Notch-ΣΔmodulator – Digital RF modulator with ΣΔ based notch filter

The Notch ΣΔ modulator (ΣΔM) is a digital RF modulator,

which uses a modified sigma-delta modulation in order to minimize unwanted emissions in the most critical frequency bands. Sigma-delta modulation is classically used to push the quantization noise to frequencies outside the signal band, where it can then be removed by filtering. Thereby, a large signal-to-noise ratio can be obtained in the signal band despite having a low DA-converter resolution. However, in mobile radio systems complex and expensive filters are needed to attenuate the emitted noise outside the signal band to an acceptable level. The Notch ΣΔM solves this problem by the integration of a notch filter in the sigma-delta modulator which reduces the noise in especially critical adjacent bands. This advantage is gained at the cost of a slightly increased noise in the adjacent frequency bands. However, this is not critical due to relaxed requirements at these frequencies.

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