Patent ID: 7054395

Claim:
A digital demodulation apparatus for amplifying, for demodulation, a digital modulated signal wave received through the air with gain automatically controlled for generating a digital signal having a predetermined amplitude, the digital demodulation apparatus comprising: receive level variation detection means for detecting receive level variation of the received digital modulated signal wave; and gain adjusting means for adjusting the gain based on the detected receive level variation, wherein said receive level variation detection means comprises: tuning means for extracting a desired digital modulated signal from received digital modulated signal waves, and generating a first digital modulated signal; automatic gain control amplification means for amplifying the first digital modulated signal with the gain, and generating a second digital modulated signal; digitizing means for converting the second digital modulated signal into a third digital modulated signal; and tuned signal receive level variation detection means for detecting receive level variation of the first digital modulated signal based on an amplitude of the third digital modulated signal, said gain adjusting means adjusts the gain based on the detected receive level variation of the third digital modulated signal, said tuned signal receive level variation detection means comprises: amplitude detection means for detecting an amplitude value of the third digital modulated signal; average-filtering means for carrying out average-filtering on the detected amplitude value with a predetermined averaging coefficient to detect an average amplitude value; error detection means for detecting an error between the detected average amplitude value and a desired average value; loop filter means for carrying out loop filtering on the detected error with a predetermined integral coefficient, and generating a stabilization signal for stabilizing an automatic gain control amplification process; and difference detection means for detecting a difference between two arbitrary values of the stabilization signal, said tuned signal receive level variation detection means detects the receive level variation based on the generated stabilization signal, the receive level variation is detected based on a comparison result obtained by comparing the difference with a predetermined threshold, said tuned signal receive level variation detection means generates a level variation signal indicating the comparison result, and said gain adjusting means controls the gain based on the level variation signal, and said average-filtering means is an adaptive averaging filter for adaptively setting the predetermined averaging coefficient based on a value of the level variation signal, to enable digital signal demodulation with high quality by appropriately setting the predetermined averaging coefficient based on the detected receive level variation.