Multistage Amplifiers Two Stage CMOS OpAMP Bipolar OpAmp SPICE March 3, 2005

HW #5 7.10, 7.21, 7.71, 7.88 Due Tuesday March 3, 2005

Why Multistage? Practical transistor amplifiers consist of a number of stages connected in cascade. First stage typically high input impedance, & CMMR Middle stages amplification Last stage, low output impedance March 3, 2005

Two stage CMOS Q8,Q5: current mirrors March 3, 2005

Usually the leakage resistances are much larger than 1/g_m3 Differential Input Usually the leakage resistances are much larger than 1/g_m3 March 3, 2005

Differential Gain March 3, 2005

Differential Input March 3, 2005

vG2=0, vG1=vid March 3, 2005

Equivalent Circuit MOSFET Opamp March 3, 2005

Bias Circuit for Opamp Bias current independent of Supply Voltage and MOSFET threshold volage Q_12, Q_13 deliberately mismatched, Q_12 4x wider March 3, 2005

Bipolar Opamp March 3, 2005

Bipolar Opamp March 3, 2005

Small Signal Analysis Input and output Impedances March 3, 2005

Gain of Second Stage March 3, 2005

Last stage March 3, 2005

Small Signal Model March 3, 2005

Frequency Response March 3, 2005

Spice Simulation March 3, 2005

Opamp Transfer Function March 3, 2005

Differential Gain March 3, 2005

Frequency Response Adjust frequency resonse by adding resistor in Q4 March 3, 2005

Common Mode Rejection Ratio March 3, 2005