Patent ID: 7352831

Claim:
A digital frequency measurement system comprising: first and second digital differentiators responsive to first and second digital quadrature signals representative of first and second quadrature modulated input signals that represent binary data having a center frequency equal to a predetermined IF frequency for generating first and second differentiated signals; first and second multiplier circuits responsive to said first and second digital quadrature signals and said first and second differentiated signals for multiplying the first differentiated signal by the second digital quadrature signal and multiplying the second differentiated signal by the first digital quadrature signal to provide first and second multiplied signals; a subtraction circuit responsive to said first and second multiplied signals for generating a density signal having a pulse density proportional to the frequency of said input signals; a digital filter responsive to said density signal for providing an output signal representing the average value of said pulse density; and an envelope detector circuit responsive to said output signal for determining the midpoint of the maximum and minimum signal level representative of said input signals and providing a digital signal that represents said center frequency of said input signals.