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 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 band-gap 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.
KeywordsAnalog Circuit Differential Pair NMOS Transistor Digital Part Substrate Noise
Unable to display preview. Download preview PDF.
- D.W.J. Groeneveld, “Groundbounce in CMOS”, Digest of technical papers, workshop on Advances in Analog Circuit design, Leuven 1993.Google Scholar
- T. J. Schmerbeck, R.A. Richetta and L.D. Smith, “A 27MHz Mixed Analog/Digital Magnetic Recording DSP Using Partial Response Signalling with Maximum Likelihood Detection”, Digest of technical papers, ISSCC 1991, Feb 1991, pp 136-137.Google Scholar