Cascode Amplifier Circuit

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written 7.3 years ago by

vedantchikhale • 900

enter image description here

Figure (a) shows a MOS cascode amplifier loaded with an ideal constant-current source. The voltage gain realized can be found from the equivalent circuit in figure (b). Since the load is an ideal constant-current source, the load resistance is infinite. That is, the amplifier is operating with an open-circuit load, and the gain is

enter image description here - (1)

Now, since Rs of Q2 is ro1, the output resistance Ro is given by the approximate expression

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Substituting in equation (1), we get

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For the case gm1 = gm2 = gm and ro1 = ro2 = ro,

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Thus cascoding increases the gain magnitude from enter image description here

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