Variable Transconductance Technique

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 V_x . is given by V₀ = gm R_L V_X where gm = I_EE /V_T is the transconductance of the stage.

 ·           Application of a second input V_y to the reference current source of the differential amplifier can vary g_m.

 ·           Thus, if R_E I_EE >>V_BE, the bias voltage Vy is related to I_EE by the relation V_y = I_EE R_E.

 ·           Then, the overall voltage transfer expression is given by

 V₀ = g_m R_LV_x = (V_y/V_TR_E)V_xR_L

= V_xV_y  RL/ V_TR_E