dbbw bandwidth for 0.1db flatness 200mv p-p,out (note 6) 130 mhz 0.5dbbw bandwidth for 0.5db flatness 200mv p-p,out (note 6) 250 mhz 1/f 1/f noise corner 12.5 khz sr slew rate differential (note 6) 4500 v/s t s1% 1% settling time 2v p-p,out (note 6) 2 ns t ovdr output overdrive recovery time 1.9v p-p,out (note 6) 7 ns t on turn-on time +out, Cout within 10% of final values 78 ns t off turn-off time i cc falls to 10% of nominal 146 ns C3dbbw cm common mode small signal C3db bw 0.1v p-p at v ocm , measured single-ended at output (note 6) 15 mhz 10mhz input signal hd 2,10m /hd 3,10m second/third order harmonic distortion 2v p-p,out , r l = 400 C122/C92 dbc 2v p-p,out , no r l C110/C103 dbc 2v p-p,outfilt , no r l C113/C102 dbc imd 3,10m third-order intermodulation (f1 = 9.5mhz f2 = 10.5mhz) 2v p-p,out composite, r l = 400 C96 dbc 2v p-p,out composite, no r l C108 dbc 2v p-p,outfilt composite, no r l C105 dbc oip 3,10m third-order output intercept point (f1 = 9.5mhz f2 = 10.5mhz) 2v p-p,out composite, no r l (note 7) 58 dbm p 1db,10m 1db compression point r l = 375 (notes 5, 7) 17.3 dbm nf 10m noise figure r l = 375 (note 5) 6.2 db e in,10m input referred voltage noise density includes resistors (short inputs) 2.1 nv/ ? h ? z e on,10m output referred voltage noise density includes resistors (short inputs) 21 nv/ ? h ? z 70mhz input signal hd 2,70m /hd 3,70m second/third order harmonic distortion 2v p-p,out , r l = 400 C91/C80 dbc 2v p-p,out , no r l C95/C88 dbc 2v p-p,outfilt , no r l C95/C88 dbc imd 3,70m third-order intermodulation (f1 = 69.5mhz f2 = 70.5mhz) 2v p-p,out composite, r l = 400 C88 dbc 2v p-p,out composite, no r l C93 dbc 2v p-p,outfilt composite, no r l C92 dbc oip 3,70m third-order output intercept point (f1 = 69.5mhz f2 = 70.5mhz) 2v p-p,out composite, no r l (note 7) 50.5 dbm p 1db,70m 1db compression point r l = 375 (notes 5, 7) 17.3 dbm nf 70m noise figure r l = 375 (note 5) 6.1 db e in,70m input referred voltage noise density includes resistors (short inputs) 2.1 nv/ ? h ? z e on,70m output referred voltage noise density includes resistors (short inputs) 21 nv/ ? h ? z 140mhz input signal hd 2,140m /hd 3,140m second/third order harmonic distortion 2v p-p,out , r l = 400 C80/C57 dbc 2v p-p,out , no r l C81/C60 dbc 2v p-p,outfilt , no r l C80/C65 dbc
ltc6401-20 5 640120f ac electrical characteristics frequency (mhz) 0 phase (degree) 100 0 ?00 ?00 ?00 ?00 group delay (ns) 1.5 1.2 0.9 0.6 0.3 0 200 400 600 800 1000 640120 g03 phase group delay test circuit b frequency (mhz) 10 100 1000 normalized gain (db) 1.0 0.8 ?.8 0.6 ?.6 0.4 ?.4 0.2 ?.2 0 ?.0 640120 g02 test circuit b frequency (mhz) 10 100 1000 3000 gain (db) 25 20 15 10 5 0 640120 g01 test circuit b 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: input pins (+in, Cin) are protected by steering diodes to either supply. if the inputs go beyond either supply rail, the input current should be limited to less than 10ma. note 3: the ltc6401c and ltc6401i are guaranteed functional over the operating temperature range of C40c to 85c. note 4: the ltc6401c is guaranteed to meet speci? ed performance from 0c to 70c. it is designed, characterized and expected to meet speci? ed performance from C40c to 85c but is not tested or qa sampled at these temperatures. the ltc6401i is guaranteed to meet speci? ed performance from C40c to 85c. note 5: input and output baluns used. see test circuit a. note 6: measured using test circuit b. note 7: since the ltc6401-20 is a feedback ampli? er with low output impedance, a resistive load is not required when driving an ad converter. therefore, typical output power is very small. in order to compare the ltc6401-20 with ampli? ers that require 50 output load, the ltc6401-20 output voltage swing driving a given r l is converted to oip 3 and p 1db as if it