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1 lt1204 4-input video multiplexer with 75mhz current feedback amplifier s f ea t u re d u escriptio the lt ? 1204 is a 4-input video multiplexer designed to drive 75 w cables and easily expand into larger routing systems. wide bandwidth, high slew rate, and low differ- ential gain and phase make the lt1204 ideal for broadcast quality signal routing. channel separation and disable isolation are greater than 90db up to 10mhz. the channel- to-channel output switching transient is only 40mv p-p , with a 50ns duration, making the transition imperceptible on high quality monitors. a unique feature of the lt1204 is its ability to expand into larger routing matrices. this is accomplished by a patent pending circuit that bootstraps the feedback resistors in the disable condition, raising the true output impedance of the circuit. the effect of this feature is to eliminate cable misterminations in large systems. the large input and output signal levels supported by the lt1204 when operated on 15v supplies make it ideal for general purpose analog signal selection and multiplexing. a shutdown feature reduces the supply current to 1.5ma. all hostile crosstalk surface mount pcb measurements frequency (mhz) 1 120 all hostile crosstalk (db) 100 ?0 ?0 ?0 10 100 1204 ta02 ?0 v s = 15v v in 0 = gnd v in 1,2,3 = 0dbm r l = 100 w n 0.1db gain flatness > 30mhz n channel separation at 10mhz: 90db n 40mv switching transient, input referred n C 3db bandwidth, a v = 2, r l = 150 w : 75mhz n channel-to-channel switching time: 120ns n easy to expand for more inputs n large input range: 6v n 0.04% differential gain, r l = 150 w n 0.06 differential phase, r l = 150 w n high slew rate: 1000v/ m s n output swing, r l = 400 w : 13v n wide supply range: 5v to 15v u s a o pp l ic at i n broadcast quality video multiplexing n large matrix routing n medical imaging n large amplitude signal multiplexing n programmable gain amplifiers , ltc and lt are registered trademarks of linear technology corporation. u a o pp l ic at i ty p i ca l + cfa v in0 v in0 75 w 1 2 v in1 v in1 75 w 3 4 v in2 v in2 75 w 5 6 v in3 v in3 75 w 7 8 +1 +1 +1 +1 v o 16 14 13 12 11 10 15 9 logic v + v fb s/d enable a1 a0 15v 15v r f 1k 75 w r g 1k v out 8.2k ?5v lt1204 6.8k gnd gnd gnd ref 1204 ta01
2 lt1204 a u g w a w u w a r b s o lu t exi t i s supply voltage ..................................................... 18v C input current (pin 13) .................................... 15ma +input and control/logic current (note 1) ........ 50ma output short-circuit duration (note 2) ......... continuous specified temperature range (note 3) ....... 0 c to 70 c operating temperature range ............... C 40 c to 85 c storage temperature range ................ C 65 c to 150 c junction temperature (note 4) ............................ 150 c lead temperature (soldering, 10 sec).................. 300 c t jmax = 150 c, q ja = 70 c/w order part number order part number lt1204cn* 1 2 3 4 5 6 7 8 top view n package 16-lead pdip 16 15 14 13 12 11 10 9 v in0 gnd v in1 gnd v in2 gnd v in3 ref v + v o v fb shdn enable a1 a0 wu u package / o rder i for atio *see note 3 *see note 3 top view sw package 16-lead plastic so 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 v in0 gnd v in1 gnd v in2 gnd v in3 ref v + v o v fb shdn enable a1 a0 t jmax = 150 c, q ja = 90 c/w consult factory for industrial and military grade parts. e lectr ic al c c hara terist ics symbol parameter conditions min typ max units v os input offset voltage any positive input, t a = 25 c514mv l 16 mv offset matching between any positive input, v s = 15v l 0.5 5 mv input offset voltage drift any positive input l 40 m v/ c i in + positive input bias current any positive input, t a = 25 c38 m a l 10 m a i in C negative input bias current t a = 25 c 20 100 m a l 150 m a e n input noise voltage f = 1khz, r f = 1k, r g = 10 w , r s = 0 w 7 nv/ ? hz +i n noninverting input noise current density f = 1khz 1.5 pa/ ? hz Ci n inverting input noise current density f = 1khz 40 pa/ ? hz c in input capacitance input selected 3.0 pf input deselected 3.5 pf c out output capacitance disabled, pin 11 voltage = 0v 8 pf r in positive input resistance, any positive input v s = 5v, v in = C 1.5v, 2v, t a = 25 c520 m w v s = 15v, v in = 5v l 420 m w 0 c t a 70 c, 5v v s 15v, v cm = 0v, pin 8 grounded and pulse tested unless otherwise noted. lt1204csw*
