Patent ID: 6246289
Filing Date: 2001-06-12
Classification: H03G

Abstract:
A variable-gain multistage amplifier with broad bandwidth and reduced phase variations, comprising a differential input stage biased by a first current source and to which a differential voltage signal is fed, said differential input stage connected to a pair of diodes in which the cathode terminals are connected to respective first and second bipolar transistors that are biased by a second current source and in which collector terminals of said first and second bipolar transistors are connected to load resistors, a differential output of said amplifier being provided at the collector terminals of said first and second bipolar transistors, and further comprising two circuit branches, each of which is constituted by a branch bipolar transistor and by a third current source, the third current source respectively connected to a collector terminal and an emitter terminal of said branch bipolar transistors, and in which base terminals of the branch bipolar transistors receive said differential voltage signal and the collector terminal of each bipolar transistor is connected to the cathode terminal of a respective one of said two diodes, said two circuit branches having emitter terminals connected by means of a pair of capacitors.