DAC_ADC_Module

DAC_ADC_Module - A/D and D/A Converters CMOS Digital...

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A/D and D/A Converters CMOS Digital Integrated Circuits assoud Pedram Massoud Pedram Spring 2007 Dept. of Electrical Engineering–Systems niversity of Southern California University of Southern California
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Motivation ± Digital systems are widely used for control, it i t t t i t communication, computers, instrumentation, etc. ± In many such applications of digital systems, signal not available in digital form is not available in digital form ± Need for converting an analog signal to digital rm form ± A digital communication system is used to transmit messages which are in the form of analog signals. ± This requires an A/D converter at the transmitting end and D/A converter at the receiving end. M. Pedram USC/EE
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Analog to Digital Conversion ± The A/D process involves four process: mpling ± Sampling ± Holding ± Quantizing ± Encoding ± Sampling and holding operations are done simultaneously mple nd old rcuit in sample and hold circuit ± Quantizing and encoding operations are done simultaneously using analog to digital converter (A/D converter or ADC) M. Pedram USC/EE
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Digital to Analog Converters ± The input to a D/A converter is an N bit binary signal, available in parallel form: Digital Input Analog utput ± The analog output voltage of D/A converter is related to the digital input by: 122 1 0 ... NN bb b b b −− Output (V) b 3 b 2 b 1 b 0 0 0 0 0 0 0 0 1 0 0 1 0 0 1 2 ± K is the proportionality factor, and for ( ) 12 2 1 2 1 0 2 2 ... 2 2 ON N VK b b b b b =+ + + + + 0 0 1 1 0 1 0 0 0 1 0 1 0 1 1 0 3 4 5 6 each b n we have: b n = 1 if the n th bit of the digital input is 1 = 0 if the n th bit of the digital input is 0 0 1 1 1 1 0 0 0 1 0 0 1 1 0 1 0 1 0 1 1 7 8 9 10 11 ± Example 1. Analog output voltage of a 4 bit D/A converter for all possible inputs with K =1 is shown on the right. 1 1 0 0 1 1 0 1 1 1 1 0 1 1 1 1 12 13 14 15 M. Pedram USC/EE
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Weighted Resistor D/A Converter ± Assume an N bit binary input to a resistor network through digitally controlled electronic switches ± The input produces a current: I corresponding to logic 1 at the most significant bit (MSB) I/2 corresponding to logic 1 at the next lower bit I/2 N 1 corresponding to logic 1 at the least significant bit (LSB) M. Pedram USC/EE
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Weighted Resistor D/A Converter (cont’d) ± The total current produced which is proportional to the digital put can be converted into a voltage using an OP AMP. input can be converted into a voltage using an OP AMP. ± The current I i is given by: 123 2 1 0 ... iN N N I II I I I I −− = +++ + + + where we have: 1 N I VR = () ( ) 11 22 n 2 33 n 2 1i f b = 1 2w h e r e 0i f b = 0 NN n IVR V IV R V V = ⎪⎪ == ⎬⎨ 1 00 2 N R = M. Pedram USC/EE
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Weighted Resistor D/A Converter (cont’d) ± If V(0)=0 and V(1) = –V R ,we have: R R R which is in the form of the original D/A equation with ( ) 12 3 0 21 ...
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This note was uploaded on 03/19/2008 for the course EE 577B taught by Professor Bhatti during the Spring '08 term at USC.

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DAC_ADC_Module - A/D and D/A Converters CMOS Digital...

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