Lect2UP190_(100327)

Lect2UP190_(100327) - Lecture 190 Differential Amplifier...

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Lecture 190 – Differential Amplifier (3/27/10) Page 190-1 CMOS Analog Circuit Design © P.E. Allen - 2010 LECTURE 190 – DIFFERENTIAL AMPLIFIER LECTURE ORGANIZATION Outline • Characterization of a differential amplifier • Differential amplifier with a current mirror load • Differential amplifier with MOS diode loads • An intuitive method of small signal analysis • Large signal performance of differential amplifiers • Differential amplifiers with current source loads • Design of differential amplifiers • Summary CMOS Analog Circuit Design, 2 nd Edition Reference Pages 180-199 Lecture 190 – Differential Amplifier (3/27/10) Page 190-2 CMOS Analog Circuit Design © P.E. Allen - 2010 CHARACTERIZATION OF A DIFFERENTIAL AMPLIFIER What is a Differential Amplifier? A differential amplifier is an amplifier that amplifies the difference between two voltages and rejects the average or common mode value of the two voltages. Differential and common mode voltages: v 1 and v 2 are called single-ended voltages. They are voltages referenced to ac ground. The differential-mode input voltage, v ID , is the voltage difference between v 1 and v 2 . The common-mode input voltage, v IC , is the average value of v 1 and v 2 . ± v ID = v 1 - v 2 and v IC = v 1 + v 2 2 ² v 1 = v IC + 0.5 v ID and v 2 = v IC - 0.5 v ID v OUT = A VD v ID ± A VC v IC = A VD ( v 1 - v 2 ) ± A VC ³ ´ ´ µ · · ¸ v 1 + v 2 2 where A VD = differential-mode voltage gain A VC = common-mode voltage gain + - + v OUT - v IC v ID 2 v ID 2 Fig. 5.2-1B
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Lecture 190 – Differential Amplifier (3/27/10) Page 190-3 CMOS Analog Circuit Design © P.E. Allen - 2010 Differential Amplifier Definitions • Common mode rejection rato ( CMRR ) CMRR = ± ± ± ± ± ± ± ± A VD A VC CMRR is a measure of how well the differential amplifier rejects the common-mode input voltage in favor of the differential-input voltage. • Input common-mode range ( ICMR ) The input common-mode range is the range of common-mode voltages over which the differential amplifier continues to sense and amplify the difference signal with the same gain. Typically, the ICMR is defined by the common-mode voltage range over which all MOSFETs remain in the saturation region. • Output offset voltage ( V OS (out)) The output offset voltage is the voltage which appears at the output of the differential amplifier when the input terminals are connected together. • Input offset voltage ( V OS (in) = V OS ) The input offset voltage is equal to the output offset voltage divided by the differential voltage gain. V OS = V OS (out) A VD Lecture 190 – Differential Amplifier (3/27/10) Page 190-4 CMOS Analog Circuit Design © P.E. Allen - 2010 Transconductance Characteristic of the Differential Amplifier Consider the following n-channel differential amplifier (called a source-coupled pair). Where should bulk be connected? Consider a p-well, CMOS technology: D1 G1 S1 S2 G2 D2 n + n + n + n + n + p + p-well n-substrate V DD Fig. 5.2-3 1.) Bulks connected to the sources: No modulation of V T but large common mode parasitic capacitance.
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Lect2UP190_(100327) - Lecture 190 Differential Amplifier...

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