differential input will provide a corresponding complementary differential output having a gain on the differential output controlled by the differential control voltage vgcp vgcn obviously while a preferred embodiment has been disclosed herein based on the use of npn bipolar transistors the invention may also be realized using pnp transistors if desired because the functions of gain and control are separated signal currents do not affect the control loop operation also identical low impedance buffers can be employed to drive all three transistors q11 q12 and q13 in the slave cell an absolute necessity to minimize harmonic distortion in the signal current in that regard the circuit shown in fig2 is intended for fabrication in integrated circuit form as proper circuit operation is dependent upon matched transistors for transistors q11 q12 q13 and q21 q26 for this purpose two transistors are considered to be matched if the two transistors will conduct current in proportion to their relative sizes when biased with the same base emitter voltages the result of the present invention is a fully integrated low power high linearity current gain cell with an extremely wide log linear gain control range in the case of the prior art circuit a circuit having a single ended current input and a single ended current output was illustrated with respect to the exemplary embodiment of the present invention a circuit having a.