An apparatus and method for estimating a frequency and/or a phase of a digital
input signal by determining phase values of the input signal. The phase values
are then added over a predetermined summation length N/B. The sampling rate of
the added-up phase values are reduced by a factor N/B in comparison with the sampling
rate of the phase values. The added-up phase values are delayed in a chain of at
least B-1 delay elements. The differently-delayed added-up phase values are then
added or subtracted to create a resulting. pulse response of the frequency such
that the resulting pulse response of the frequency is constant positive in a first
interval, is zero in a second interval and is constant negative in a third interval,
so that a resulting pulse response of the phase is constant in at least a middle
interval or is otherwise zero.