Tunable linear MOS resistor for RF applications

Abstract

This paper discusses a continuously tunable linear MOS resistor with bi-directional characteristics. The proposal is based on a 2nd order nonlinearity cancellation and is implemented by quasi-floating-gate (QFG) technique. The resistor is optimized for speed, noise and linearity, which makes it well-suited for tunable RF amplifiers. Parallel slices were introduced to enlarge the tuning range. A switching strategy is implemented to guarantee monotonic tuning with limited linearity loss. A testchip is fabricated in 65nm CMOS technology, which shows a -40dB distortion with moderate overdrive voltage and 200mV peak to peak signal amplitude and a high tuning ratio of 19. This MOS resistor has no static power consumption and a layout area of 39μm × 37μm.