were driving a 50 load. using this modi? ed convention, 2v p-p is by de? nition equal to 10dbm, regardless of the actual r l . typical performance characteristics frequency response gain 0.1db flatness s21 phase and group delay vs frequency symbol parameter conditions min typ max units imd 3,140m third-order intermodulation (f1 = 139.5mhz f2 = 140.5mhz) 2v p-p,out composite, r l = 400 C71 dbc 2v p-p,out composite, no r l C74 dbc 2v p-p,outfilt composite, no r l C72 dbc oip 3,140m third-order output intercept point (f1 = 139.5mhz f2 = 140.5mhz) 2v p-p,out composite, no r l (note 7) 41 dbm p 1db,140m 1db compression point r l = 375 (notes 5, 7) 18 dbm nf 140m noise figure r l = 375 (note 5) 6.4 db e in,140m input referred voltage noise density includes resistors (short inputs) 2.1 nv/ ? h ? z e on,140m output referred voltage noise density includes resistors (short inputs) 22 nv/ ? h ? z imd 3,130m/150m third-order intermodulation (f1 = 130mhz f2 = 150mhz) measure at 170mhz 2v p-p,out composite, r l = 375 (note 5) C61 C69 dbc speci? cations are at t a = 25c. v + = 3v, v C = 0v, +in and Cin ? oating, v ocm = 1.25v, ? e ? n ? a ? b ? l ? e = 0v, no r l unless otherwise noted.
ltc6401-20 6 640120f time (ns) 0 output voltage (v) 2.5 0.5 1.0 2.0 1.5 0 50 100 150 200 640120 g10 ?ut +out r l = 87.5 per output time (ns) 0 settling (%) 5 4 3 2 1 ? ? ? ? ? 0 123 5 4 6 640120 g11 r l = 87.5 per output 0 5 10 15 20 time (ns) output voltage (v) 2.5 0.5 1.0 2.0 1.5 0 640120 g09 ?ut +out r l = 87.5 per output time (ns) 0 output voltage (v) 1.35 1.20 1.25 1.30 1.15 51015 20 640120 g08 ?ut +out r l = 87.5 per output frequency (mhz) 10 noise figure (db) 15 10 2 4 12 14 6 8 0 11 3 5 13 7 9 1 input referred noise voltage (nv/ hz) 6 4 2 0 100 1000 640120 g07 noise figure e in frequency (mhz) 1 impedance magnitude ( ) 250 200 150 100 50 0 225 175 125 75 25 impedance phase (degree) 100 80 60 40 20 ?0 ?0 ?0 ?0 0 ?00 10 100 1000 640120 g05 z in z out z in z out phase impedance magnitude frequency (mhz) 10 s parameters (db) 0 ?0 ?0 ?0 ?0 ?0 ?0 ?0 ?0 100 1000 3000 640120 g04 s11 s22 s12 test circuit b typical performance characteristics input and output re? ection and reverse isolation vs frequency input and output impedance vs frequency psrr and cmrr vs frequency overdrive transient response 1% settling time for 2v output step noise figure and input referred noise voltage vs frequency small signal transient response large signal transient response frequency (mhz) 1 psrr, cmrr (db) 100 90 80 70 60 50 40 30 0 10 20 10 100 1000 640120 g06 psrr cmrr
ltc6401-20 7 640120f output common mode voltage (v) 1.0 1.1 1.2 1.3 1.4 1.5 640120 g18 hd2 hd3 distortion (dbc) ?0 ?0 ?0 ?0 ?0 ?0 ?00 differential input v out = 2v p-p at 100mhz r l = 400 frequency (mhz) third order imd (dbc) 640120 g17 0 50 100 150 200 ?0 ?0 ?0 ?0 ?0 ?0 ?20 ?10 ?00 unfiltered no r l unfiltered 200 r l filtered no r l single-ended input v out = 2v p-p composite ?0 ?0 ?0 ?0 ?0 ?0 ?20 ?10 ?00 0 50 100 150 200 frequency (mhz) harmonic distortion (dbc) 640120 g16 hd2 hd3 single-ended input v out = 2v p-p no r l 0 50 100 150 200 hd2 no r l hd2 200 r l hd3 no r l hd3 200 r l single-ended input v out = 2v p-p ?0 ?0 ?0 ?0 ?0 ?0 ?20 ?10 ?00 frequency (mhz) harmonic distortion (dbc) 640120 g15 640120 g13 frequency (mhz) harmonic distortion (dbc) ?0 ?0 ?0 ?0 ?0 ?0 ?20 ?10 ?00 hd2 hd3 differential input v out = 2v p-p no r l 0 50 100 150 200 0 50 100 150 200 ?0 ?0 ?0 ?0 ?0 ?0 ?20 ?10 ?00 frequency (mhz) third order imd (dbc) 640120 g14 unfiltered no r l unfiltered 200 r l filtered no r l differential input v out = 2v p-p composite frequency (mhz) harmonic distortion (dbc) 640120 g12 0 50 100 150 200 hd2 no r l hd2 200 r l hd3 no r l hd3 200 r l differential input v out = 2v p-p ?0 ?0 ?0 ?0 ?0 ?0 ?20 ?10 ?00 typical performance characteristics harmonic distortion (un? ltered) vs frequency harmonic distortion (filtered) vs frequency third order intermodulation distortion vs frequency harmonic distortion (un? ltered) vs frequency harmonic distortion (filtered) vs frequency third order intermodulation distortion vs frequency harmonic distortion vs output common mode voltage (un? ltered outputs) equivalent output 1db compression point vs frequency frequency (mhz) 50 output 1db compression (dbm) 20 19 18 16 17 15 80 110 140 170 200 640020 g19 differential input r l = 400 (note 7)
