A Process-Tolerant, Low-Voltage, Inverter-Based OTA for Continuous-Time Σ-Δ ADC

Inverter-based implementation of operational-transconductance amplifiers is an attractive approach for low-voltage realization of analog subsystems. However, the high sensitivity of inverterlike amplifiers' performance to process and temperature variations limit the achievable performance of the whole system across process and temperature corners. In this paper, a tuning technique is proposed to maintain the inverter-based amplifier performance across the 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 sigma-delta (Sigma-Delta) analog-to-digital converter (ADC). The main building block of the implemented ADC is an inverter-based amplifier. This makes the resulting Sigma-Delta ADC easier to scale to different technology nodes. A 74-dB signal-to-noise and distortion ratio is achieved, for a signal bandwidth of 64 kHz at a sampling frequency of 6.4 MHz, while consuming 400 mu A from a 0.8 V supply in 65-nm CMOS technology.