Analog Electronics AGH Exercices

2 Transistor amplifiers

Exercise 1 Bipolar transistor

The circuit shown in Fig 1 shows the transistor amplifier in common emitter structure

E=10V,,RL=4kΩ

Operation point is to be fixed as:

Vbeo=0.6V, Vceo=5 V;, Iceo=1 mA

Fig 1

1. Using the input and output characteristics, Illustrate the input and output lines of load and the operation point

2. Find the values of resistivity’s R_B ,R_C, in order to fix the required operation point. β=100

3. For operation point fixed as above, the dynamic parameters of transistor are as follows

h₁₁=1000Ω, h₂₁=β=100, h₁₂=0, h₂₂=10^-5S

Illustrate the equivalent circuit (4 pole type) of transistor and complete schema of the amplifier for dynamic (small signals) operation.

Determine the gain G of amplifier for case C1, C2=∞ and illustrate u_B(t), u_C(t), u_s(t) and u_e(t) for e_g(t)=E_mcos(wt), E_m= 10 mV

4 Determine the G (ω) for the case where C1 is not neglected. The minimum cut off frequency of this amplifier is fixed as to be 10 Hz

Propose the value for C₁

What is the maximum cut off frequency of this amplifier? How maximize the frequency bandwidth

5. The cable of capacity C_p =10 nF is connected in parallel with R_L (suppose C1, C2=∞) . Illustrate its influence. Determine the corresponding cut off frequency

6. How to proceed in order to minimize the influence of this cable.

7. The amplifier is used as the signal presence detector, which lights the LED diode, when Em >2 mV. Propose the adequate solution, complete the circuit

Exercise 2 Field Effect Transistor (FET)

The circuit shown in Fig 2 shows the FET transistor amplifier in common source mode

E=20 V,

Fig 2

1. Operation point is to be fixed as:

V_GSo=-1 V, V_GSo=-1 V ,I_DSo=4 mA, U_D,=10V; Ε=20V

Find the values of resistivity’s R_G, R_s , R_D,

1. For operation point fixed as above, the dynamic parameters of transistor are as follows

G_d=10^-5S; g_m=2mS

Illustrate the equivalent circuit (4 pole type) of transistor and complete schema of the amplifier for dynamic (small signals) operation.

Determine the gain G of amplifier for case C1=∞ and

G_d=∞

Illustrate u_G(t), u_D (t), for e_g(t)=E_mcos(wt), E_m= 10 mV

Determine Input resistance R_e and minimum cut off frequency as a function of R_G and C1