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Combinational and Sequential Circuits

GATE CSE 2021 Set 2 · Q5

MCQ1 markEasy

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Which one of the following circuits implements the Boolean function given below? f(x,y,z)=m0+m1+m3+m4+m5+m6, where mi is the ith minterm.f(x, y, z) = m_0 + m_1 + m_3 + m_4 + m_5 + m_6\text{, where } m_i \text{ is the } i^{\text{th}} \text{ minterm.}

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Solution

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Official answer: A)

Combinational and Sequential Circuits

The given Boolean function is:

f(x,y,z)=∑m(0,1,3,4,5,6)f(x, y, z) = \sum m(0, 1, 3, 4, 5, 6)

In all given 4×14 \times 1 multiplexers, the select lines are s1=ys_1 = y and s0=zs_0 = z. The output of a 4×14 \times 1 multiplexer with select lines yy and zz is:

f=y′z′I0+y′zI1+yz′I2+yzI3f = y^{\prime}z^{\prime} I_0 + y^{\prime}z I_1 + yz^{\prime} I_2 + yz I_3

Let us determine the required inputs I0,I1,I2,I3I_0, I_1, I_2, I_3 as functions of xx:

  1. For yz=00yz = 00 (I0I_0): Minterms corresponding to yz=00yz = 00 are m0m_0 (x=0,y=0,z=0x=0, y=0, z=0) and m4m_4 (x=1,y=0,z=0x=1, y=0, z=0). Since both m0m_0 and m4m_4 are present in ff, I0=1I_0 = 1.

  2. For yz=01yz = 01 (I1I_1): Minterms corresponding to yz=01yz = 01 are m1m_1 (x=0,y=0,z=1x=0, y=0, z=1) and m5m_5 (x=1,y=0,z=1x=1, y=0, z=1). Since both m1m_1 and m5m_5 are present in ff, I1=1I_1 = 1.

  3. For yz=10yz = 10 (I2I_2): Minterms corresponding to yz=10yz = 10 are m2m_2 (x=0,y=1,z=0x=0, y=1, z=0) and m6m_6 (x=1,y=1,z=0x=1, y=1, z=0). Since m2m_2 is absent and m6m_6 is present, I2=xI_2 = x.

  4. For yz=11yz = 11 (I3I_3): Minterms corresponding to yz=11yz = 11 are m3m_3 (x=0,y=1,z=1x=0, y=1, z=1) and m7m_7 (x=1,y=1,z=1x=1, y=1, z=1). Since m3m_3 is present and m7m_7 is absent, I3=x′I_3 = x^{\prime}.

Thus, the required data inputs are:

I0=1,I1=1,I2=x,I3=x′I_0 = 1, \quad I_1 = 1, \quad I_2 = x, \quad I_3 = x^{\prime}

This configuration corresponds to Option (A).

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This Combinational and Sequential Circuits previous year question is Q5 of the GATE CSE 2021 Set 2 paper. Find more GATE CSE PYQs on Combinational and Sequential Circuits in Digital Logic, or browse all GATE CSE PYQs.

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Combinational and Sequential Circuits in GATE CSE

Combinational and Sequential Circuits has 32 GATE CSE PYQs across 22 papers from 2011 to 2026. 8 of them are 1-mark MCQs like this one, and GATE CSE 2021 Set 2 has 2.

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GateAI solution cardGATE CSE 2021 Set 2 · Q5 · MCQ

Which one of the following circuits implements the Boolean function given below? f(x, y, z) = m0 + m1 + m3 + m4 + m5 + m6, where mi is the ith minterm.

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