ISCAS’05 1V Compact Class-AB CMOS Log Filters Intro Class-A Class-AB Example Conclusions 1/23 1V Compact Class-AB CMOS Log Filters X. Redondo and F. Serra-Graells Circuits and Systems Group Institut de Microelectrònica de Barcelona Centre Nacional de Microelectrònica - CSIC Spain 25th May 2005 X. Redondo and F. Serra-Graells Institut de Microelectrònica de Barcelona
ISCAS’05 1V Compact Class-AB CMOS Log Filters Intro Class-A Class-AB Example Conclusions 2/23 1 Introduction 2 Basic Class-A Operation 3 New Class-AB Proposal 4 Design Example 5 Conclusions X. Redondo and F. Serra-Graells Institut de Microelectrònica de Barcelona
ISCAS’05 1V Compact Class-AB CMOS Log Filters Intro Class-A Class-AB Example Conclusions 3/23 1 Introduction 2 Basic Class-A Operation 3 New Class-AB Proposal 4 Design Example 5 Conclusions X. Redondo and F. Serra-Graells Institut de Microelectrònica de Barcelona
ISCAS’05 1V Compact Class-AB CMOS Log Filters Intro Class-A Class-AB Example Conclusions 4/23 Companding filtering scenario MOS log-mapping G instantaneous instantaneous non-linear�integration V GB compression expansion I D D S -1 V out I out I in V in V state V DB V SB F F G B C weak inversion: V SB,DB ≫ VGB − VT O n externally�linear�processing forward saturation: log-domain: F ( x ) = e x V DB − V SB ≫ U t � Low-voltage VGB − VT O e − VSB I D = I S e nUt Ut ? Low-current vs dynamic range IC = I D ? Low-area vs auxiliary circuitry I S = 2 nβU 2 t I S . . . the answer is compact Class-AB ! X. Redondo and F. Serra-Graells Institut de Microelectrònica de Barcelona
ISCAS’05 1V Compact Class-AB CMOS Log Filters Intro Class-A Class-AB Example Conclusions 5/23 1 Introduction 2 Basic Class-A Operation 3 New Class-AB Proposal 4 Design Example 5 Conclusions X. Redondo and F. Serra-Graells Institut de Microelectrònica de Barcelona
ISCAS’05 1V Compact Class-AB CMOS Log Filters Intro Class-A Class-AB Example Conclusions 6/23 Compressor and expander � V ref used to optimize low-voltage: M3,12 do I ref not need saturation! M8 M9 I ref K 1 I in I out K � K allows simple C in I ref I ref M6 M7 frequency compensation V ref V in V out V ref � KC comp M1 M2 M10 M11 ζ = 1 2 C in C comp C in K ≥ 2 M3 M12 C comp × I ref limits the full-scale boxed devices in weak inversion saturation: due to log-mapping: I max ≡ I ref 2 V − Vref I = F ( V ) = I ref e I > 0 nUt with thermal noise: ∆ SNR = +3 dB /oct ( I ref ) . . . poor improvement! Note: presented by same authors in ISCAS’00 X. Redondo and F. Serra-Graells Institut de Microelectrònica de Barcelona
ISCAS’05 1V Compact Class-AB CMOS Log Filters Intro Class-A Class-AB Example Conclusions 7/23 Integrator M4 M5 I tun ◮ ODE in the lineal I -domain: V in V out d I out = ± 1 τ I in M1 M2 I cap d t C ◮ ODE in the compressed V -domain: M3 d V out = ± nU t Vin − Vout τ e nUt � Tunable time constant d t ◮ ODE in the circuit Q -domain: � Single dis/charge due to log mapping ( I in > 0 ), op d Q out = C d V out ensured at filter level Vin − Vout = ± I tun e nUt d t d t � Half integrator shared � �� � I cap × SNR issues ( I tun ≥ I ref ) τ = nU t C cause high-value C ! I tun X. Redondo and F. Serra-Graells Institut de Microelectrònica de Barcelona
ISCAS’05 1V Compact Class-AB CMOS Log Filters Intro Class-A Class-AB Example Conclusions 8/23 1 Introduction 2 Basic Class-A Operation 3 New Class-AB Proposal 4 Design Example 5 Conclusions X. Redondo and F. Serra-Graells Institut de Microelectrònica de Barcelona
ISCAS’05 1V Compact Class-AB CMOS Log Filters Intro Class-A Class-AB Example Conclusions 9/23 Input Splitter and Compressor M7 ◮ Differential signaling: M8 M6 I ref K 1 K I in = I inp − I inn I in I ref I inp,n > 0 I inn I inp I ref I ref ◮ Constant geometric V ref V ref M1 M5 M2 M3 M4 mean splitting: I inp I inn = I 2 V inn V inp ref � Same low-voltage • current multiplier M1-M4 capability as Class-A I 2 • I inp feedback M6-M8 ref � Full-scale I max � I ref • M2 shared by TL+compressors � Optimization : I ref ↓ ∆ SNR ≃ +6 dB /oct ( I max ) X. Redondo and F. Serra-Graells Institut de Microelectrònica de Barcelona
ISCAS’05 1V Compact Class-AB CMOS Log Filters Intro Class-A Class-AB Example Conclusions 10/23 Differential Integrator with CMFB (1) ◮ ODE in the linear I -domain for multiple-inputs: dI out = 1 � ± I inK (even different τ K ) dt τ K ◮ High-gain CMFB to ensure geometric-mean common-mode: �� � dI outp = 1 ± I inpK − I outp I outn + I ref � Does not affect I out dt τ I ref K � CMFB overhead �� � ∝ filter order dI outn = 1 ± I innK − I outp I outn + I ref � filter complexity dt τ I ref K X. Redondo and F. Serra-Graells Institut de Microelectrònica de Barcelona
