Frequency Reference for Capacitive Sensor Applications

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 BIASING CIRCUIT OSCILLATOR COMPARATOR noise and jitter agree well with the simulations. Fig. 1. Presented frequency reference circuit.