A Tunable Inverter-Based, Low-Voltage OTA for Continuous-Time ΣΔ ADC

Inverter-based implementation of operational-transconductance amplifiers (OTAs) is an attractive approach for low-voltage realization of analog sub-systems. However, the high sensitivity of inverter-like amplifiers performance to process and temperature variations limits the achievable performance of the whole system, across process and temperature corners. In this paper, a tuning technique is proposed to maintain inverter-based amplifier performance across process and temperature corners without requiring additional voltage headroom than that required by the inverter circuit. The introduced technique is used to implement a third order continuous-time (CT) ΣΔ analog-to-digital converter (ADC). A 74 dB signal-to-noise and distortion ratio (SNDR) is achieved, for a signal bandwidth of 64 kHz at a sampling frequency of 6.4 MHz, while consuming 400 μA from 0.8 V, supply, in 65 nm CMOS technology.

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