3 lt1204 e lectr ic al c c hara terist ics symbol parameter conditions min typ max units input voltage range, any positive input v s = 5v, t a = 25 c 2.0 2.5 v C1.5 C2.0 v v s = 15v l 5.0 6.0 v v s = 15v, pin 8 voltage = C 5v l 3.75 4.0 v cmrr common mode rejection ratio v s = 5v, v cm = C 1.5v, 2v, t a = 25 c4855 db v s = 15v, v cm = 5v l 48 58 db negative input current v s = 5v, v cm = C 1.5v, 2v, t a = 25 c 0.05 1 m a/v common mode rejection v s = 15v, v cm = 5v l 0.05 1 m a/v psrr power supply rejection ratio v s = 4.5v to 15v l 60 76 db negative input current power supply rejection v s = 4.5v to 15v l 0.5 5 m a/v a vol large-signal voltage gain v s = 15v, v out = 10v, r l = 1k l 57 73 db v s = 5v, v out = 2v, r l = 150 w l 57 66 db r ol transresistance v s = 15v, v out = 10v, r l = 1k l 115 310 k w d v o / d i in C v s = 5v, v out = 2v, r l = 150 w l 115 210 k w v out output voltage swing v s = 15v, r l = 400 w , t a = 25 c 12 13.5 v l 10 v v s = 5v, r l = 150 w , t a = 25 c 3.0 3.7 v l 2.5 v i out output current r l = 0 w , t a = 25 c 35 55 125 ma i s supply current (note 5) pin 11 = 5v l 19 24 ma pin 11 = 0v l 19 24 ma pin 12 = 0v l 1.5 3.5 ma disabled output resistance v s = 15v, pin 11 = 0v, v o = 5v, r f = r g = 1k l 14 25 k w v s = 15v, pin 11 = 0v, v o = 5v, r f = 2k, r g = 222 w l 820 k w 0 c t a 70 c, 5v v s 15v, v cm = 0v, pin 8 grounded and pulse tested unless otherwise noted. 0 c t a 70 c, v s = 15v, r f = 2k, r g = 220 w , r l = 400 w unless otherwise noted. symbol parameter conditions min typ max units v il input low voltage pins 9, 10, 11, 12 l 0.8 v v ih input high voltage pins 9, 10, 11, 12 l 2v i il input low current pins 9, 10 voltage = 0v l 1.5 6 m a i ih input high current pins 9, 10 voltage = 5v l 10 150 na enable low input current pin 11 voltage = 0v l 4.5 15 m a enable high input current pin 11 voltage = 5v l 200 300 m a i shdn shutdown input current pin 12 voltage 0v v shdn 5v l 20 80 m a t sel channel-to-channel select time (note 6) pin 8 voltage = C 5v, t a = 25 c 120 240 ns t dis disable time (note 7) pin 8 voltage = C 5v, t a = 25 c 40 100 ns t en enable time (note 8) pin 8 voltage = C 5v, t a = 25 c 110 200 ns t shdn shutdown assert or release time (note 9) pin 8 voltage = C 5v, t a = 25 c 1.4 10 m s digital i put characteristics u
4 lt1204 ac characteristics symbol parameter conditions min typ max units t r , t f small-signal rise and fall time r l = 150 w , v out = 125mv 5.6 ns sr slew rate (note 10) r l = 400 w 400 1000 v/ m s channel select output transient all v in = 0v, r l = 400 w , input referred 40 mv t s settling time 0.1%, v out = 10v, r l = 1k 70 ns all hostile crosstalk (note 11) so pcb #028, r l = 100 w , r s = 10 w 92 db disable crosstalk (note 11) so pcb #028, pin 11 voltage = 0v, r l = 100 w , r s = 50 w 95 db shutdown crosstalk (note 11) so pcb #028, pin 12 voltage = 0v, r l = 100 w , r s = 50 w 92 db all hostile crosstalk (note 11) pdip pcb #029, r l = 100 w , r s = 10 w 76 db disable crosstalk (note 11) pdip pcb #029, pin 11 voltage = 0v, r l = 100 w , r s = 50 w 81 db shutdown crosstalk (note 11) pdip pcb #029, pin 12 voltage = 0v, r l = 100 w , r s = 50 w 76 db differential gain (note 12) v s = 15v, r l = 150 w 0.04 % v s = 5v, r l = 150 w 0.04 % differential phase (note 12) v s = 15v, r l = 150 w 0.06 deg v s = 5v, r l = 150 w 0.12 deg t a = 25 c, v s = 15v, r f = r g = 1k, unless otherwise noted. the l denotes specifications which apply over the specified operating temperature range. note 1: analog and digital inputs (pins 1, 3, 5, 7, 9, 10, 11 and 12) are protected against esd and overvoltage with internal scrs. for inputs < 6v the scr will not fire, voltages above 6v will fire the scrs and the dc current should be limited to 50ma. to turn off the scr the pin voltage must be reduced to less than 2v or the current reduced to less than 10ma. note 2: a heat sink may be required depending on the power supply voltage. note 3: commercial grade parts are designed to operate over the temperature range of C 40 c to 85 c but are neither tested nor guaranteed beyond 0 c to 70 c. industrial grade parts specified and tested over C 40 c to 85 c are available on special request. consult factory. note 4: t j is calculated from the ambient temperature t a and power dissipation p d according to the following formulas: lt1204cn: t j = t a + (p d )(70 c/w) lt1204cs: t j = t a + (p d )(90 c/w) note 5: the supply current of the lt1204 has a negative temperature coefficient. for more information see typical performance characteristics. note 6: apply 0.5v dc to pin 1 and measure the time for the appearance of 5v at pin 15 when pin 9 goes from 5v to 0v. pin 10 voltage = 0v. apply 0.5v dc to pin 3 and measure the time for the appearance