Free Bachelor of Electrical Engineering Digital Circuits Questions and Answers — Questions and Answers

Question 1: What exactly is digital electronics?

Engineering of devices that digital signal
Engineering of devices that produce digital signal
Field of electronics involving the study of digital signal
All pf the mentioned (Correct answer)

Correct answer: All pf the mentioned

Digital electronics is a comprehensive field that involves the study, design, and application of electronic circuits that process digital signals. This includes the engineering of devices capable of producing, manipulating, and interpreting these discrete signals. Consequently, all the mentioned aspects—engineering devices that handle, produce, and involve the study of digital signals—accurately define digital electronics.

Question 2: What statement about digital circuits is accurate?

Use transistors to create logic gates to perform Boolean logic
Easier to perform error detection and correction with digital signal
Less susceptible to noise or degradation in quality
All of the mentioned (Correct answer)

Correct answer: All of the mentioned

Digital circuits fundamentally use transistors as switches to implement logic gates, which perform Boolean logic operations. Their discrete nature (typically 0s and 1s) makes them less susceptible to noise and degradation compared to analog signals, as they only need to distinguish between distinct voltage levels. This characteristic also simplifies the implementation of error detection and correction mechanisms, enhancing data reliability.

Question 3: What exactly is a circuit?

Closed-loop through which Neutrons can pass
Open-loop through which electrons can pass
Closed-loop through which electrons can pass (Correct answer)
None of the mentioned

Correct answer: Closed-loop through which electrons can pass

An electrical circuit is defined as a closed-loop path that allows for the continuous flow of electric current. For current to exist, charge carriers (typically electrons) must be able to move from a region of higher potential to lower potential without interruption. An open loop would break this path, preventing sustained electron flow.

Question 4: Which of the following is a digital electronic example?

Digital cameras
Computers
Information appliances
All of the mentioned (Correct answer)

Correct answer: All of the mentioned

Digital electronics deals with devices that process information in discrete, binary formats. Digital cameras capture and store images as digital data, computers operate entirely on digital instructions and data, and information appliances like smartphones are essentially specialized digital computing devices. All these examples fundamentally rely on digital circuits and principles for their operation.

Question 5: What kind of circuit is a digital logic circuit?

Sequential logic circuits
Combinational logic circuits
Both Combinational & Sequential logic circuits (Correct answer)
None of the mentioned

Correct answer: Both Combinational & Sequential logic circuits

Digital logic circuits are broadly classified into two main types: combinational and sequential. Combinational circuits produce outputs based solely on current inputs, while sequential circuits incorporate memory elements (like flip-flops) and their outputs depend on both current and past inputs. Most complex digital systems integrate both combinational elements (e.g., adders) and sequential elements (e.g., counters, registers) to perform their functions.

Question 6: Which of the following alternatives belongs to the digital electronics non-saturated logic family?

Diode – Transistor Logic
High-Threshold Logic
Integrated – injection Logic
Emitter – coupled Logic (Correct answer)

Correct answer: Emitter – coupled Logic

Non-saturated logic families are designed to prevent transistors from entering the saturation region, which significantly reduces switching time and increases operating speed. Emitter-Coupled Logic (ECL) achieves this by using a differential amplifier configuration and operating transistors in the active region, making it the fastest logic family among the options. Other families like DTL, HTL, and IIL typically allow transistors to saturate, leading to slower operation.

Question 7: What does a switching function with several outputs in digital electronics go by?

Multiple-output function
Multi-gate function
Multi-output function (Correct answer)
Multiple-gate function

Correct answer: Multi-output function

In digital electronics, a switching function describes the logical relationship between inputs and outputs of a circuit. When a single logic circuit or system is designed to produce multiple distinct outputs based on its inputs, it is accurately termed a 'multi-output function.' This terminology directly reflects the characteristic of having more than one output signal.

Question 8: Which IC feature in digital circuits corresponds to the switching time of a certain transistor?

Fan – in
Propagation delay (Correct answer)
Fan – out
Power dissipation

Correct answer: Propagation delay

Propagation delay is a critical IC feature that quantifies the time required for a signal to travel from the input of a logic gate to its output. This delay directly corresponds to the inherent switching time of the transistors within the gate, as it represents the time taken for the transistors to respond and change state in response to an input transition. Other parameters like fan-in, fan-out, and power dissipation describe different operational characteristics.

