Substrate noise reduction using active guard band filters in mixed-signal integrated circuits

A substrate noise reduction technique using an "active guard band filter", is developed for analog and digital mixed-signal integrated circuits. A noise cancellation signal generated by operational amplifiers is actively input into a guard band to cancel substrate noise. In a 0.8 /spl mu/m CMOS test chip, substrate noise was experimentally suppressed to less than 1% of the original non-canceled noise for frequencies below 1 MHz by using this technique.