Lect2UP310_(100328)

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

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon
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
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
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
Background image of page 2
Lecture 310 – Open-Loop Comparators (3/28/10) Page 310-5 CMOS Analog Circuit Design © P.E. Allen - 2010 Finite Gain Comparator Voltage transfer curve: where for a noninverting comparator, V IH = smallest input voltage at which the output voltage is V OH V IL = largest input voltage at which the output voltage is V OL Model: The voltage gain is A v = V OH ± V OL V IH ± V IL v o V OH v P -v N V OL Fig. 8.1-4 V IH V IL f 1 ( v P - v N ) + v O + - - v P v N v P - v N Comparator f 1 ( v P - v N ) = V OH for ( v P - v N ) > V IH V OL for ( v P - v N ) < V IL Fig. 8.1-5 A v ( v P - v N ) for V IL < ( v P - v N )< V IH Lecture 310 – Open-Loop Comparators (3/28/10) Page 310-6 CMOS Analog Circuit Design © P.E. Allen - 2010 Input Offset Voltage of a Comparator Voltage transfer curve: v o V OH v P -v N V OL Fig. 8.1-6 V IH V IL V OS V OS = the input voltage necessary to make the output equal V OH + V OL 2 when v P = v N . Model: f 1 ( v P ' - v N ' ) + v O + - - v P v N v P ' - v N ' Comparator Fig. 8.1-7 v P ' v N ' ± V OS Other aspects of the model: ICMR = input common mode voltage range (all transistors remain in saturation) R in = input differential resistance R icm = common mode input resistance
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Lecture 310 – Open-Loop Comparators (3/28/10) Page 310-7 CMOS Analog Circuit Design © P.E. Allen - 2010 Comparator Noise Noise of a comparator is modeled as if the comparator were biased in the transition region.
Background image of page 4
Image of page 5
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 16

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

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online