Patent ID: 6608502
Filing Date: 2003-08-19
Classification: H03D

Abstract:
A transmitter detection circuit comprising:a first rectifying circuit to rectify a transmission signal output from a power amplifier; a second rectifying circuit having the same structure as that of the first rectifying circuit; and a logarithmic amplifier, said logarithmic amplifier including; a voltage-to-current converting circuit to output an electric current that is proportional to an output voltage of said first rectifying circuit; and a two-terminal p-n junction electronic device through which the electric current flows to produce a voltage thereacross that is proportional to a logarithm of the electric current wherein the voltage-to-current converting circuit includes first and second transistors which perform a differential operation, a constant-current source connected to one of a collector and an emitter of the first and second transistors, and a first current-mirror circuit connected to the other of the one of the collector and the emitter of the first and second transistors, the output voltage of the first rectifying circuit is input to a base of one of the first transistor and the second transistor; an input end of the first current-mirror circuit is connected to the first transistor, and an output end of the first current-mirror circuit is connected to the second transistor, thereby causing an electric current that is equal to a difference between an electric current which flows to the second transistor and an electric current which flows to the transistor at an output end side of the current-mirror circuit to flow to the p-n junction electronic device, the same bias voltage is applied to rectifiers of the first and second rectifying circuits, the output voltage of one of the first and second rectifying circuits is input to the base of the first transistor, and the output voltage of the other rectifying circuit is input to the base of the second transistor.