**9.100 Figure P9.100 shows a modified cascode differential amplifier. Here Q 3 : and Q 4 : are…

**9.100 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?

 

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