Build an active loaded difference amplifier biased with a cu

Build an active loaded difference amplifier biased with a current sink. Discuss the current flow through the circuit. Discuss the common mode gain Discuss the differential gain.

Solution

Differential Amplifier with Active

Loads

Active load basics

PNP BJT current mirror

Small signal model

Design example and simulation

Comparison of CMRR with resistive load design

Differential amplifier:                                                                                                          Slope for Q2 and Q7

                      

By placing the resistors in transitor:

  

VCC=VEB1+I RREF

I =VCC0.7/RREF

Adm=vodm/vindm=g mr o2r o8

Adm    = 55.5 dB at 1 kHz

= 52.5 dB at 1.43 MHz

CMRR = 135 dB at 1 kHz