Que.76 What is a Crystal oscillator? What is the application of a crystal oscillator?
Answer: It is an LC oscillator in which a quartz crystal is used in place of the inductor.
- Quartz is a piezoelectric material that converts energy from electrical to mechanical and mechanical to electrical. The circuit diagram includes R, L, and C as components of quartz material in parallel with a capacitor.
Application of crystal oscillator:
- crystal oscillators are used when a stable frequency is needed such as to generate a clock signal for the microprocessor.
- All electronic watches use a crystal oscillator.
Que.77 Where do we use the Hartley oscillator?
Answer: Hartley oscillator is used as a voltage-controlled oscillator or FM generator if a varactor diode is used in place of the capacitor.
Que. 78 What is the difference between a waveform generator circuit and an oscillator circuit
- Waveform generator circuit: A circuit that generates non-sinusoidal output such as square wave, triangular wave, etc. is known as a waveform generator.
- Oscillator Circuit: A circuit that generates an AC waveform without using AC input is called an oscillator. Oscillators generate sinusoidal output.
Que.79 How does a ramp generator circuit work?
- Ramp generator circuit: As the name suggests, ramp generator circuits generate a ramp waveform or sawtooth waveform.
- The sawtooth waveform consists of a voltage that increases linearly with time until it reaches a predetermined final value, instantaneously returns to zero, and immediately increases again as the cycle repeat again.
- It can be generated by using an IC-555 timer circuit, in which a constant current source is used in place of the resistor.
- When the constant current source is used, the charging current of the capacitor remains constant and thereby capacitor voltage increases linearly and the ramp signal is generated.
Que.80 Types of audio-frequency amplifiers and their application.
Answer: Audio frequency oscillator circuits are used in the audio systems to generate audible sound. For example, doorbells, and alarm systems.
There are two types of audio frequency oscillators:
- Wein bridge oscillator: it consist of a noninverting amplifier that provides zero phase shift and an RC feedback network that also provides zero phase shift. Hence phase shift remains zero and oscillation occur at frequency fo. These are mostly used for audio testing.
- RC phase shift oscillator: which can be made using either BJT, FET, or OP-AMP. These oscillators are used in musical instruments, GPS units, and voice synthesis.
Que.81 Voltage to frequency converter circuit.
- It is an oscillator circuit whose frequency is linearly proportional to control voltage.
- When in an IC-555 astable multivibrator circuit, a control voltage is applied at the control pin, and the circuit act as a voltage-controlled oscillator or voltage to frequency converter.
Que. 82 Why two differential amplifiers are used in the internal structure of IC-741?
Answer: Two differential amplifiers are used in the internal structure of op-amp IC-741 to obtain high voltage and high CMRR.
Que.83 Why opamp is used in the analog system over BJT and FET?
Answer: Opamp is preferred in analog systems over BJT and FET because circuit design becomes easier with an opamp circuit.
Que. 84 What is a differential amplifier? What are the different modes of operation of the differential amplifier?
- Differential amplifier: A circuit that amplifies the difference between two input voltages.
- A differential amplifier can be used in 4 different modes:
- Dual input balanced output- it is also called fully differential mode.
- Dual input unbalanced output mode or semi-differential mode.
- Single input balanced output
- Single input unbalanced output
Que. 85 What is a level shifter circuit? Where do we use a level shifter circuit?
- It is a circuit that shifts the DC voltage level of a signal to 0 volts.
- It is the opposite of clamper. it is basically a common collector circuit that has unity voltage gain, high input resistance, and low output resistance.
- It is designed to eliminate a particular DC voltage.
- It is mainly used in the internal structure of opamp to prevent the loading effect and to eliminate the undesired DC signal.
Que. 86 What is a precision diode or super diode? Application of the same.
- It is the interconnection of op-amp and a normal diode. It is equivalent to the ideal diode.
- When the input signal lies in milli or microvolt, then a precision diode is used for signal processing such as clipping and rectification.
- Precision diodes are used for half-wave and full-wave rectification of AC signal using opamp.
Que. 87 What is a delay equalizer circuit?
Answer: All pass filter passes all frequencies but provides different phase shift to each frequency, it is used for phase equalization or delay equalization in a communication system. Hence also known as a delay equalizer.
Que. 88 What is the role of the input follower and output follower circuit used in the sample and hold circuit.
