607 Lect 7B-FBFS_FINAL_ESSCIRC_01

607 Lect 7B-FBFS_FINAL_ESSCIRC_01 - A Low-Voltage Fully...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: A Low-Voltage Fully Balanced OTA with Common-Mode Feedforward and Inherent Common-Mode Feedback Detector Reference: A. N. Mohieldin, A.N.,E. Sanchez-Sinencio, J. Silva-Martinez, "A fully balanced pseudo-differential OTA with common-mode feedforward and inherent common-mode feedback detector", IEEE Journal of Solid-State Circuits , Volume: 38 Issue: 4 , Apr 2003 , Page(s): 663 -668 3/10/2009 Analog & Mixed Signal Center, Texas A&M University 1 Outline Introduction Introduction Pseudo differential OTA Pseudo Proposed OTA architecture Proposed Design Considerations Design Measurement Results Measurement Conclusions Conclusions 3/10/2009 Analog & Mixed Signal Center, Texas A&M University 2 Simple Differential OTA With tail Current Source VDD Introduction Differential Mode VDD Common Mode VDD M2 Vbias M2 M2 Vbias M2 M2 Vbias M2 Vout- Vout+ VoutVi- Vout+ Gm=gm1 Vcm Vout- Vout+ Vi+ M1 M1 Vd M1 M1 -Vd M1 M1 Vcm VSS Itail VSS Gm = g m1 1 + g m1 R S VSS Rs Limited linear input range Limited Limited tuning range Limited 3/10/2009 Reasonable Common-mode gain Reasonable Reasonable PSRR Reasonable 3 Analog & Mixed Signal Center, Texas A&M University Pseudo Differential Transconductance VDD Advantages M2 M2 Vbias Suitability for low voltage Wider common-mode input range Vout- Vout+ Disadvantages Vi- Vi+ M1 M1 VSS Simple Pseudo Differential OTA 3/10/2009 Poor common-mode gain ACM=ADM>>1 Poor PSRR Need for fast and strong Extra CMFB Circuit to (1) Fix output common-mode voltage (2) Suppress common-mode signals Analog & Mixed Signal Center, Texas A&M University 4 What are the Solutions to Overcome those Limitations? 3/10/2009 Analog & Mixed Signal Center, Texas A&M University 5 Solution In the Literature Differential Mode OTA Vi+=Vicm+Vd/2 Gm(Vicm+Vd/2) + Gm Vi-=Vicm-Vd/2 _ _ Gm(Vicm-Vd/2) -GmVd/2 VoutVout+ Icm 2Icm Icm VDD + GmVd/2 M2 M2 2M2 + Gm + _ _ GmVicm GmVicm Vi+ M1 M1 Vi- Vi+ M1 M1 Vi- VSS VSS Common Mode OTA Pseudo differential OTA With CMFF CMFF is applied to cancel the common mode input signal CMFF Add load to the driving stage, input capacitance doubles Add CMFB is still needed CMFB 3/10/2009 Analog & Mixed Signal Center, Texas A&M University 6 Proposed OTA Block Diagram Gm(Vicm+Vd/2) Vi+=Vicm+Vd/2 ++ + Gm Gm(Vicm+Vd/2) GmVd/2 Vi =Vicm-Vd/2 - _ _ _ Gm(Vicm-Vd/2) -GmVicm Gm(Vicm-Vd/2) 1 Σ 2 -GmVd/2 -GmVicm Common-mode detection using the same differential Common transconductance by making copies of the current Input capacitance is not increased Input CMFF is inherently achieved CMFF CMFB can be easily arranged CMFB 3/10/2009 Analog & Mixed Signal Center, Texas A&M University 7 How to Implement the Proposed OTA? 3/10/2009 Analog & Mixed Signal Center, Texas A&M University 8 Proposed OTA Architecture VDD M3 M3 VX VDD M3 M3 I1 + I 2 2 I11 + I 2 I 2 Vout+ I 01 = I 2 − I1 2 I1 Vi+ M1 M1 Vi- I2 Vout I0 = I1 − I 2 2 I1 I1 I2 I2 M2 M2 M2 M2 M2 M2 VSS Inherent common-mode detection Inherent Inherent common-mode Feedforward Inherent 3/10/2009 Analog & Mixed Signal Center, Texas A&M University 9 Combine CMFB and CMFF VDD