Low -voltage and low -power, deep -submicron analog circuits for single -chip, mixed -signal microinstrumentation systems.

Abstract

Shrinking process feature size has promoted the system-on-a-chip concept. Combining analog and RF circuits, sensor and actuator technology, and digital signal processing on a single-chip microinstrument profits many applications. Exploiting the logic density of deep-submicron digital processes compared to more expensive mixed-signal processes enables significant signal processing. The deep-submicron processing techniques developed to optimize digital performance, however, lead to analog performance degradation: reduced small-signal output resistance and increased 1/<italic>f</italic> noise. Shrinking supply voltages and relatively constant threshold voltages exacerbate these problems. Additionally, CMOS switches cannot pass rail-to-rail signals when supply voltages are under a Volt. In portable devices, supply voltage and power consumption limits are also driven by battery characteristics. This research promotes the application of weak-inversion biasing, switched-opamp, and reset-opamp, and develops new low-voltage and low-power circuit topologies to address the analog performance degradation. A mixed-signal microcontroller was developed that integrates sensor interface circuitry, a temperature sensor, and analog and digital signal processing. At 3 V, the signal chain achieves a dynamic range of 58 dB (50 Hz bandwidth). Functionality of the micro-instrument is verified through measurements with capacitive-based pressure sensors and amperometric and potentiometric chemical sensors. A 900 mV, 128 muA, 0.18 mum CMOS, rail-to-rail opamp was developed using weak-inversion biasing and threshold shifting and achieves a gain of 80 dB, a gain-bandwidth of 1.3 MHz, and a 60&deg; phase margin when driving a 10 kO 150 pF load. The enabler of a sub-1 V SigmaDelta modulator is a new dynamically-biased pseudo-differential integrator. This integrator supports low-voltage operation by employing the reset-opamp technique, which removes high-swing switches. Although functional at 700 mV, at 900 mV, the modulator achieves a dynamic range of 62 dB (100 Hz bandwidth) and consumes 370 nW---a new level of performance for reset-opamp modulators. Finite gain-compensation circuits are proposed to enhance this performance. This research identified the challenges in designing low-voltage and low-power analog circuits in deep-submicron digital processes and developed circuit solutions in the context of single-chip microinstruments.