Automatic tuning circuit for bulk-controlled subthreshold MOS resistors

A simple automatic tuning circuit is proposed which is suitable for controlling very large channel resistance of weak-inverted transistors operated in the linear regime. The channel resistance for 1.2 MΩ nominal value presents about ± 0.6% variation for -20-80°C temperature range, ±5% variation at process/temperature (P/T) corners and total harmonic distortion = -42 dB for differential signals. The supply voltage was V_DD = 1 V and the current consumption was about 470 nA. The proposed concept and the performance were confirmed and evaluated by simulations using standard 0.35 μm CMOS process.