This is one of a type of Analog to Digital Converter (ADC). Through this presentation, you will have a clear view of how an ADC works. This one specifies one of the types of Analog to Digital Convertor.

1. Abhay Dhupar (01)
Abhay s. bhadoriya(02)
Aditi Tomar (17)
Aditya Sahu (19)
Presented by :-
CS - 304
DIGITAL SYSTEM
Successive Approximation ADC

2. A/D CONVERTER
I. An analog to digital(A/D) converter takes an analog
input voltage and after a certain amount of time
produces a digital output code which represent the
analog input .
II. This type of converter is used to convert analog voltage
to its corresponding digital output.
I. The function of the analog to digital converter is
exactly opposite to that of a DIGITAL TO ANALOG
CONVERTER. Like a D/A converter, an A/D converter is
also specified as 8, 10, 12 or 16 bit. Though there are
many types of A/D converters, we will be discussing
only about the successive approximation type.

4. APPLICATION OF
(A/D)CONVERTER
– ADC are used virtually everywhere where an analog signal has to be
processed, stored, or transported in digital form.
❑ Microphones - take your voice varying pressure waves in the air and
convert them into varying electrical signals
❑ Strain Gages - determines the amount of strain (change in
dimensions) when a stress is applied
❑ Thermocouple – temperature measuring device converts thermal
energy to electric energy
❑ Voltmeters
❑ Digital Multimeters

5. TYPES OF A/D CONVERTER
– Successive approximation type A/D converter
– Simultaneous or Flash type A/D converter
– Counter type A/D converter
– Continuous type A/D converter
– Single slope type
– Dual slope type
– Voltage to Frequency (integrating) type

6. Successive approximation type A/D
converter
– A successive approximation A/D converter consists of a
comparator, a successive approximation register (SAR),
output latches, and a D/A converter. The circuit diagram is
shown below.
– A successive-approximation ADC is a type of analog-to-
digital converter that converts a
continuous analog waveform into a
discrete digital representation using a binary
search through all possible quantization levels before finally
converging upon a digital output for each conversion.

8. Working
● At the start of a conversion cycle, the SAR is reset by
making the start signal (S) high. The MSB of the SAR
(Q7) is set as soon as the first transition from LOW to
HIGH is introduced.
● The output is given to the D/A converter which
produces an analog equivalent of the MSB and is
compared with the analog input Vin.
● If comparator output is LOW, D/A output will be
greater than Vin and the MSB will be cleared by the
SAR.

9. ● If comparator output is HIGH, D/A output will be less than Vin
and the MSB will be set to the next position (Q7 to Q6) by the SAR.
● According to the comparator output, the SAR will either keep or
reset the Q6 bit. This process goes on until all the bits are tried.
After Q0 is tried, the SAR makes the conversion complete (CC)
signal HIGH to show that the parallel output lines contain valid
data.
● The CC signal in turn enables the latch, and digital data appear at
the output of the latch. As the SAR determines each bit, digital
data is also available serially. As shown in the figure, the CC
signal is connected to the start conversion input in order to
convert the cycle continuously.

11. Advantages and disadvantages
ADVANTAGES
1. The main merit of the successive
approximation type A/D converter is
speed.
1. It takes only n-clock pulses to
produce n-bit resolution of the analog
signal.
2. Low power consumption.
DISADVANTAGE
1. It requires a digital to analog
converter.
1. Circuit is complex.
1. The conversion time is more compared
to flash type ADC.
1. Limited resolution due to limits of
DAC and Comparator
1. Size increases with number of bits.

12. APPLICATION
1. Ideal for multichannel data acquisition systems
with sampling frequencies under 10 MHz and
resolutions between 8-16 bits.
1. The SAR ADC will used widely data acquisition
techniques at the sampling rates higher than
10KHz