Self-Exercise 3.3 Find I, and V, and verify the bias state consistency of your choice of MOS drain current model for V.0.5 V, K, = 25 A/V , WIL 3. 10 V 50 K 3.0 V Answer: Io = 188.7 pA, Vo = 0.562 V Self-Exercise 3.4 Calculate Vas and give the correct bias state for transistor M1 where Von = 0.5 V. 5 V 20 K 4V M. Answer: Vas = 3.333 V 40 k Self-Exercise 3.5 6V Find lo and V, and verify the bias state consistency of your choice of MOS drain current model for V = 0.5 V. K. = 50 A/ VW/L = 2 50k 2.0 V Answer: Vo = 0.434 V, l= 111.3 A 3-14 Example 3.5 Determine the bias state for the pMOS transistors where Vo = -0,4 V. It is helpful with pMOS transistors to first identify and label the source and drain terminals. The source terminal in a pMOS transistor has a higher voltage than the drain terminal. 2.5 V 1.5 V -1.1 V OV 1.3 V -2.5 V -2.3 V OV (b) (c) (a) Vos = -2.5 V, Vps = -2.5 V, therefore Vas > Vps + Vor - 2.5 V > - 2.5+(-0.4) V, so the transistor is in saturation. (b) The gate voltage is not sufficiently more negative than either drain or source terminal to invert holes at the oxide interface, so that the transistor is in the off- state. (c) Vas = -2.5-(-1.1)=-1.4 V. Vos = 0 - (-1.1) = 1.1 V. What is wrong? The gate voltage is sufficiently negative to turn on the transistor, but the source to drain voltage is negative. Holes must leave the source and flow to the drain, but they can't under this conclusion. The answer is that the drain terminal with a lower voltage is on the top and the source on the bottom so that Vos=-2.5 -0 =-2.5 V, Vos = -1.1 -0 = -1.1 V. Therefore Vos > Vps + Vuor -2.5 V