5.FEEDBACK AMPLIFIERS
1.In a positive feedback amplifier the phase difference between input signal and feedback signal is [ ]
a)00 b)1800 c)2700 d)900
2. In a negative feedback amplifier the phase difference between input signal and feedback signal is [ ]
a)00 b)1800 c)2700 d)900
3.The positive feedback reduces [ ]
a)instability b)distortion c)noise d)bandwidth
4.The negative feedback increases [ ]
a)instability b)distortion c)noise d)bandwidth
5. The negative feedback decreases [ ]
a)bandwidth b)noise c)stability d)none
6. In a negative feedback amplifier, the bandwidth is given by [ ]
a)BW(1+Aβ) b) BW/(1+Aβ) c) BW(1-Aβ) d) BW/(1-Aβ)
7.In a current series feedback amplifier ,the voltage gain [ ]
a)decreases b)increases c)first increases &then decreases d)first decreases &then increases
8.In a negative feedback amplifier, the stability changes by a factor of [ ]
a)Aβ b)zero c)(1-Aβ) d)(1+Aβ)
9.The noise in a negative feedback amplifier [ ]
a)increases b)decreases
c)first increases &then decreases d)first decreases &then increases
10.A series-derived ,shunt-fed feedback amplifier is otherwise called a ------feedback amplifier [ ]
a)voltage –serie s b)voltage shunt c)current-series d)current –shunt
11.The nyquist criterion for stability states that an amplifier is unstable if the nyquist curve encloses the
--------------------------- point [ ]
a)1+0j b)-1+j0 c)0+0j d)0-1j
12.The feedback factor b for a voltage-shunt feedback amplifier is given by [ ]
a)β=vf/vo b)β=if/io c)β=if/vo d)β=vf/io
13.The current series feedback amplifier is also known as ---------------- amplifier [ ]
a)voltage b)current c)trans-conductance d)trans –resistance
14.The term selectivity is given by [ ]
a)1/(1+Aβ) b) (1+Aβ) c) 1/(1-Aβ) d) Aβ
15.The upper &lower 3-dB frequencies of an amplifier with negative feedback [ ]
a)increase, increase b) increase,decrease c) decrease , increase d) decrease, decrease
16.The emitter follower is an example of --------------------------feedback amplifier [ ]
a)voltage series b)current series c)voltage shunt d)current shunt
17.Noise in anegative feedback amplifier is given by [ ]
a)Nf=N/(1+Aβ) b) Nf=N*(1+Aβ) c) Nf=N/(1-Aβ) d)none
18.Output resistance decreases in-------------feedback amplifier [ ]
a)voltage series b)current series c)current shunt d)none
19. Output resistance increases in-------------feedback amplifier [ ]
a)current series b)voltage series c)voltage shunt d)none
20.The feeback factor for a current shunt feedback amplifier is β= [ ]
a)β=vf/vo b)β=if/io c)β=if/vo d)β=vf/io
21. current shunt feedback amplifier is also called as [ ]
a)current amplifier b)voltage amplifier c)power amplifier d)none
22.In series feedback amplifiers -------------------- increases [ ]
a)input resistance b)output resistance c)harmonic distortion d)noise
23.By shorting the output if feedback signal becomes zero then it is called -----sampling [ ]
a)voltage sampling b)current sampling c)power sampling d)none
24. By opening the output loop if feedback signal becomes zero then it is called -----sampling [ ]
a) current sampling b) voltage sampling c)power sampling d)none
25.In negative feedback amplifiers ----------------decreases [ ]
a)voltage gain b)noise c)harmonic distortion d)all
6.oscillators
1. The main advantage of using crystal oscillator is [ ]
a)high frequency stability b)suitability for low voltages c)high efficiency d)hgh output voltage
2. LC oscillators can be used to produce frequencies as high as [ ]
a)1MHZ b)5MHZ c)50MHZ d)500MHZ
3. A crystal oscillator is used because [ ]
a)it gives high output voltage b)it works at high efficiency c)it require low dc supply voltage
d)the frequency of oscillations remains substantially constant
4. The crystal oscillator frequency is very stable due to [ ]
a)rigidity of crystal b)size of crystal c)structure of crystal d)high Q of crystal
5. When L is doubled and Cis halved, the frequency of oscillation is [ ]
a)doubled b)halved c)one quarter d)unchanged
6. An oscillator using a capacitive voltage divider to provide feedback is [ ]
a)Hartley b)colpitts c)tuned collector d)none of the above
7. A phase shift oscillator circuit consists of [ ]
a)R&C components b)R&L components c)L&C components d)R,L&C components
8. The device used in negative resistance oscillator is [ ]
a)BJT b)SCRc)tunnel diode d)FET
9. The stability of oscillations is better in a [ ]
a)Wien-bridge oscillator b)Hartley oscillator c)Colpitts oscillator d)Crystal controlled oscillator
10. An oscillator uses a [ ]
a)positive feedback b)negative feedback c)none of these
11.The essential conditions for sustained oscillations are [ ]
a)|Aβ|=1&phase of Aβ=00 b) |Aβ|<1&phase of Aβ=00
c) |Aβ|>1&phase of Aβ=00 d) |Aβ|<1&phase of Aβ=1800
12.A Hartley oscillator use a [ ]
a)capacitive feedback b)a tapped inductor c)a tapped capacitor d)a tapped inductor for inductive feedback
13.The oscillator with highest Q factor is [ ]
a)crystal controlled oscillator b)tuned oscillator c)wien-bridge oscillator d)colpitts oscillator
14.For good stability the tuned circuit of a tinnel collector oscillator should have [ ]
a)lowQ b)low R c)low L d)low c
15.In an RC phase shift oscillator ,oscillations will occur if the voltage gain of its internal amplifier is [ ]
a)unity b)less than unity c)around 3 d)more than 29
16.For a stable oscillator the barkhausen criterion is [ ]
a) Aβ= 0 b)| Aβ|=1 c)- Aβ=1 d)A=1/(β)1/2
17.Ina practical oscillations | Aβ|= [ ]
a)slightly less than 1 b)1 c)-1 d) slightly greater than 1
18.The phase shift of each R-C network of an RC phase shift oscillator is [ ]
a)60▪ b)90▪ c)180▪ d)360▪
19.The condition to stop oscillations in an oscillator is [ ]
a)increase in transistor gain b)reduction in transistor gain c)elimination of triggered pulse d)none
20.A typical value of Q factor o a crystal is [ ]
a)25 b)250 c)2500 d)25000
21. A typical value of resonant frequency of a crystal oscillator is [ ]
a)50hz b)327.5hz c)30275khz d)3.275Mhz
22.RF feedback oscillators are usually tuned by varying the [ ]
a)bias b)supply voltage c)L or C d)load impedance
23.Spot the odd one out : [ ]
a)quartz b)satellite c)Rochelle salt d)tourmaline
24.Positive feedback is same as [ ]
a)frequency synthesis b)negative feedback c)degeneration d)regeneration
25.The frequency of negative resistance oscillators is upto [ ]
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