Feedback Transimpedance & Current Amplifiers Willy Sansen KULeuven, ESATMICAS Leuven, Belgium willy.sansen@esat.kuleuven.be Willy Sansen 1005 141
Table of contents Introduction Shuntshunt FB for Transimpedance amps. Shuntseries FB for Current amplifiers Transimpedance amplifiers for low noise and high frequencies Willy Sansen 1005 14
Input & output impedances 1 H = Output Shunt Series Input R OUT = R OUTOL 1LG R OUT = R OUTOL (1LG) Shunt R IN = R INOL 1LG = A R i OUT = A I Series R IN = R INOL (1LG) v IN = A V i OUT v IN = A G Willy Sansen 1005 143
Table of contents Introduction Shuntshunt FB for Transimpedance amps. Shuntseries FB for Current amplifiers Transimpedance amplifiers for low noise and high frequencies Willy Sansen 1005 144
Shuntshunt FB configuration R IN v IN A 0 v IN A 0 10 4 10 6 R OUT R O << R NP >> A R = = R IN 0 R OUT 0 Willy Sansen 1005 145
Shuntshunt FB : loop gain A 0 v IN v INLG = 0 v IN R O << LG LG = LG v INLG R NP >> A vol A 0 10 4 10 6 Willy Sansen 1005 146
Shuntshunt FB : input resistance R IN v IN A 0 v IN A 0 10 4 10 6 R OUT R O << R IN = v IN = R INOL 0 LG R NP >> Open Loop R INOL = R IN (A v = 0) = R NP //( R O ) Willy Sansen 1005 147
Shuntshunt FB : output resistance = 0 v IN A 0 v IN A 0 10 4 10 6 R OUT R O << Open Loop R OUTOL R OUT = 0 LG R NP >> R OUTOL = R OUT (A v = 0) = R O //( R NP ) R O Willy Sansen 1005 148
Shuntshunt FB pair V DD M1 M A R = = LG = g m1 r o1 R IN = 0? LG 1/g m R OUT = 0 LG Willy Sansen 1005 149
Shuntshunt FB pair with resistors v IN M3 M1 R 1 V DD M v IN M M3 R M1 V DD R 1 vout1 A R = = A R1 = A R = R 1 R R Ref.Cherry, Proc. IEE, Feb.63, 375389; Holdenried, JSSC Nov.04, 19591967 Willy Sansen 1005 1410
Current detector with voltage amp. R L Q Q 3 = Q 1 R E C L = 360 Ω f T = 40 GHz r B = 0 Ω BW = 10 GHz I TOT = 10 ma Ref.Baureis, JSSC June 1993, 701706 Willy Sansen 1005 1411
Shuntshunt FB triple M1 M M3 M4 V DD LG = A v1 A v A v3 A vi = g mi r oi A R = R IN = 0 LG 1/g m4 R OUT = 0 LG Willy Sansen 1005 141
Shuntshunt FB triple: easier biasing V DD A R = M3 LG = A v1 A v A v3 M M4 A vi = g mi r oi M1 R IN = 0 LG 1/g m4 R OUT = 0 LG Willy Sansen 1005 1413
CMOS preamplifier for optical communications Two stages possible if fully differential! 0 kω 500 Ω tracking of R1 & Rf Ref.Phang, Johns, CASII July 1999 Willy Sansen 1005 1414
Differential shuntshunt FB pair A R = LG = A v1 A v A v1 = g m1 r o1 A v = g m r o R IN = 0 LG /g m3 R OUT = 0 LG Willy Sansen 1005 1415
Current detector with voltage amplifier R IN = v IN = A 1 A C p R L A A R = LG = A 1 A = A 1 =g m R L A f 3dB = 1 π R IN C p Willy Sansen 1005 1416
Single MOST with shuntshunt FB V DD A R = (if >> 1/ g m ) LG = g m r o R R IN = F r o 0? LG r o R OUT = 0? LG Ref.Cherry, Proc. IEE, Feb.63, 375389 Willy Sansen 1005 1417
Single bipolar transistor with shuntshunt FB V DD A R = (if >> 1/ g m ) Far from ideal!! Output loading : r π r o reduces the LG!! LG = g m r o r π r o r π ( r o ) // r π R IN = 0? LG r R OUT = o // ( r π ) 0? LG Willy Sansen 1005 1418
