Abstract: A tree mixer includes a first differential pair of transistors which divide current from a first current source between the transistors in dependence upon a first differential input signal supplied to first input terminals. Two second differential pairs of transistors have controlled paths which conduct current, divided between the transistors of the differential pair in dependence upon a second differential input signal supplied to second input terminals, dependent upon current passed by a respective transistor of the first pair of transistors, to produce a product signal at output terminals. One or more second current sources provide for the total current passed by the first pair of transistors to be greater than the total current passed by the two second pairs of transistors, for improved linearity without increasing noise. A quadrature phase modulator can include two such mixers with common output circuitry.