Linearity enhancement in the entire tuning range of CMOS OTA using a new tune compensated source degeneration technique

This paper presents a tunable linear OTA based on an improved adaptive biasing of degeneration triode-mode transistor and a new technique for compensating the linearity degradation due to the tuning action. Using the adaptive biasing circuit, the degeneration resistance is modulated such that to make constant transconductance in a wide range of input voltages. As the linearity would be lost at higher values of transconductance, a tune-dependent current is injected to the adaptive biasing circuit to remove the nonlinearities of OTA's second stage. Using 1.8 V supply voltage, the proposed OTA consumes 600μW in which the portion of adaptive biasing and the tune compensation circuits is 37μW. When a 0.9 Vp-p, 10 MHz input voltage is applied to the OTA which is tuned at highest Gm, HD3 decrement due to using adaptive biasing circuit is 3.7 dB, while it reduces to 11.3 dB due to using both adaptive biasing and tune compensation circuits.