## Designing of Counter Type ADC

In electronics, the term “analog to digital conversion” can be denoted with ADC, A/D or A to D. It is one kind of system used to convert analog signal to digital signal. An A/D may also give an inaccessible dimension like an electronic device that changes an analog i/p current or voltage to a digital number representing the magnitude of the voltage or current. Normally the digital o/p is a 2’s complement binary number that is relative to the i/p, but there are other possibilities. There are numerous ADC architectures, but some of the specific ADCs ate implemented as ICs (integrated circuits) due to the complexity and the requirement for exactly matched components. A digital-to-analog converter (DAC) performs the reverse function; it converts a digital signal into an analog signal. The different types of ADCs available in different speeds, interfaces and accuracy, namely a Flash type ADC, Counter type ADC, sigma-delta ADC and successive approximation ADC.

### What is Counter Type ADC?

The Counter type ADC can be defined as, it is the basic type of ADC, which is also known as staircase approximation ADC, or a ramp type ADC. The circuit diagram of counter type ADC is shown below. The circuit diagram of Counter Type ADC can be built with N-bit counter, digital to analog converter, and op-amp comparator.

### Counter Type ADC Operation

The N-bit counter produces an n-bit digital o/p which is given as an i/p to the digital to analog circuit (DAC). The analog output equivalent to the digital i/p from DAC is contrasted with the i/p analog voltage with the help of an op-amp comparator. This Integrated Circuit evaluates the two voltages and if the produced DAC voltage is low, it gives a high pulse to the N-bit counter as a CLK pulse to raise the counter.

The similar procedure will be continued until the output of the DAC equals to the i/p analog voltage then it produces a low CLK pulse and also gives a clear signal to the counter as well as a load signal to the storage resistor. Here storage resistor is used to store the corresponding digital bits. These digital values are strongly matched with the analog input values with a small error.

For each sampling interval, the output of DAC tracks a rampway so that it is named as a Digital ramp kind ADC. And this ramp seems like staircases for each sampling moment, so that it is also named as a staircase approximation kind ADC.

### Counter Type ADC Conversion Time

The ADC conversion time is the time taken the process to change the input sampled analog price to a digital value. Here the most conversions of high i/p voltage for an N-bit ADC is the CLK pulses necessary to the counter to calculate its maximum count value. So

The Counter type ADC conversion can be done by this formula, that is = (2N-1) T

Where ‘T’ is the time period of the CLK pulse.

If N=3 bits, then the Tmax = 7T.

By viewing the above change time of Counter type ADC it is demonstrated that the sampling phase of Counter type ADC should be as shown below.

Ts >=(2N-1) T

• Counter type ADC is very simple to understand and also to operate.
• Counter type ADC design is less complex, so the cost is also less