ltc6401-20 8 640120f time (ns) ?00 0 voltage (v) 3.5 2.0 2.5 1.0 1.5 3.0 ?.5 0.5 0 100 200 300 400 500 640120 g22 supply current (ma) 70 40 60 ?0 20 30 50 10 0 r l = 87.5 per output +out ?ut i cc enable time (ns) ?00 0 voltage (v) 3.5 2.0 2.5 1.0 1.5 3.0 ?.5 0.5 0 100 200 300 400 500 640120 g21 supply current (ma) 70 40 60 ?0 20 30 50 10 0 r l = 87.5 per output +out ?ut i cc enable 0 50 100 150 200 frequency (mhz) 640120 g20 output ip3 (dbm) 70 60 50 40 20 10 30 0 unfiltered no r l unfiltered 200 r l filtered no r l differential input v out = 2v p-p composite (note 7) typical performance characteristics equivalent output third order intercept vs frequency turn-on time turn-off time
ltc6401-20 9 640120f block diagram pin functions v + (pins 1, 3, 10): positive power supply (normally tied to 3v or 3.3v). all three pins must be tied to the same voltage. bypass each pin with 1000pf and 0.1f capaci- tors as close to the pins as possible. v ocm (pin 2): this pin sets the output common mode voltage. a 0.1f external bypass capacitor is recom- mended. v C (pins 4, 9, 12, 17): negative power supply. all four pins must be connected to the same voltage/ground. Cout, +out (pins 5, 8): un? ltered outputs. these pins have 12.5 series resistors. Coutf, +outf (pins 6, 7): filtered outputs. these pins have 50 series resistors and a 1.7pf shunt capacitance. ? e ? n ? a ? b ? l ? e (pin 11): this pin is a logic input referenced to v C . if low, the part is enabled. if high, the part is disabled and draws approximately 1ma supply current. +in (pins 13, 14): positive input. pins 13 and 14 are internally shorted together. Cin (pins 15, 16): negative input. pins 15 and 16 are internally shorted together. exposed pad (pin 17): v C . the exposed pad must be con- nected to the same voltage/ground as pins 4, 9, 12. 13 640120 bd 1 v + 2 v ocm 14 7 15 +out +outf ?utf ?ut +in in+ out in out+ +in ?n ?n 5 16 r g 100 r out 12.5 r f 1000 r g 100 2k r f 1000 6 4 v 3 v + 12 v 11 enable 9 v 10 v + common mode control bias control 8 r out 12.5 r filt 50 r filt 50 c filt 1.7pf 5.3pf
ltc6401-20 10 640120f applications information circuit operation the ltc6401-20 is a low noise and low distortion fully differential op amp/adc driver with: ? operation from dc to 1.3ghz C3db bandwidth impedance ? fixed gain of 10v/v (20db) ? differential input impedance 200 ? differential output impedance 25 ? differential impedance of output ? lter 100 the ltc6401-20 is composed of a fully differential ampli? er with on chip feedback and output common mode voltage control circuitry. differential gain and input impedance are set by 100 /1000 resistors in the feedback network. small output resistors of 12.5 improve the circuit stability over various load conditions. they also provide a possible external ? ltering option, which is often desirable when the load is an adc. filter resistors of 50 are available for additional ? ltering. lowpass/bandpass ? lters are easily implemented with just a couple of external components. moreover, they offer single-ended 50 matching in wideband applications and no external resistor is needed. the ltc6401-20 is very ? exible in terms of i/o coupling. it can be ac- or dc-coupled at the inputs, the outputs or both. due to the internal connection