Consider the following statements regarding combinational circuits : 1. A ripple carry adder is a parallel adder in which the carry-out of each full-adder is the carry-in to the next most significant adder. 2. Look-ahead carry adder speeds up the process by eliminating the end carry. 3. A priority encoder is a logic circuit that responds to just one input, in accordance with some priority system, among those that may be simultaneously HIGH. Which of the above statements are correct?
Combinational Circuits Statement Analysis
Let's evaluate each statement regarding combinational circuits:
Statement 1 Analysis: Ripple Carry Adder
Statement 1 describes a ripple carry adder as a parallel adder where the carry-out from one full-adder stage becomes the carry-in for the next more significant stage. This sequential carry propagation is the defining characteristic of a ripple carry adder. Thus, statement 1 is correct.
Statement 2 Analysis: Look-ahead Carry Adder
Statement 2 claims a look-ahead carry adder speeds up addition by "eliminating the end carry." While look-ahead carry adders significantly reduce carry propagation delay compared to ripple carry adders, the mechanism isn't described as "eliminating the end carry." Instead, they generate carry signals in parallel using logic that anticipates (looks ahead) the carry status based on input bits. This parallel generation reduces the delay inherent in waiting for the carry to ripple through all stages. The wording "eliminating the end carry" is imprecise and potentially misleading. Thus, statement 2 is incorrect.
Statement 3 Analysis: Priority Encoder
Statement 3 defines a priority encoder as a logic circuit that prioritizes multiple simultaneous HIGH inputs, activating only the output corresponding to the highest priority input. This is an accurate description of a priority encoder's function. Thus, statement 3 is correct.
Conclusion on Correct Statements
Based on the analysis:
- Statement 1 is correct.
- Statement 2 is incorrect.
- Statement 3 is correct.
Therefore, the correct statements are 1 and 3.
Important Questions from Combinational Circuits
Carry input is present in which of the following?
The time delay in a look-ahead carry adder is independent of
The characteristics of the combinational circuits are :
A. Output at any time is function of inputs at that time
B. Contains memory elements
C. Do not have feedback paths
D. Clock is used to trigger the circuits to obtain outputs
Choose the correct answer from the options given below :
Match the terms in List - I with the options given in List - II :
List - I
List – II
(a)
Decoder
(i)
1 line to 2 nlines
(b)
Multiplexer
(ii)
n lines to 2 nlines
(c)
De multiplexer
(iii)
2 nlines to 1 line
(iv)
2 nlines to 2 n−1 lines
Which of the following represents the borrow in a half subtraction?