VX (from next stage) VDD VX (from next stage) Vref M1 M 3' M3 M3 VX VDD M3 M3 M 3' Vout+ I1 Vi+ M1 M1 Vi- I2 Vout- I1 VY M2 ' M4 I2 M4 M4 M2 M2 VZ M4 M4 ' M4 VY VSS CMFB is arranged exploiting the direct connection of the OTAs CMFB Avoid using a separate common-mode detector Avoid Differential-mode signals and common-mode signals share Differential basically the same loop Analog & Mixed Signal Center, 3/10/2009 Texas A&M University 10 Small Signal Analysis The path from the differential signal to the ouput The encounters one pole The other path is a common-mode path The gm2 g m1 iod ≅ g m1 = g m (s) = vd g m 2 + sC Z 1 + s / ω nd ω nd gm2 = CZ Δφ ≅ − tan −1 (ω / ω nd 1 ) min VDD = max{(VTN + Vov1 + Vov 2 + V peak ), (VTP + Vov 3 + Vov 4 )} 3/10/2009 Analog & Mixed Signal Center, Texas A&M University 11 Simulation Results Icm + g m1 Vin+ + _ Vo+ C + g m2 + _ Vin- _ VoIcm _ CMFB Information Output voltage applying common-mode current step (Icm) 3/10/2009 Analog & Mixed Signal Center, Texas A&M University 12 Sources of Nonlinearity Short Channel Effects Short Mobility degradation Mobility Cross product of differential and commonCross mode signals Even order harmonics Even Nonlinear mixing components due to CMFB Nonlinear Due to the nonlinear common-mode detection Due 3/10/2009 Analog & Mixed Signal Center, Texas A&M University 13 Short Channel Effects μ= 1 + θ (VGS − VT ) θ= 1 LE C μ0 2 2 θ .Vin _ rms θ .VPeak HD3 ≅ = 2 16Vov (1 + θVov ) (2 + θVov ) 8Vov (1 + θVov ) 2 (2 + θVov ) L HD3 Tradeoff: Linearity-Frequency response ⎤ ⎡ ⎥ ⎢ 2 ⎡Vin _ rms ⎤ 3.HD3 .Vov (1 + θVov ) 2 (2 + θVov ).g m1 ⎥ SNR = 10 log ⎢ 2 ⎥ ≅ 10 log ⎢ ⎢ ⎛ g + 2 g m3 + 2 g m 4 ⎞ ⎥ ⎢ Vn _ rms ⎥ ⎣ ⎦ ⎟⎥ 2.BW .KT .θ ⎜1 + m 2 ⎢ ⎜ ⎟ g m1 ⎢ ⎝ ⎠⎥ ⎦ ⎣ Maximize gm1 Maximize Vov 3/10/2009 Analog & Mixed Signal Center, Texas A&M University 14 Cross product of differential and common-mode signals K i1 = P 2 2 ⎞ vd vd β⎛ 2 ⎛W ⎞ ⎡ ⎤ 2 ⎜ ⎟ ⎢VDD − VICM − VTP + + vcm ⎥ = ⎜Vov + vdVov + + 2Vov vcm + vcm + vd vcm ⎟ ⎟ 2 2⎜ 4 ⎝ L ⎠1 ⎣ ⎦ ⎝ ⎠ 2 Differential second harmonic 2 ⎞ KP ⎛W ⎞ ⎡ β⎛ 2 vd vd ⎤ 2 i2 = ⎜ ⎟ ⎢VDD − VICM − VTP − + vcm ⎥ = ⎜Vov − vdVov + + 2Vov vcm + vcm − vd vcm ⎟ ⎟ 2 ⎝ L ⎠1 ⎣ 2 2⎜ 4 ⎦ ⎝ ⎠ 2 Common-mode signal allowed at the input of the filter must be low For example an HD2 of –50dB and Vov=0.6V, the maximum tolerated common-mode signal is 3.8mVPeak Previous stage should take care of this HD2 3/10/2009 Analog & Mixed Signal Center, Texas A&M University 15 Nonlinear components due to CMFB VDD K ⎛W ⎞ ⎡ i1 + i2 = 2. P ⎜ ⎟ ⎢(VDD − VICM − VTP 2 ⎝ L ⎠1 ⎣ = β .V + 2γ .v 2 ov 2 d ) 2 2 vd ⎤ +⎥ 4⎦ 2M3 M3 M3 VDD (i1+i2) I DC A 2 + I γvd 1+ A I DC + AI 2 γv d 1+ A Nonlinear CM detection id/2 Vo1 Z i1 i2 M1 M1 Vo2 Z -id/2 M2 M2 VSS A = g m × Z × AI ⎡ ⎤ A 1 HD3CMFB ≅ HD3 ⎢1 + ⎥ ⎣ 1 + A θVov (1 + 0.5θVov ) ⎦ = HD3 × F 3/10/2009 Analog & Mixed Signal Center, Texas A&M University 16 How to use OTAs as CM Detector? VBP1+ Vin+ VLP1+ + _ + g m1 Vin - + + _ C + + _ g m1 _ + _ g m1 + _ g m2 _ VBP1- C _ VLP1 CMFB Information - CMFB Information A 2nd Order Filter is used as an example Exploit direct connection of the cascaded OTAs in the filter Exploit Differential OTA used as CM detector also Differential 3/10/2009 