between input and output, users are advised to keep input common mode voltage between 1v and 1.6v for proper operation. if the inputs are ac-coupled, the input common mode voltage is automatically biased close to v ocm and thus no external circuitry is needed for bias. the ltc6401-20 provides an output common mode voltage set by v ocm , which allows driving an adc directly without external components such as a transformer or ac coupling capacitors. the input signal can be either single-ended or differential with only minor differences in distortion performance. input impedance and matching the differential input impedance of the ltc6401-20 is 200 . if a 200 source impedance is unavailable, then the differential inputs may need to be terminated to a lower value impedance, e.g. 50 , in order to provide an imped- ance match to the source. several choices are available. one approach is to use a differential shunt resistor (figure 1). another approach is to employ a wideband transformer (figure 2). both methods provide a wideband match. the termination resistor or the transformer must be placed close to the input pins in order to minimize the re? ection due to input mismatch. alternatively, one could apply a narrowband impedance match at the inputs of the ltc6401- 20 for frequency selection and/or noise reduction. referring to figure 3, ltc6401-20 can be easily con? gured for single-ended input and differential output without a balun. the signal is fed to one of the inputs through a matching network while the other input is connected to the same matching network and a source resistor. because the return ratios of the two feedback paths are equal, the figure 1. input termination for differential 50 input impedance using shunt resistor figure 2. input termination for differential 50 input impedance using a 1:4 balun 640120 f01 in+ out in out+ 100 66.5 12.5 1000 ltc6401-20 100 25 25 v in 1000 12.5 50 50 13 14 15 16 7 5 6 8 + +out +outf ?utf ?ut +in +in ?n ?n 1.7pf 640120 f02 in+ out in out+ 100 12.5 1000 ltc6401-20 100 25 25 v in 1000 12.5 50 50 13 14 15 16 7 5 6 8 + 1:4 +out +outf ?utf ?ut +in +in ?n ?n 1.7pf
ltc6401-20 11 640120f two outputs have the same gain and thus symmetrical swing. in general, the single-ended input impedance and termination resistor r t are determined by the combination of r s , r g and r f . for example, when r s is 50 , it is found that the single-ended input impedance is 200 and r t is 66.5 in order to match to a 50 source impedance. the ltc6401-20 is unconditionally stable. however, the overall differential gain is affected by both source imped- ance and load impedance as shown in figure 4: a v vr r r v out in s l l == ++ 2000 200 25 the noise performance of the ltc6401-20 also depends upon the source impedance and termination. for example, an input 1:4 balun transformer in figure 2 improves snr by adding 6db of gain at the inputs. a trade-off between gain and noise is obvious when constant noise ? gure circle and constant gain circle are plotted within the same figure 4. calculate differential gain input smith chart, based on which users can choose the optimal source impedance for a given gain and noise requirement. output match and filter the ltc6401-20 can drive an adc directly without external output impedance matching. alternatively, the differential output impedance of 25 can be matched to higher value impedance, e.g. 50 , by series resistors or an lc network. the internal low pass ? lter outputs at +outf/Coutf have a C3db bandwidth of 590mhz. external capacitor can reduce the low pass ? lter bandwidth as shown in figure 5. a bandpass ? lter is easily implemented with only a few components as shown in figure 6. three 39pf capacitors and a 16nh inductor create a bandpass ? lter with 165mhz center frequency, C3db frequencies