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Lect2UP310_(100328)

Lect2UP310_(100328) - Lecture 310 Open-Loop Comparators...

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Lecture 310 – Open-Loop Comparators (3/28/10) Page 310-1 CMOS Analog Circuit Design © P.E. Allen - 2010 LECTURE 310 – OPEN-LOOP COMPARATORS LECTURE ORGANIZATION Outline • Characterization of comparators • Dominant pole, open-loop comparators • Two-pole, open-loop comparators • Summary CMOS Analog Circuit Design, 2 nd Edition Reference Pages 439-461 Lecture 310 – Open-Loop Comparators (3/28/10) Page 310-2 CMOS Analog Circuit Design © P.E. Allen - 2010 CHARACTERIZATION OF COMPARATORS What is a Comparator? The comparator is a circuit that compares one analog signal with another analog signal or a reference voltage and outputs a binary signal based on the comparison. The comparator is basically a 1-bit analog-to-digital converter: 060808-01 1-Bit Quantizer 1-Bit Encoder Reference Voltage Analog Input 1-Bit Digital Output 1-Bit ADC Analog Input 1 Analog Input 2 1-Bit Encoder 1-Bit Quantizer Comparator Comparator symbol: + - v P v N v O Fig. 8.1-1
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Lecture 310 – Open-Loop Comparators (3/28/10) Page 310-3 CMOS Analog Circuit Design © P.E. Allen - 2010 Noninverting and Inverting Comparators The comparator output is binary with the two-level outputs defined as, V OH = the high output of the comparator V OL = the low level output of the comparator Voltage transfer function of a Noninverting and Inverting Comparator: v o V OH v P -v N V OL Noninverting Comparator v o V OH v P -v N V OL Inverting Comparator Fig. 8.1-2A Lecture 310 – Open-Loop Comparators (3/28/10) Page 310-4 CMOS Analog Circuit Design © P.E. Allen - 2010 Infinite Gain Comparator Voltage transfer function curve: v o V OH v P -v N V OL Fig. 8.1-2 Model: f 0 ( v P - v N ) + v O + - - v P v N v P - v N Comparator f 0 ( v P - v N ) = V OH for ( v P - v N ) > 0 V OL for ( v P - v N ) < 0 Fig. 8.1-3 Gain = A v = lim ± V ± 0 V OH - V OL ± V where ± V is the input voltage change
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