Direct phase and frequency demodulation
View Patent ↗The present invention, generally speaking, provides a time shift angle demodulator that is of simple construction and has an extended linear range. Range extension is achieved by using the input signals directly, not simply post-processing the S-PFD outputs. In accordance with one embodiment of the invention, a method of measuring the phase or frequency of a periodic input signal uses a periodic reference signal and includes comparing the input signal to the reference signal to obtain a lead signal and a lag signal; changing the count of an up/down counter in dependence on the input signal, the reference signal, the lead signal and the lag signal; and using the lead signal, the lag signal and the count signal to produce a phase or frequency signal. In accordance with another embodiment of the invention, an apparatus for measuring the phase or frequency of a periodic input signal uses a periodic reference signal and includes a comparison circuit for comparing the input signal to the reference signal to obtain a lead signal and a lag signal; a logic circuit, including an up/down counter, responsive to the input signal, the reference signal, the lead signal and the lag signal to change the count of the up/down counter; and circuitry for using the lead signal, the lag signal and the count signal to produce a phase or frequency signal.
1. A method of measuring the phase or frequency of a periodic input signal using a periodic reference signal, comprising:
comparing the input signal to the reference signal to obtain a lead signal and a lag signal; and
changing the count of an up/down counter in dependence on the input signal, the reference signal, the lead signal and the lag signal; and
using the lead signal, the lag signal and the count signal to produce a phase or frequency signal, including:
forming from the lead and lag signal a difference signal;
filtering the difference signal to produce a filtered signal; and
adding to the filtered signal a correction signal of a magnitude determined in accordance with the count signal.
2. The method of claim 1 , wherein the difference signal is filtered to produce an aliased output signal.
3. The method of claim 2 , wherein the aliased output signal has added to it a correction signal representing a positive or negative phase increment to form an unwrapped output signal.
4. Apparatus for measuring the phase or frequency of a periodic input signal using a periodic reference signal, comprising:
a comparison circuit for comparing the input signal to the reference signal to obtain a lead signal and a lag signal;
a logic circuit, including an up/down counter, responsive to the input signal, the reference signal, the lead signal and the lag signal to change the count of the up/down counter; and
means for using the lead signal, the lag signal and the count signal to produce a phase frequency signal, including:
means for forming from the lead and lag signal a difference signal;
means for filtering the difference signal to produce a filtered signal; and
means for adding to the filtered signal a correction signal of a magnitude determined in accordance with the count signal.
5. The apparatus of claim 4 , wherein the means for forming and means for filtering comprise a pulse combiner/filter, and the pulse combiner/filter filters the difference signal to produce an aliased output signal.
6. The apparatus of claim 5 , wherein the adder adds to the aliased output signal a correction signal representing a positive or negative phase increment to form an unwrapped output signal.
7. The apparatus of claim 6 , further comprising circuitry for forming the correction signal using the count of the up/down counter.
8. The apparatus of claim 7 , wherein the circuitry for forming the correction signal comprises a multiplier having as one input signal a constant value and having as another input signal the count of the up/down counter.