Variable Transconductance Technique:
· The variable transconductance technique makes use of the dependence characteristic of the transistor transconductance parameter on the emitter current bias applied. A simple differential circuit arrangement depicting the principle is shown in figure.
· The relationship between V0 and Vx . is given by V0 = gm RL VX where gm = IEE /VT is the transconductance of the stage.
· Application of a second input Vy to the reference current source of the differential amplifier can vary gm.
· Thus, if RE IEE >>VBE, the bias voltage Vy is related to IEE by the relation Vy = IEE RE.
· Then, the overall voltage transfer expression is given by
V0 = gm RLVx = (Vy/VTRE)VxRL
= VxVy RL/ VTRE