Analog to Digital Convertor

 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: -

Digital to Analog Convertor

Dual Slope and successive ADC part-3