250 MHz nMOS relaxation oscillator with enhanced linear voltage-frequency characteristic and temperature stability

The design of an nMOS relaxation oscillator with an operating frequency of 60-250 MHz is presented. The design can be incorporated in a PLL system with centre frequency up to 190 MHz. The oscillator gives a highly linear voltage-frequency characteristic and its temperature coefficient is maintained within +or-200 p.p.m. for temperatures ranging from 0 to 80 degrees C. The design was found to be suitable in PLL system applications.