** Analog to Digital Convertor **

**Unit-06**

** **

A/D AND D/A CONVERTERS

Analog to digital convertor,

Digital to Analog Convertor,

ADC comparator,

Dual Slope ADC,

Successive ADC.

*Analog to digital convertor: - *

An
**analog-to-digital converter** (ADC) is an electronic device that converts an
analog signal into a digital signal.

The
analog signal can be a voltage, current, or any other continuous signal, and
the digital signal is a binary representation of the analog signal that can be
processed by digital systems such as computers.

The
purpose of an **ADC** is to sample and quantize an analog signal to produce a
digital representation of the signal that can be processed and analyzed by
digital systems.

An
**analog-to-digital converter **(ADC) is an electronic device that converts analog
signals, which are continuous in time and amplitude, into digital signals,
which are discrete in time and amplitude.

The
purpose of an ADC is to digitize a continuous analog signal so that it can be
processed by digital systems such as computers

ADCs
are used in many applications, such as data acquisition systems, instrumentation,
and control systems.

The
process of converting an analog signal into a digital signal involves three
main steps: **sampling, quantization, and encoding.**

1.
**Sampling:**

a. This
step involves measuring the value of the analog signal at regular intervals of
time.

b. The
rate of sampling is determined by the Nyquist-Shannon sampling theorem, which
states that the sampling rate must be at least twice the highest frequency
component in the analog signal.

2.
**Quantization:**

a. This
step involves converting the continuous analog signal into a series of discrete
values, called samples.

b. The
range of the analog signal is divided into a fixed number of levels or steps,
and each sample is assigned to the nearest level.

c. The
number of levels is determined by the resolution of the ADC, which is usually
specified in bits.

d. **For
example**, an 8-bit ADC can represent the analog signal with
2^8 = 256 discrete levels.

3.
**Encoding:**

a. This
step involves converting the quantized samples into a binary code that can be
processed by digital systems.

b. The
most common encoding scheme is the straight binary code, where each level is
represented by a binary number.

c. The
output of an ADC is a digital signal that can be further processed and analyzed
by digital systems.

d. The
performance of the ADC, such as its resolution, accuracy, and speed, determines
the quality of the digital signal produced.

*Types
of ADC convertor *

There
are several types of analog-to-digital converters (ADCs), each with its own
advantages and disadvantages.

**The
main types of ADCs are: **

1.
**Successive Approximation ADC (SAR):**

a. SAR
ADCs are one of the most common types of ADCs.

b. They
work by successively comparing the input signal to a series of reference
voltages, with each comparison refining the digital output.

c. SAR
ADCs are fast, have high resolution, and are relatively low in cost.

2.
**Delta-Sigma ADC (ΔΣ):**

a. Delta-sigma
ADCs work by oversampling the input signal, converting it to a high-frequency
bitstream, and then filtering the bitstream to produce the final output.

b. ΔΣ
ADCs are known for their high resolution and low noise, but they can be slow
and have high latency.

3.
**Pipeline ADC: **

a. Pipeline
ADCs use a series of stages to convert the input signal to a digital output.

b. Each
stage is responsible for a portion of the conversion process, and the outputs
of each stage are cascaded to produce the final output.

c. Pipeline
ADCs are fast, have moderate resolution, and are widely used in applications
such as high-speed data acquisition.

4.
**Flash ADC:**

a. Flash
ADCs use a ladder of resistors and comparators to convert the input signal to a
digital output in a single step.

b. Flash ADCs are very fast and have high
resolution, but they are expensive and require a large number of components.

5.
**Integrating ADC:**

a. Integrating
ADCs work by integrating the input signal over a fixed period of time and then
converting the integrated signal to a digital output.

b. Integrating
ADCs are known for their high accuracy and low noise, but they can be slow and
require precise timing.

6.
**Dual Slope ADC: **

a. Dual
slope ADCs work by integrating the input signal for a fixed period of time, and
then integrating a known reference voltage for a variable period of time until
the integrator output returns to zero.

b. Dual
slope ADCs are known for their high accuracy and low cost, but they are slow
and require a stable reference voltage.

*Block Diagram of Analog to Digital Convertor: -*

* *

*1.
**Analog Signal: *

a. The
input signal to the ADC is an analog signal, which can be a voltage, current,
or any other continuous signal.

b. This
signal is often generated by a sensor or transducer that converts a physical
parameter into an electrical signal.

*2.
**Sampling: *

a. The
analog signal is sampled at a fixed rate by the ADC.

b. This
means that the continuous signal is sampled at discrete time intervals, and
each sample represents the value of the signal at that point in time.

c. The
sampling rate is usually determined by the Nyquist-Shannon sampling theorem,
which states that the sampling rate must be at least twice the highest
frequency component in the analog signal.

*3.
**Quantization: *

a. The
samples obtained from the analog signal are then quantized into discrete
levels.

b. This
process involves dividing the range of the analog signal into a number of
levels or steps.

c. The
number of levels is determined by the resolution of the ADC, which is usually
specified in bits.

d. For
example, an 8-bit ADC can represent the analog signal with 2^8 = 256 discrete
levels.

*4.
**Encoding: *

a. The
quantized samples are then encoded into digital form.

b. The
encoding process involves converting each quantized level into a binary code.

c. The
most common encoding scheme is the straight binary code, where each level is
represented by a binary number.

*5.
**Digital Signal: *

a. The
output of the ADC is a digital signal, which is a sequence of binary codes that
represent the original analog signal.

b. This
digital signal can be further processed and analyzed by digital systems such as
computers.

*Circuit Diagram of Analog to Digital Convertor: -*

**Dual Slope and successive ADC part-3**

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