Abstract: Methods and circuits for chain ring oscillators having a constant duty cycle and being insensitive to ground noise have been disclosed. The ring oscillator generates n outputs with 360°/n phase shift and each stage is delayed by T 2 × n . The output of a suitable stage is selected so that a digital XOR-gate, using the output of a selected stage and the output of the nth stage, eliminates variations of the duty cycle caused by temperature and process variations. In case a 50% duty cycle is desired the stage number N of the selected stage can be calculated using the equation N=(n?1)/2. The duty cycle can be varied by selecting the output of another gate. A D-flipflop, clocked by the output of the XOR-gate removes noise from the clock pulses.