of 5v at pin 15 when pin 9 goes from 0v to 5v. pin 10 voltage = 0v. apply 0.5v dc to pin 5 and measure the time for the appearance of 5v at pin 15 when pin 9 goes from 5v to 0v. pin 10 voltage = 5v. apply 0.5v dc to pin 7 and measure the time for the appearance of 5v at pin 15 when pin 9 goes from 0v to 5v. pin 10 voltage = 5v. note 7: apply 0.5v dc to pin 1 and measure the time for the disappearance of 5v at pin 15 when pin 11 goes from 5v to 0v. pins 9 and 10 are at 0v. note 8: apply 0.5v dc to pin 1 and measure the time for the appearance of 5v at pin 15 when pin 11 goes from 0v to 5v. pins 9 and 10 are at 0v. above a 1mhz toggle rate, t en reduces. note 9: apply 0.5v dc at pin 1 and measure the time for the appearance of 5v at pin 15 when pin 12 goes from 0v to 5v. pins 9 and 10 are at 0v. then measure the time for the disappearance of 5v dc to 500mv at pin 15 when pin 12 goes from 5v to 0v. note 10: slew rate is measured at 5v on a 10v output signal while operating on 15v supplies with r f = 2k, r g = 220 w and r l = 400 w . note 11: v in = 0dbm (0.223v rms ) at 10mhz on any 3 inputs with the 4th input selected. for disable crosstalk and shutdown crosstalk all 4 inputs are driven simultaneously. a 6db output attenuator is formed by a 50 w series output resistor and the 50 w input impedance of the hp4195a network analyzer. r f = r g = 1k. note 12: differential gain and phase are measured using a tektronix tsg120 yc/ntsc signal generator and a tektronix 1780r video measurement set. the resolution of this equipment is 0.1% and 0.1 . five identical muxs were cascaded giving an effective resolution of 0.02% and 0.02 .
5 lt1204 measurements taken from so demonstration board #028. typical ac perfor a ce w u small signal small signal small signal v s (v) a v r l ( w )r f ( w )r g ( w ) C 3db bw (mhz) 0.1db bw (mhz) peaking (db) 15 1 150 1.1k none 88.5 48.3 0.1 1k 1.6k none 95.6 65.8 0 12 1 150 976 none 82.6 49.1 0.1 1k 1.3k none 90.2 63.6 0.1 5 1 150 665 none 65.5 43.6 0.1 1k 866 none 68.2 42.1 0.1 15 2 150 787 787 75.7 45.8 0 1k 887 887 82.2 61.3 0.1 12 2 150 750 750 71.9 45.0 0 1k 845 845 77.5 52.1 0 5v 2 150 590 590 58.0 32.4 0 1k 649 649 62.1 42.7 0.1 15 10 150 866 95.3 44.3 28.7 0.1 1k 1k 110 47.4 30.9 0.1 12 10 150 825 90.9 43.5 27.2 0 1k 931 100 46.3 32.1 0.1 5 10 150 665 73.2 37.2 22.1 0 1k 750 82.5 39.3 27.8 0.1 truth table channel a1 a0 enable shutdown selected 00 1 1 v in0 01 1 1 v in1 10 1 1 v in2 11 1 1 v in3 x x 0 1 high z output x x x 0 off
6 lt1204 cc hara terist ics uw a t y p i ca lper f o r c e 12v frequency response, a v = 1 5v frequency response, a v = 1 frequency (hz) 1m ? gain (db) ? 0 1 2 10m 100m 1g 1204 g01 ? ? ? ? 3 4 ?20 phase (deg) ?00 ?0 ?0 ?0 ?40 ?60 ?80 200 ?0 0 phase gain v s = 12v r l = 150 w r f = 976 w frequency (hz) 1m ? gain (db) ? 0 1 2 10m 100m 1g 1204 g04 ? ? ? ? 3 4 ?20 phase (deg) ?00 ?0 ?0 ?0 ?40 ?60 ?80 200 ?0 0 phase gain v s = 5v r l = 150 w r f = 655 w 12v frequency response, a v = 2 5v frequency response, a v = 2 frequency (hz) 1m 4 gain (db) 5 6 7 8 10m 100m 1g 1204 g02 3 2 1 0 9 10 ?20 phase (deg) ?00 ?0 ?0 ?0 ?40 ?60 ?80 200 ?0 0 phase gain v s = 12v r l = 150 w r f = 750 w r g = 750 w frequency (hz) 1m 4 gain (db) 5 6 7 8 10m 100m 1g 1204 g05 3 2 1 0 9 10 ?20 phase (deg) ?00 ?0 ?0 ?0 ?40 ?60 ?80 200 ?0 0 gain v s = 5v r l = 150 w r f = 590 w r g = 590 w phase 12v frequency response, a v = 10 5v frequency response, a v = 10 frequency (hz) 1m 18 gain (db) 19 20 21 22 10m 100m 1g 1204 g03 17 16 15 14 23 24 ?20 phase (deg) ?00 ?0 ?0 ?0 ?40 ?60 ?80 200 ?0 0 phase gain v s = 12v r l = 150 w r f = 825 w r g = 90.9 w frequency (hz) 1m 18 gain (db) 19 20 21 22 10m 100m 1g 1204 g06 17 16 15 14 23 24 ?20 phase (deg) ?00 ?0 ?0 ?0 ?40 ?60 ?80 200 ?0 0 gain v s = 5v r l = 150 w r f = 665 w r g = 73.2 w phase
7 lt1204 cc hara terist ics uw a t y p i ca lper f o r c e 15v all hostile crosstalk vs frequency disable and shutdown crosstalk vs frequency amplifier output impedance vs frequency maximum undistorted output vs frequency total harmonic distortion vs frequency frequency (mhz) 1 0 output voltage (v p-p ) 5 10 15 20 10 100 1204 g07 25 v s = 15v r l = 1k r fb = 1k a v = 10 a v = 2 a v = 1 maximum capacitive load vs feedback resistor feedback resistor (k w ) 10 capacitive load (pf) 1000 10000 023 1204 g08 1 100 r l = 1k a v = 2 t a = 25 c 5db peaking v s = 5v v s = 15v frequency (hz) 10 0.001 total harmonic distortion (%) 0.1 1k 100k 1204 g09 100 10k v o = 6v rms v o = 1v rms v s = 15v r l = 400 w r f = r g = 1k 0.01 all hostile crosstalk vs frequency, various source resistance frequency (mhz) 1 120 all hostile crosstalk (db) 100 ?0 ?0 ?0 10 100 1204 g12 110 ?0 ?0 ?0 ?0 v s = 15v r l = 100 w r f = r g = 1k demo pcb #028 130 r s = 37.5 w r s = 75 w r s = 0 w r s = 10 w 5v all hostile crosstalk vs frequency frequency (mhz) 1 120 all hostile crosstalk (db) 100 ?0 ?0 ?0 10 100 1204 g11 110 ?0 ?0 ?0 ?0 ?0 v s = 5v r l = 100 w r f = r g = 1k r s = 0 w demo pcb #028 any channel frequency (mhz) 1 C120 all hostile crosstalk (db) C100 C80 C60 C40 10 100 1204 g10 C110 C90 C70 C50 C30 C20 v s = 15v r l = 100 w r f = r g = 1k r s = 0 w demo pcb #028 ch1 ch4 ch3 ch2 frequency (mhz) 1 120 all hostile crosstalk (db) 100 ?0 ?0 ?0 10 100 1204 g13 110 ?0 ?0 ?0 ?0 ?0 v s = 15v r l = 100 w r f = r g = 1k r s = 50 w demo pcb #028 all channels driven shutdown crosstalk disable crosstalk spot noise voltage and current vs frequency frequency (hz) 10 1 10 100 1k 100k 1204 g14 spot noise (nv/ ? hz or pa/ ? hz) 100 10k ? n e n +i n frequency (hz) 10k output impedance ( w ) 1 1000 1m 100m 1204 g15 0.1 10 100 100k 10m r fb = r g = 2k r fb = r g = 750 w v s = 15v
8 lt1204 output short-circuit current vs temperature settling time to 10mv vs output step output saturation voltage vs temperature input voltage range vs pin 8 voltage input voltage range vs supply voltage power supply rejection vs frequency maximum channel switching rate vs pin 8 voltage output disable v-i characteristic voltage on pin 8 (v) 0 ? input voltage range (v) ? ? 0 4 ? ? ? ? 6 2 ? ? ? ? ? 1204 g19 v s = 15v a v = 1 ?5 c, 25 c, 125 c supply voltage ( v) 2 ? input voltage range (v) ? ? 0 4 4 8 10 16 6 2 6 12 14 pin 8 = 0v 25 c 125 c ?5 c 125 c ?5 c 25 c 1204 g20 frequency (hz) 20 power supply rejection (db) 40 50 70 10k 1m 10m 100m 1204 g21 0 100k 60 30 10 ?0 v s = 15v r fb = r g = 1k positive negative temperature ( c) ?0 1.0 v + 25 75 1204 g22 1.0 ?5 0 50 100 125 0.5 v 0.5 output saturation voltage (v) r l = temperature ( c) ?0 30 output short-circuit current (ma) 50 80 0 50 75 1204 g23 40 70 60 ?5 25 100 125 settling time (ns) 30 output step (v) 2 6 10 70 1204 g24 ? ? ?0 40 50 60 80 0 4 8 ? ? v s = 15v r f = r g = 1k typical perfor m a n ce characteristics uw output voltage (v) ? output current ( m a) 100 200 3 1204 g16 0 100 ? ? 1 5 200 50 150 ?0 150 ? 4 ? 0 2 v s = 15v r f = r g = 1k slope = 1/18k frequency (hz) 1 disabled output impedance (k w ) 10 1k 100k 1m 10m 1204 g17 0 10k 100 100m v s = 15v r f = r g = 1k disabled output impedance vs frequency channel switching rate (mhz) 1.0 voltage on pin 8 (v) ? ? ? 2.5 3.5 1204 g18 ? ? ? 1.5 2.0 3.0 ? ? 0 4.0 v in = 1v dc r l = 100 w r fb = r g = 1k
9 lt1204 cc hara terist ics uw a t y p i ca lper f o r c e disabled and shutdown supply current vs supply voltage settling time to 1mv vs output step enabled supply current vs supply voltage settling time ( m s) 0 output step (v) 2 6 10 16 1205 g25 ? ? ?0 4 8 12 20 0 4 8 ? ? v s = 15v r f = r g = 1k 218 6 10 14 supply voltage ( v) 0 12 supply current (ma) 13 15 16 17 22 19 4 8 10 18 1204 g26 14 20 21 18 26 12 14 16 25 c 125 c ?5 c supply voltage ( v) 0 0 supply current (ma) 1 15 16 17 22 19 4 8 10 18 1204 g27 2 20 21 18 26 12 14 16 25 c 125 c ?5 c ?5 c, 25 c, 125 c i shdn u s a o pp l ic at i wu u i for atio specified over a very wide range of conditions. an advan- tage of the current feedback topology used in the lt1204 is well-controlled frequency response. in all cases of the performance table, the peaking is 0.1db or less. if more peaking can be tolerated, larger bandwidths can be obtained by lowering the feedback resistor. for gains of 2 or less, the 0.1db bandwidth is greater than 30mhz for all loads and supply voltages. at high gains (low values of r g ) the disabled output resistance drops slightly due to loading of the internal buffer amplifier as discussed in multiplexer expansion. logic inputs the logic inputs of the lt1204 are compatible with all 5v logic. all pins have esd protection (> 2kv), and shorting them to 12v or 15v will cause excessive currents to flow. limit the current to less than 50ma when driving the logic above 6v. power supplies the lt1204 will operate from 5v (10v total) to 15v (30v total) and is specified over this range. it is not necessary to use equal value supplies, however, the offset voltage and inverting input bias current will change. the offset voltage changes about 600 m v per volt of supply mismatch. the inverting bias current changes about 2.5 m a per volt of supply mismatch. the power supplies should be bypassed with quality tantalum capacitors. feedback resistor selection the small-signal bandwidth of the lt1204 is set by the external feedback resistors and internal junction capaci- tors. as a result the bandwidth is a function of the supply voltage, the value of the feedback resistor, the closed- loop gain and the load resistor. these effects are outlined in the resistor selection guide of the typical ac perfor- mance table. bandwidths range as high as 95mhz and are small-signal rise time, a v = 2 1204 ai01 v s = 15v r l = 150 w r f = 1k r g = 1k
