# Analog to Digital Converter (ADC) – Block Diagram, Factors & Applications

**What is Analog To Digital Converter (ADC)? Block Diagram, Factors & Applications Of ADC**

Table of Contents

**What is ADC (Analog To Digital Converter)?**

**ADC** stands for **analog to digital converter**. It is an electronic device used for converting an **analog signal** into a **digital signal**.

The analog input signal of ADC is **continuous time** & **continuous amplitude** signal. The output of ADC is a **discrete time** and **discrete amplitude** digital signal.

**Why ADC?**

In the real world, every real quantity such as voice, temperature, weight etc exists in the **analog state**. And it cannot be processed by any digital device such as a computer or a cell phone.

These analog quantities are converted into digital form so that a digital device can process it. This conversion is done using **analog to digital converter**.

### Block Diagram of ADC

The analog signal is first applied to the ‘**sample**‘ block where it is sampled at a specific sampling frequency. The sample amplitude value is maintained and held in the ‘**hold**‘ block. It is an analog value. The hold sample is quantized into discrete value by the ‘**quantize**‘ block. At last, the ‘**encoder‘** converts the discrete amplitude into a binary number.

#### Analog To Digital Conversion Steps

The conversion from analog signal to a digital signal in an analog to digital converter is explained below using the block diagram given above.

**Sample**

The **sample** block function is to sample the input analog signal at a specific time interval. The samples are taken in **continuous amplitude** & possess real value but they are **discrete** with respect to **time**.

The sampling frequency plays important role in the conversion. So it is maintained at a specific rate. The sampling rate is set according to the requirement of the system.

**Hold**

The second block used in ADC is the ‘**Hold’** block. It has no function. It only holds the sample amplitude until the next sample is taken. The hold value remains unchanged till the next sample.

**Quantize**

This block is used for **quantization**. It converts the analog or continuous amplitude into discrete amplitude.

The on hold continuous amplitude value in hold block goes through ‘**quantize’** block & becomes **discrete** in **amplitude**. The signal is now in digital form as it has **discrete time **&** discrete amplitude**.

**Encoder**

The **encoder** block converts the digital signal into **binary form** i.e. into bits.

As we know that the digital devices operate on binary signals so it is necessary to convert the digital signal into the binary form using the Encoder.

This is the whole process of converting an Analog signal into digital form using an **Analog to Digital Converter**. This whole conversion occurs in a microsecond.

**Factors Of ADC**

**Resolution:**

Resolution of an ADC is the **number of bits** that represents the digital signal’s **amplitude**.

The analog signal has continuous amplitude. It can have **infinite values** i.e. real, floating basically any value one can imagine. On the other hand, the digital signal has a discrete and finite number of values. These discrete values are represented using **binary numbers** (bits).

To better understand the idea of resolution of **ADC**,

**1-Bit Resolution**

The figure above shows an analog signal represented in a digital form which is either 0 or 1. This is a 1-bit resolution. The **resolution** of **ADC** defines its **number of steps**.

**number of steps = 2 ^{n}**

Where **n** is the number of bits. Therefore, there are 2 steps in 1-bit resolution.

**2-Bit Resolution**

This figure shows the conversion of analog to digital in 2-bit resolution. There are 4 steps or **quantization levels**.

**No of steps = 2 ^{n} = 2^{2} = 4**

**4-Bit Resolution**

This figure shows 4-bit resolution. The number of steps in 4-bit resolution is 16.

**No of steps = 2 ^{n} = 2^{4 }= 16**

The number of steps increases **exponentially** with increase in the **bit-resolution**. It also implies that by increasing the bits of resolution the converted digital signal becomes more like the original analog signal. So ideally, we can say that a digital signal with **infinite resolution** is an analog signal.

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**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 = v _{ref}/2^{n}**

Where **v _{ref }**is the maximum voltage being converted &

**n**represents the bits of resolution.

For example:

**v _{ref }= 10.24v & n = 10 bits**

Then:

**Δv = 10.24/2 ^{10}**

**Δv = 10.24/1024**

**Δv = 0.01v**

Thus the step-size or width of the step is **0.01v**. In this ADC, a single bit increase represents a **0.01v** of increase in the analog input. If analog input is increased by **0.01v** then the output is increased by **1 bit.**

**Quantization Error**

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.

The increase in the **resolution** of the ADC decreases the **step-size** if the **v _{ref}** remain constant. Consequently, the

**quantization error**decreases.

**Sampling Rate**

The number of samples taken during a single second is known as **sampling rate** or **sampling frequency**.

The sampling rate should be set according to the input signal. It should not be **very low** or **very high**.

Example of sampling:

This example shows that the sampling rate is 0.5 sec, as it takes 2 samples in one second.

**Aliasing**

If the sampling rate is **very low** then the resultant signal will not look anything like the original signal. In fact, it will become a different signal after reconstruction. This problem is known as **aliasing**.

To avoid this problem, the sampling rate should be kept **higher** than **twice the frequency** of the input signal. **Anti-aliasing filters** are also used for removing the frequency components higher than one half of the sampling rate. it blocks the aliasing components from being sampled.

**Nyquist Criteria**

**Nyquist criteria** suggest the **minimum** possible **sampling rate** for an analog signal which can be **reconstructed** successfully. If the highest frequency of the analog signal is **f**, the signal can be reconstructed successfully from its samples, if the samples are taken at a sampling frequency greater than **2f**.

**Offset**

The **offset** in ADC is the **shift** in the digital output. For example, for input **v _{in} = 0**, the output might not necessarily be digital

**0**. It can be digital

**5**, which will be the offset of the

**ADC**.

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**Application of ADC**

In the modern world of growing technology, we are dependent on digital devices. These digital devices operate on the digital signal. But not every quantity is in digital form instead they are in analog form. So an ADC is used for converting analog signals into digital signals. The **applications** of ADC are limitless. Some of these **applications** given below:

**Cell phones**operate on the digital voice signal. Originally the voice is in analog form, which is converted through ADC before feeding to the cell phone transmitter.**Images**and**videos**captured using camera is stored in any digital device, is also converted into digital form using ADC.- Medical Imaging like
**x-ray**&**MRI**also uses**ADC**to convert images into Digital form before modification. They are then modified for better understanding. - Music from the
**cassette**is also converted into the digital form such as**CDs**and**thumb drives**using**ADC**converters. **Digital Oscilloscope**also contains**ADC**for converting Analog signal into a digital signal for display purposes & different other features.**Air conditioner**contains**temperature sensors**for maintaining the room temperature. This temperature is converted into digital form using ADC so that onboard controller can read & adjust the cooling effect.

In today’s modern world almost every device has become the **digital version** of itself & they need to have ADC in it. Because it has to operate in digital domain which can be only acquired using **analog to digital converter (ADC)**.

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