Page 228 - DCAP108_DIGITAL_CIRCUITS_AND_LOGIC_DESIGNS

Unit 12: A/D and D/A Converters

Notes
Figure 12.13: 4-bit D/A Converter
Digital input data

Input gates

N-bit register
N lines
Level amplifiers
N lines
Resistive divider V A
a
()
Digital input
2 0 2 0 2 1 2 1 2 2 2 2 2 3 2 3 READ IN
(strobe)
pulse

S Q S Q S Q S Q
R Q R Q R Q R Q
+10 V Precision
voltage
source
Level Level Level Level
amplifier amplifier amplifier amplifier
2R 2R 2R 2R
2R R R R
V A
()
b
Figure 12.14: Decoding a Number of Signals—(a) Channel Selection Method,
(b) Multiplex Method
Digital input lines

D/A converter V A1

Channel D/A converter V A2 Analog
outputs
selector
D/A converter V A3
a
()
Sample and hold
amplifiers
Digital input lines
Multiplex V A1
V A1
V A V A2 V A2
D/A converter
V V
A3 A3
V An
V An
b
()
The first and most obvious method is simply to use one D/A converter for each multiplexing
signal. This method, shown in Figure 12.14a, has the advantage that each signal to be decoded
is held in its register and the analog output voltage is then held fixed. The digital input lines are

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