All questions of Data Selectors and Multiplexers for Electrical Engineering (EE) Exam

1-to-4 Demultiplexer:
A 1-to-4 demultiplexer is a digital circuit that takes one input signal and selects one of the four output channels based on the control signals. It is the opposite of a multiplexer, which takes multiple input signals and selects one output channel.

Working of a 1-to-4 Demultiplexer:
A 1-to-4 demultiplexer has one input line and four output lines. The number of select lines determines the number of output channels and the corresponding decoder logic. Each select line enables one of the four output channels.

Number of Select Lines:
The number of select lines required in a 1-to-4 demultiplexer can be determined by the formula 2^n, where 'n' is the number of select lines. In this case, we have four output channels (2^2 = 4), so the number of select lines required is '2'.

Explanation:
To understand why the correct answer is option 'A' (2 select lines), let's consider the truth table of a 1-to-4 demultiplexer.

Truth Table:
| S1 | S0 | D0 | D1 | D2 | D3 |
|----|----|----|----|----|----|
| 0 | 0 | I | 0 | 0 | 0 |
| 0 | 1 | 0 | I | 0 | 0 |
| 1 | 0 | 0 | 0 | I | 0 |
| 1 | 1 | 0 | 0 | 0 | I |

In the truth table above, 'S1' and 'S0' are the select lines, 'I' is the input signal, and 'D0', 'D1', 'D2', and 'D3' are the output signals.

Analysis:
From the truth table, we can observe that:
- When 'S1' and 'S0' are both '0', the input signal 'I' is transmitted to the output line 'D0'.
- When 'S1' is '0' and 'S0' is '1', the input signal 'I' is transmitted to the output line 'D1'.
- When 'S1' is '1' and 'S0' is '0', the input signal 'I' is transmitted to the output line 'D2'.
- When 'S1' and 'S0' are both '1', the input signal 'I' is transmitted to the output line 'D3'.

Conclusion:
From the above analysis, it is clear that with two select lines, we can control the selection of one of the four output channels. Thus, the correct answer is option 'A' (2 select lines) for a 1-to-4 demultiplexer.

Answer:

To understand the answer to this question, let's first discuss the basic concept of a digital multiplexer.

A digital multiplexer, also known as a data selector, is a combinational circuit that selects one of many input signals and routes it to a single output line based on the control inputs. It is widely used in various electronic applications, such as data transmission, signal routing, and digital communication systems.

A multiplexer can have multiple inputs, outputs, and selection lines. The selection lines determine which input signal gets routed to the output line. The number of selection lines in a multiplexer is determined by the number of input lines and is given by the equation:

n = log2(N)

Where n is the number of selection lines and N is the number of input lines. For example, if we have 4 input lines, we would need 2 selection lines (n = log2(4) = 2).

In the given question, it is mentioned that an enable or strobe input undergoes an expansion of two or more multiplexer ICs. This means that multiple multiplexer ICs are cascaded together to form a larger multiplexer.

When multiple multiplexer ICs are cascaded, the enable or strobe input of each IC is connected in parallel. This allows the enable or strobe input to control the operation of all the cascaded ICs simultaneously.

By expanding the multiplexer using multiple ICs, we can increase the number of inputs that can be selected. Each IC will have a certain number of inputs, outputs, and selection lines. By cascading multiple ICs together, we can effectively increase the number of inputs of the multiplexer.

However, it is important to note that the number of outputs and selection lines remains the same, as these are determined by the individual ICs. Only the number of inputs can be increased by cascading multiple ICs.

Therefore, the correct answer to the given question is option 'A' - Inputs.

Explanation:

A multiplexer is a device that combines multiple signals into one output signal. It is also known as a data selector, as it selects one of several input signals and forwards the selected signal to the output. The number of input signals can be two or more, and the selection of the input signal can be done through a control signal.

Working Principle:

The working principle of a multiplexer is based on the Boolean expression. A multiplexer has n input lines and one output line. The control signal selects which input to send to the output. The control signal is converted into a binary number, which is used to select one of the input lines.

Types of Multiplexers:

There are different types of multiplexers, including:

1. 2:1 Multiplexer: It has two input lines and one output line.

2. 4:1 Multiplexer: It has four input lines and one output line.

3. 8:1 Multiplexer: It has eight input lines and one output line.

