Digital FM demodulator having an address circuit for a lookup ta

Details Digital FM demodulator having an address circuit for a lookup ta Digital FM demodulator having an address circuit for a lookup ta

1994-09-08

1995-08-08

Grimm, Siegfried H.

Demodulators

Frequency modulation demodulator

Having specific distortion, noise or other interference...

329320, 329336, 329341, 375324, 455214, H03D 302

Patent

active

054402697

ABSTRACT:
In a digital frequency demodulator, data representing the input signal to be demodulated is prestored in a look-up table and signal processing is digitally performed to generate a read address required for reading out the data stored in the look-up table using a phase shift method of operation. Phase-shifting is performed by determining the slope of a frequency-modulated signal containing a signal which does not cross the zero axis. Thus, the precision of the frequency demodulation is enhanced, and the frequency demodulation data stored in the look-up table is minimized to reduce the size of a ROM used for the look-up table. The digital frequency demodulator includes a look-up table for storing frequency demodulation data, an address generating circuit for comparing the magnitude of the absolute value of frequency modulated signal and a phase-shifted version thereof so as to generate address information for the look-up table and a comparison signal, a circuit for determining the slopes of the frequency-modulated and phase-shifted signals and, responsive thereto, generating slope determination signals, and a phase compensator for operating on the output from the look-up table in response to the slope determination signals and the comparison signal to thereby expand the phase value output from the look-up table. A method for operating a digital frequency demodulator is also revealed.

REFERENCES:
patent: 4862099 (1989-08-01), Nakai et al.
patent: 4994754 (1991-02-01), Ohta

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