at 138mhz and 200mhz. applications information figure 3. input termination for single-ended 50 input impedance figure 5. ltc6401-20 internal filter topology modi? ed for low filter bandwidth (three external capacitors) 640120 f03 in+ out in out+ 100 r t 66.5 0.1 f 0.1 f 12.5 1000 ltc6401-20 100 r s 50 r s 50 v in 1000 12.5 50 50 13 14 15 16 7 5 6 8 + 0.1 f r t 66.5 +out +outf ?utf ?ut +in +in ?n ?n 1.7pf 640120 f04 in+ out in out+ 100 12.5 1000 ltc6401-20 100 1/2 r s 1/2 r s v in v out 1000 12.5 50 50 13 14 15 16 7 5 6 8 + 1/2 r l 1/2 r l +out +outf ?utf ?ut +in +in ?n ?n 1.7pf 640120 f05 in+ out in out+ 100 12.5 1000 ltc6401-20 100 1000 12.5 50 50 13 14 15 16 7 5 6 8 8.2pf 8.2pf 12pf filtered output (87.5mhz) +out +outf ?utf ?ut +in +in ?n ?n 1.7pf figure 6. ltc6401-20 application circuit for bandpass filtering (three external capacitors, one external inductor) ltc2208 10 10 4.99 4.99 39pf 16nh 39pf 39pf 640120 f06 in+ out in out+ 100 12.5 1000 ltc6401-20 100 1000 12.5 50 50 13 14 15 16 7 5 6 8 +out +outf ?utf ?ut +in +in ?n ?n 1.7pf
ltc6401-20 12 640120f output common mode adjustment the ltc6401-20s output common mode voltage is set by the v ocm pin, which is a high impedance input. the output common mode voltage is capable of tracking v ocm in a range from 1v to 1.6v. bandwidth of v ocm control is typically 15mhz, which is dominated by a low pass ? lter connected to the v ocm pin and is aimed to reduce com- mon mode noise generation at the outputs. the internal common mode feedback loop has a C3db bandwidth around 300mhz, allowing fast common mode rejection at the outputs of the ltc6401-20. the v ocm pin should be tied to a dc bias voltage where a 0.1f bypass capacitor is recommended. when interfacing with a/d converters such as the lt22xx families, the v ocm can be normally connected to the v cm pin of the adc. driving a/d converters the ltc6401-20 has been speci? cally designed to inter- face directly with high speed a/d converters. in figure 7, an example schematic shows the ltc6401-20 with a single-ended input driving the ltc2208, which is a 16-bit, 130msps adc. two external 10 resistors help eliminate potential resonance associated with stray capacitance of pcb traces and bond wire inductance of either the adc input or the driver output. v ocm of the ltc6401-20 is connected to v cm of the ltc2208 at 1.25v. alternatively, a single-ended input signal can be converted to differential signal via a balun and fed to the input of the ltc6401-20. the balun also converts input impedance to match 50 source impedance. figure 7. single-ended input to ltc6401-20 and ltc2208 applications information 29 66.5 0.1 f 640120 f07 ltc6401-20 v ocm enable if in ltc2208 10 0.1 f ltc2208 130msps 16-bit adc 1.25v 10 20db gain ain + ain v cm ?n +in +out +outf ?utf ?ut test circuits due to the fully-differential design of the ltc6401 and its usefulness in applications with differing characteristic speci? cations, two test circuits are used to generate the information in this datasheet. test circuit a is dc987b, a two-port demonstration circuit for the ltc6401 family. the schematic and silkscreen are shown below. this circuit includes input and output transformers (baluns) for single-ended-to-differential conversion and imped- ance transformation, allowing direct hook-up to a 2-port network analyzer. there are also series resistors at the output to present the ltc6401 with a 375 differential load, optimizing distortion performance. due to the input and output transformers, the C3db bandwidth is reduced from 1.3ghz to approximately 1.1ghz. test circuit b uses a 4-port network analyzer to measure s-parameters and gain/phase response. this removes the effects of the wideband baluns and associated circuitry, for a true picture of the >1ghz s-parameters and ac characteristics.
