100 Figure P9.100 shows a modified cascode differential amplifier. Here Q3:
and Q4:
are the cascode transistors. However, the manner in which Q3:
is connected with its base current feeding the current mirror Q7:
Q8:
results in very interesting input properties. Note that for simplicity the circuit is shown with the base of Q2:
grounded. Assume that all transistors have equal β's.

(a) With vI =0 V dc, find the input bias current IB assuming all transistors have equal value of β. Compare with the case without the Q7:
Q8:
connection. b) With vI =0 V (dc) + vid , find the input signal current ii and hence the input differential resistance Rid . Compare with the case without the Q7:
Q8:
connection. By what factor does Rid increase?