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Choose the correct alternatives (more than one may be correct) and write the corresponding letters only:

Advantage of synchronous sequential circuits over asynchronous ones is:

  1. faster operation
  2. ease of avoiding problems due to hazards
  3. lower hardware requirement
  4. better noise immunity
  5. none of the above
asked in Digital Logic by Veteran (59.5k points)
edited by | 3.1k views
+2
0
Which book contains these details? How am I supposed to search for EVERYTHING (research papers and other stuff - as described in the answers) during my preparation...? How do I know which papers are really important ?

2 Answers

+13 votes
Best answer

Synchronization means less chance of hazards but can only increase the delay. So, synchronous circuits cannot have faster operation than asynchronous one but it is easier to avoid hazards in synchronous circuits. So, (A) is false and (B) is true.

(C) is false if we don't consider how to avoid the hazards in asynchronous circuits.

(D) Is not necessarily true - often asynchronous circuits have better noise immunity. Reasons are given here: http://www.cs.columbia.edu/~nowick/async-applications-PIEEE-99-berkel-josephs-nowick-published.pdf

https://en.wikipedia.org/wiki/Asynchronous_circuit

answered by Veteran (355k points)
edited by
+7
  • In asynchronous circuits, local signaling eliminates the need for global synchronization which exploits some potential advantages in comparison with synchronous ones. They have shown potential specifications in low power consumption, design reuse, improved noise immunity and electromagnetic compatibility. Asynchronous circuits are more tolerant to process variations and external voltage fluctuations.

Found this from wiki page you mentioned. Please give source for Point (d)

+2

better noise immunity  is not an advantage of  synchronous sequential circuits

Read this paper 

" Asynchronous circuits seem to be a good candidate to alleviate the problems originated by simultaneous switching noise. However, they are also more sensitive than synchronous ones to spurious signal transitions and delay variations produced by crosstalk noise ...." 
 

+10

option A is wrong , why so because ---> asynchronous circuits can be faster than synchronous circuits,

............." In asynchronous circuits, there is no clock, and the state of the circuit changes as soon as the input changes. Since they don't have to wait for a clock pulse to begin processing inputs, asynchronous circuits can be faster than synchronous circuits, and their speed is theoretically limited only by the propagation delays of the logic gates. so option a in this qs is wrong .

and option B is True because --> If transitions on two inputs arrive at almost the same time, the circuit can go into the wrong state depending on slight differences in the propagation delays of the gates. This is called a race condition or hazard situation . In synchronous circuits this problem is " less severe" because race conditions can only occur due to inputs from outside the synchronous system .... see here https://en.wikipedia.org/wiki/Asynchronous_circuit#Synchronous_vs_asynchronous_logic 

0
what about hardware requirement and noise immunity?
0

(c) is false if we don't consider how to avoid the hazards in asynchronous circuits. 
 

D) is also False , as better noise immunity  is not an advantage of  synchronous sequential circuits .

Reference: 

[1]  Click here 

0
@arjun sir

Same question asked in isro 2017

But option B is not given

Options given are

A. Lower hardware requirement

B. Better noise immunity

C. Faster Operation

D. All of the above

So, may be more than one options are correct in this question

and faster operation is also correct answer
+1
I think No option is correct.
+1

.......

+1

@yes

The snap you posted have no relation with Asynchronous Circuit .

"Most digital devices today use synchronous circuits. However asynchronous circuits have the potential to be faster, and may also have advantages in lower power consumption, lower electromagnetic interference, and better modularity in large systems."

Read the first paragraph here ->  https://en.wikipedia.org/wiki/Asynchronous_circuit 

Also search for this line too " Since asynchronous circuits don't have to wait for a clock pulse to begin processing inputs, they can be faster than synchronous circuits, and their speed is theoretically limited only by the propagation delays of the logic gates.  " 

So combining all these is it not clear that Asynchronous circuit is faster than synchronous circuit ?

+1

Option D " better noise immunity" is NOT TRUE/ Not a correct option 

This paper  says  "Asynchronous circuits seem to be a good candidate to alleviate ( means reduce ) the problems originated by simultaneous switching noise.  However, they are also more sensitive than synchronous ones to spurious signal transitions .... "

This line means asynchronous circuits are better to handle noise than synchronous circuits

. So option D is not true here.. as question asked Advantage of synchronous sequential circuits over asynchronous one .

0

However, they are also more sensitive than synchronous ones to spurious signal transitions

0

yes Asynchronous circuits are more sensitive than synchronous ones , here more sensitive means Asynchronous circuits  are quick to detect or respond to slight changes in signals than synchronous circuits.

+1

Proof for option D is also False

+1

@Bikram Yes, I was wrong -- corrected now. Also, this paper shows it. 

http://www.cs.columbia.edu/~nowick/async-applications-PIEEE-99-berkel-josephs-nowick-published.pdf

0

@Arjun sir,

Can you share some reference for 

Synchronization means less chance of hazards but can only increase the delay. 

?

0
is false if we don't consider how to avoid the hazards in asynchronous circuits......... meaning??

I am not able to comprehend it.
+2 votes

Correct option is B, 

ease of avoiding problems due to hazards

option B is True because --> If transitions on two inputs arrive at almost the same time, the circuit can go into the wrong state depending on slight differences in the propagation delays of the gates. This is called a race condition or hazard situation . In synchronous circuits this problem is " less severe" because race conditions can only occur due to inputs from outside the synchronous system .... see here https://en.wikipedia.org/wiki/Asynchronous_circuit#Synchronous_vs_asynchronous_logic 

And option A, C and D all are false...

answered by Veteran (67.9k points)
0
@Bikram Sir.

1. You said that in asynchronous we dont have clock operation.

But If i consider the case of counters.Now asynchronous counters are slower than synchronous counters as in asynchronous counters the clock is cascaded.

2. How synchronous will handle hazards easily?By hazards i am assuming static hazard.If i am not covering any adjacent group of minterms then hazards are possible. I think hazards are dependent upon the expresion that i am implementing in the circuit irrespective of synchronous or async ?


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