| 摘要 |
PROBLEM TO BE SOLVED: To provide an amplifier circuit that attenuates an undesired input signal. SOLUTION: An amplification factor of a voltage controlled amplifier section 120 is changed by a control voltage Vc in response to an input voltage Vin, and when the input voltage Vin reaches a prescribed level especially, a collector current of a 18-the transistor(TR) 18 is only a base current of 7th and 9th TRs 7, 9, and a prescribed constant current 14 flows to a 19th TR 19, resulting that the voltage controlled amplifier section 120 provides a large attenuation expressed in ATT=I1/(2I4.hfe) to a current Ii. On the other hand, in the case that the input voltage Vin exceeds a level of the input voltage Vin when the attenuation above is caused, the voltage controlled amplifier section 120 amplifies the input current Ii at an amplification factor expressed in expression of relations of Io=Ii.exp (Vc/Vt) and provides an output of an output current Io.
|
