Question

For the differential amplifier shown in Figure (2),

assume \(\mathrm{VCC}=12 \mathrm{~V}, \mathrm{VEE}=-12 \mathrm{~V}, \mathrm{Rc}=2 \mathrm{k} \Omega\), and \(\beta=100\) for all transistors.

For the current source circuit (Transistor \(\left.Q_{3}\right): R_{1}=4 k \Omega, R_{2}=4 k \Omega, R_{3}=3 \mathrm{k} \Omega\), and \(r_{0}=100 \mathrm{k} \Omega\).

a) In differential amplifier circuits, what do "well-matched transistors" mean?

b) Why it is important to use well-matched transistors in differential amplifier circuits?

c) What are the operating \(Q\) point values \(\left(I_{c Q}\right.\) and \(\left.V_{C Q}\right)\) for the transistors \(Q_{1}\) and \(Q_{2}\) ?

d) Draw the ac equivalent circuit for the differential amplifier shown.

e) Derive an expression for the differential mode gain for a double-ended configuration.

f) Calculate the double-ended differential gain of the circuit.

g) Calculate the differential mode input and output resistances for the circuit.

h) What is the common mode gain?

i) What is the common mode rejection ratio in dB?

j) Suggest a current source circuit for which the source current is less dependent on variations of the DC supply voltage VEE.

Answer 1