1
GATE ECE 2012
+1
-0.3
The current ib through the base of a silicon npn transistor is $$1\;+\;0.1\;\cos\left(10000\;\mathrm\pi\;\mathrm t\right)$$ mA . At 300 K, the $$r_\mathrm\pi$$ in the small signal model of the transistor is
A
$$250\;\Omega$$
B
$$27.5\;\Omega$$
C
$$25\;\Omega$$
D
$$22.5\;\Omega$$
2
GATE ECE 2011
+1
-0.3
In the circuit shown below, capacitors C1 and C2 are very large and are shorts at the input frequency. Vi is a small signal input. The gain magnitude $$\left|\frac{{\mathrm V}_0}{{\mathrm V}_\mathrm i}\right|$$ at 10 Mrad/s is
A
maximum
B
minimum
C
unity
D
zero
3
GATE ECE 2010
+1
-0.3
In the silicon BJT circuit shown below, assume that the emitter area of transistor Q1 is half that of transistor Q2.The value of current I0 is approximately
A
0.5 mA
B
2 mA
C
9.3 mA
D
15 mA
4
GATE ECE 2010
+1
-0.3
The amplifier circuit shown below uses a silicon transistor. The capacitors CC and CE can be assumed to be short at signal frequency and the effect of output resistance r0 can be ignored. If CE is disconnected from the circuit, which one of the following statements is TRUE?
A
The input resistance Ri increases and the magnitude of voltage gain AV decreases
B
The input resistance Ri decreases and the magnitude of voltage gain AV decreases
C
Both input resistance Ri and the magnitude of voltage gain AV decrease
D
Both input resistance Ri and the magnitude of voltage gain AV increase
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