Analog Multiplier - Variable Transconductance Technique | Linear Integrated Circuits : Analog Multiplier and PLL

Chapter: Linear Integrated Circuits : Analog Multiplier and PLL

Variable Transconductance Technique

The variable transconductance technique makes use of the dependence characteristic of the transistor transconductance parameter on the emitter current bias applied.

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

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Linear Integrated Circuits : Analog Multiplier and PLL : Variable Transconductance Technique | Analog Multiplier