Question

5). In this problem, you are asked to consider the ac hybrid-t model for an NMOS transistor and to relate the capacitors to the physical device structure. Recall the oxide capacitance per unit area (Cox) appears in the DC ID-Vos relationship for triode and saturation regions. The NMOS transistor has kn-0.2 mA/V2, w-10 μm, L-1 μm and μ,-1000 cm2/Vsec. a) Find the total gate-to-channel capacitance for small Vos, CG-cho. Hint: this is the parallel-plate capacitance between the gate and the full channel area. b) Next, consider a bias point in the saturation regime. Since the channel charge density at the drain end of the channel decreases with increasing Vos ("pinch-off"), CG-cho does not divide equally between G-S and G-D components. Assuming that Cgs is 80% of CG-cho and Cad is 10% of CG-cho, find Cgs and Cgd. c) Suppose that this transistor is used in a CS amplifier with the topology of the 2nd stage in Prob. 1 (i.e. this transistor is used as M6). The DC hybrid-t parameters at the DC bias point are gm 2 mS and ro-100 k(2. Find the Miller capacitance (CM) for this CS stage. Note that for an inverting amplifier, CM Cgd (1-Av) d) Find the total effective capacitance between G and S (Cgs +CM)

Answer 1

レー 2. 100C×Cot 10 /sec 3 ut

节 t-Av) 201 d nn= 201 0.2 사 in satuuroution !'bt-402