EE 204 Analog Circuits
Tutorial Problems
1. A signal generator generates 330 mVpp signal under unloaded condition. The voltage drops
down to 30 mVPP when a load RL is directly connected to the signal generator. When the
same signal generator is connected to the input of an amplifier having an inherent voltage
gain of 100, input resistance of 1 KΩ and output resistance of 225 Ω, the voltage observed
across the same load RL (which is now connected to the output of the amplifier) is 4 Vpp.
Write the expression of the overall voltage gain. Find out the probable values of the load
resistance RL and the source resistance Rs of the signal generator.
2. For the MOSFET circuit shown in Fig. 1, nCox = 100 A/V2 and the threshold voltage VT
= 1 V. What will the voltage Vx at the source of upper transistor? Also determine drain
current.
Fig. 1
3. Fig. 2 shows a discrete-circuit amplifier with parameters VDD = 15 V, Rsig = 100 kΩ, RG1 =
20 MΩ, RG2 = 10 MΩ, CC1 = 0.01 μF, RS = 3 kΩ, CS = 10 μF, RD = 4.7 kΩ, RL = 10 kΩ,
CC2 = 1 μF.
LARGE SIGNAL ANALYSIS
MEIN VCC SHORT NAHI KARTE!!!!!!
Always and only
this VGS = VG - VS
nothing else
Fig. 2
2
a) If the transistor has Vt = 1 V, and kn = 2 mA/V , find out the VGS, ID and VD. overall
b) Find gm and ro if VA = 100 V.
c) Draw a complete small-signal equivalent circuit of the amplifier, assuming all capacitors
behave as short circuit at signal frequencies. Find Rin, Rout and mid band voltage gain AM.
d) Determine poles and zeros fP1, fP2, fZ, fP3, and lower 3 dB cutoff frequency fL.
e) If MOSFET internal capacitances are Cgs = 1 pF and Cgd = 0.2 pF, determine the expected
3-dB cutoff frequency fH.
f) Draw frequency response (bode plot) of this amplifier and determine its bandwidth.
4. A common source amplifier is shown in Fig. 3 All
transistors have same parameters 𝑘𝑛 =
1 𝑊
𝜇 𝑛 𝐶𝑜𝑥 ( ) = 1𝑚𝐴/𝑉 2 , 𝑉𝑡ℎ = 2 𝑉, channel
2 𝐿
length factor 𝑛 = 0 𝑉 −1, 𝑉𝑑𝑑 = 12 𝑉, 𝐶𝐶1 =
𝐶𝐶2 = 10 𝐹.
(a) Find out the resistor RB to set ID3 = 1 mA.
(b) Find ratio RG1/RG2 such that DC voltage at the
drain of M2 is equal to the minimum required
voltage to keep M2 in saturation. Use this value
of RG1/RG2 ratio for the subsequent parts of this
question.
(c) Find RD for maximum symmetric swing at the
output. Use this value of RD for the subsequent
parts of this question.
Fig. 3
(d) Find the small signal voltage gain from Vin to Vout.
(e) Find the low frequency, high-pass pole resulting from Cc2 (i.e. lower cut-off frequency
is defined by Cc2).
(f) Find RG1 and RG2 (for the ratio determined in (b)), such that the low frequency pole
arising due to RG1 and RG2 (i.e., the lower cut-off frequency defined by Cc1, RG1 and
RG2) is at least 10 times lower than the pole found in (e).
5. For the feedback transconductance
amplifier of Fig. 4 derive expressions for A,
β, Aβ, Af , Ro, and Rof . Evaluate Af and Rof
for the case of gm1 = gm2 = 4 mA/V, RD = 20
k, ro2 = 20 k, RF = 100 , and RL = 1
k. For simplicity, neglect ro1 and take ro2
into account only when calculating output
resistances.
Fig. 4
