D *8.65 For a cascode current source, such as that in Fig. 8.30, show that if the two transistors are identical, the current I supplied by the current source and the output resistance Ro are related by
Now consider the case of a 0.18-µm technology for which and let the transistors be operated at |VOV| = 0.2 V. Find the figure-of-merit IRo for the three cases of L equal to the minimum channel length, twice the minimum, and three times the minimum. Complete the entries of the table at the bottom of the page. Give W/L and the area 2WL in terms of n, where n is the value of W/L for the case I = 0.01 mA. In the table, Av denotes the gain obtained in a cascode amplifier such as that in Fig. 8.31 that utilizes our current source as load and which has the same values of gm and Ro as the current-source transistors.
(a) For each current value, what is the price paid for the increase in Ro and Av obtained as L is increased?
(b) For each value of L, what advantage is obtained as I is increased, and what is the price paid? (Hint)
(c) Contrast the performance obtained from the circuit with the largest area with that obtained from the circuit with the smallest area.