Applications:

Multiplexers are used in various applications, including:

1. Communication systems: Multiplexers are used in communication systems to combine multiple signals into a single output signal.

2. Computer memory: Multiplexers are used in computer memory to select a particular memory cell.

3. Data transmission: Multiplexers are used in data transmission systems to select a particular data stream.

4. Digital circuit design: Multiplexers are used in digital circuit design to select an input signal based on a control signal.

Conclusion:

In conclusion, a multiplexer is a device that combines multiple signals into one output signal. It is widely used in various applications, including communication systems, computer memory, data transmission, and digital circuit design.

Series to Parallel Converter:
A series to parallel converter is a circuit that takes a series input and converts it into a parallel output. This type of converter is commonly used in various applications where the input needs to be distributed to multiple outputs.

Options:
a) Encoder: An encoder is a circuit that converts multiple inputs into a coded output. It is used in applications such as data compression, error detection, and data transmission. It does not perform the function of converting a series input into a parallel output, so it cannot be used as a series to parallel converter.

b) Decoder: A decoder is a circuit that performs the reverse operation of an encoder. It takes a coded input and converts it into multiple outputs. Like an encoder, it does not convert a series input into a parallel output, so it cannot be used as a series to parallel converter.

c) De-multiplexer: A de-multiplexer, also known as a demux, is a circuit that takes a single input and directs it to one of several outputs based on control signals. It has multiple outputs, making it suitable for converting a series input into a parallel output. Therefore, a de-multiplexer can be used as a series to parallel converter.

d) Multiplexer: A multiplexer, also known as a mux, is a circuit that combines multiple inputs into a single output based on control signals. It does not convert a series input into a parallel output, so it cannot be used as a series to parallel converter.

Conclusion:
The correct option is c) De-multiplexer, as it can be used as a series to parallel converter by directing a series input to multiple parallel outputs based on control signals.

The major functioning responsibility of a multiplexing combinational circuit is the generation of a selected path between multiple sources and a single destination. Let's break down this answer in detail:

1. What is a multiplexing combinational circuit?
A multiplexing combinational circuit is a digital circuit that allows multiple input signals to be transmitted over a single transmission line or channel. It uses a combination of logic gates to select and route the desired input signal to the output.

2. Understanding the options:
a) Decoding the binary information:
Decoding refers to the process of converting a binary code into a more meaningful form. While decoding can be a part of the multiplexing process, it is not the major functioning responsibility of the circuit.

b) Generation of all minterms in an output function with OR-gate:
A minterm is a product term in Boolean algebra that represents a specific combination of input variables. While generating minterms can be a part of the multiplexing process, it is not the major functioning responsibility of the circuit.

c) Generation of selected path between multiple sources and a single destination:
This is the correct answer. The main purpose of a multiplexing combinational circuit is to select and route the desired input signal to a single output destination. It allows multiple sources to share a common transmission line or channel, enabling efficient communication.

d) Encoding of binary information:
Encoding refers to the process of converting meaningful data into a coded form. While encoding can be a part of the multiplexing process, it is not the major functioning responsibility of the circuit.

3. Importance of selecting a path:
In many applications, especially in communication systems, there is a need to transmit multiple signals over limited resources. Multiplexing allows efficient utilization of these resources by selecting and routing the desired signals to their respective destinations. By choosing the appropriate path, the multiplexing combinational circuit ensures that the desired signal reaches the destination without interference or loss.

4. How the circuit works:
The multiplexing combinational circuit uses logic gates, such as AND gates and OR gates, to select the desired input signal based on control signals. These control signals determine which input signal is routed to the output. By manipulating the control signals, different input signals can be selected and transmitted at different times, effectively sharing the transmission line or channel.

In conclusion, the major functioning responsibility of a multiplexing combinational circuit is to generate a selected path between multiple sources and a single destination. It allows efficient utilization of resources and enables the transmission of multiple signals over a common transmission line or channel.

IC 74154 is used for the implementation of 1-to-16 DEMUX.

Explanation:
1-to-16 DEMUX is a digital circuit which takes one input and distributes it across the 16 output lines based on the input binary address. It is used in various applications such as memory addressing, data routing, and selection of input/output lines.

