Design Of A CMOS Digital-Trim On-Chip RC Oscillator

The application of electronic technology in the fields of medical, finance and Internet provides a new direction for the development of IC and also drives the rapid development of IC. The operating frequency of IC is more and more high and has reached GHz. So high performance, high speed, low-voltage and low-power IC chip has already become a new research hotspot. At the same time, it also puts forward higher and higher requirement for the system clock. It is an urgent need for the equipment to provide a reliable, low-voltage and low-power clock module.In this thesis, a kind of oscillator for mobile display driver IC or power management IC is designed. It is based on traditional RC relaxation oscillator by 8-bit digital calibration to stabilize the output frequency. The structure reduces the variation of frequency with the changed process, voltage and temperature and makes the output frequency of the oscillator stability at 12 MHz under different conditions. The normal operating voltage is 1.5V in the design and it changes from 1.35 V to 1.65 V. The temperature changes from-40℃ to 85℃. The maximum operating current of the design is less than 200μA. The variation of frequency is less than 1%.UMC 0.13μm CMOS process was used in the CMOS digital-trim on-chip RC oscillator. Decoder, comparator, bias and frequency generating module was included in the designed oscillator. By researching the digital-trim structure, three trimming methods have been presented, and then their range of output frequency and gear step interval was analyzed. Finally a best digital-trim method is achieved that uses 256 gears and gear step interval is 0.44% along with 256 trimming resisters were calculated. From the results of HSPICE simulation, the frequency meets the anticipative design specification. The variation of frequency changes from-0.906% to +0.408% and the max operating current of the circuit is 184.7μA on all kinds of MOS corners and typical resistor and capacitor corner. So it has small variation and low-power consumption. The layout is designed by Cadence Virtuoso and verified DRC, ERC and LVS by Mentor Calibre. So the CMOS digital-trim on-chip RC oscillator outputs a reliable, low-voltage and low-power clock which is used in mobile display driver chips or power management chips.