A signal processor for 1-bit signals comprises a fifth order Delta-Sigma Modulator (DSM) having an input 4 for receiving a 1-bit signal and an output 5 at which a processed 1-bit signal is produced by a quantizer Q. The quantizer Q receives a p-bit signal from a series of 5 signal integration stages. Each stage comprises a first 1-bit multiplier An coupled to the input 4, a second 1-bit multiplier Cn coupled to the output 5, an adder 6n which sums the outputs of the coefficient multipliers and an integrator 7n which integrates the output of the adder 6n. A final stage comprises a coefficient multiplier An+1 and an adder 6n+1. The adder 6n+1 sums the output of the coefficient multiplier An+1 and the output of the integrator of the preceding integration stage. The coefficients An and Cn are chosen to provide an overall attenuation of the input signal and of the quantization noise produced by the quantizer and also to provide a low pass filter which provides a compensating gain to the input signal. In this way the quantization noise outside the band of the input signal is reduced. Reduction of quantization noise enhances stability of the circuit and also allows several DSMs to be connected in series by preventing the build-up of excess noise which may compromise stability. IMAGE
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