Digital modulator having a digital filter including low-speed circuit components
First Claim
Patent Images
1. A digital demodulator comprising:
- a converter for converting an analog input signal into a digital signal, said converter operating so as to satisfy
space="preserve" listing-type="equation">f.sub.s =4·
f.sub.IF /(2n+1), wherein fIF indicates an intermediate carrier frequency, fs is a sampling frequency and n indicates a positive integer;
a signal processing section for quadrature demodulating said digital signal output from said converter by mixing with quadrature local oscillation signals, a frequency fc'"'"', of said quadrature local oscillation signal is
space="preserve" listing-type="equation">f.sub.c'"'"' =f.sub.s /4, wherein said signal processing section extracts a first and a second digital signal being orthogonal in phase to each other, and said first and second digital signals being alternately inverted in polarities with said sampling frequency;
at least one digital filter section coupled with said signal processing section for sampling said first and second digital signals, said digital filter section comprising;
first switching means, andsecond switching means,said first switching means conducting a change-over operation between said digital signals and a signal at binary zero with a frequency m·
fs, and said second switching means receiving the signals from said first switching means and intermittently outputting therefrom signals at a period corresponding to a frequency m·
fs /M, wherein m and M are positive integers and M>
m; and
at least one filter arithmetic section coupled with said digital filter section, for producing demodulated signals.
1 Assignment
0 Petitions
Accused Products
Abstract
A digital demodulator which demodulates an analog signal obtained through a quadrature amplitude modulation to produce a digital demodulated signal includes a converter to convert the analog signal into a digital signal and a signal processor to quadrature-demodulating the digital signal from the converter. Assuming that the analog signal has a carrier frequency of fIF and the signal conversion is accomplished with the sampling frequency fs, the demodulator is set to satisfy fs=4·fIF /(2n+1), where n denotes a positive integer. The signal processing section conducts the quadrature demodulation according to a quadrature local oscillation signal having a frequency fc satisfying fc=fs/4.
-
Citations
3 Claims
-
1. A digital demodulator comprising:
-
a converter for converting an analog input signal into a digital signal, said converter operating so as to satisfy
space="preserve" listing-type="equation">f.sub.s =4·
f.sub.IF /(2n+1),wherein fIF indicates an intermediate carrier frequency, fs is a sampling frequency and n indicates a positive integer; a signal processing section for quadrature demodulating said digital signal output from said converter by mixing with quadrature local oscillation signals, a frequency fc'"'"', of said quadrature local oscillation signal is
space="preserve" listing-type="equation">f.sub.c'"'"' =f.sub.s /4,wherein said signal processing section extracts a first and a second digital signal being orthogonal in phase to each other, and said first and second digital signals being alternately inverted in polarities with said sampling frequency; at least one digital filter section coupled with said signal processing section for sampling said first and second digital signals, said digital filter section comprising; first switching means, and second switching means, said first switching means conducting a change-over operation between said digital signals and a signal at binary zero with a frequency m·
fs, and said second switching means receiving the signals from said first switching means and intermittently outputting therefrom signals at a period corresponding to a frequency m·
fs /M, wherein m and M are positive integers and M>
m; andat least one filter arithmetic section coupled with said digital filter section, for producing demodulated signals. - View Dependent Claims (2, 3)
-
Specification