(a) Determine the truth table for the circuit. What logic function does it imple

Question

(a) Determine the truth table for the circuit. What logic function does it implement?

(b) Assuming 0 and 2.5 V inputs, size the PMOS transistor to achieve an output node (OUT) voltage, VOL = 0.2 V. (VTHP = VTHN = 0.5 V) Assume VOL is small enough so that higher order terms of VOL can be neglected in the IDS expression of NMOS transistors. Also, assume µn/µp = 2.

(c) What will be problem(s) if the PMOS is removed?

Thank you

VDD OUT Bo-L 15/0.25 (a) Determine the truth table for the circuit. What logic function does it implement? (5) (b) Assuming 0 and 2.5 V inputs, size the PMOS transistor to achieve an output node (OUT) voltage, VOL = 0.2 V. (VTH,-VTHN = 0.5 V) Assume VoL is small enough so that higher order terms of Vou can be neglected in the Ios expression of NMOS transistors. Also, assume c) What will be problem(s) if the PMOS is removed? (10)

Explanation / Answer

(a) Truth table:

The circuit is an EX-NOR gate.

(b) Assuming all transistors have length 0.5um.

input A = 0 and B = 2.5V

(W/L) of transistor A : 0.25u / 0.5u and (W/L) of transistor B: 1.5u / 0.5u

so choose width of PMOS equal to 0.1um and length 0.5um to get VOL = 0.2V

(c) If PMOS is removed the entire circuit behavior is changed to 'AND' gate.

Logic 1 levels are not completely passed as PMOS is a good passer of logic 1.

A B OUT 0 0 1 0 1 0 1 0 0 1 1 1

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