Cascode with shuntshunt FB V DD A R = LG = g m1 r o1 g m r o r R IN = OUT 1 M 0 LG g m1 M1 r OUT = r o1 g m r o r OUT R OUT = 0 LG 1 g m1 Willy Sansen 1005 1419
MOST Shuntshunt FB triple V DD A R = M3 LG = A v1 A v A v3 M1 M A vi = g mi r oi r o3 R IN = 0 LG r o3 R OUT = 0 LG Willy Sansen 1005 140
Bipolar Transistor Shuntshunt FB triple V DD A R = LG = A v1 A v A v3 Q1 Q Q3 A v1 = g m1 (r o1 //r π ) A v = g m (r o //r π3 ) A v3 = g m3 R OUTOL R OUTOL = r o3 //( r π1 ) R OUT = R OUTOL 0 LG Output loading : r π3 r o3 reduces the LG!! (R R IN = F r o3 ) //r π1 0 LG Willy Sansen 1005 141
Shuntshunt FB with nonideal current source R IN = R G R IN RG A 0 RS A 0 A R = A R = if R S > A0 LG = A 0 LG = A 0 R IN = A 0 R G = A0 R IN = R G // R S Willy Sansen 1005 14
Shuntshunt FB with voltage source R IN RG R IN R G RS A 0 R v S OUT v IN A0 A R = if R S > A0 A R = if R S > A0 LG = A 0 LG = A 0 R G = A0 R IN = R G //R S R G = A0 R IN = R G R S Willy Sansen 1005 143
Shuntshunt feedback : Gain and ROUT R v IN R 1 LG = A A 0 10 4 10 6 0 R A A R = R if R 1 > 0 A0 v IN = v IN 1 A v = A R R 1 ROUT = R OUTOL LG R A v = R1 Willy Sansen 1005 144
Shuntshunt FB pair with with voltage source R G V DD A R = A v = R S v IN R S M1 M LG = g m1 r o1 R IN = R S R G R G = = 0 LG g m1 r o1 if R S > A0 1/g m R OUT = 0 LG Willy Sansen 1005 145
Shuntshunt FB pair with input loading V DD A R = Q1 Input loading : r π1 Q LG = g m1 r o1 R R IN = F // r π1 0 LG R OUTOL R OUT = 0 LG 1 R OUTOL = g m r π1 r π1 r o1 β = gm1 r o1 Willy Sansen 1005 146
Shuntshunt FB pair with voltage source R B R L V DD A R = A v = R S v IN R S Q1 Q R E LG = g m1 R L r π1 r π1 //r π1 R B = 0 LG R IN = R S R B Input loading : r π1 R OUTOL R OUT = 0 LG 1 R OUTOL = g m R L β Willy Sansen 1005 147
Nonideal singletransistor shuntshunt FB R B R S R L V DD A R LG g m r olf R IN = R S R B A v R S v IN r π //( r ol ) R B 0 LG r olf R OUT 0?? LG Output loading : r ol r ol = r o //R L r olf = r o //R L // Input loading : r π Willy Sansen 1005 148
Nonideal singletransistor Feedback R L V DD A R = LG =? A v = R S R S R IN =? v IN R E R OUT =? Output loading : r ol r ol = r o //R L Input loading : r π Willy Sansen 1005 149
Shuntshunt feedback in Rightleg drive i B i B d R A A 0 vb R P v B R B A 0 R P i B 10 µa RMS for 0 V RMS (50 Hz) through 150 pf v B i B = R P R B A 0 1 Willy Sansen 1005 1430
Table of contents Introduction Shuntshunt FB for Transimpedance amps. Shuntseries FB for current amplifiers Transimpedance amplifiers for low noise and high frequencies Willy Sansen 1005 1431
Shuntseries feedback : Gain, RIN & ROUT V DD LG = A 0 R IN A 0 R i OUT R OUT R //R E i OUT R E A I = 1 R R E R IN = R * LG 0 R OUTOL = r o (1 g m R E ) R OUT =R OUTOL LG R E > 1/g m R > 1/g m R * = R R E /(1g m R E ) R Willy Sansen 1005 143
