A new low-noise 100-MHz balanced relaxation oscillator

A novel fully balanced architecture for high-frequency, low-noise relaxation oscillators is presented. Differential operation is achieved with the use of two grounded capacitors utilizing the circuit parasitics. Bypassing of the regenerative memory function in the oscillator benefits both high-speed and low-noise operation. A detailed analysis of phase noise in relaxation oscillators is performed. Results obtained from a test chip have verified the viability of the new oscillator and the developed phase-noise theory. The oscillator circuit has been realized in a medium-frequency (f_τ=3 GHz) bipolar process. The tuning range extends to 150 MHz. At an oscillation frequency of 115 MHz, measured phase noise was -118 dBc/Hz at 1-MHz distance from the carrier