ISCAS’05 1V Compact Class-AB CMOS Log Filters Intro Class-A Class-AB Example Conclusions 11/23 Differential Integrator with CMFB (2) ◮ ODE in the compressed V -domain: �� � dV outp = nU t ± I inpK − I outn + I ref dt τ I outp I ref I outp K �� � dV outn = nU t ± I innK − I outp + I ref dt τ I outn I ref I outn K ◮ Finally, ODE in the circuit Q -domain: �� � dQ outp VinpK − Voutp Voutn − Vref Vref − Voutp = I tun ± e − e + e nUt nUt nUt dt K cross � coupled �� � dQ outn Voutp − Vref Vref − Voutn VinnK − Voutn = I tun ± e − e + e nUt nUt nUt dt K X. Redondo and F. Serra-Graells Institut de Microelectrònica de Barcelona
ISCAS’05 1V Compact Class-AB CMOS Log Filters Intro Class-A Class-AB Example Conclusions 12/23 Differential Integrator with CMFB (and 3) ◮ Realization: �� dQ outp VinpK − Voutp I tun = I tun ± e nUt dt V outp K � M1 ... M K I capp Voutn − Vref Vref − Voutp − e + e nUt nUt C V inp 1 ... V inpK �� dQ outn VinnK − Voutn ± e = I tun nUt dt K � Voutp − Vref Vref − Voutn − e + e nUt nUt � Low-voltage capability � Most CMFB shared by 1. . . K I tun V outn � Half CMFB shared by all C ’s ... I capn � I ref ↓ allows I tun ↓ , so C V inn 1 ... V innK downscaling C (Si area) X. Redondo and F. Serra-Graells Institut de Microelectrònica de Barcelona
ISCAS’05 1V Compact Class-AB CMOS Log Filters Intro Class-A Class-AB Example Conclusions 13/23 Differential Integrator with CMFB (and 3) ◮ Realization: �� dQ outp VinpK − Voutp I tun = I tun ± e nUt dt V outp K � M1 ... M K MC1 I capp Voutn − Vref Vref − Voutp − e + e nUt nUt C V inp 1 ... V inpK V ref �� dQ outn VinnK − Voutn ± e = I tun nUt dt K � Voutp − Vref Vref − Voutn − e + e nUt nUt � Low-voltage capability � Most CMFB shared by 1. . . K I tun V outn � Half CMFB shared by all C ’s ... I capn � I ref ↓ allows I tun ↓ , so C V inn 1 ... V innK V ref downscaling C (Si area) X. Redondo and F. Serra-Graells Institut de Microelectrònica de Barcelona
ISCAS’05 1V Compact Class-AB CMOS Log Filters Intro Class-A Class-AB Example Conclusions 14/23 Differential Integrator with CMFB (and 3) ◮ Realization: �� dQ outp VinpK − Voutp I tun = I tun ± e nUt dt V outp K � M1 ... M K MC1 I capp Voutn − Vref Vref − Voutp − e + e nUt nUt C V inp 1 ... V inpK V ref �� dQ outn VinnK − Voutn ± e = I tun I tun nUt dt K V ref � Voutp − Vref Vref − Voutn MC2 − e + e nUt nUt � Low-voltage capability � Most CMFB shared by 1. . . K I tun V outn � Half CMFB shared by all C ’s ... I capn � I ref ↓ allows I tun ↓ , so C V inn 1 ... V innK V ref downscaling C (Si area) X. Redondo and F. Serra-Graells Institut de Microelectrònica de Barcelona
ISCAS’05 1V Compact Class-AB CMOS Log Filters Intro Class-A Class-AB Example Conclusions 15/23 Differential Integrator with CMFB (and 3) ◮ Realization: �� dQ outp VinpK − Voutp I tun = I tun ± e nUt dt V outp K � M1 ... M K MC1 I capp Voutn − Vref Vref − Voutp − e + e nUt nUt C V inp 1 ... V inpK V ref �� dQ outn VinnK − Voutn ± e = I tun I tun nUt dt K V ref � Voutp − Vref Vref − Voutn MC2 − e + e nUt nUt � Low-voltage capability � Most CMFB shared by 1. . . K I tun V outn � Half CMFB shared by all C ’s ... I capn � I ref ↓ allows I tun ↓ , so C V inn 1 ... V innK V ref downscaling C (Si area) X. Redondo and F. Serra-Graells Institut de Microelectrònica de Barcelona
ISCAS’05 1V Compact Class-AB CMOS Log Filters Intro Class-A Class-AB Example Conclusions 16/23 Output Expanders I out I ref ◮ Differential to single-ended: V ref M1 M2 M3 I out = I outp − I outn � � Voutp − Vref Voutn − Vref I out = I ref e − e nUt nUt V outn V outp � Low-voltage capability like Class-A � Same I ref ↓ as compressors � M1,2 expanders share half circuitry � For multiple outputs, all expanders can share this part. . . X. Redondo and F. Serra-Graells Institut de Microelectrònica de Barcelona
ISCAS’05 1V Compact Class-AB CMOS Log Filters Intro Class-A Class-AB Example Conclusions 17/23 1 Introduction 2 Basic Class-A Operation 3 New Class-AB Proposal 4 Design Example 5 Conclusions X. Redondo and F. Serra-Graells Institut de Microelectrònica de Barcelona
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