Match the following : Codes :List – I List – II a. voltage shunt negative feedback i. increase of CMRR b. constant current source differential amplifier ii. O/P voltage attenuated by a factor 1/29 c. Phase shift oscillator iii. FSK decoder d. PLL iv. decrease of O/P impedance
a-iv, b-i, c-ii, d-iii
Each item in List II is a number or a phrase belonging unambiguously to one circuit: a-iv, b-i, c-ii, d-iii — option 2.
| Circuit | Match | Why |
|---|---|---|
| a. Voltage shunt feedback | iv. Lower output impedance | Voltage sampling always lowers Zout |
| b. Current-source diff amp | i. Higher CMRR | The tail source resists common-mode change |
| c. Phase shift oscillator | ii. Attenuation of 1/29 | The RC ladder's loss at oscillation |
| d. PLL | iii. FSK decoder | Its classic application |
a — why voltage sampling lowers output impedance. The feedback network samples the output voltage, so any tendency of that voltage to sag under load is detected and opposed by the amplifier. The circuit works to hold its output voltage constant, which is precisely what a low output impedance means:
\(Z_{out}'=\dfrac{Z_{out}}{1+A\beta}\)
The shunt half of the name refers to the input, where current mixing lowers the input impedance instead.
b — how a current source raises CMRR. Common-mode rejection is limited by the tail resistance:
\(CMRR\approx\dfrac{g_{m}R_{tail}}{1}\)
A common-mode input tries to change the total current through the tail. An ordinary resistor permits that change, so a common-mode signal gets through; a constant-current source presents a dynamic resistance of hundreds of kilohms while dropping only a volt or two of DC. It holds the sum of the two collector currents fixed, so a common-mode input produces almost no output at all — while a differential input merely redistributes that fixed current between the two halves and is amplified normally.
c — the number 1/29. The three-section RC ladder that supplies 180° of phase shift attenuates by exactly 29 at that frequency, which is why the amplifier's gain must be at least 29 for oscillation to start. The figure is unique to this circuit — the Wien bridge's counterpart is 1/3.
d — the PLL as an FSK decoder. Frequency-shift keying sends two tones for the two binary states. A phase-locked loop tracking those tones produces a control voltage on its VCO input that jumps between two levels as the frequency shifts — so the loop's error voltage, passed through a comparator, is the recovered data. The 565 PLL was sold with exactly this application in its data sheet.
Hence, the correct code is a-iv, b-i, c-ii, d-iii.
Similar Questions
Match the following lists :
List – I List – II a. Voltage series feedback i. Trans resistance amplifier b. Current series feedback ii. Current shunt feedback c. Current amplifier iii. Trans-conductance d. Voltage shunt feedback iv. Voltage amplifier Codes :
Negative feedback in amplifier results in
1. reduced voltage gain
2. reduced bandwidth
3. increased S/N ratio
4. reduced distortionAn amplifier has open-loop voltage gain of 40. 10 % of negative feedback is effected. What will be the gain with feedback ?
Match List - I with List - II.
List - I (Feedback connection type) List - II (Input/output impedance) (A) Voltage series feedback (I) \(Z_{of}=\dfrac{Z_{o}}{1+\beta A}\) (B) Voltage shunt feedback (II) \(Z_{of}=Z_{o}\left(1+\beta A\right)\) (C) Current series feedback (III) \(Z_{if}=\dfrac{Z_{i}}{1+\beta A}\) (D) Current shunt feedback (IV) \(Z_{if}=Z_{i}\left(1+\beta A\right)\) Choose the correct answer from the options given below :
Given below are two statements :
Statement I : For negative feedback systems, the open loop gain decreases by a certain factor.
Statement II : Negative feedback systems are better in terms of system stability
In the light of the above statements, choose the correct answer from the options given below :
Negative Feedback in amplifiers :
(a) improves signal to noise ratio at the output
(b) increases distortion
(c) reduces input offset voltage
(d) increases bandwidth
Options :
Read the following statements :
(a) Whatever the mode of feedback be, the gain after negative feedback is \(\dfrac{A}{1+A\beta}\)
(b) A negative feedback reduces the bandwidth of the amplifier.
(c) A negative feedback increases the output impedance
(d) A negative feedback enhances the stability of operationWhich of the above statements are correct ?
Important Questions from Feedback Amplifier
The effect of negative feedback is to increase the __________ of a series voltage negative feedback amplifier by a factor of (1 + A vβ).
Which of the following improvement is obtained in negative feedback amplifier?
Feedback in an amplifier always helps to ________
What is the effect of current shunt feedback in an amplifier?
- The output impedance of a voltage series feedback is 10 Ω, If the gain of the basic amplifier is 100 and feedback fraction is 0.01, what is the output impedance without feedback?
