BIPOLAR ANALOG MULTIPLIERS FOR LOW VOLTAGE APPLICATIONS

An analog circuit for multiplying a first input signal with a second input signal. The inventive analog circuit is capable of linear operation with a low voltage power source. A first pair of transistors is coupled as a first differential pair, and a second pair of transistors is coupled as a second differential pair. The first differential pair is coupled to the second differential pair in a manner that is similar to the corrections made between a first and second differential pair of a conventional Gilbert mixer. However, the emitter degeneration resistors of the present invention are not coupled to the collectors of a third differential pair, as is the case in conventional Gilbert mixers. Rather, the degeneration resistors of the present invention are coupled directly to the negative power supply terminal. Instead of the third differential pair used in a conventional Gilbert mixer, a third differential pair of transistors, having degeneration resistors coupled to each emitter, is coupled generally in parallel with the first and second differential pair. The collectors of each of the transistors of the third differential pair are coupled to the positive power supply terminal. Each degeneration resistor is coupled to a different one of the two tail resistors. An LO signal is input across the bases of the differential pair. The third differential pair provides a means for modulating the tail current of the first two differential pairs.