| 摘要 |
PURPOSE:To invert arbitrarily an input phase through a switch operation and to simplify the circuit constitution by equipping two differential amplifiers so as to invert the input polarity and increasing and decreasing the action current of the operable differential amplifier in accordance with a contol voltage so as to control an amplification gain. CONSTITUTION:When a switch 90 is closed, an operation is switched from the differential amplifier 46A to the differential amplifier 46B. When the switch 90 is opened, the operation is switched from the amplifier 46B to that 46A. Corresponding to the selection of the differential amplifiers 46A and 46B, input phases of input terminals 60A and 60B are inverted. When the current of a variable currentsource 124 is changed by a control voltage Vc, a control current is applied to the differential amplifier 46A from a transistor 112 through a transistor 114. Moreover a control current is applied to the differential ampli fier 46B through a transistor 116. Thus amplification gains of the differential amplifiers 46A and 46B can be controlled in accordance with the switching action of said amplifiers 46A and 46B. |
