Dual slope and Successive Analog to digital convertor

 Dual Slope and Successive ADC (Part-3)

Unit-06

 

A/D AND D/A CONVERTERS

Analog to digital convertor,

Digital to Analog Convertor,

ADC comparator,

Dual Slope ADC,

Successive ADC.

 

ADC comparator: -

An ADC comparator is a component of an analog-to-digital converter (ADC) that compares the input analog signal to a reference voltage and generates a digital output based on the result of the comparison.

The comparator is the key element in determining the binary output of the ADC.

The operation of an ADC comparator is as follows:

1.    The input analog signal is compared to a reference voltage using a high-gain amplifier, which is typically implemented with an operational amplifier (op-amp).

2.    If the input voltage is greater than the reference voltage, the comparator outputs a high voltage (usually the digital value '1'), indicating that the input voltage is higher than the reference voltage.

3.    If the input voltage is less than the reference voltage, the comparator outputs a low voltage (usually the digital value '0'), indicating that the input voltage is lower than the reference voltage.

4.    The output of the comparator is fed into the digital logic circuitry of the ADC, which performs further processing to generate the final digital output.

The reference voltage can be a fixed voltage or a variable voltage that is adjusted based on the input signal.

The accuracy of the reference voltage is critical to the performance of the ADC, and various techniques such as trimming and calibration are used to improve the accuracy of the reference voltage.

The speed and accuracy of the ADC comparator are key factors in determining the performance of the ADC, and various techniques such as hysteresis, offset compensation, and input filtering are used to improve the performance of the comparator.

 

Dual Slope ADC: -

A dual-slope ADC (analog-to-digital converter) is a type of integrating ADC that is commonly used for low-speed and high-precision applications.

It works by integrating the input signal for a fixed period of time and then integrating a known reference voltage for a variable period of time until the integrator output returns to zero.

The process starts by resetting the integrator to zero and starting a fixed-duration integration of the input voltage.

At the end of this time period, the integrator output is transferred to a digital counter.

The counter is then enabled to count pulses from a clock source while the integrator integrates a known reference voltage.

The counter is stopped when the integrator output returns to zero, which occurs after a variable period of time that is determined by the value of the input voltage.

The digital output of the counter represents the value of the input voltage, and the integration time of the reference voltage is proportional to the input voltage.

This process of integrating the input voltage and the reference voltage for a fixed and variable duration, respectively, is called dual-slope integration.

Dual-slope ADCs are known for their high accuracy and low cost, but they are relatively slow and require a stable reference voltage.

They are widely used in applications such as digital mustimeters, data acquisition systems, and process control.

Successive ADC: -

A successive approximation ADC (analog-to-digital converter) is a type of ADC that is commonly used in medium- to high-speed applications.

It works by sequentially comparing the input voltage to a set of reference voltages and using a binary search algorithm to determine the digital output.

The conversion process starts by setting the most significant bit of the digital output to 1 and the other bits to 0.

The input voltage is compared to a reference voltage that is equal to half the maximum analog input voltage.

If the input voltage is greater than the reference voltage, the most significant bit is left at 1, and the next reference voltage is set to the sum of the previous reference voltage and half the remaining voltage range.

If the input voltage is less than the reference voltage, the most significant bit is set to 0, and the next reference voltage is set to the difference between the previous reference voltage and half the remaining voltage range.

This process is repeated for each bit of the digital output, with the reference voltage being adjusted based on the previous comparison result.

The result is a binary code that represents the input voltage with a resolution that is determined by the number of bits used in the ADC.

Successive approximation ADCs are known for their high speed, high resolution, and low power consumption.

They are widely used in applications such as data acquisition systems, medical equipment, and digital audio.

 

 Analog to Digital Computer Part-01

 Digital to Analog Convertor Part-2