Lect2UP280-(100328)

# Lect2UP280-(100328) - Lecture 280 – Differential-In...

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Unformatted text preview: Lecture 280 – Differential-In, Differential-Out Op Amps (3/28/10) Page 280-1 CMOS Analog Circuit Design © P.E. Allen - 2010 LECTURE 280 – DIFFERENTIAL-IN, DIFFERENTIAL-OUT OP AMPS LECTURE ORGANIZATION Outline • Introduction • Examples of differential output op amps • Common mode output voltage stabilization • Summary CMOS Analog Circuit Design, 2 nd Edition Reference Pages 384-393 Lecture 280 – Differential-In, Differential-Out Op Amps (3/28/10) Page 280-2 CMOS Analog Circuit Design © P.E. Allen - 2010 INTRODUCTION Why Differential Output Op Amps? • Cancellation of common mode signals including clock feedthrough • Increased signal swing v 1 v 2 v 1- v 2 t t t A-A A-A 2 A- 2 A Fig. 7.3-1 • Cancellation of even-order harmonics Symbol:- + v in v out +-- +- + Fig. 7.3-1A Lecture 280 – Differential-In, Differential-Out Op Amps (3/28/10) Page 280-3 CMOS Analog Circuit Design © P.E. Allen - 2010 Common Mode Output Voltage Stabilization If the common mode gain not small, it may cause the common mode output voltage to be poorly defined. Illustration: V DD v od t 070506-01 V SS V DD v od t V SS V DD v od t V SS CM output voltage properly defined, V cm = 0 CM output voltage too large, V cm = 0.5 V DD CM output voltage too small, V cm = 0.5 V SS Remember that: v OUT = A vd ( v ID ) ± A cm ( v CM ) Lecture 280 – Differential-In, Differential-Out Op Amps (3/28/10) Page 280-4 CMOS Analog Circuit Design © P.E. Allen - 2010 EXAMPLES OF DIFFERENTIAL OUTPUT OP AMPS (OTA’S) Two-Stage, Miller, Differential-In, Differential-Out Op Amp Note that the upper ICMR is V DD - V SGP + V TN ( OCMR ) = V DD + | V SS | - V SDP (sat) - V DSN (sat) The maximum peak-to-peak output voltage ¡ 2· OCMR Conversion between differential outputs and single-ended outputs: v od C L +- +- +- v id +- v o 1 2 C L +- +- +- v id +- v o 2 +- 2 C L Fig. 7.3-4 v i 1 M1 M2 M3 M4 M5 M6 M8 V DD V SS V BN +- C c M9 C c V BP +- v i 2 v o 1 v o R z R z M7 Fig. 7.3-3 Lecture 280 – Differential-In, Differential-Out Op Amps (3/28/10) Page 280-5 CMOS Analog Circuit Design © P.E. Allen - 2010 Two-Stage, Miller, Differential-In, Differential-Out Op Amp with Push-Pull Output v i 1 M1 M2 M3 M4 M5 M6 M7 V DD V SS V BN +- C c M9 C c V BP +- v i 2 v o 1 v o 2 R z R z M8 Fig. 7.3-6 M10 M12 M13 M14 Comments: • Able to actively source and sink output current • Output quiescent current poorly defined Lecture 280 – Differential-In, Differential-Out Op Amps (3/28/10) Page 280-6 CMOS Analog Circuit Design © P.E. Allen - 2010 Folded-Cascode, Differential Output Op Amp 060717-01 V PB 1 M4 M5 I 6 V PB 2 I 4 I 5 V DD I 7 M6 M7 V NB 2 M8 M9 M10 M11 + − v IN v OUT V NB 1 I 1 I 2 M1 M2 M3 I 3 C L V NB 1 + − C L • No longer has the low-frequency asymmetry in signal path gains....
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Lect2UP280-(100328) - Lecture 280 – Differential-In...

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