1. Principles & Applications
Digital Electronics
Principles & Applications
Fifth Edition
Roger L. Tokheim
Chapter 13
Connecting with
Analog Devices
© Glencoe/McGraw-Hill

2. CHAPTER 13 PREVIEW Hybrid System (analog-to-digital-to-analog)
A/D and D/A Converters (block diagrams)
Simple 4-bit D/A Converter
Simple D/A Converter Operation
Counter-ramp-type A/D Converter
Ramp-type A/D Converter
Successive-approximation A/D Converter
Flowcharting- Successive Approximation
A/D Converter Specifications

3. HYBRID SYSTEM (BOTH ANALOG AND DIGITAL)
input
Encoder
A/D
Converter
Digital
Processing
Unit
Decoder
D/A
Converter
Analog
output
Converts from analog input
to digital output
Converts from digital input
to analog output

4. A/D AND D/A CONVERTERS Digital-to-analog converter
Processing
Unit
Decoder
D/A
Converter
Encoder
A/D
Analog
output
input
Digital-to-analog converter
A/D
Analog-to-digital converter
Resistor
Network
Summing
Amplifier
Analog
Voltage
INPUT

5. SIMPLE D/A CONVERTER 2N = 16 Vreference 150 k 75 k 37.5 k 18.7 k
Binary inputs
N = 4
3 V
Feedback resistor
Vreference
10 k
2N = 16
18.7 k
37.5 k
75 k
150 k
Summing amplifier
(inverting)
Input resistors
This circuit can produce 16 different analog output voltages.

6. D/A CONVERTER OPERATION
Binary input = 0000
0001
3 V
10 k
= 0.2 V
= 0 V
18.7 k
37.5 k
150 k
75 k
Vout =
x 3 V = 0.2 V
10 k
150 k
The smallest step size for this circuit is 0.2 V.

7. 4-BIT D/A CONVERTER As the binary input steps from 0000 to 1111
Vout(max) = (2N - 1) x 0.2 V = 3 V
3 V
Vout steps from
0 V to 3 V
0 V
3 V
10 k
The total span for this circuit is from 0 to 3 V.

8. COUNTER-RAMP TYPE A/D CONVERTER
Clock
Binary
output
Vin
Comparator
HIGH
LOW
D/A
Converter
ramp
Vin
When the ramp exceeds Vin
the comparator output goes
LOW and the clock is disabled.
ramp

9. RAMP-TYPE A/D CONVERTER
Counter
Binary
output
Clock
Comparator
Vin
LOW
Ramp
Generator
Vin = + 5 V
Comparator output
Clock pulses to counter

10. SUCCESSIVE-APPROXIMATION TYPE A/D CONVERTER
Binary output
Clock
Successive
Approximation
Logic
7V input
Vin
Voltage
Comparator
D/A
Converter

11. FLOWCHARTING SUCCESSIVE APPROXIMATION
Assume an input of
7V to a 4-bit binary output
A/D converter using
successive approximation
Start
7 V input
Set MSB
to 1
Is 0100
high or low?
HIGH
LOW
Set 2s place
to 1
Is 1000
high or low?
LOW
HIGH
Is 0110
high or low?
HIGH
LOW
Clear 8s.
Set 4s to 1.
Set 1s place
to 1
STOP
Final result= 0111

12. A/D CONVERTER SPECIFICATIONS
Type of output
Binary (microprocessor-type)
Decimal (digital meter type)
Resolution
Binary output- number of bits (such as 4, 6, 8, 12, 14 or 16)
Decimal output- number of digits on display (such as 3 1/2 or 4 1/2)
Accuracy
Binary output- (ranges from +/- 1/2 LSB to about +/- 2 LSB)
Decimal output- (ranges from about 0.01 to 0.05 percent)
Conversion time is the time it takes for the IC to convert the analog input voltage to digital output. Binary output A/D converters commonly have faster conversion times than decimal output types.