10 lt1204 u s a o pp l ic at i wu u i for atio capacitance on the inverting input current feedback amplifiers require resistive feedback from the output to the inverting input for stable operation. take care to minimize the stray capacitance between the output and the inverting input. capacitance on the invert- ing input to ground will cause peaking in the frequency response and overshoot in the transient response. capacitive loads the lt1204 can drive capacitive loads directly when the proper value of feedback resistor is used. the graph of maximum capacitive load vs feedback resistor should be used to select the appropriate value. the value shown is for 5db peaking when driving a 1k load at a gain of 2. this is a worst-case condition. the amplifier is more stable at higher gains and driving heavier loads. alterna- tively, a small resistor (10 w to 20 w ) can be put in series with the output to isolate the capacitive load from the amplifier output. this has the advantage that the ampli- fier bandwidth is only reduced when the capacitive load is present. the disadvantage is that the gain is a function of load resistance. slew rate the slew rate of the current feedback amplifier on the lt1204 is not independent of the amplifier gain the way slew rate is in a traditional op amp. this is because both the input and the output stage have slew rate limitations. in high gain settings the signal amplitude between the nega- tive input and any driven positive input is small and the overall slew rate is that of the output stage. for gains less than 10, the overall slew rate is limited by the input stage. the input slew rate of the lt1204 is approximately 135v/ m s and is set by internal currents and capacitances. the output slew rate is set by the value of the feedback resistors and the internal capacitances. at a gain of 10 with a 1k feedback resistor and 15 supplies, the output slew rate is typically 1000v/ m s. larger feedback resistors will reduce the slew rate as will lower supply voltages, similar to the way the bandwidth is reduced. the graph, maximum undistorted output vs frequency, relates the slew rate limitations to sinusoidal inputs for various gain configurations. large-signal transient response large-signal transient response 1204 ai02 1204 ai03 v s = 15v a v = 2 r f = 1k r g = 1k r l = 400 w v s = 15v a v = 10 r f = 910 w r g = 100 w r l = 400 w switching characteristics and pin 8 switching between channels is a make-before-break condition where both inputs are on momentarily. the buffers isolate the inputs when the make-before-break switching occurs. the input with the largest positive voltage determines the output level. if both inputs are equal, there is only a 40mv error at the input of the cfa during the transition. the reference adjust (pin 8) allows the user to trade off positive input voltage range for switching time. for example, on 15v supplies, setting the voltage on pin 8 to C 6.8v reduces the switching transient to a 50ns duration, and reduces the positive input range from 6v to 2.35v. the negative input range remains unchanged at C 6v. when switching video in picture, this short transient is imperceptible even on high quality
11 lt1204 u s a o pp l ic at i wu u i for atio monitors. the reference pin has no effect when the lt1204 is operating on 5v, and should be grounded. on supply voltages above 8v, the range of voltages for pin 8 should be between C 6.5v and C 7.5v. reducing pin 8 voltage below C 7.5v turns on the off tee switch, and the isolation between channels is lost. 1204 ai04 channel-to-channel switching v out pin 15 transient at input buffer v in0 and v in1 connected to 2mhz sinewave competitive muxs crosstalk the crosstalk, or more accurately all hostile crosstalk, is measured by driving a signal into any three of the four inputs and selecting the 4th input with the logic control. this 4th input is either shorted to ground or terminated in an impedance. all hostile crosstalk is defined as the ratio in decibel of the signal at the output of the cfa to the signal on the three driven inputs, and is input-referred. disable crosstalk is measured with all four inputs driven