Shuntseries feedback with load RL R IN A 0 R E > 1/g m R R L R > 1/g m R E R OUTT V DD R OUT LG = A 0 A I = 1 R R E AR =A I R L R R IN = 0 LG R OUT =R OUTT //R L R L R OUTT =R OUTTOL LG R OUTTOL = r o (1 g m R E ) Willy Sansen 1005 1433
Ideal current buffer i OUT A I = 1 R IN A 0 R OUT 0 R E LG = A 0 1/g m R IN = 0 LG R OUTOL = r o (1 g m R E ) R E > 1/g m R OUT =R OUTOL LG Willy Sansen 1005 1434
Ideal current mirror R IN M1 V ref 0. V A 0 1 : B i OUT = B A I = B R OUT M R INOL LG = g m1 r o1 A 0 R IN = = 0 LG R INOL = r o1 1 g m1 A 0 R OUT = r o Willy Sansen 1005 1435
Gain boosting V B A gb I B v out LG = A gb v in M M1 C L 1/g m R E = 0 LG R OUTOL = r o (1 g m r o1 ) A v = A gb (g m r DS ) 1 (g m r DS ) R OUT =R OUTOL LG Hosticka, JSSC Dec.79, pp. 11111114; Sackinger, JSSC Febr.90, pp. 8998; Bult JSSC Dec.90, pp. 13791384 Willy Sansen 1005 1436
Differential current amplifier Ref. Umminger, JSSC Dec.95, 1381390 Willy Sansen 1005 1437
Linear laser diode driver i D v IN R 1 A 0 g m i OUT Opt. fiber i OUT = k = k v IN R 1 i D = i OUT k LG = g m A 0 k Willy Sansen 1005 1438
Table of contents Introduction Shuntshunt FB for Transimpedance amps. Shuntseries FB for Current amplifiers Transimpedance amplifiers for low noise and high frequencies Willy Sansen 1005 1439
Optical receiver : Current or voltage amplifier I IN I IN A v A R = I IN = A R I IN Willy Sansen 1005 1440
Current detector with voltage amplifier v IN = A 1 A 1 C 1 R P F A s 1 A C P =C D C GS R L A 1 =g m R L A=A 1 A A T = = 1 C 1 R P F A s 1 A A 1 A 1 RF C P s Noise matching : C D = C GS A R BW (THzΩ) = A 1 A π C P Willy Sansen 1005 1441
Current detector with voltage amplifier v IN R = F 1 R L C L s A 1 as bs 1 A R L C L A=A 1 A A a = C P A 1 A b = C P R L C L A 1 A C P =C D C GS A 1 =g m R L No peaking if R L < 4g m A C P C L 1 = 1 as bs Willy Sansen 1005 144
BW in voltage/current amplifier R L M M1 M M1 R E R E R S R S >> 1/g m1 BW = A v1 π (C GS1 C D ) BW = 1 π (C GD C DB1 ) Willy Sansen 1005 1443
Current detector with input cascode BW = A v R L1 R L π //R L1 C T M1 M M3 CT = CGS Av CGD A v = g m R L R S R E C L = Z IN independent of f! R S >> 1/g m1 R OUT = 1/g m3 Av Vanisri, etal, JSSC June 95, pp. 677685 Willy Sansen 1005 1444
Current detector with regulated cascode 5 V 17 ma C D = 0.5 pf = 800 Ω BW = 1 GHz g mb = 3 g m1 BW independent of C D! Current noise : R S & // R 1 Park, JSSC Jan. 04, 1110 Willy Sansen 1005 1445
Noise sources of detector voltage amplifier di R di D dv A i i R L C L di D = qi D df 4kT di R = df dv A = 4kT ( /3 ) df g m Willy Sansen 1005 1446
Noise density of detector voltage amplifier di ieq i i R L CL dv A di ieq = di D di R di D di R if > /3 g m Willy Sansen 1005 1447
Noise sources of detector current amplifier di D di A i i C L di D = q I D df di A = 4kT g m df 3 Willy Sansen 1005 1448
Noise density of detector current amplifier di ieq di A i i C L di ieq = di D 4kT g m df is transistor noise! 3 Willy Sansen 1005 1449
