Analog to Digital and Digital to Analog Converter

2. Introduction
• Microprocessor is a logical device which performs
complex processing on digital signals.
• The real world physical quantities such as temperature,
pressure, speed and displacement are continuous in nature.
• These continuous signals are analog signals.
• Analog signals are more susceptible to the deleterious
effects of additive noise.
• These data converters are available as integrated circuits.
DATA Converters A/D (Converts an analog signal to a digital signal)
D/A (Converts a digital signal to an analog signal)

3. Digital to Analog Converter
• Digital to Analog (D/A) converter can be classified as:
 current output D/A converters
 voltage output D/A converters.
• Operational amplifier converts the current signal into a
voltage signal.
 The performance is limited by:
 the number of samples it can process
 number of bits that is used in converting the digital code
into an analog signal

4. 000 001 010 011 100 101 110 111
1/8
2/8
3/8
4/8
5/8
6/8
7/8
Digital Input
Analog
Output
D0
D1
D2
Digital Input
Analog Output
D/A
Converter
A 3-Bit D/A Converter

5. • N-bit D/A converter has n input lines, it can have 2n input
combinations.
• If the full scale analog voltage is 1V, the smallest unit or LSB
is equivalent to 1/2n of 1V. This is defined as resolution.
• The MSB represents the half of the full-scale value.
• For the maximum input signal, the output is equal to the value
of the full scale input signal minus the value of the 1 LSB
input signal.

6. Binary Weighted Input Resistors
D2
D1
D0
R1=2K
R2=4K
R3=8K
I1
I2
I3
Rf=1K
I0
V0
IT
IT
-
+
V0=-RfIT
Io= (
Vin
2
+
Vin
4
+
Vin
8
)
Vin

7. D0
D1
D2
R1=2K R2=4K R3=8K
Vref=1V
Rf
V0
-
+
Weighted Resistor D/A Converter

8. Rf
V0
-
+
D0 D1
D2
R
R
2R
2R
2R 2R
1 0 0
Vref=1V
R/2R Ladder Network
R/2R LADDDER NETWORK

9. Analog to Digital Converter
• The output of transducer gives output which are in analog
form, these are converted to digital signals using an ADC.
• An ADC is an encoding device since it is used to encode
analog signals for i/p into a digital system.
• In many servo-controlled system & variable speed drive
system use digital sensors.
• The feedback information from the digital sensors have to be
converted into analog signals by means of DAC.
• Since DAC is used to decode a digital signal into an analog
form, it is referred to as decoder.

10. SENSORS AND
SIGNAL
CONDITIONER
ANALOG TO
DIGITAL
CONVERTER
(ADC)
SIGNAL
CONDITIONER
DIGITAL TO
ANALOG
CONVERTER
(DAC)
DIGITAL
SYSTEM
(COMPUTER)
DIGITAL
SYSTEM
(COMPUTER)
Analog to digital conversion
Digital to analog conversion

11. Counter Type ADC
Counter type ADC or Digital Ramp type
• The Counter type ADC is the basic type of ADC which is also
called as digital ramp type ADC or staircase approximation
ADC.
• This circuit consists of N bit counter, DAC and Op-amp
comparator.

12.  The N bit counter generates an n bit digital output which
is applied as an input to the DAC.
 The analog output corresponding to the digital input from
DAC is compared with the input analog voltage using an
op-amp comparator.
 The op-amp compares the two voltages and if the
generated DAC voltage is less, it generates a high pulse to
the N bit counter as a clock pulse to increment the counter.
 The same process will be repeated until the DAC output
equals to the input analog voltage.

13.  If the DAC output voltage is equal to the input analog
voltage, then it generates low clock pulse and it also
generates a clear signal to the counter and load signal to
the storage resistor to store the corresponding digital bits.
 These digital values are closely matched with the input
analog values with small quantization error.
 For every sampling interval the DAC output follows a
ramp fashion so that it is called as Digital ramp type ADC.
 This ramp looks like staircases for every sampling time so
that it is also called as staircase approximation type ADC.

14. Successive Approximation ADC
• It includes three major elements: D/A converter, successive
approximation register and the comparator.
• The conversion process involves comparing the output of the D/A
converter Vo with the analog input signal Vin.
• The digital input to the DAC is generated using the successive-
approximation method.
• When the DAC output matches the analog signal, the input to the
DAC is the equivalent digital signal.

15. +
-
Comparator
4 bit D/A
converter
Output
Register
Control
Successive
Approximation
Register
D3 D2 D1 D0
Analog
Reference
Vin
Analog
Input
V0
Status
CLK
Start
Data
Ready

16. • 4-bit A/D converter
• Initially Bit D3 is turned on first.
• The output of the DAC is compared with an analog signal.
• If the comparator changes the state, indicating that the output
generated by D3 is larger than the analog signal, bit D3 is
turned off and D2 is turned on.
• The process continues until the input reaches bit D0.