What is an ADC? Analog-to-digital converter

What is an ADC?

An analog-to-digital converter ( ADC ) is an electronic integrated circuit used to convert analog signals such as voltages into digital or binary form consisting of 1s and 0s. Most ADCs use voltage inputs such as 0 to 10V, -5V to +5V, etc., and box correspondingly produce a digital output of some binary number.

Analog-to-digital converter can be expressed in terms of A/D, ADC, A to D, which works in the opposite process to the digital-to-analog converter DAC.

What is an ADC? Analog-to-digital converter

The process of converting an analog signal to a digital signal can be done in a number of ways, and there are different types of ADC chips from different manufacturers on the market today, such as the ADC08xx series. 

Hence, a simple ADC can be designed with the help of discrete components. The main features of an ADC are the sampling rate and bit resolution, where: The sampling rate of an ADC is nothing but the bit resolution.

The sampling rate of an ADC is nothing but the speed at which the ADC converts the signal from analog to digital.

The bit resolution is nothing but the precision with which the analog-to-digital converter can convert the signal from analog to digital.

One of the main advantages of digital-to-analog converters is the high data acquisition rate even with multiple inputs. With the invention of a wide variety of ADC integrated circuits (ICs), data acquisition from a variety of sensors has become more accurate and faster. 

The dynamic characteristics of high-performance ADCs include improved measurement repeatability, low power consumption, accurate throughput, high linearity, excellent signal-to-noise ratio (SNR), and more.

The various applications for digital-to-analog converters include measurement and control systems, industrial instrumentation, communication systems, and all other sensing-based systems. ADCs can be categorized on the basis of performance, bit rate, power, cost, and other factors.

Performance Influencing Factors

ADC performance can be evaluated by its performance based on different factors, the following two main factors are described here.

SNR (Signal to Noise Ratio): SNR reflects the average number of bits without noise in any given sample.

Bandwidth: The bandwidth of an ADC can be determined by estimating the sampling rate, which can sample an analog source every second to produce discrete values.

Types of Analog to Digital Converters

There are different types of analog to digital converters, some of the types of analog to digital converters include.

1. Dual slope analog-to-digital converters

2. Flash analog-to-digital converters

3. Successive Approximation Analog-to-Digital Converters

4. Half-flash analog-to-digital converters

5. Sigma-delta analog-to-digital converters

6. Pipelined analog-to-digital converter

Double slope analog-to-digital converter:

In this type of ADC converter, the comparative voltage is generated by an integration circuit consisting of a combination of resistors, capacitors, and operational amplifiers. The integrator generates a sawtooth wave from zero to the value Vref on its output by setting the value of Vref

When the integrator waveform starts accordingly, the counter starts counting from 0 to 2^n-1, where n is the number of bits in the ADC.

When the input voltage Vin equals the waveform voltage, the control circuit captures the counter value, which is the digital value corresponding to the analog input value. This dual slope ADC is a relatively medium-cost and slow device.

Flash analog-to-digital converter:

This analog-to-digital converter IC, also known as a parallel ADC, is the most widely used high-efficiency ADC in terms of speed. 

This flash analog-to-digital converter circuit consists of a series of comparators, each of which compares the input signal with a unique reference voltage. 

On each comparator, when the analog input voltage exceeds the reference voltage, the output will be high. 

This output is further provided to the priority encoder for generating binary code based on higher-order input activity by ignoring other active inputs. It is a high-cost and high-speed device.

Successive approximation type analog to digital converter:

Successive Approximation Analog-to-Digital Converter (SARADC) is the most modern ADC IC and is much faster than dual slope and flash ADCs because it uses digital logic to converge the analog input voltage to the closest value.

The circuit consists of a comparator, an output latch, a successive approximation register (SAR), and a D/A converter.

At the beginning, the SAR is reset and the MSB of the SAR is set as the transition from LOW to HIGH is introduced. This output is then provided to the D/A converter which generates the analog equivalent of the MSB and further compares it with the analog input Vin

If the comparator output goes low, the SAR clears the MSB, otherwise, the MSB is set to the next position. This process continues until all bits are tried and after Q0, the SAR makes the parallel output line contain valid data.

Half-Flash Analog-to-Digital Converter:

This type of analog-to-digital converter operates primarily around its limiting size through two separate flash converters, where each converter has half the resolution of a semi-embedded device. 

The capacity of a single flash converter is to handle the MSB (Maximum Significant Bit) while the other handles the LSB (Lowest Significant Bit).

Sigma-delta analog-to-digital converter:

Sigma Delta ADCs (ΣΔ) are fairly new designs. These designs are very slow compared to other types of designs, but they provide the highest resolution for a wide range of ADCs. 

As a result, they are very compatible with high fidelity-based audio applications, however, they are not usually applicable where high BW (bandwidth) is required.

Pipelined analog-to-digital converter:

A pipelined ADC, also known as a sub-ranging quantizer, is conceptually related to the successive pass approximation type of ADC but is a bit more complex. While successive approximation grows in each step by moving to the next MSB.

A pipelined ADC uses the following process:

First, it is used for rough conversion. After that, it evaluates the change in the input signal.

Performs better conversions by allowing temporary conversions using a range of bits.

Often, pipelined designs provide the central foundation between SAR and flash analog-to-digital converters by balancing their size, speed, and high resolution.

Key Applications

The use of digital devices is currently increasing. These devices work based on digital signals. Therefore, analog-to-digital converters play a key role in converting signals from analog to digital in such devices. 

Applications of analog-to-digital converters include the following -

1. Air conditioners include temperature sensors to maintain the temperature in the room. Hence, this temperature conversion can be done from analog to digital with the help of ADC.

2. Used in digital oscilloscopes to convert signals from analog to digital for display.

3. Used in cell phones to convert analog voice signals to digital signals because cell phones use digital voice signals but actually the voice signals are in analog form. 

Therefore, the ADC is used to convert the signal before it is sent to the transmitter of the cell phone.

4. Used in medical equipment such as MRIs and X-rays to convert the image from analog to digital before it is changed.

5. The camera in a cell phone is mainly used to capture images and videos. These are stored in digital devices and hence ADCs are used to convert them into digital form.

6. Cassette music can also be converted to digital like CDS and thumb drives using ADC.

Almost all the devices available in the market today are digital versions, so all these devices can use ADCs.

To summarize

In fact, the main benefit of digital data is that you can store it easily and the chances of data corruption due to any analog signal are very less. As a result, most computing has shifted to the digital realm.

Digital data also has the advantage of accuracy (depending on the ADC process) and efficient processing speed. However, the world we see is analog. 

Therefore, data converters such as ADCs must be used to convert these analog signals to digital values so that digital devices can easily process, store, analyze, and calculate the data.

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