This paper describes fully integrated active guard band filters for suppressing the substrate coupling noise and their noise suppression effect measured by test chip experiments. The noise cancellation circuit of the active guard band filters simply consists of an inverter and a source follower. The substrate noise suppression effect was measured by using a test chip fabricated in a 0.18 µm CMOS triple-well process for system-on-a-chip. The noise with the filter was less than 5% of that without the filter and the noise suppression effect was observed from 1 MHz to 200 MHz by the statistical measurement of the voltage comparator. The noise suppression effect was also observed for actual digital switching noise produced by digital inverters. Configuration of the active guard band filter was investigated by simulation and it is shown that high and uniform noise suppression effect is achieved by placing the guard bands in the L-shape around the target triple-well area on the p-substrate.

A noise suppression algorithm with high speech quality based on weighted noise estimation and MMSE STSA is proposed. The proposed algorithm continuously updates the estimated noise by weighted noisy speech in accordance with an estimated SNR. The spectral gain is modified with the estimated SNR so that it can better utilize the improvement in noise estimation. With a better noise estimate, a more correct SNR is obtained resulting in the enhanced speech with low distortion. Subjective evaluation results show that five-grade mean opinion scores of the new algorithm with and without a speech codec are improved by as much as 0.35 and 0.40 respectively, compared with either the original MMSE STSA or the EVRC noise suppression algorithm.

An AC coupling configuration for the active guard band filters is introduced for suppressing substrate coupling noise in analog and digital mixed-signal integrated circuits. With this method, a substrate-coupling-noise cancellation signal can be supplied to a ground-level substrate by using a single 3-V supply on-chip circuits. Noise was suppressed to a maximum of less than 0.05 from 100 Hz to 2 MHz in a 0.35-µm CMOS test chip. Both experiments and a simulation based on the substrate extraction model showed the similar dependence of the noise-suppression effect on the arrangement of the guard-bands and analog circuits. The simulation is thus effective for optimizing the arrangement to suppress noise effects when designing a chip.

This letter proposes the method using a filter to suppress the very large noise obstructive to the radio pulsar surveys. This noise suppression filter is constructed from the average of the amplitude spectrum of pulsar signal for each channel. Using this method, the dispersion measure, one of the important parameters in the pulsar surveys, can easily be extracted.