07_diff_amps

# 07_diff_amps - EECE 416/501 Analog Circuit Design...

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

This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: EECE 416/501 Analog Circuit Design Differential Amplifiers Christopher M. Twigg Assistant Professor BINGHAMTON U N I V E R S I T Y STATE UNIVERSITY OF NEW YORK Department of Electrical and Computer Engineering October 31, 2009 Diff Amps: Differential Signals Differential Inputs, Differential Outputs Differential Inputs, Single-Ended Output Vi+ Vi- + - + V oV o+ Vi+ Vi- + - Vo Absolute Voltages Differential-Mode and Common-Mode Voltages Vid 2 Vid 2 + - + + Vo + Vi+ + + - - Vi- + - Vic EECE 416/501, C. M. Twigg October 31, 2009 2/16 Diff Amps: Differential Pair ("Diff Pair") Ideal Differential Pair I+ IIb Vi+ ViVi+ Ib I+ IVi- Practical Differential Pair I+ I- Ib ViVi+ ViI+ I- Vi+ Ib EECE 416/501, C. M. Twigg October 31, 2009 3/16 Diff Amps: Diff Pair, Sub-Threshold I + I - I+ = (W/L)i I0 e(Vi Vi- +-V) /UT I- = (W/L)i I0 e(Vi --V) /UT Vi+ () Vb W L i () V W L i () Ib W L b Iout = I+ - I- = IB tanh IB Vid 2UT Common-Mode Input Range IB = I+ + I- IB = (W/L)i I0 e(Vi UT ln L W i +-V) /UT 0 IB I0 = Vi+ - V L W i V = Vi+ - UT ln Vi+ UT IB I0 I+ I- I+ - I - -6*UT -4*UT -2*UT 0 Vid 2*UT 4*UT 6*UT 8*UT 4 + ln L W i IB I0 -IB -8*UT EECE 416/501, C. M. Twigg October 31, 2009 4/16 Diff Amps: Diff Pair, Above-Threshold I+ = I = + IB 2 i 2 [Vi+ - VT0 - V]2 2 i Vid 4IB I- = i 2 Vi- - VT0 - V 2 1 + Vid i IB 1- I = - IB 2 1 - Vid 1- 2 i Vid 4IB i IB 1- 2 i Vid 4IB Iout = I - I = IB Vid Model Predicts IB IB + - i IB Actual Response 0 0 -IB 0 Vid I I- + - I -I + -IB 0 Vid I+ I- I+ - I - EECE 416/501, C. M. Twigg October 31, 2009 5/16 Diff Amps: Diff Pair, Above-Threshold (cont) Common-Mode Input Range Assume =1 IB = I+ + I- IB = 2IB i i 2 [Vi+ - VT0 - V]2 = Vi+ - VT0 - V 2IB i V = Vi+ - VT0 - Vi+ Vb + 2IB i EECE 416/501, C. M. Twigg October 31, 2009 6/16 Diff Amps: OpAmps vs. OTAs Operational Transconductance Amplifier + - Operational Amplifier + - EECE 416/501, C. M. Twigg October 31, 2009 7/16 Diff Amps: OTA, Resistive Load (Differential-Mode Gain) VDD VDD R Vo Vi+ V Vb Ib I+ I- R Vo Vi- EECE 416/501, C. M. Twigg October 31, 2009 8/16 Diff Amps: OTA, Resistive Load (Common-Mode Gain) VDD VDD R Vo Vi+ V Vb Ib I+ I- R Vo Vi- EECE 416/501, C. M. Twigg October 31, 2009 9/16 Diff Amps: OTA, Resistive Load (Power Supply Gain) VDD VDD R Vo Vi+ V Vb Ib I+ I- R Vo Vi- EECE 416/501, C. M. Twigg October 31, 2009 10/16 Diff Amps: OTA, Diode and Current Source Loads VDD VDD VDD Vbp Vo Vi+ V Vbn Ib Vbn I+ IVo ViVo Vi+ V Ib I+ IVo ViVDD EECE 416/501, C. M. Twigg October 31, 2009 11/16 Diff Amps: OTA, Current Mirror Load VDD VDD I+ Vo I Vi+ V Vb Ib - Vi- EECE 416/501, C. M. Twigg October 31, 2009 12/16 Diff Amps: OTA, Problems with the 5T OTA VDD VDD I+ Vo I Vi+ V Vb Ib 4 3.5 3 Vo (V) 2.5 2 1.5 1 0.5 0 0 0.5 1 1.5 2 2.5 Vi+ (V) EECE 416/501, C. M. Twigg October 31, 2009 13/16 - 5 Vi4.5 Vi- = 1 V Vi- = 2 V Vi- = 3 V Vi- = 4 V Vi- = 5 V 3 3.5 4 4.5 5 Diff Amps: Wide-Range OTA VDD Vi- V + i I+ IVo Vb Ib EECE 416/501, C. M. Twigg October 31, 2009 14/16 Diff Amps: Why Gain Matters Open Loop Vi+ Vi- + - Vo Vo = Closed Loop (Feedback) Vi + - Vo Vo = How do we increase gain? EECE 416/501, C. M. Twigg October 31, 2009 15/16 Diff Amps: Cascoded, Wide-Range OTA VDD Vcp ViIb Vi+ Vo Vb Vcn EECE 416/501, C. M. Twigg October 31, 2009 16/16 ...
View Full Document

Ask a homework question - tutors are online