| 摘要 |
PURPOSE:To avoid the leakage and change in a gain control signal, by the AM modulation of a current with an input signal, while supplying the current for the gain control to a variable resistance element. CONSTITUTION:N sets of diodes D11, D12..., D1N are in series connection between the output of an operational amplifier 1 and an inverse input to constitute the impedance element for a negative feedback circuit. Further, a current supply source 2 is provided to supply the operating current to diodes D11-D1N. Further, a gain control current Icont is supplied to the diodes D11-D1N via a current AM modulator 3 from a supply source 2. In this case, the gain G is expressed as G=N.KT/Rin.ID.q (where; K is Boltzmann constant, T is absolute temperature, Rin is input resistance, ID is forward current of the diode, and (q) is charge of electrons). Since the ID is the Icont, the gain can be controlled by controlling the current of the supply source 2. |
