Narrow band noise suppression scheme for improving signal to noise ratio

In mixed signal systems, a weak signal is buried in strong interferers. The signal to noise ratio is poor. To convert the signal to digital, the dynamic range of the analog to digital converter cannot be efficiently utilized. The interference has to be reduced before the conversion. A notch filter can remove this interference. To allow for the uncertainty of the interference frequency, process variations, and ageing of components, it has to be self-correcting. This paper presents a scheme that improves the signal to noise ratio. This system will form the front end of any mixed mode system where the signal is known to be buried in narrow-band noise. The self-tuned notch filter has two parts: a tunable notch filter (a transconductor implementation of the universal active filter) and a control circuit. This has been implemented in 0.35 μm CMOS technology.