and the part disabled. crosstalk is critical in many applications where video multiplexers are used. in professional video systems, a crosstalk figure of C 72db is a desirable specification. the key to the outstanding crosstalk performance of the lt1204 is the use of tee switches (see figure 1). when the tee switch is on (q2 off) q1 and q3 are a pair of emitter followers with excellent ac response for driving the cfa. a0 pin 9 v in0 and v in1 connected to 2mhz sinewave pin 8 voltage = C6.8v, v s = 15v a0 pin 9 v in0 pin 1 1204ai05 switching between v in0 and v in1 r s = 50 w , v ref = C 6.8v, v s 15v competitive video multiplexers built in cmos are bidirec- tional and suffer from poor output-to-input isolation and cause transients to feed to the inputs. cmos muxs have been built with break-before-make switches to eliminate the talking between channels, but these suffer from output glitches large enough to interfere with sync circuitry. multiplexers built on older bipolar processes that switch lateral pnp transistors take several microseconds to settle and blur the transition between pictures. bipolar mux cmos mux 1204 ai06 + cfa r f v out fb i 2 r g v in0 to logic q2 q1 i 1 q3 1204 f01 v + v ? figure 1. tee switch
12 lt1204 u s a o pp l ic at i wu u i for atio when the decoder turns off the tee switch (q2 on) the emitter base junctions of q1 and q3 become reverse- biased while q2 emitter absorbs current from i 1 . not only do the reverse-biased emitter base junctions provide good isolation, but any signal at v in0 coupling to q1 emitter is further attenuated by the shunt impedance of q2 emitter. current from i 2 is routed to any on switch. crosstalk performance is a strong function of the ic package, the pc board layout as well as the ic design. the die layout utilizes grounds between each input to isolate adjacent channels, while the output and feedback pins are on opposite sides of the die from the input. the layout of a pc board that is capable of providing C 90db all hostile crosstalk at 10mhz is not trivial. that level corresponds to a 30 m v output below a 1v input at 10mhz. a demonstra- tion board has been fabricated to show the component and ground placement required to attain these crosstalk num- bers. a graph of all hostile crosstalk for both the pdip and so packages is shown. it has been found empirically from these pc boards that capacitive coupling across the pack- age of greater than 3ff (0.003pf) will diminish the rejec- tion, and it is recommended that this proven layout be copied into designs. the key to the success of the so pc board #028 is the use of a ground plane guard around pin 13, the feedback pin. pdip pc board #029, component side 1204 ai09 gnd v v+ (408) 432-1900 lt1204 video mux demonstration board vin0 vin1 vin2 vin3 r1 r2 r6 c4 c2 c1 c3 u1 r3 rf ro vout enable r1 r0 s/d ref + + frequency (mhz) 1 120 all hostile crosstalk (db) 100 ?0 ?0 ?0 10 100 1204 ai07 ?0 v s = 15v v in0 = gnd v in1,2,3 = 0dbm r l = 100 w pdip demo pcb #029 so demo pcb #028 all hostile crosstalk
13 lt1204 u s a o pp l ic at i wu u i for atio sol pc board #028, component side 1204 ai08 gnd v+ vout enable a1 a0 ref (408) 432-1900 lt1204 video mux demonstration board vin3 vin2 vin1 vin0 c2 c4 u1 c1 ro r3 r2 r1 rf rg c3 s/d v
14 lt1204 u s a o pp l ic at i wu u i for atio all hostile crosstalk test setup* demonstration pc board schematic 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 v in0 gnd v in1 gnd v in2 gnd v in3 ref + c1 4.7 m f c2 0.1 m f + c3 4.7 m f c4 0.1 m f r f 750 w r o 75 w r g 750 w r3 10k r1 10k r2 10k enable a1 a0 ref v + v gnd lt1204 v in0 v in1 v in2 v in3 v + v o v fb shdn enable a1 a0 shutdown resistors r1, r2 and r3 are pull-down and pull-up resistors for the logic and enable pins. they may be omitted if the lt1204 is driven from ttl levels or from 5v cmos. l1204 ai10 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 v in0 gnd v in1 gnd v in2 gnd v in3 ref lt1204 v + v o v fb shdn enable a1 a0 15v 15v *see pc board layout 1k 10 1k 50 50 splitter osc ref v in 50 50 hp4195a network analyzer 50 1204 ai11 10k 50 alternate all hostile crosstalk setup* 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 v in0 gnd v in1 gnd v in2 gnd v in3 ref lt1204 v + v o v fb shdn enable a1 a0 15v 15v *see pc board layout 1k 10 w 1k 50 w 50 w splitter osc ref v in 50 w 50 w hp4195a network analyzer 50 w 1204 ai12 10k 50 w 50 w 50 w
