This problem assumes a MOSFET circuit to the right, with the following parameters: Ith = 125nA, K = 80 uA/V2, VT = 0.6V, VA = 25V. The drain voltage is biased at 2.5V; assume the MOSFET is in saturation throughout this problem. Also assume k = 1.
MOSFET Small Signal Modeling
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This problem assumes a MOSFET circuit to the right, with the following parameters: Ith = 125nA, K = 80 uA/V2, VT = 0.6V, VA = 25V. The drain voltage is biased at 2.5V; assume the MOSFET is in saturation throughout this problem. Also assume k = 1. |
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(a) What is the minimum drain voltage bias required to keep
this MOSFET in saturation as a function of gate voltage? This should be for both subthreshold and
above-threshold operation.
(b) Compute and draw the small signal model of this MOSFET circuit (not including the capacitors yet). Evaluate the transconductance at a bias current of 100nA and 10mA.
(c) Qualitatively, how would this model change for a BJT device instead of a MOSFET transistor (assume the collector replaces the drain and the base replaces the gate).
(d) Solve for the expression for the maximum gain from this device? Evaluate again at bias currents of 100nA and 10mA.
(e) Solve for the expression of unity gain frequency when the output is driving a 2fF load. Plot the log of unity-gain frequency (fT) versus log of channel current. Extra credit: Add an additional curve to the graph illustrating the effects of velocity saturation.
(f) Calculate the power consumed at a bias current of 100nA and 10mA.