Digital FSK demodulator
AssigneeElsag International N.V.
InventorJoseph C. Nemer
Life of this patent
Estimating the term…
Abstract
A FSK demodulator which uses the combination of a digital phase comparator and a digital controlled oscillator (DCO) in the form of a state machine to demodulate an FSK signal. The phase comparator compares the phase of the FSK signal with the output of the DCO to provide a signal to the DCO having a level dependent on the phase relationship between the two signals at the input to the comparator. The demodulator also includes a filter to obtain the data from the signal at the output of the comparator.
Claims17
A demodulator for demodulating a FSK modulated signal having a level and data therein to obtain said data comprising:
- a) a phase comparator for generating a first signal with either one or the other of two levels depending on the phase relationship of said FSK modulated signal level to the level of a second signal;
- b) a state machine having a closed loop, said closed loop having a predetermined total number of states, said state machine responsive to said first signal for producing said second signal with a frequency that is a function of said first signal level, said first signal level determining how many of said predetermined total number of states said state machine must traverse to complete said closed loop;
- and
- c) first means for filtering said first signal to obtain said data in said FSK modulated signal.
A method for demodulating a FSK modulated signal having a level and data therein to obtain said data comprising the steps of:
- a) generating a first signal with either one or the other of two levels depending on the phase relationship of said FSK modulated signal level to the level of a second signal;
- b) traversing a loop of a state machine having a predetermined total number of states in response to said first signal, said first signal level determining how many of said predetermined total number of states said state machine must traverse to complete said loop;
- c) producing said second signal from said state machine with a frequency that is a function of said first signal level;
- and
- d) filtering said first signal to obtain said data in said FSK modulated signal.
A demodulator for demodulating a FSK modulated signal having data therein to obtain the data comprising:
- a) a phase comparator for generating an output signal in response to said FSK modulated signal and a signal from a state machine, said output signal having a pulse width which is proportional to the difference in phase between said FSK modulated signal and said signal from said state machine;
- b) said state machine having a closed loop, said closed loop having a predetermined total number of states, said state machine responsive to said phase comparator output signal for producing said signal from said state machine with a frequency that is a function of said phase comparator output signal pulse width, said phase comparator output signal pulse width determining how many of said predetermined total number of states said state machine must traverse to complete said closed loop;
- and
- c) means for filtering said phase comparator output signal to obtain said data in said FSK modulated signal.
A method for demodulating a FSK modulated signal having data therein to obtain the data comprising the steps of:
- a) generating a first signal with a pulse width which is dependent on the difference in phase between said FSK modulated signal and a signal from a state machine having a predetermined total number of states;
- b) traversing a loop of said state machine in response to said first signal, said first signal pulse width determining how many of said predetermined total number of states said state machine must traverse to complete said loop;
- c) producing said signal from said state machine with a frequency that is a function of said first signal pulse width;
- and
- d) filtering said first signal to obtain said data in said FSK modulated signal.
Dependencies are inferred from the claim text.