Parallel oversampled decimator filter
The decimator filter includes at least three identical undersampled filters out-of-phase with each other and connected in parallel, and an interpolator connected to the output of each filter. The decimator filter includes a triple integrator having an output connected to each of the filters. Each filter defines a channel that includes in sequence an undersampling circuit, a differentiator and a multiplier. The outputs of the multipliers are connected to an adder. The input signals to each of these channels are offset by a delay equal to one period of the oversampled frequency. Each undersampling circuit and each multiplier has a second input receiving a signal from a state machine. The decimator filter improves the required phase extraction time and the precision defined in the ISDN U interface specifications. By combining the decimation filter and the extraction functions, a device is produced in a small area, which consequently, consumes low power.