Supply and temperature compensated oscillator for super twisted nematic (STN) application

In a single-chip LCD (liquid crystal display) driver system, the oscillator provides accurate clock signals for timing generation and DC-DC conversion. Two mechanisms affect the accuracy of the oscillator: (1), ambient temperature fluctuations result in oscillator frequency shift, which could also affect the response time of liquid crystal; and (2) an LCD driver has to be designed to serve a wide range of input supply voltages, which could affect the performance of the oscillator. For portable applications, the oscillator should consume very low power, preferably below 100μW, and it should be designed to work with very low supply voltages. Therefore, it is critical to design a low-voltage low-power oscillator that is temperature and supply independent. This research presents the design of a low-power, supply and temperature independent on-chip oscillator fabricated in AMS 0.35μm N-well CMOS process. The nominal oscillating frequency is 390kHz, and the total oscillating frequency variation is only ±2.0% for a supply voltage range of 1.6V to 3.3V, and a temperature range of -35oC to 85oC. It only dissipates less than 23μW at a supply voltage of 2.775V. The high tolerance against voltage and temperature variations and low-power characteristics make this oscillator design particularly favourable for LCD display driver applications