EECS 105 Spring 2002 Lecture 26 R. T. Howe Lecture 26 • Last time: – Finish methods for finding two-port model parameters – Start common-source amplifier • Today : – Current-source supplies – Common-gate amplifier Dept. of EECS University of California at Berkeley EECS 105 Spring 2002 Lecture 26 R. T. Howe Non-Ideal Current Sources We want to have both RD and a very large gm at the same time … how to do it? The gain depends on the small-signal resistance; the DC current can be set by a supply ! modify load line ISUP resistor VSUP Dept. of EECS University of California at Berkeley EECS 105 Spring 2002 Lecture 26 R. T. Howe Current Source Supply Dept. of EECS University of California at Berkeley EECS 105 Spring 2002 Lecture 26 R. T. Howe Common-Source Amplifier with Current Source Supply Dept. of EECS University of California at Berkeley EECS 105 Spring 2002 Lecture 26 R. T. Howe Load Line for DC Biasing Both the I-source and the transistor are idealized for DC bias analysis Dept. of EECS University of California at Berkeley EECS 105 Spring 2002 Lecture 26 R. T. Howe Two-Port Parameters From current source supply Rin = Gm = Rout = Dept. of EECS University of California at Berkeley EECS 105 Spring 2002 Lecture 26 R. T. Howe P-Channel CS Amplifier DC bias: VSG = VDD – VBIAS sets drain current –IDp = ISUP Dept. of EECS University of California at Berkeley EECS 105 Spring 2002 Lecture 26 R. T. Howe Two-Port Model Parameters Small-signal model for PMOS and for rest of circuit Dept. of EECS University of California at Berkeley EECS 105 Spring 2002 Lecture 26 R. T. Howe Common Gate Amplifier DC bias: Dept. of EECS University of California at Berkeley EECS 105 Spring 2002 Lecture 26 R. T. Howe CG as a Current Amplifier: Find Ai iout = id = - ig – is= -it Dept. of EECS University of California at Berkeley EECS 105 Spring 2002 Lecture 26 R. T. Howe CG Input Resistance At input: Output voltage: Dept. of EECS University of California at Berkeley EECS 105 Spring 2002 Lecture 26 R. T. Howe CG Output Resistance Dept. of EECS University of California at Berkeley