EECS 105 Spring 2002 Lecture 40 R T Howe Lecture 40 Last time Bias and output swing for BiCMOS voltage amp Start open circuit time constant analysis back to Chapter 10 Today Applications of open circuit time constant analysis CE amplifier and cascode amplifier Dept of EECS University of California at Berkeley EECS 105 Spring 2002 Lecture 40 R T Howe Common Emitter Voltage Amplifier Time constant for base emitter capacitance C Dept of EECS University of California at Berkeley EECS 105 Spring 2002 Lecture 40 R T Howe Base Collector Time Constant Must apply a test source can t see RT by inspection Dept of EECS University of California at Berkeley EECS 105 Spring 2002 Lecture 40 R T Howe Solving for RT Find v v it RS r it Rin it g m v Rout it 1 g m Rin Rout Find vo vo io Rout Find vt it Rin vt vo v it 1 g m Rin Rout Solve for Th venin resistance Dept of EECS University of California at Berkeley EECS 105 Spring 2002 Lecture 40 R T Howe Dominant Pole of CE Amplifier Estimate dominant pole as inverse of sum of OCTCs 1 C 1 g m Rin Rout C 1 Rin C Rin Rout C Identical to the exact analysis in Chapter 10 Why bother with the OCTC technique add effect of Ccs Dept of EECS University of California at Berkeley EECS 105 Spring 2002 Lecture 40 R T Howe Multistage Amplifier Frequency Response CS CB cascode Dept of EECS University of California at Berkeley EECS 105 Spring 2002 Lecture 40 R T Howe Systematic Approach 1 Construct two port small signal models for each stage 2 Add the capacitors for each device across the appropriate nodes in the two port models Make sure how the gate drain and source or base collector and emitter terminals of each device fit onto the two port models 3 Optional Use Miller s Theorem to transform capacitors across amplifiers into effective capacitances to ground note that we ignore the output Miller in this course Dept of EECS University of California at Berkeley EECS 105 Spring 2002 Lecture 40 R T Howe Cascode Two Port Model Add capacitors Cgs1 Cgd1 C 2 C 2 what about Cdb1 Ccs2 Dept of EECS University of California at Berkeley EECS 105 Spring 2002 Lecture 40 R T Howe Finding the Th venin Resistances Cgs1 RTC gs1 RS g m1 Rin Rout Cgd1 RTC gd 1 Rin Rout C 2 RTC 2 C 2 RTC 2 Dept of EECS University of California at Berkeley EECS 105 Spring 2002 Lecture 40 R T Howe Dominant Pole Applying the theorem 1 1 RS C gs1 RS 1 g m1 g m 2 C gd 1 1 g m 2 C 2 RL C 2 Find approximate voltage transfer function vout Avo vs Dept of EECS RS R L ro1 o ro 2 roc 2 RL g m1 ro1 1 g m 2 University of California at Berkeley EECS 105 Spring 2002 Lecture 40 R T Howe Gain Bandwidth Product Metric for amplifier performance note that Av j 1 when Avo 1 g m1 RL Avo 1 RS C gs1 RS 1 g m1 g m 2 C gd 1 C 2 g m 2 RL C 2 Special case small RS g m1 RL Avo 1 C 2 g m 2 RL C 2 Dept of EECS University of California at Berkeley
View Full Document
Unlocking...