The parallel adder which we use in the digital circuits ,the carry output of each full adder stage is connected to the carry input of the next higher order stage.therefore,the sum and carry outputs of any stage cannot be produced until the input carry occurs;
This leads to a time delay in the addition process.This delay is known as carry propagation delay.
to the second question the propagation delay can be avoided in the binary parallel adder with the help of look ahead carry generator
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time delay
relatively large propagation delay.
Two half adders, an OR gate, and a delay.
Propagation Delay In digital logic, every gate has got some finite amount of delay because of which the change in the output is not instantaneous to the change in the input. In simple terms, the times it takes for an input to appear at the output is called the propagation delay. In Figure 6, tPHL, describes the time it takes for an input to cause the output to change from logic-level-high to logic-level-low. Similarly, tPLH, refers to the delay associated when an input change causes the output to change from logic-level-low to logic-level-high. The overall delay is average of these two delays.
The main criterion for the design of digital circuits is to simplify your circuit so you don't get to use so many circuit elements there by improving upon the propagation delay of the circuit in effect.
You use a look ahead carry adder to reduce the propagation delay effects caused by the ripple carry that would otherwise be used. With ripple carry, each stage is dependent on the preceding stage, and this is cumulative. With look ahead carry, the carries are computed in parallel, speeding up the overall process.
You use a look ahead carry adder to reduce the propagation delay effects caused by the ripple carry that would otherwise be used. With ripple carry, each stage is dependent on the preceding stage, and this is cumulative. With look ahead carry, the carries are computed in parallel, speeding up the overall process.
Another name for propagation delay is latency.
time delay
Propagation delay is the time it takes for electronic devices to switch from one logic state to another.
The primary disadvantage of a ripple carry adder is its speed, as it suffers from propagation delay. In this architecture, each bit of the sum must wait for the carry bit from the previous stage, leading to a cumulative delay that increases with the number of bits. Consequently, for larger bit-width adders, this can result in slower overall performance, making ripple carry adders less suitable for high-speed applications. Additionally, the increased delay can limit the maximum clock frequency of the circuit.
Processing delay Queuing delay Transmission delay Propagation delay
TTL
A full adder has three inputs - A, B, and CarryIn from the prior stage. It generates a Result and a Carryout with the truth table... ABC-RC 000-00 001-10 010-10 011-01 100-10 101-01 110-01 111-11 The adder can be a ripple adder, in which the propogation delay depends on the carry "rippling" through the logic, or it can be a look-ahead-carry type, which has constant propagation delay time, at the expense of more logic.
propagation delay in the ring/transmission delay of the packet<1
it is in micro seconds
relatively large propagation delay.