# VLSI Questions and Answers – LFSR-2

This set of VLSI online test focuses on “LFSR-2”.

1. Primitive polynomial should have a minimum number of zero coefficient.
a) true
b) false

Explanation: Primitive polynomials with a minimum number of zero coefficients are the desired characteristic polynomial for the LFSR.

2. The minimum number of EX-OR gates used is in between
a) 0 to 2
b) 1 to 3
c) 2 to 5
d) 3 to 7

Explanation: The minimum number of EX-OR gates used for the linear feedback shift register is in between 1 and 3.

3. The LFSR takes reasonable time if the n value is
a) below 50
b) below 100
c) below 10
d) below 25

Explanation: The LFSR’s degree value is limited to 22 to 25 for producing maximal length sequence in reasonable amount of time.

4. Which is used to initialize the LFSRs?
a) zeroes
b) ones
c) preset of flip-flop
d) EX-OR gate

Explanation: The preset of each flip-flop in LFSR to used to initialize the LFSRs and initial non-zero coefficient or state ensures maximal length sequence is obtained.

5. The beginning and end of the maximal length sequence can be determined using
a) AND gate
b) NAND gate
c) AND or NAND gate
d) Both AND and NAND gate

Explanation: The beginning and end of the maximal length sequence of the LFSR can be determined using AND gate or NAND gate.
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a) seeding
b) reseeding
c) deseeding
d) pre-seeding

Explanation: Initializing with a specific value to the LFSR is called as seeding and preloading different starting value is called as reseeding.

7. The primitive polynomial has a property according to which the runs of 1s ______ to runs of 0s.
a) equal
b) greater
c) lesser
d) not related

Explanation: The primitive polynomial has a property of randomness according to which the runs of 1s equal to runs of 0s.

8. The total number of runs is given mathematically as
a) 2n
b) 2(n-1)
c) 2(n+1)
d) 2n-1

Explanation: The total number of runs is given as 2(n-1) which is the total number of transitions from 1 to 0 or from 0 to 1.

9. ______ of the runs will have a length of 1.
a) one third
b) one fourth
c) half
d) one eight

Explanation: The length of the runs are distributed as – half of the runs have length 1, quarter with length 2, a eight length 3 and a sixteenth length 4 and so on.

10. The length of the runs is dependent on whether the LFSR is internal or external feedback.
a) true
b) false

Explanation: The length of the run is independent of whether the LFSR is internal or external feedback and LFSR is also known as pseudo random pattern generator.

11. Which process is used to develop the LFSR method?
a) random method
b) gaussian method
c) deterministic method
d) bernoulli method

Explanation: Bernoulli method is used in modelling the linear feedback shift register testing method and this is called as random pattern generation method.

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