4. Consider the cascode current mirror circuit comprising PMOS transistors M1-M4 as shown in Figure 4. Assume all the transistors are identical and in saturation. Perform small-signal analysis, indicating clearly the gm and ro of the i-th transistor as gm, and roi. For example, the gm and ro for transistor M, should be written as gm and rol, respectively. (a) Draw the AC small signal model of the circuit and derive the expression for the output resistance Rour in terms of the small signal parameters gm and ro of the MOSFET. (b) (c) (10 Marks) Given that IREF 200 μA, Kp for the MOSFET is 100 μA/V2, |VTP = 0.5 V and A=0.01 V-1,find the value of the output resistance Rout based on the expression in part (a) if the drain of M2 is connected to 0 V. (5 Marks) Using the same MOSFET parameter values given in part (b), find the value of the maximum voltage on the drain of M2 such that all the transistors are in the saturation region. VDD=10 V (5 Marks) M3 M4 M₁₂ M₁ IREF Figure 4 Rout == ID:= Iout