A Trimmable RC-Oscillator for Automotive Applications, with Low Process, Supply, and Temperature Sensitivity

The design of a stable over temperature RC-oscillator for automotive applications is presented in this paper. The oscillator is designed and fabricated in a 0.35μm BCD6 technology, using a 3.3V supply voltage. The stability over temperature of the oscillation frequency is quite independent on process and supply voltage variations: the oscillator shows a frequency drift from 27°C lower than 0.5% in all conditions (supposing to use an off-chip ideal resistance), over a temperature range from -40 to +125°C and a ±10% supply voltage variation around its typical value. A topology exploiting two capacitors driven by non-overlapping phases is proposed to ensure the proper timing for charge and discharge. A digital trimming is also provided to compensate process variations. The nominal output frequency can be set up to about 1MHz simply by changing the value of the external resistor. Detailed circuit design and simulation results are presented