In a successive approximation ADC:a)SAR register is a shift registerb)...
Successive Approximation type DVM:
- The successive approximation type digital voltmeter works on the principle of balancing the weights in a simple balance.
- To understand the concept clearly, let us consider whether we want to
- measure the weight of some unknown quantity of sugar.
- What do we do? First, we approximate the weight of sugar to some known weight,
- If the weight of sugar is more than the known weight, then we add some more weight to the known weight.
- If it is less, then we replace the weight with a lesser value.
- This process is repeated until the pointer balances the two weights.
- The successive approximation type DVM uses the same principle.
- A simple block diagram of SADVM is given below

An elaborated block diagram of SADVM is given below

- Consists of an input attenuator for selecting the desired range of input voltage and also to attenuate any noise in the given voltage.
- Selected input is applied to the comparator through a sample and holds circuit.
- The successive approximation register (SAR) receives its 8-bit input from the ring counter after each clock pulse.
- This input is applied to the Digital to Analog Converter (DAC) which converts the digital data into an analog voltage.
- This voltage is applied as a second input to the comparator.
- The output of the AND gate goes high when there is a positive o/p at the comparator.
- Finally, the digital output is taken out from the successive approximation register with input voltages other than dc; the input level changes during digitization, and decisions made during conversion are not consistent.
- To avoid this error, a sample and hold circuit is used and placed in the input directly following the input attenuator.
- This digital voltmeter is capable of 1000 readings per second.
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In a successive approximation ADC:a)SAR register is a shift registerb)...
Explanation:
Successive Approximation ADC:
Successive Approximation Register (SAR) is an important component in a Successive Approximation ADC. It is used to generate the input to the Digital-to-Analog Converter (DAC) by changing bits one by one from the Most Significant Bit (MSB) to the Least Significant Bit (LSB) in order to approximate the analog input voltage.
Function of SAR register:
The SAR register acts as a binary up counter in a Successive Approximation ADC. It starts by setting the MSB to 1 and then successively tests each bit by changing it from 1 to 0 and back to 1 based on the comparison of the DAC output with the input voltage. This process continues until all the bits have been tested and the closest digital representation of the analog input voltage is achieved.
Binary Search Algorithm:
The operation of the SAR register in a Successive Approximation ADC can be likened to a binary search algorithm. By successively changing the bits from MSB to LSB, the SAR register narrows down the possible range of the input voltage until the closest digital approximation is found. This iterative process allows for a high-speed and accurate conversion of analog signals to digital values.
Conclusion:
In summary, the SAR register in a Successive Approximation ADC is a crucial component that performs a binary search algorithm to approximate the analog input voltage. By changing bits one by one from the MSB to the LSB, the SAR register generates the input to the DAC and facilitates the conversion process with high speed and accuracy.