ISRO ECE 2016 | Digital logic

Question

Which shift register counter requires the most decoding circuitry?

• A. Johnson Counter
• B. Ring Counter
• C. Ripple Counter
• D. $\text{MOD}$ counter

Answer 1

As far as i know Ripple counter may require maximum decoding ckt.

A johnson counter divides the clk by the factor of 2N where N is no. Of ff required.

A ring counter can also be worked out be a simple shift register. And work synchronously.

A ripple counter however requires maximum propagation delay for counting therefore increasing the number of ckt for every count exceeded.

Answer 2

Ripple counters require less complex circuit than synchronous counters. So lets look at Johnson and ring counters which are synchronous. Out of both, Johnson counter is more complex.

Answer 3

 

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A. Johnson Counter

• Also known as twisted ring counter.

• Requires less decoding circuitry than a ripple counter.

• Each state is unique and has a pattern that makes decoding relatively simple.

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B. Ring Counter

• A type of shift register where the output of the last flip-flop is fed to the input of the first.

• Requires minimal decoding, since only one flip-flop is high at any time.

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C. Ripple Counter 

• Asynchronous counter where each flip-flop triggers the next.

• The outputs are in binary, but due to its asynchronous nature, decoding intermediate or specific states requires more complex logic to account for propagation delays.

• Also, decoding specific binary states typically involves more logic gates.

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D. Counter

• This is a generic term and not specific enough. Could refer to any of the above.

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Correct Answer: C. Ripple Counter — because it typically requires the most decoding circuitry to identify specific states reliably.