Analog & Mixed Signal Center, Texas A&M University 17 Filter Architecture CMFF+CMFB Vin+ C L1 VBP1+ CMFF+CMFB CMFF + + _ gm2 A g m1 A C L1 VLP1+ + CMFF _ g m1 A + g m1 A + _ C L1 + _ C L1 + _ VBP1_ + _ VLP1- Vin- _ Common Mode Information VBP2+ CMFF CMFF+CMFB VLP2+ CL 2 CMFF + _ gm2B CMFF+CMFB CL 2 + _ g m1B + + _ g m1B + + g _ m1B _ CL 2 + _ + _ _ VBP2- VLP2CL 2 Common-mode level sensed only once per output Common Common-mode level is fixed only once per node Common 3/10/2009 Analog & Mixed Signal Center, Texas A&M University 18 Chip Micrograph X=350μm, Y= 450μm 3/10/2009 Analog & Mixed Signal Center, Texas A&M University 19 Measurement Results: Frequency response Frequency Magnitude Response Phase Response 20 -3dB cutoff frequency is 100MHz 3/10/2009 Analog & Mixed Signal Center, Texas A&M University Measurement Setup: Frequency response Frequency Vin CB Bias Rg Rg CB C Vout Linear Phase Filter R R C Network analyzer 3/10/2009 Analog & Mixed Signal Center, Texas A&M University 21 Measurement Setup: Intermodulation distortion Intermodulation Signal generator VF1 Vin CB Bias Rg Rg CB C Power combiner Vout VF2 Linear Phase Filter R R C Spectrum analyzer 3/10/2009 Analog & Mixed Signal Center, Texas A&M University 22 Measurement Results: Frequency response Frequency Magnitude Response Phase Response 23 -3dB cutoff frequency is 100MHz 3/10/2009 Analog & Mixed Signal Center, Texas A&M University Measurement Results: Group delay Group Group delay ripple <3% up to 100MHz 3/10/2009 Analog & Mixed Signal Center, Texas A&M University 24 Measurement Results: IM3 IM3≤40 dB over the whole baseband for twin tones of 350mVp-p 3/10/2009 Analog & Mixed Signal Center, Texas A&M University 25 Comparison with previously published work JSSC-1997 Filter Type and Order JSSC-1999 7th Order 0.050 Equirriple +filter boost This Work 4th Order Bessel 100 MHz < 3% @ f < f3dB 350 mVp-p* -46 dB 700 μVrms 45 dB 3.3 V 26 mA 0.5 μm CMOS Cut- Off Frequency 7th Order 0.050 Equirriple 50 MHz 100 MHz < 5% @ f < 2f3dB 100 mVp-p -46 dB N/A > 40 dB 3V 40 mA 0.29 μm BiCMOS Ripple on Group Delay < 2% @ f < 1.5f3dB Max Input Signal for 0.5% THD THD Output Noise Level Dynamic Range @ THD=-46dB Supply Voltage Current Consumption 200 mVp-p -46 dB 1.7 mVrms 32 dB 3V 27 mA 0.72 μm CMOS Technology * Maximum differential input is 500 mVp-p for 1% THD Analog & Mixed Signal Center, Texas A&M University 26 3/10/2009 Conclusions A pseudo differential fully symmetric fully balanced pseudo OTA architecture has been presented The OTA has inherently the common-mode detector, The hence CMFB is economically implemented CMFF and CMFB are combined to exploit the direct CMFF connection of the cascaded OTAs in a filter Design trade-offs have been demonstrated Design The OTA achieves -43dB [email protected] and The 9.8nV/√Hz noise spectral density The filter achieves group delay ripple of 3% up to The 100MHz, 45dB of [email protected]=-46dB in 0.5μm CMOS 3/10/2009 Analog & Mixed Signal Center, Texas A&M University 27 ...
View Full Document

This note was uploaded on 05/11/2011 for the course ELECTRICAL 721 taught by Professor Alen during the Spring '11 term at Berklee.

Ask a homework question - tutors are online