Question 9: When in digital electronics can one logic gate drive numerous other logic gates?

When its output impedance is low and the input impedance is high (Correct answer)
When its output impedance is low and the input impedance is low
When its output impedance is high and the input impedance is high
When its output impedance is high and the input impedance is low

Correct answer: When its output impedance is low and the input impedance is high

For a logic gate to drive multiple other gates (high fan-out), it must be able to supply sufficient current without significant voltage drop and draw minimal current from the preceding stage. A low output impedance allows the driving gate to efficiently deliver current to multiple loads, while a high input impedance of the driven gates ensures each draws very little current, minimizing the overall load on the driving gate. This combination maximizes the number of gates that can be driven reliably.

Question 10: Which of the subsequent digital logic circuits can add more than one bit at a time? Which of the subsequent digital logic circuits can add more than one bit at a time?

Serial adder
Half – adder
Full – adder
Ripple – carry adder (Correct answer)

Correct answer: Ripple – carry adder

A ripple-carry adder is a digital logic circuit constructed by chaining multiple full-adder circuits together. Each full-adder adds one bit along with a carry-in, and the carry-out 'ripples' to the next stage. This architecture allows the circuit to add more than one bit at a time, making it suitable for multi-bit addition, unlike half-adders or single full-adders which handle only one bit at a time.

Question 11: Which gates in digital circuits are necessary to transform a NOR-based SR latch into an SR flip-flop?

Two 3 input OR gates
Two 2 input AND gates (Correct answer)
Two 3 input OR gates
Two 2 input OR gates

Correct answer: Two 2 input AND gates

An SR latch is an asynchronous device, meaning its state can change immediately with input changes. To convert it into a synchronous SR flip-flop, a clock input is needed to control when state changes can occur. This is typically achieved by adding two 2-input AND gates at the S and R inputs of the NOR-based SR latch, where the clock signal enables these AND gates, allowing S and R to affect the latch only when the clock is active.

Question 12: When does a flip-flop in digital electronics change state after being triggered by a negative level?

When the inputs are all one
When the inputs are all zero
When the clock is positive
When the clock is negative (Correct answer)

Correct answer: When the clock is negative

A flip-flop described as 'triggered by a negative level' or 'negative edge-triggered' will only change its state when the clock signal is at a low voltage level or transitions from high to low. If it is level-triggered, it will respond to its inputs as long as the clock is negative. Therefore, the state change occurs specifically when the clock is negative.

Question 13: Which of the following alternatives best describes an S-R flip flop's synchronous control inputs?

Clock
S
R
Both S and R (Correct answer)

Correct answer: Both S and R

In an S-R (Set-Reset) flip-flop, S and R are the primary synchronous control inputs. These inputs determine the desired next state of the flip-flop (setting it to 1 or resetting it to 0) when the clock signal is active. The clock input itself synchronizes the operation, but S and R provide the specific command for the state change.

Question 14: What is required in order to cause a change in the flip flop in addition to synchronous control inputs?

Previous output
0
1
Clock (Correct answer)

Correct answer: Clock

A flip-flop is a synchronous sequential circuit, meaning its state changes are synchronized to a clock signal. While synchronous control inputs (like S, R, or D) determine the intended next state, the actual change in the flip-flop's output only occurs in response to an active transition (edge or level) of the clock signal. Therefore, the clock is essential for enabling and timing any state change.

Question 15: Which of the following factors mostly affects how many emitters a TTL digital circuit has?

Noise immunity
Propagation delay
Fan – out
Fan – in (Correct answer)

Correct answer: Fan – in

In Transistor-Transistor Logic (TTL) circuits, the input stage often utilizes a multi-emitter transistor. The number of emitters on this input transistor directly dictates the number of inputs the logic gate can accept. This characteristic, representing the maximum number of inputs a gate can handle, is defined as its fan-in.

Question 16: If the clock is low and D = 0, what will the output of a D flip-flop be?

1
0
Toggle between 0 and 1
No change (Correct answer)

Correct answer: No change

A D flip-flop is a synchronous device, meaning its output (Q) can only change state on the active edge of the clock signal (either positive or negative edge, depending on its design). If the clock is low, the flip-flop is in a 'hold' state, and its output will retain its previous value, regardless of the current state of the D input. Thus, there will be no change in the output.

Free Bachelor of Electrical Engineering Digital Circuits Questions and Answers

What exactly is digital electronics?