SUMMARYA continuous-time accelerometer interface is feasible when high dynamic range together with wide signal band is required. In this paper, design of interface electronics for a capacitive sensor is presented. The interface design is focused on attaining resolutions up to 120 dB together with a signal bandwidth of 300 Hz. The essential circuit structures of the interface will be presented and analyzed in detail. Important sources of instabilities and issues that affect the dynamic properties of the sensor are discussed. Measured and simulated results of the closed-loop sensor will be provided to support the theory.
In this paper, measurement results for a micropower 2MHz CMOS frequency reference circuit fabricated with a ml2 13 M7 M5 M6 M8 :Ml8 M19 0.13 ,um CMOS process are presented. This frequency reference circuit, based on source-coupled CMOS multivibrator, provides M14 m 2 M22 the clock signal for a read-out circuit of a capacitive sensor. In Cm addition to a low power consumption, a good frequency stability M15 OUT is required. Supply independent biasing and symmetrical loads are used to optimize the frequency stability. The typical power C X16 M17 consumption is 3.0 ,uW at room temperature with 1.8 V supply _ voltage. When properly calibrated, the frequency stays within M(MlM 2 2 ±2.5% of the nominal oscillation frequency in the operating Rm voltage range of 1.8 -2.5 V (with ±10 % variation) over a temperature range from -35 to +85 C. The measured phase BIASINGCIRCUIT OSCILLATOR COMPARATOR noise and jitter agree well with the simulations.Fig. 1. Presented frequency reference circuit.
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