All signals in nature are in analog form. They need to be converted into digital forms for understanding and processing. The analog nature of signals creates difficulties in designing and verification of analog circuits. Analog to digital converters (ADC) help in this conversion for better understanding, smooth processing, better usability, and better storage. Moreover, the demand for low-power consuming electronic devices has increased exponentially with time. ADC is an important building block of the electronics industry.
What is an ADC? And how does it work?
Nowadays, all electronic devices need fast functioning and less power-consuming components for better operation. ADC deciphers real-world signals like temperature, pressure, current, or light intensity into digital formats. The scaling process is the mapping of the continuous values signals into binary form.
The working of ADC involves two steps
The sample and hold process is simply a signal holding process. In this, the analog signals are sampled and then they are on hold for a particular period. According to the Nyquist theorem, the minimum sampling rate is two times the maximum input frequency.
fNyquist = 2fMax
fs (Sampling frequency) = 1/T(time period)
The process of Quantization is related to the bit resolution in the analog to digital converter. A minute deviation in the analog signal can result in a change in the digital output.
After sampling the signal is obtained in a series of pulses. The amplitude of that signal is proportional to the instantaneous value of the operation and is called pulse amplitude modulation. During this process, all the samples are compared to their scale of digital values and given a binary number that represents their approximate amplitude. After the quantization is done, the signals are converted into a binary code number by the encoder circuit.
Why do we need ADC?
To amplify an audio signal it must be converted into an electrical voltage waveform using a transducer. The obtained waveform will also be continuous which can be converted into the required form in two ways.
1. Amplify the continuous-time waveform directly and then reconvert it to Audio using a speaker.
2. Convert the continuous-time waveform to digital, do processing in digital and then reconvert it to analog and then use the speaker to convert electrical waveform into Audio signal back
The need for higher resolution (N-bit), good sampling rates, and quick conversion are the parameters that are need of the hour in all electronics components.
Why is the Flash-type ADC the preferred choice?
The flash ADC has three important components when described in the form block diagram i.e. resistive ladder, a comparator & an encoder. The comparator is an important part of the ADC. N-bit ADC will have 2N resistors in it. The reference voltage is given as an input to the comparator with the help of a resistive ladder network. After the reference and input voltages are compared, the output signal is fed to the encoder circuit. The reason behind the preferred nature of the flash type is that it possesses parallelism in its architecture. The parameters like precision and higher resolution of ADC are directly dependent on the functioning of the comparator. It is a challenging process to make a comparator amplify a smaller signal to a sufficiently higher and stable signal output voltage..
The comparator’s basic function is referencing and differentiating voltages. It depends on certain characteristics which are divided into two types:
• Static Comparators
The output of the comparator will depend on the difference between the input terminals of the operational amplifier. When the two terminals of the opamp have positive voltage as a difference, the output will be positive whereas when they have a negative difference, the output will be negative. Common mode rejection ratio(CMRR) is an important parameter that determines the range of rejecting voltage signals.
• Dynamic Comparators
The behavior or response of the comparator is a function of time. These contain small and large signal models, delay signals, and propagation delay.
According to a report published on 18th April 2019 on globenewswire.com, the ADC’s market globally will touch USD 3.61 billion by 2026. The market for ADC is flourishing year by year globally. The North American region will be the key revenue generator with an expected CAGR growth of 5.1%.
The key findings of the report are -:
• The demand for flash-type ADC will dominate the market. ADCs help in building the resolution to the higher value of the image.
• The sampling rate is responsible for processing higher resolution and fast data conversion processes. High-speed convertors in the sampling segment are anticipated to grow to the highest CAGR of 5.3%.
• IT & Telecommunications sector is the largest shareholder of 34% of the data converter market. The factors contributing to this growth are advancement in the 4G sector, improved voice modulation, and data services.
The major semiconductors companies manufacturing ADCs are -:
1. Analog devices
2. Maxim integrated
3. ST microelectronics
4. Texas instruments
5. NXP Semiconductors
7. Western digital
8. Microchip technology
9. On semiconductors and many more.
The factors responsible for the ADC’s global growth are technological advancements, the need for high performance & enhanced efficiency of the device, complex design of the device, and encouragement in the digitization of work processes by the government in emerging economies.
According to the report published by ReportsandData.com on 1/7/2020, in the COVID-19 pandemic demand and supply across the globe for ICs has decreased. The estimated decline during this period is 5% to 15% in the year 2020 compared to 2019. The most affected sector was consumer electronics and the automotive sector. Restriction on movements, imposition of lockdowns has led to a decline in sales and purchases. And high complexity in the designing of analog-to-digital converters is also a hindrance in the growth of the market.
In order to enhance the performance and functionality of the comparators, parameters like delays and power consumption need to be improved. Advancement in technology with time has paved the path for exponential growth in the market of ADC. So in a nutshell, if the speed and power consumption of the comparators are improved, the results will be reflected back in the enhanced functionality of the ADC.
•Sagar Kumar Vinodiya, R. S. Gamad 2017,” Analysis and Design of Low Power, High-speed Comparators in 180nm Technology with Low Supply Voltages for ADCs “, 8th ICCCNT IEEE.