This section contains carefully selected MCQs and Previous Year Questions with explanations to help students understand concepts and prepare effectively for examinations, interviews, and competitive tests.
Q: 1A ripple counter is a(n) _____________ counter where only the ____________ flip-flop is clocked by an external clock.
Option C
A counter is a sequential digital circuit that counts the number of clock pulses received at its input.
Counters are widely used in digital systems for counting events, measuring frequency, generating timing signals, and many other applications. Counters are mainly of two types:
A Ripple Counter is a type of asynchronous counter in which the clock signal is applied only to the first flip-flop. The remaining flip-flops do not receive the external clock directly. Instead, each flip-flop is triggered by the output of the previous flip-flop.
Because the change in state travels from one flip-flop to the next like a ripple in water, it is called a Ripple Counter.
The word asynchronous means "not occurring at the same time." Since all flip-flops do not change simultaneously, the counter is called an asynchronous counter.
| Feature | Ripple (Asynchronous) Counter | Synchronous Counter |
|---|---|---|
| Clock Input | Only first flip-flop receives clock. | All flip-flops receive clock. |
| Speed | Slower. | Faster. |
| Propagation Delay | More. | Less. |
| State Change | One after another. | Simultaneous. |
| Circuit Complexity | Simple. | More complex. |
Q: 2The number of unused states in a 4-bit switch tail ring counter, (Johnson Counter) are
Option C
In a 4-bit Johnson counter (also called a switch-tail ring counter), the total number of possible states is 24=16. However, a Johnson counter produces only 2n unique states, where n is the number of flip-flops. For n=4, the number of valid states is 2×4=8. Therefore, the number of unused or invalid states is 16−8=8.
Q: 3If n flip-flops are used in a ripple counter, then it will count from __________ to __________.
Option B
A ripple counter is made up of flip-flops connected in series. Each flip-flop can store only one binary digit (bit), which can have two possible values: 0 or 1.
Because each flip-flop has two possible states, adding more flip-flops increases the total number of combinations that can be represented.
If a counter contains n flip-flops, then the total number of possible states is 2n. These states are counted starting from 0 because initially all flip-flops are reset.
Therefore, an n-bit ripple counter counts from 0 to (2n-1).
Example : 3-Bit Ripple Counter:
Counting Sequence:
| Binary | Decimal |
|---|---|
| 000 | 0 |
| 001 | 1 |
| 010 | 2 |
| 011 | 3 |
| 100 | 4 |
| 101 | 5 |
| 110 | 6 |
| 111 | 7 |
After 111, the counter returns to 000. Thus, the counting range is 0 to 7, i.e., 0 to (2n-1).
Q: 4In a 4-stage ripple counter, the propagation delay of a flip-flop is 50ns. If the pulse width of the strobe is 30ns, find the maximum frequency at which the counter operates reliably.
Option D
Q: 5How many unique states can a K-bit switch tail ring counter generate?
Option A
Q: 6How many decade counters are connected in cascade to count from 0 to 999?
Option D
Q: 7Which of the following statements is/are true about Ripple Counter?
1. It is an asynchronous counter.
2. Constitutes of Logic Gates and Flip-flops.
3. It is affected by propagation delay of Flip-flops.
4. Constitutes only Flip-flops.
5. It is affected by propagation delay of Flip-flops and Logic gates.
Option B
A Ripple Counter is a type of counter in which the output of one flip-flop serves as the clock input for the next flip-flop. Because the clock signal does not reach all flip-flops simultaneously, it is called an asynchronous counter.
Q: 8A MOD-16 ripple counter using J—K flip-flop has a current state 1001. How many clock pulses are required to get the state 0000?
(a) 8
(b) 6
(c) 7
(d) 5
Option C
A MOD-16 ripple counter is a 4-bit binary counter that counts from 0000 (0) to 1111 (15) and then repeats. Each clock pulse increases the count by 1.
The current state is 1001, which is 9 in decimal. To reach 0000, the counter must first count up to 1111 (15) and then roll over to 0000.
| Clock Pulses | Counter State | Decimal Value |
|---|---|---|
| Current State | 1001 | 9 |
| 1 | 1010 | 10 |
| 2 | 1011 | 11 |
| 3 | 1100 | 12 |
| 4 | 1101 | 13 |
| 5 | 1110 | 14 |
| 6 | 1111 | 15 |
| 7 | 0000 | 0 |
Therefore, 7 clock pulses are required to reach 0000.
Q: 9State whether the following statements are true or false.
(i) The JK flip-flop is a basic building block of combinational logic circuits.
(ii) In a ripple counter, if the uncomplemented output counts up, then the complemented output counts down.
Option C
Statement (i), "The JK flip-flop is a basic building block of combinational logic circuits." This statement is False.
A JK Flip-Flop is a memory device that can store one bit of information. Since it can remember its previous state, its output depends on:
Such circuits are called Sequential Circuits.
Examples of sequential circuits are:
On the other hand, Combinational Circuits do not have memory. Their output depends only on the current inputs.
Examples of combinational circuits are:
Therefore, JK Flip-Flop is a building block of Sequential Logic Circuits, not Combinational Logic Circuits.
Statement (ii), "In a ripple counter, if the uncomplemented output counts up, then the complemented output counts down." This statement is True.
Every flip-flop provides two outputs:
These outputs are always opposite to each other. If Q outputs count upward (0 to 2n-1), the Q̅ outputs count downward (2n-1 to 0).
You have reached the end of this topic. Continue learning with the next topic below.
Thank you so much for taking the time to read my Computer Science MCQs section carefully. Your support and interest mean a lot, and I truly appreciate you being part of this journey. Stay connected for more insights and updates! If you'd like to explore more tutorials and insights, check out my YouTube channel.
Don’t forget to subscribe and stay connected for future updates.
| Student Name | |
|---|---|
| College |
| What's Say |
|---|