Comparison of noise densities Voltage amp.: i IN = di 4kT R = df Current amp.: i IN = di A = 4kT g m df 3 Voltage amplifier better when > 3 1 g m Willy Sansen 1005 1450
Comparison of integrated noise Large I D : i IN = di π D (BW ) Small I D : Voltage amp.: i IN = di π R (BW ) = kt R L R ( L ) g m C P Current amp.: i IN = di π A (BW ) = 3 kt g m C L Voltage amplifier better when > 3 4 R L Willy Sansen 1005 1451
CMOS photodiode amplifier M M1 M3 150 kω x 10 MHz = 18 THzΩ 0.5 pa/ Hz 450 MHz per cell Ref.Ingels, JSSC Dec 1994, 1551559 Willy Sansen 1005 145
CMOS wideband amplifier cell M I DS M 1 & M 3 : same V GS & V DS K n K p All L are L min M1 M3 A v = g m1 g m g m3 g m = K n I DS W/L I DS1 = λ I DS I DS3 = (1 λ) I DS V GS1 = V GS3 : W 3 = W 1 1 λ λ Willy Sansen 1005 1453
CMOS wideband amplifier : gain and bandwidth 10 8 A v λ 1 λ W ( 1 ) λw 1 6 4 0 BW 0 0. 0.4 0.6 0.8 1 λ BW = g m3 π C n (1 λ) λw ~ 1 W 1 ( λ) λw W 1 = W = 4 C n = C DB1 C GS3 C DB3 C DB C DB C GS kw k ff/µm Willy Sansen 1005 1454
Integrated resistor M? Poly R : large size : large L distributed C : 45 o phase shift at 100 MHz M1 M3 f 3dB = 1 π.43 R S C 0 L R S = sheet res. (Ω / ) C 0 = unit cap. (F/cm ) MOST : W = 1.3 µm & L = 1 µm allows dynamic compression Glaser; IC Engineering Add.Wesley, p.13 Willy Sansen 1005 1455
Gain compression F Willy Sansen 1005 1456
1 Gb/s 1 kω transimpedance stage pmost vs nmost : nmost R increases for larger diode currents! pmost gives compression! C d = 0.8 pf C GS Capacitive noise matching! BW = 500 MHz 5 ma (5V) 0.7 µm CMOS Ref.Ingels, JSSC July 1999, 971977 Willy Sansen 1005 1457
Highfrequency Resistance RF R 4 R = = R 3 R 1 R 1 R = 00 kω R 3 R 4 = 4 kω 0.5 pf sees 1/g m1 Poly = 00 kω would cut off around 67 MHz! C d = 0.1 pf 180 kω 380 MHz 68 THzΩ 14 ma (5 V) 0.6 µm BiCMOS Seidl, ISSCC 04, 470471 Willy Sansen 1005 1458
BICMOS transimpedance amplifier 178 MHz 8 kω 178 MHz 1 pa/ Hz Ref.Meyer, JSSC June 1994, 701706 Willy Sansen 1005 1459
BICMOS transimpedance amplifier R A v = 1 //.. 5 kω = = 15 1 1/g m4 1 8 1 R i = = 40 Ω 1 A v C i = (1 A v ) C = 4 pf di 4kT i = qi B1 df df 1 = (0.4 0.6)10 4 10 4 A /Hz 8 kω 178 MHz 1 pa RMS / Hz 178 MHz Ref.Meyer, JSSC June 1994, 701706 Willy Sansen 1005 1460
Lowvoltage transimpedance amplifier I B1 I B I B1 I B M1 M1 M1 M1 If > 1/g m1 : = Ref.Phang, Johns, ISSCC 001, 1819 Willy Sansen 1005 1461
75 Mb/s optical receiver in CMOS C d = 1 pf (40 µa).4 kω 45 MHz 75 Mb/s 11 pa RMS / Hz 0.35 µm CMOS 1 V (1 ma) Ref. Phang, ISSCC 001 1819 Willy Sansen 1005 146
GaAs 10 Gb/s receiver HP GaAs MODIC : depletion nmost s 560 V/W flipchip PD : 3 db at 7. GHz 10 pa/ Hz wire bond : 3 db at 4. GHz 0 pa/ Hz Willy Sansen 1005 1463
Table of contents Introduction Shuntshunt FB for Transimpedance amps. Shuntseries FB for Current amplifiers Transimpedance amplifiers for low noise and high frequencies Willy Sansen 1005 1464