Noise reduction in CMOS driver using capacitor discharge to generate a control voltage

摘要

A pull-up or pull-down transistor in an output buffer or the like is controlled to limit dI/dt and thus reduce noise. This control employs a series transistor in the driver circuit which has a modulating voltage applied to its gate. This modulating voltage is generated in a circuit which uses precision-timed clocks as a reference so that variations in electrical parameters (process, temperature and power supply dependent) will not cause variation in circuit noise. A dummy driver circuit is used to discharge a capacitor at a rate dependent upon the modulating voltage, and the capacitor voltage is compared with a reference at a time determined by the precision clock. The result of the comparison is used to increment or decrement the modulating voltage.