15 lt1204 u s a o pp l ic at i wu u i for atio multiplexer expansion pin 11 and pin 12 to expand the number of mux inputs, lt1204s can be paralleled by shorting their outputs together. the multi- plexer disable logic has been designed to prevent shoot- through current when two or more amplifiers have their outputs shorted together. (shoot-through current is a spike of power supply current caused by both amplifiers being on at once.) monitoring supply current spikes the multiplexer uses a circuit to ensure the disabled amplifiers do not load or alter the cable termination. when the lt1204 is disabled (pin 11 low) the output stage is turned off and an active buffer senses the output and drives the feedback pin to the cfa (figure 2). this boot- straps the feedback resistors and raises the true output impedance of the circuit. for the condition where r f = r g = 1k, the disable output resistance is typically raised to 25k and drops to 20k for a v = 10, r f = 2k and r g = 222 w due to loading of the feedback buffer. operating the disable feature with r g < 100 w is not recommended. a shutdown feature (pin 12 low) reduces the supply current to 1.5ma and lowers the power dissipation when the lt1204 is not in use. if the part is shut down, the bootstrapping is inoperative and the feedback resis- tors will load the output. if the cfa is operated at a gain of +1, however, the feedback resistor will not load the output even in shutdown because there is no resistive path to ground, but there will be a C 6db loss through the cable system. a frequency response plot shows the effect of using the disable feature versus using the shutdown feature. in this example four lt1204s were connected together at their outputs forming a 16-to-1 mux. the plot shows the effect of the bootstrapping circuit that eliminates the + + + + lt1204 1 3 5 7 13 14 11 en v 16 v + to scope 15 75 w + + + + lt1204 1 3 5 7 13 14 11 en v 16 15 1k 1k 75 w v + 74hc04 75 w tek ct-1 o 5v oscillator 1204 ai13 1k 1k timing and supply current waveforms oscillator 5v/div v out 1v/div i s 10ma/div 74hc04 output 5v/div 1204 ai14 tee switch v in0 tee switch v in1 tee switch v in2 tee switch v in3 v lt1204 ?n + cfa ?ff fb r f r g v out 75 w 75 w cable 1204 f02 a v = +1 75 w figure 2. active buffer drives fb pin 13
16 lt1204 u s a o pp l ic at i wu u i for atio improper cable termination due to feedback resistors loading the cable. the limit to the number of expanded inputs is set by the acceptable error budget of the system. 16-to-1 mux response using disable vs shutdown for a 64-to-1 mux we need sixteen lt1204s. the equivalent load resistance due to the feedback resistor r eq in disable is 25k/15 = 1.67k. see figure 3. v o = 75r eq 75(75) + 150r eq , v o = 0.489v this voltage represents a 2.1% loading error. if the shutdown feature is used instead of the disable feature, then the lt1204 could expand to only an 8-to-1 mux for the same error. as a practical matter the gain error at frequency is also set by capacitive loading. the disabled output capaci- tance of the lt1204 is about 8pf, and in the case of sixteen lt1204s, it would represent a 128pf load. the combination of 1.67k and 128pf correspond to about a 0.3db roll-off at 5mhz. figure 3. equivalent loading schematic 16-to-1 multiplexer all hostile crosstalk frequency (mhz) 1 ? gain (db) ? ? 0 2 10 100 1204 ai15 4 v s = 15v r l = 100 w r f = r g = 1k disable shutdown frequency (mhz) 1 120 all hostile crosstalk (db) 100 ?0 ?0 ?0 10 100 1204 ai16 ?0 v s = 15v r l = 100 w r f = r g = 1k r s = 0 shutdown crosstalk disable crosstalk on 75 w 1v lt1204 off 75 w lt1204 75 w v out cable 75 w v out r eq 75 w 1v 1204 f03
17 lt1204 u s a o pp l ic at i ty p i ca l by 1, 0.5, 0.25 and 0.125 to form an amplifier with a gain of 16, 8, 4, 2, when lt1204 #1 is selected. lt1204 #2 is connected to the same attenuator. when enabled (lt1204 #1 disabled), it results in gain of 1, 0.5, 0.25 and 0.125. the wide input common mode range of the lt1204 is needed to accept inputs of 8v p-p . 4-input differential receiver lt1204s can be connected inverting and noninverting as shown to make a 4-input differential receiver. the receiver can be used to convert differential signals sent over a low cost twisted pair to a single-ended output or used in video loop-thru connections. the logic inputs a0 and a1 are tied together because the same channels are selected on each lt1204. by using the disable feature, the number of differential inputs can be increased by adding pairs of lt1204s and tying the outputs of the noninverting lt1204s (#1) together. switching transients are reduced in this receiver because the transient from lt1204 #2 subtracted from the transient of lt1204 #1. programable gain amplifier (pga) two lt1204s and seven resistors make a programable gain amplifier with a 128-to-1 gain range. the gain is proportional to 2 n where n is the 3-bit binary value of the select logic. an input attenuator alters the input signal 4-input differential receiver 1 3 5 7 13 + 1 3 5 7 13 + + + + lt1204 #1 1.5k 100 w lt1204 #2 1.5k 124 w 124 w 249 w 499 w v in = 62.5mv p-p to 8v p-p + + + v out = 1v p-p 1204 ta03 programable gain amplifier accepts inputs from 62.5mv p-p to 8v p-p in 1 in 2 in 3 in 4 in 1 in 2 in 3 in 4 1k 1k 1k 1k 75 w en shdn a1 a0 68 w 68 w 1k* 1k* twisted pair cable 1k* 1k* 1204 ta04 *optional 75 w v out + + + lt1204 #2 a0 a1 en shdn + + + + lt1204 #1 a0 a1 en shdn +