ltc6401-20 13 640120f applications information top silkscreen
ltc6401-20 14 640120f version ic r3 r4 t1 sl1 sl2 sl3 -g ltc6401cud-20 open open mini-circuits tcm4-19 (1:4) 6db 20db 14db t1 (2) t3 tcm 4-19 1:4 t4 tcm 4-19 1:4 640120 ta03 r10 86.6 r8 (1) r7 (1) r9 86.6 c3 0.1 f c4 0.1 f c1 0.1 f c2 0.1 f ltc6401-20 v ocm v + v + v v v + v cc v cc v enable +in +in ?n ?n ?ut +outf ?utf +out enable dis 12 11 10 9 1234 5 6 7 8 16 15 14 13 sl1 (2) sl2 (2) j2 ?n j1 +in j5 ?ut sl3 (2) j4 +out c22 0.1 f c21 0.1 f c18 0.1 f c13 0.1 f c17 1000pf r16 0 tp2 v cc 2.85v to 3.5v 13 2 jp1 v cc v cc v cc c12 1000pf c9 1000pf c10 0.1 f c15 1 f v cc c14 4.7 f c7 0.1 f r4 (2) 1 3 2 3 1 2 5 4 4 5 tp5 v ocm r2 (1) r1 0 r3 (2) j6 test in c19 0.1 f 1 3 2 5 4 c20 0.1 f r21 (1) r22 (1) r20 1k r19 1.5k r14 (1) r13 0 c6 0.1 f c5 0.1 f c24 0.1 f c23 0.1 f j7 test out note: unless otherwise specified. (1) do not stuff. (2) sl = signal level 3 1 2 4 5 tp3 gnd r17 0 r25 0 r18 0 r26 0 r12 0 r11 (1) r24 (1) r6 0 r5 (1) 0db t2 tcm 4-19 1:4 typical application demo circuit 987b schematic (test circuit a)
ltc6401-20 15 640120f information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. package description 3.00 0.10 (4 sides) recommended solder pad pitch and dimensions 1.45 0.05 (4 sides) note: 1. drawing conforms to jedec package outline mo-220 variation (weed-2) 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package pin 1 top mark (note 6) 0.40 0.10 bottom view?xposed pad 1.45 0.10 (4-sides) 0.75 0.05 r = 0.115 typ 0.25 0.05 1 pin 1 notch r = 0.20 typ or 0.25 45 chamfer 15 16 2 0.50 bsc 0.200 ref 2.10 0.05 3.50 0.05 0.70 0.05 0.00 ?0.05 (ud16) qfn 0904 0.25 0.05 0.50 bsc package outline ud package 16-lead plastic qfn (3mm 3mm) (reference ltc dwg # 05-08-1691) typical application test circuit b, 4-port analysis 0.1 f 13 640120 ta02 1 v + 2 v ocm 14 7 15 +out +outf ?utf ?ut +in in+ out in out+ +in ?n ?n 5 16 r g 100 r out 12.5 r f 1000 r g 100 r f 1000 6 4 v 3 v + v ocm v + v + 12 v 11 enable 9 v 10 v + common mode control 1/2 agilent e5o71a bias control 8 r out 12.5 37.4 37.4 r filt 50 r filt 50 c filt 1.7pf 1000pf 0.1 f 0.1 f 0.1 f port 3 (50 ) port 4 (50 ) 1/2 agilent e5o71a 200 0.1 f 0.1 f port 1 (50 ) port 2 (50 ) 0.1 f 1000pf
ltc6401-20 16 640120f linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 2007 lt 0907 ? printed in usa related parts part number description comments high-speed differential ampli? ers/differential op amps lt1993-2 800mhz differential ampli? er/adc driver a v = 2v/v, oip3 = 38dbm at 70mhz lt1993-4 900mhz differential ampli? er/adc driver a v = 4v/v, oip3 = 40dbm at 70mhz lt1993-10 700mhz differential ampli? er/adc driver a v = 10v/v, oip3 = 40dbm