IC 74154 is a 4-to-16 decoder/demultiplexer IC with active-low outputs. It has 4 select inputs (A, B, C, D) and 16 output lines. Each output line corresponds to a unique combination of the select inputs. When a particular combination of select inputs is enabled, the corresponding output line goes low while all other output lines remain high.

To implement a 1-to-16 DEMUX using IC 74154, we can connect the input to one of the select inputs (e.g. A) and tie the remaining select inputs (B, C, D) to ground. This enables the output line corresponding to the input address (A=1) while keeping all other output lines high.

Therefore, IC 74154 is the correct choice for implementing a 1-to-16 DEMUX due to its multiple output lines and select inputs, making it suitable for addressing and routing applications.

The IC 74LS138 is an 8-line demultiplexer. Let's break down the answer and understand why option 'B' is the correct answer.

1. What is a demultiplexer?
- A demultiplexer, also known as a demux, is a combinational logic circuit that takes a single input and distributes it to one of several possible outputs based on the control signals.

2. Understanding the IC 74LS138:
- The IC 74LS138 is a specific type of demultiplexer that is commonly used in digital circuits.
- It has 3 input pins, A, B, and C, which are used to select the output line.
- The demultiplexer has 8 output pins, Y0 to Y7, which correspond to 8 possible outputs.
- The demultiplexer also has an active low enable input, called E1, which is used to enable or disable the demultiplexer operation.

3. Function of the IC 74LS138:
- The demultiplexer takes in a 3-bit binary input (A, B, and C) and uses these inputs to select one of the 8 output lines.
- The selected output line is then activated, while all other output lines remain inactive.
- The demultiplexer operates based on the combination of the input signals and the enable input.
- When the enable input (E1) is low (0), the demultiplexer is enabled and the selected output line is activated.
- When the enable input is high (1), the demultiplexer is disabled and none of the output lines are activated.

4. Applications of the IC 74LS138:
- The demultiplexer is widely used in digital circuits for various applications such as data routing, address decoding, memory interfacing, and signal distribution.
- It is commonly used in microprocessors and microcontrollers to decode address lines and select specific memory or peripheral devices.
- It can be used to implement complex logic functions by combining multiple demultiplexers.

In conclusion, the IC 74LS138 is an 8-line demultiplexer that takes a 3-bit binary input and selects one of the 8 output lines based on the input signals and the enable input. It is widely used in digital circuits for various applications including address decoding and data routing.

The function of an enable input on a multiplexer chip is to activate or deactivate the entire chip. When the enable input is high (or active), the multiplexer chip is enabled and can perform its intended function. On the other hand, when the enable input is low (or inactive), the multiplexer chip is disabled and its outputs are in a high-impedance state.

When the enable input is active, the multiplexer chip acts as a data selector, allowing one of multiple inputs to be selected and routed to the output. The selection of the input is determined by the control inputs of the chip.

Below is a detailed explanation of the function of the enable input on a multiplexer chip:

1. Multiplexer Basics:
- A multiplexer, also known as a data selector, is a digital circuit that selects one of many inputs and routes it to a single output.
- It is commonly represented by the symbol ⊕ or MUX.

2. Enable Input:
- The enable input on a multiplexer chip is denoted as EN or E, and it controls the activation of the chip.
- The enable input is typically an active-high input, meaning that when it is high (logic 1), the chip is enabled.

3. Chip Activation:
- When the enable input is active (high), the multiplexer chip is enabled and can perform its function.
- The chip becomes operational, and its outputs are determined by the control inputs and the selected input.
- The selected input is determined by the control inputs, such as address lines or select inputs.

4. Chip Deactivation:
- When the enable input is inactive (low), the multiplexer chip is disabled.
- The chip enters a high-impedance state, which means that its outputs are effectively disconnected and do not drive any signal.
- This high-impedance state prevents any interference or conflicts with other circuitry that may be connected to the outputs of the disabled chip.

5. Usefulness of Enable Input:
- The enable input is useful in applications where the activation or deactivation of the multiplexer chip needs to be controlled.
- It allows for greater flexibility in circuit design by providing the ability to enable or disable the chip as needed.

In summary, the enable input on a multiplexer chip is responsible for activating or deactivating the entire chip. When the enable input is high, the chip is enabled and can perform its function of selecting and routing one of multiple inputs to the output. When the enable input is low, the chip is disabled, and its outputs are in a high-impedance state.