A Low 1/f Noise CMOS Low-Dropout Regulator with Current-Mode Feedback Buffer Amplifier

Transcription

1 A Low 1/ Noise CMOS Low-Dropout Regulator with Current-Mode Feedback Buer Ampliier Wonseok Oh, Bertan Bakkaloglu, Bhaskar Aravind*, Siew Kuok Hoon* Arizona State University *Texas Instruments Inc

2 Motivation or Local Supply Management With the reduction o the supply voltage, noise and cross-coupling on the power supply line starts playing a dominant role in an RF transceiver noise budget. Synthesizer and TCXO phase noise, LNA and mixer noise igure, and adjacent channel power ratio (ACPR) o the PA are heavily inluenced by the supply noise and ripple. Linear low dropout (LDO) regulators shield sensitive blocks rom high requency luctuations on the power supply and provide high accuracy, ast response supply regulation

3 Application Example: RF Synthesizers AGGRESSORS AND VICTIMS: PFD/CP Drivers/Multimodulus dividers generate high current spikes with spectral content that can corrupt global supply. Low slew rate clock xtal osc./xtal buers/drivers/vco are sensitive to supply noise. Supply partitioning should not only isolate noise into sensitive blocks but should also improve kickback rom noisy blocks into global supply plane.

4 Low Dropout (LDO) Regulators : Conventional Architecture Pros High PSR 10KHz) Low Dropout Voltage Good Line Regulation (ΔVout/ΔIout) Good Line Regulation (ΔVout/ ΔVin) Cons High 1/ noise Slow transient response Potential peaking in PSR response

5 Bandgap noise V 2 re is usually iltered and can be ignored. Pass transistor noise can be ignored due to large output (pass) transistor size and large output current. Low Dropout (LDO) Regulators : Noise Analysis Vre S n,re - + Error Ampliier S n,e r oe + Voltage Buer 2 2 R R Sn,o Sn,e Sn,R2 Sn,R1 R2 R2 ( ) ( ) ( ) + ( ) Cc S n,p R 1 R 2 Unregulated Input Voltage Regulation FET Low requency output reerred noise can be estimated as: Flicker(1/) noise o the error ampliier becomes a dominant actor, especially or sub-micron processes at low requencies. S n,r1 S n,r2 S n,o R esr C o

6 Low Dropout (LDO) Regulators : Transient Analysis Δt 1 (Δt 3 )is a unction o bandwidth as well as slew rate o the buer ampliier driving the parasitic gate capacitor (C p ) o regulation FET. V out I Load t 2 t 3 t 4 V out The settling time Δt 2 is dependent on the time requirement or the regulation FET to ully charge the load capacitor and the phase margin o the open loop response. Δt 4 is the time required to discharge the output to its inal value. t 1 t 1 1 BW cl + t sr = 1 BW cl + C I Load time[sec] p V I sr [1] [1] G.A. Rincon-Mora, and P. E. Allen, A Low-Voltage, Low Quiescent Current, Low Drop-Out Regulator, IEEE J. Solid State Circuits, vol. 33, no.1, pp.36-44, Jan.1998

7 Chopping Technique or Reducing 1/ noise and DC oset Commonly used or low requency instrumentation applications such as low noise, high precision analog IC, and audio applications Vin() Vout() Signal ater Chopping 0 m 1 (t) 0 chop 3 chop 5 chop 0 2 chop 4 chop 6 chop m 2 (t) Vin(t) A Vout(t) Noise & oset ater Chopping S() Noise + Osets S n () S 1/ S Thermal 0 chop 3 chop 5 chop Modulate the baseband signal to high requency Error ampliication & regulation processing at high requency, push DC osets & 1/ noise to high requency Demodulate back the baseband signal Filter out the harmonics using LPF

8 Proposed LDO Architecture: Chopper Stabilized LDO Ae S e( ) S o3 ( ) 2 π A e S n ( c ) - c - m 0 m c 2 c ( + ( + ) ) + + ( + ) j( 2k+ 1π ) ( ) S () n k c Sos k c S () + y t Ae S e t k= S o ( ) A e ( )S e ( ) g Z ( ) mo o

9 Current-Mode Feedback Buer Ampliier A s 1 V CFA + o ω z Vx V y = 0 1 s 1 s + ω + p1 ω p2 gm13 g R m16 x = g ds13+2gds16 ACFA gm13gm18gmp Ra Rb rdsmp, GBW = gm13gm18 gmpra R b/co Co+ Ccgmpgm18RaRb ωp1 1 Cr o dsmp, ωp2, ωz 1 CR o esr CLp Cg c mpgm RR a b ( + 18 ) CR o esr

10 Proposed LDO Regulators : Top Level Schematic

11 Experimental Results : PSRR & Ripple Voltage Power Supply Ripple Rejection (PSRR,PSR) Ripple Voltage vs. Chopping Freq PSR[dB] mA 4mA 8mA 12mA 16mA 20mA requency[khz] Power Supply Ripple Rejection Ripple Voltage 10uV with 1kHz chopping req. 53uV with 1MHz chopping req.

12 Experimental Results : Load Regulation & Output Noise 7.0E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 V/sqrt(Hz) 2.0E Load Regulation Noise Density Chopper_O Output noise is reduced by 35 1kHz chop=1mhz chop=750khz chop=500khz 0-5 requency[khz] Output Voltage[V] Load Current[mA] Load Regulation : 5mV/25mA with 1MHz Chopping Freq. Output Noise Density : Chopper_O :6.7uV/ 1kHz Chopper_On(1MHz) :190nV/ 1kHz :32nV/

13 Die Photo The proposed LN-LDO is designed and abricated on a 0.25μm CMOS process with ive layers o metal, occupying 0.88mm 2.

14 Perormance comparison o previous published low dropout linear regulators [2] [3] [4] This work Year Process 0.6µm 0.5μm 90nm 0.25μm Vin[V] 1.5~ ~2.5 Vout[V] ~2 Output noise [nv/ Hz] 70@ 100k 1,360@100kHz - 32@100K Integrated output noise(µv rms ) 936@100K 14@100K I max [ma] I Q [ma] Current Eiciency [%] PSR 26dB -20@50K - >43dB@30K, 200K [2] K. N Leung., P. K. T. Mok, and S. K. Lau, A Low Voltage CMOS Low-Dropout Regulator with Enhance Loop Response, Proc.o ISCAS 04, vol. 1, pp May 2004 [3] C.K. Chava and J. Silva-Martinez, A requency compensation scheme or LDO voltage regulators, IEEE Trans. on Circuits and Systems I, vol 51, no 6. pp , June 2004 [4] P. Hazucha, T. Karnik, B.A. Bloechel, and C. Parsons, Area-Eicient Linear Regulator With Ultra-Fast Load Regulation, IEEE J. o Solid-State Circuits, vol. 40, no. 4, pp , Apr. 2005

15 Conclusion A Novel Low Noise Low Dropout Voltage Regulator have been proposed. A low 1/ noise linear regulator with ast transient response secondary current-eedback ampliier is presented. This is the irst application o chopper stabilization and CFAs to linear regulators, enabling a 14μVrms integrated output noise rom 1kHz to 100kHz. Chopper Stabilized LDO with Current Mode Feedback Buer Ampliier Using Chopper Stabilization Technique Low Noise LDO has been achieved Using PSR Subtraction Stage PSR has been improved Using CFA Fast Transient Response LN-LDO has been achieved. As uture work SD noise shaping techniques on the chopping clock can be used to dither and spread 1/ noise urther at higher requencies.