A wide-band NMOS balanced modulator/amplifier which uses 1- mu m transistors for linearity

The saturated drain current of short-channel (1 mu m) NMOS transistors is nearly linear with gate drive. A wideband balanced modulator/amplifier which exploits this property to achieve low distortion is described. Operated with a 5-V power supply, the circuit has a gain of 10 with respect to the modulating input, an intrinsic 3-dB bandwidth near 100 MHz, and nonlinearity less than 0.5% for a voltage swing of +or-2 V. This input can serve as modulation for a square wave carrier with equally good linearity.<>