Abstract: Apparatus and methods for demodulation are provided. In one embodiment, a method includes receiving an input signal having a frequency that varies in relation to a state of the signal, calculating a sine and cosine of a phase control signal, generating a first signal proportional to the sine of a product of a first quantity and the frequency of the input signal, generating a second signal proportional to the cosine of a product of the first quantity and the frequency of the input signal, and summing a product of the first signal and the cosine of the phase control signal with a product of the second signal and the sine of the phase control signal to generate a demodulator output for resolving the state of the input signal. In certain implementations, the phase control signal is controlled so as to reduce a frequency error of the input signal.

Abstract: Apparatus and methods for demodulation are provided. In one embodiment, a method includes receiving an input signal having a frequency that varies in relation to a state of the signal, calculating a sine and cosine of a phase control signal, generating a first signal proportional to the sine of a product of a first quantity and the frequency of the input signal, generating a second signal proportional to the cosine of a product of the first quantity and the frequency of the input signal, and summing a product of the first signal and the cosine of the phase control signal with a product of the second signal and the sine of the phase control signal to generate a demodulator output for resolving the state of the input signal. In certain implementations, the phase control signal is controlled so as to reduce a frequency error of the input signal.

Abstract: 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 d

Abstract: An FSK demodulator system with tunable spectral shaping including a pair of quadri-correlators responsive to first and second quadrature signals, one of the pair deriving first and second signals representative of the frequency deviation of the quadrature signals at even integer multiples of the frequency deviation and for resolving the modulated FSK data represented by the quadrature signals and the other of the pair deriving first and second signals representative of the frequency deviation of the quadrature signals at odd integer multiples of the deviation frequency and for resolving the modulated FSK data represented by the quadrature signals, and a delay control circuit for setting a delay to each of the pair of quadri-correlators to control the first and second signals representative of the frequency deviation of the quadrature signals derived by each of the pair of quadri-correlators and generate a tuned spectral response at both even and odd integer multiples of the frequency deviation.