at 70mhz lt1994 low noise, low distortion differential op amp 16-bit snr and sfdr at 1mhz, rail-to-rail outputs lt5514 ultralow distortion if ampli? er/adc driver with digitally controlled gain oip3 = 47dbm at 100mhz, gain control range 10.5db to 33db lt5524 low distortion if ampli? er/adc driver with digitally controlled gain oip3 = 40dbm at 100mhz, gain control range 4.5db to 37db ltc6400-20 1.8ghz low noise, low distortion, differential adc driver a v = 20db, 90ma supply current, imd 3 = C65dbc at 300mhz lt6402-6 300mhz differential ampli? er/adc driver a v = 6db, distortion < C80dbc at 25mhz lt6402-12 300mhz differential ampli? er/adc driver a v = 12db, distortion < C80dbc at 25mhz lt6402-20 300mhz differential ampli? er/adc driver a v = 20db, distortion < C80dbc at 25mhz ltc6406 3ghz rail-to-rail input differential op amp 1.6nv/hz noise, C72dbc distortion at 50mhz, 18ma lt6411 low power differential adc driver/dual selectable gain ampli? er 16ma supply current, imd3 = C83dbc at 70mhz, a v = 1, C1 or 2 high-speed single-ended output op amps lt1812/lt1813/ lt1814 high slew rate low cost single/dual/quad op amps 8nv/hz noise, 750v/s, 3ma supply current lt1815/lt1816/ lt1817 very high slew rate low cost single/dual/quad op amps 6nv/hz noise, 1500v/s, 6.5ma supply current lt1818/lt1819 ultra high slew rate low cost single/dual op amps 6nv/hz noise, 2500v/s, 9ma supply current lt6200/lt6201 rail-to-rail input and output low noise single/dual op amps 0.95nv/hz noise, 165mhz gbw, distortion = C80dbc at 1m hz lt6202/lt6203/ lt6204 rail-to-rail input and output low noise single/dual/quad op amps 1.9nv/hz noise, 3ma supply current, 100mhz gbw lt6230/lt6231/ lt6232 rail-to-rail output low noise single/dual/quad op amps 1.1nv/hz noise, 3.5ma supply current, 215mhz gbw lt6233/lt6234/ lt6235 rail-to-rail output low noise single/dual/quad op amps 1.9nv/hz noise, 1.2ma supply current, 60mhz gbw integrated filters ltc1562-2 very low noise, 8th order filter building block lowpass and bandpass filters up to 300khz lt1568 very low noise, 4th order filter building block lowpass and bandpass filters up to 10mhz ltc1569-7 linear phase, tunable 10th 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, 4th order filter lt6600-5 very low noise differential 5mhz lowpass filter snr = 82db at 3v supply, 4th order filter lt6600-10 very low noise differential 10mhz lowpass filter snr = 82db at 3v supply, 4th order filter lt6600-15 very low noise differential 15mhz lowpass filter snr = 76db at 3v supply, 4th order filter lt6600-20 very low noise differential 20mhz lowpass filter snr = 76db at 3v supply, 4th order filter

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