This question was asked inGPSC Deputy Executive Engineer (Electrical) Class-2 Master Paper 2026Question 63 of 195 published · Gujarat Public Service CommissionOpen paper
Q63EasyCombinational Circuits

Consider the following statements regarding Decoder circuit:
1. Decoder converts binary input into one-hot output activating only one output line.
2. It can be used for function generation and memory addressing operations.
3. All outputs of decoder remain active simultaneously during operation.
Which of the above statements is/are correct?

Answer & step-by-step solution
Correct answer: C. 1 and 2 only
Quick explanation

A decoder maps an n-bit code to one of up to 2^n output lines, commonly as a one-hot output. Decoders are used in memory/address selection and can implement minterm-based logic functions. Key relation: n inputs → up to 2^n decoded outputs.

Exam focus: Only the selected output is asserted in ideal one-hot decoding. Common trap: All decoder outputs are not active simultaneously.

n inputs → up to 2^n decoded outputs.

Statement-wise Verification

  • Statement 1 - Correct.
    Decoder converts binary input into one-hot output activating only one output line.
    A decoder maps an n-bit code to one of up to 2^n output lines, commonly as a one-hot output.
  • Statement 2 - Correct.
    It can be used for function generation and memory addressing operations.
    Decoders are used in memory/address selection and can implement minterm-based logic functions.
  • Statement 3 - Incorrect.
    All outputs of decoder remain active simultaneously during operation.
    A conventional decoder asserts only the selected one-hot output (subject to active-high/low convention)

Core Concept

A decoder maps an n-bit code to one of up to 2^n output lines, commonly as a one-hot output. Decoders are used in memory/address selection and can implement minterm-based logic functions.

Formula / Key Relationship

n inputs → up to 2^n decoded outputs.

Why the Other Options Are Wrong

Option A is incorrect because it includes incorrect statement(s) 3 and omits correct statement(s) 2. Option B is incorrect because it includes incorrect statement(s) 3 and omits correct statement(s) 1. Option D is incorrect because it includes incorrect statement(s) 3.

Exam Shortcut / Approach

Only the selected output is asserted in ideal one-hot decoding.

Common Mistake

All decoder outputs are not active simultaneously.

Quick Revision

One-Hot Decoding and Addressing is linked with Decoders, Combinational Logic and Digital Electronics. Only the selected output is asserted in ideal one-hot decoding.

Exam tipOnly the selected output is asserted in ideal one-hot decoding.
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