18 lt1204 u s a o pp l ic at i ty p i ca l cable output lt1204 #2 output a0 pin 9 1204 ta05 differential receiver switching waveforms frequency (hz) ?0 differential receiver response (db) ?0 ?0 0 20 10k 1m 10m 100m 1204 ta06 100k v s = 15v r l = 100 w differential mode response common mode response 4-input twisted-pair driver it is possible to send and receive color composite video signals appreciable distances on a low cost twisted pair. the cost advantage of this technique is significant. stan- dard 75 w rg-59/u coaxial cable cost between 25 and 50 per foot. pvc twisted pair is only pennies per foot. differential signal transmission resists noise because the interference is present as a common mode signal. the lt1204 can select one of four video cameras for instance, and drive the video signal on to the twisted pair. the circuit uses an lt1227 current feedback amplifier connected with a gain of C 2, and an lt1204 with a gain of 2. the 47 w resistors back-terminate the low cost cable in its charac- teristic impedance to prevent reflections. the receiver for the differential signal is an lt1193 connected for a gain of 2. resistors r1, r2 and capacitors c1, c2 are used for cable compensation for loss through the twisted pair. alternately, a pair of lt1204s can be used to perform the differential to single-ended conversion. multiburst pattern passed through 1000 feet of twisted pair, no cable compensation multiburst pattern passed through 1000 feet of twisted pair, with cable compensation 1204 ta08 output input input output 1204 ta09 differential receiver response
19 lt1204 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 represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. package descriptio u dimensions in inches (millimeters) unless otherwise noted. n package 16-lead pdip (narrow 0.300) (ltc dwg # 05-08-1510) n16 1197 0.255 0.015* (6.477 0.381) 0.770* (19.558) max 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0.020 (0.508) min 0.125 (3.175) min 0.130 0.005 (3.302 0.127) 0.065 (1.651) typ 0.045 ?0.065 (1.143 ?1.651) 0.018 0.003 (0.457 0.076) 0.100 0.010 (2.540 0.254) 0.009 ?0.015 (0.229 ?0.381) 0.300 ?0.325 (7.620 ?8.255) 0.325 +0.035 0.015 +0.889 0.381 8.255 () *these dimensions do not include mold flash or protrusions. mold flash or protrusions shall not exceed 0.010 inch (0.254mm) s16 (wide) 0396 note 1 0.398 ?0.413* (10.109 ?10.490) 16 15 14 13 12 11 10 9 1 23 4 5 6 78 0.394 ?0.419 (10.007 ?10.643) 0.037 ?0.045 (0.940 ?1.143) 0.004 ?0.012 (0.102 ?0.305) 0.093 ?0.104 (2.362 ?2.642) 0.050 (1.270) typ 0.014 ?0.019 (0.356 ?0.482) typ 0 ?8 typ note 1 0.009 ?0.013 (0.229 ?0.330) 0.016 ?0.050 (0.406 ?1.270) 0.291 ?0.299** (7.391 ?7.595) 45 0.010 ?0.029 (0.254 ?0.737) note: 1. pin 1 ident, notch on top and cavities on the bottom of packages are the manufacturing options. the part may be supplied with or without any of the options dimension does not include mold flash. mold flash shall not exceed 0.006" (0.152mm) per side dimension does not include interlead flash. interlead flash shall not exceed 0.010" (0.254mm) per side * ** sw package 16-lead plastic small outline (wide 0.300) (ltc dwg # 05-08-1620)
20 lt1204 ? linear technology corporation 1993 1204fas, sn1204 lt/tp 0898 2k rev a ? printed in usa typical applicatio n u 4-input twisted-pair driver/receiver + v in0 + + + v in1 v in2 v in3 + 1k 1k 2k lt1204 lt1227 47 w 47 w + + lt1193 91 w 300 w 300 w 200 w 390 w 300pf 18 w 680pf 75 w 75 w 1204 ta07 1000 ft of twisted pair linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 l fax: (408) 434-0507 l www.linear-tech.com part number description comments lt1203/lt1205 150mhz video multiplexer high speed, but no cable driving lt1259/lt1260 dual and triple current feedback amplifiers low cost, with shutdown lt1675 rgb multiplexer with current feedback amplifiers very high speed, pixel switching related parts

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