This paper gives experimental proof of an intriguing physical effect: periodic on-off switching of MOS transistors in a CMOS ring oscillator reduces their intrinsic 1=f noise and hence the oscillator's close-in phase noise. More specifically, it is shown that the 1=f 3 phase noise is dependent on the gate-source voltage of the MOS transistors in the off state. Measurement results, corrected for waveform-dependent upconversion and effective bias, show an 8-dB-lower 1=f 3 phase noise than expected. It will be shown that this can be attributed to the intrinsic 1=f noise reduction effect due to periodic on-off switching.

No abstract

No abstract

Substrate noise is one of the key problems in mixed analog/digital ICs. Although measures are known to reduce substrate noise, the noise will never be completely eliminated since this requires larger chip area or exotic packages and thus higher cost. Analog circuits on digital ICs simply have to be resistant to substrate noise. A general strategy is given which can be summarized as: the supply of the analog circuits must be referred to the substrate and the analog signals must be referred to a clean analog ground. Furthermore several design constraints are given to minimize the effect of substrate noise on analog. Two bandgap circuits are discussed and it is shown that apparently minor design issues, such as the connection of an n-well of a PMOS differential pair, can have large impact on the substrate sensitivity of this circuit. This has been verified by measurements.