Analog to Digital Converter, Types, Circuit, Block Diagram, Applications
Table of Contents
What is ADC (Analog To Digital Converter)?
Analog to digital converter is referred to as ADC. It is a piece of technology that transforms analog signals into digital signals.
Continuous time and continuous amplitude signals are the analog input signals used by ADCs. Digital signals with discrete time and discrete amplitude are produced by the ADC.
Why Analog to Digital Converter?
Every real quantity, including voice, temperature, weight, etc., exists in the analog state in the real world. And no digital device, including a computer or a phone, can process it. To enable processing by a digital device, these analog quantities are transformed into digital form. A converter from analog to digital is used for this conversion.
Block Diagram of Analog to Digital Converter
The ‘sample’ block receives the analog signal first, and samples it at a predetermined sampling frequency. The ‘hold’ block preserves and holds the sample amplitude value. This value is analog. The ‘quantize’ block quantizes the hold sample into discrete values. The discrete amplitude is finally transformed into a binary number by the “encoder.”
Analog To Digital Conversion Steps
Using the block diagram provided above, the conversion of an analog signal to a digital signal in an analog to digital converter is described below.
The sample block function samples the analog input signal once every predetermined amount of time. The samples are real, have continuous amplitude, and are taken, but they are discrete in time. The conversion depends heavily on the sampling frequency. As a result, it is kept at a particular rate. The sampling rate is set in accordance with the system’s requirements.
The ‘Hold’ block is the second block in ADC. It serves no purpose. Only the sample amplitude is retained until the subsequent sample is taken. Until the subsequent sample, the hold value does not change.
It is possible to quantize using this block. It transforms the continuous or analog amplitude into the discrete amplitude. The hold block’s on-hold continuous amplitude value passes through the quantize block and changes to a discrete amplitude. Since the signal has discrete time and discrete amplitude, it is now in digital form.
The encoder block transforms the digital signal into bits (binary form). Since binary signals are used by digital devices, it is necessary to use an encoder to transform the digital signal into binary form. This is the entire process of using an analog to digital converter to transform an analog signal into digital form. The entire conversion happens in a single microsecond.
Factors Of Analog to Digital Converter
The number of bits used by an ADC to represent the amplitude of a digital signal is known as resolution. The amplitude of the analog signal is constant. It can have any value one can think of, including real, floating, and infinite values. The digital signal, on the other hand, has a discrete and limited range of values. Bits (binary numbers) are used to represent these discrete values.
To better understand the idea of resolution of ADC,
An analog signal is represented in the figure above as a digital signal that can either be 0 or 1. This resolution is 1 bit. ADC’s number of steps is determined by its resolution.
number of steps = 2n
Where n is the number of bits. Therefore, there are 2 steps in 1-bit resolution.
The conversion of analog to digital in 2-bit resolution is depicted in this figure. There are 4 steps or levels of quantization.
No of steps = 2n = 22 = 4
This figure shows 4-bit resolution. The number of steps in 4-bit resolution is 16.
No of steps = 2n = 24 = 16
As bit-resolution increases, the number of steps also grows exponentially. Additionally, it implies that the converted digital signal resembles the original analog signal more closely as resolution bits are increased. Therefore, in theory, we can state that an analog signal is a digital signal with infinite resolution.
Width Of The Step
The voltage difference between two adjacent steps is known as the width of the step. It is denoted by Δv.
So a single step represents a fixed voltage that is
Δv = vref/2n
Where vref is the maximum voltage being converted & n represents the bits of resolution.
vref = 10.24v & n = 10 bits
Δv = 10.24/210
And Δv = 10.24/1024
Δv = 0.01v
As a result, the step’s size or width is 0.01v. A single bit increase in this ADC corresponds to a 0.01v increase in the analog input. So The output is increased by 1 bit if the analog input is raised by 0.01 volts.
The ADC updates its value if the increase or decrease in its input voltage is greater than Δv/2. Any change less than Δv/2 will not be registered. This is known as Quantization Error.
In other words, the difference between the input and the digital round-off figure of output is known as quantization error. So The increase in the resolution of the ADC decreases the step-size if the vref remain constant. Consequently, the quantization error decreases.
Sampling rate or sampling frequency refers to the number of samples taken in a second. The input signal should be taken into account when setting the sampling rate. It shouldn’t be excessively high or low.
Example of sampling:
So As it takes two samples in a second, this example demonstrates that the sampling rate is 0.5 seconds.
The resultant signal won’t resemble the original signal at all if the sampling rate is very low. In actuality, the signal will change after reconstruction. The term “aliasing” refers to this issue. The sampling rate should be kept higher than twice the frequency of the input signal to avoid this issue. Additionally, frequency components higher than 0.5 times the sampling rate are removed using anti-aliasing filters. It prevents sampling of the aliasing components.
The smallest sampling rate that can be used to successfully reconstruct an analog signal is suggested by the Nyquist criteria. If the samples are taken at a sampling frequency greater than 2f and the highest frequency of the analog signal is f, the signal can be successfully reconstructed from its samples.
The shift in the digital output is known as the ADC offset. For instance, the output for input vin = 0 might not always be a digital 0. It might be digital 5, which would be the ADC’s offset.
Application of Analog to Digital Converter
We are reliant on digital devices in the modern, evolving technological world. On the digital signal, these digital gadgets function. The majority of quantities, however, are analog rather than digital. So analog signals are transformed into digital signals using an ADC. ADC is a technology with countless uses. the following list of some of these applications:
- Camera-generated images and videos are stored on any digital device and converted into digital format using ADC.
- The digital voice signal is what powers mobile phones. Prior to being fed to the cell phone transmitter, the voice is converted from its original analog format through an ADC.
- ADC is also used in medical imaging, such as x-ray and MRI, to convert images into digital form prior to modification. Then, for easier comprehension, they are changed.
- ADC converters are used to transfer audio from cassettes into digital formats like CDs and thumb drives.
- Temperature sensors are used in air conditioners to regulate the room’s temperature. In order for the onboard controller to read and adjust the cooling effect, this temperature is converted into digital form using an ADC.
- ADC is a feature of digital oscilloscopes that allows analog signals to be converted into digital signals for display purposes.
- Nearly every device in the modern world has evolved into a digital version of itself, so they all require ADC. due to the fact that it must operate in the digital domain, which can only be acquired using an analog to digital converter (ADC).