A
ring oscillator circuit, such as a VCO, with a relatively high level of
noise rejection for
noise originating from both the
voltage supply and ground. The
ring oscillator circuit is composed of a plurality of differential
delay circuits, each differential
delay circuit generating a differential output
signal that is a delayed (and preferably inverted) version of a differential input
signal. ‘Each differential
delay circuit includes first and second input transistors for receiving the differential input
signal. Each differential delay circuit also includes first and second load transistors coupled in parallel with the respective first and second input transistors. Each differential delay circuit further includes a first
current source coupled between the first input
transistor and a first power supply terminal (e.g., a
voltage supply terminal), a second
current source coupled between the second input
transistor and the first power supply terminal and a third
current source coupled between the first and second input transistors and a second power supply terminal (e.g., a ground terminal). The first and second current sources reduce the
coupling of
noise from the first power supply terminal to the output. The third current source reduces the
coupling of noise from the second power supply terminal to the output.