Response to the following problem:
Figure 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?
