Answer Key

1. A unidirectional signal flows in only one direction, either positive or negative, with a pulse signal being a key example. In contrast, a bidirectional signal alters in both positive and negative directions, crossing the zero point, as seen in a sinusoidal signal.
2. The three types of switches are mechanical, electromechanical (relays), and electronic. Mechanical switches have high inertia and can spark, while relays are faster and reduce sparking. Electronic switches, such as transistors, offer the highest operating speed and have no moving parts or sparking.
3. When a transistor is used as a switch, the cut-off region is its “OFF” state, where no collector current flows (ideally) and VCE equals VCC. The saturation region is its “ON” state, where the maximum collector current flows and the collector-emitter voltage (VCE) is ideally zero.
4. An Astable Multivibrator is a switching circuit that has no stable states and continuously switches between two quasi-stable states on its own. It is called a “Free-running Multivibrator” because it automatically and continuously generates a square wave output without needing any external trigger pulse.
5. Hysteresis in a Schmitt Trigger circuit means the output values depend on both the present and past values of the input. This is represented by a loop in its transfer characteristics, where the input voltage must cross a higher threshold (UTP) to switch high and a lower threshold (LTP) to switch low, preventing unwanted frequency switching.
6. “Trace” is the deflection of an electron beam over a screen, typically from left to right, as the sweep voltage increases linearly. “Retrace,” or “Fly back,” is the rapid return of the beam from the right side back to its starting point on the left.
7. The defining characteristic of a UJT’s V-I curve is the region where an increase in emitter current results in a decrease in emitter voltage. This property is known as “negative resistance,” and this section of the curve is called the “Negative resistance region.”
8. A Blocking Oscillator is a waveform generator used to produce narrow or trigger pulses. It uses a regenerative feedback mechanism that it blocks for a predetermined time after each cycle, with a pulse transformer being the key component used to provide this feedback.
9. A sampling gate is a circuit, also called a linear or transmission gate, that transmits an input signal to the output only during a selected time interval. The “Transmission Period” is this specific interval, controlled by a gating signal, during which the output is a replica of the input; otherwise, the output is zero.
10. A “Pedestal” is the unwanted output voltage level observed in a sampling gate during the transmission period even when the input signal is absent (VS = 0). It is caused by the control or gating voltage itself being passed to the output.

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