hw08 - ECE 315 Homework 8 Due 11:15am, November 9, 2007 in...

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ECE 315 Homework 8 Due 11:15am, November 9, 2007 in the drop box 1. (Cascode amplifier derivation) Use Fig. 6.36 for the MOSFET cascode amplifier considering the Early effect but ignore the body effect, (a) Use the small-signal KCL to derive R out = r o2 + A vo2 r o1 and R in2 = 1/g m2 + R L /A vo2 . Confirm this result with the intuitive observation in Fig. 6.29. (4 pts) (b) If Q 1 and Q 2 are identical, derive A v = -A 0 2 R L /(R L + A 0 r o ) with A 0 defined as g m r o . (4 pts) (c) If Q 1 and Q 2 have different W but the same L (still both are in saturation), if we want a larger R out , which transistor should be larger? (4 pts) 2. (Cascode as shielding point of view) Following Question 1, the cascode transistor Q 2 can be thought of as providing a “shield” for the input transistor Q 1 from the voltage variation at the output. For the cascode circuit below, we have grounded the input terminal (i.e., reduce the small-signal input v i to zero). Apply a small change v x to the output node, and denote the voltage change that results at the
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