Abstract: A variable gain control circuit comprises first, second, third and fourth transistors each having an emitter, a base and a collector. The bases of the first and second transistors are connected to receive a control signal. The collector of the first transistor is connected to a first reference power source through a resistor. An output is generated from the node of the collector of the first transistor and the resistor. The collector of the second transistor is connected to the first reference power source, too. The emitter of the first transistor is connected to the base of the third transistor and the collector of the fourth transistor. The emitter of the second transistor is connected to the collector of the third transistor, and the base of the fourth transistor.

Abstract: A voltage controlled oscillator is provided with an LC parallel resonance circuit connected to the collector of one of a differential pair of transistors, and an amplifier and a capacitor which are connected between the collector of the one transistor and the base of the other transistor. The bases of the differential pair of transistors are equally biased. The emitters of the transistors are connected to a variable current source. The variable current source produces a current proportional to the square of control voltage. The frequency of the VCO can be changed by the control voltage with good linearity over a wide dynamic range. The variable current source causes the VCO characteristic to be linear. The value of the capacitor can be small, making the oscillator circuit well suited for integrated circuit fabrication.

Abstract: A variable gain controller comprising an amplifier having a feed back terminal which is connected to a variable resistor including a current controller for controlling current flowing through the variable resistor, a filter connected to the variable resistor for attenuating frequency components of input signals in accordance with the values of the variable resistor and a resistor inserted between output terminal of the amplifier and the connection of the variable resistor to the filter.