Patent ID: 8521798

Claim:
A digital all pass filter of at least the second order, comprising: a first filter of the first order nested within a second filter of the first order; the first filter comprising: a first subtractor having a plus input providing an input to the first filter and a minus input; a first summer having first and second inputs and output providing an output of the first filter; and a first multiplier coupled between the output of the first subtractor and the first input of the first summer; and a feedforward first delay element coupled between the plus input of the first subtractor and the second input of the first summer; and the second filter comprising: a second subtractor having a plus input providing an input to the second filter and a minus input; a second summer having first and second inputs and an output providing an output of the second filter; a second delay element having an output coupled to the first input of the second summer and an input; a feedforward second multiplier coupled between the first input of the second subtractor and the second input of the second summer; a feedback third multiplier between the output of the second summer and the minus input of the second subtractor; and said first filter being coupled between the output of the second summer and the input of the second delay element; and a feedback loop between the output of the second delay element and the minus input of the first subtractor.