| 摘要 |
A digital frequency measurement system including 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 processing circuits responsive to the first and second digital quadrature signals representative of the modulated input signals and the first and second differentiated signals for multiplying the first differentiated signal by the second quadrature digital representation of the input signals and multiplying the second differentiated signal by the first quadrature digital representation of the input signals to provide first and second multiplied signals, a combining circuit responsive to the first and second multiplied signals for generating a density signal having a pulse density proportional to the frequency of the input signals, a digital filter responsive to the density signal for providing an output signal representing the average value of the pulse density, and an envelope detector circuit responsive to the output signal for determining the midpoint of the maximum and minimum signal level representative of the input signals and providing a digital signal that represents the center frequency of the input signals. |