Answer: An input follower in the sample and hold circuit is used to eliminate the effect of source resistance whereas an output follower is used to prevent the discharging of the capacitor during the hold interval.
Que. 89 What is unity-gain bandwidth in an opamp?
- Unity gain bandwidth (UGB): is a frequency at which the open-loop gain of op-amp becomes unity. It is also called a gain-bandwidth product of opamp. It is the highest frequency up to which op-amp can provide amplification.
Que. 90 What is the Schmitt trigger oscillator?
- An astable multivibrator is equivalent to Schmitt trigger with an additional RC network, hence called a Schmitt trigger oscillator.
- It is a circuit whose output does not have any stable state. Output has two quasi-stable states, and output keeps toggling between these two states without any external input. Hence it generates a square waveform. So this circuit is also known as a square waveform generator or free-running oscillator.
Que.91 What is a monostable multivibrator?
- It is a circuit whose output has one stable state and one quasi-stable state, if external input is not applied then it remains in the stable state forever.
- If the trigger input is applied, then the output goes into a quasi-stable state but again returns to a stable state after a short duration of time. Thus a monostable ckt. generates pulse output when the trigger is applied.
Que.92 What is the diode-connected MOSFET?
Answer: When the drain is shorted to the gate, then MOSFET will always be in the saturation region, this is called diode-connected MOSFET. It is used as an active load in IC MOS amplifiers.
Que. 93 What is a pass transistor?
- It is a MOSFET used as a switch to pass logic levels between nodes of a circuit instead of a switch connected directly to a supply voltage.
- When the gate voltage is equal to (source) input voltage, switch ON and the output becomes equal to (Vdd – Vt).
- When the input voltage is zero, the output voltage is zero. The switch is OFF.
Que.94 How BJT can be used as a switch?
- When we operate BJT as a switch, it must be operated in such a way that power loss during ON and OFF should be nearly zero or very low.
- To operate BJT as a switch, it can be operated in cut-off and saturation regions.
- In the cut-off region: the base current is nearly zero, hence Ic (collector current) has a very small constant value for a wide range of Vce( collector to emitter voltage), hence power loss across the transistor is ( Ic*VCE) is negligible. So, in the cut-off region, BJT act as an OFF switch as the transistor act as an open circuit, and the entire open-circuit voltage appear across the load.
- In saturation region: base current becomes much higher than collector current or we can say IB > IC, and Vce becomes less than or equal to 0.2, then again the power loss across transistor becomes negligible. Here transistor behaves ON switch because the entire load current flow through the transistor.
Que.95 What are the advantages of the self-bias circuit in BJT over fixed bias and collector to base bias?
Advantage of the self-bias circuit:
- Least stability factor or better stability in Ic.
- The stability factor is independent of load resistance.
- It can be used in all the three configurations of BJT, while fixed bias and collector to base bias are appropriate only for common emitter configuration
Que.96 When do the virtual short ckt and virtual ground concepts fail in opamp?
Answer: When opamp enters saturation, the concept of virtual ground and virtual short circuit fails. Because this concept is applicable for negative feedback opamp circuit. which has linear characteristics and when opamp enters saturation, it becomes a positive feedback circuit, and the concept of linearity is not applicable in this case output saturates to a particular voltage.
Que.97 When compensation resistors are used in an op-amp circuit?
- When the opamp has a non-zero input bias current, then the amplifier generates a non-zero output for zero input, the output voltage is called output offset voltage.
- In order to make this offset zero, compensation resistors are required in inverting amplifier as this offset is negligible in the case of the non-inverting amplifier.
- This resistor is connected to the non-inverting node and its value should be equal to the value of the parallel combination of all the resistors at inverting node.
Que.98 How can you design a current to voltage converter using an op-amp circuit? Application of the same.
- The current to voltage converter is used to convert the output current of a transducer into proportionate voltage. It is also called a trans-resistance amplifier.
- Example: Photodiode uses an I to V converter.
Que.99 What is the purpose of using a shunt capacitor in a BJT amplifier?
Answer: Shunt capacitor in BJT amplifier is used to limit the bandwidth of amplifier as bandwidth is inversely related to shunt capacitor.
Que.100 What is a microwave amplifier?
Answer: It is the amplifier used in cellular communication and microwave communication. It amplifies frequencies that lie in GHz, which are microwave signals.