KR20090038967A

KR20090038967A - Demodulator

Info

Publication number: KR20090038967A
Application number: KR1020070104302A
Authority: KR
Inventors: 임재원
Original assignee: (주)텔리뷰
Priority date: 2007-10-17
Filing date: 2007-10-17
Publication date: 2009-04-22

Abstract

The present invention relates to a method and apparatus for demodulating a modulated signal by direct downconversion with or without a valid signal component in the center of a signal band.

Description

Demodulation Method and Demodulation Device Using Frequency Shifter {DEMODULATOR}

Various modulation methods are used to transmit information. Among these modulation schemes, signals modulated by Quadrature Phase Shift Keying (QPSK) or Quadrature Amplitued Modulation (QAM), etc., have no signal component other than a carrier in the center of the signal band. Quadrature demodulators are not applicable to modulated signals that have a valid signal component in the center of the band. When the quadrature demodulator of FIG. The leakage signal of the direct current (DC) frequency band caused by the frequency / phase mismatch of the signal damages the valid signal component. Therefore, a DVB-T direct down conversion demodulator cannot be used for a signal modulated by a VSB modulation or OFDM scheme.

The present invention relates to a quadrature demodulation method and apparatus, and more particularly, to a method and apparatus for demodulating a modulated signal by direct downconversion regardless of the presence or absence of a valid signal component in the center of a signal band. It is about.

Even in the case of a modulated signal having a valid signal component in the center of the signal band, a frequency shifter that simplifies the high frequency processing circuitry by directly converting and demodulating without being affected by a leakage signal of a DC frequency is provided. It is an object of the present invention to provide a direct conversion demodulation method and a demodulation device.

The direct conversion demodulation method and demodulation apparatus using the frequency shifter according to the present invention for achieving the above object, in demodulating a target signal having a center of fc and the bandwidth of W in the RF signal, the frequency of the oscillation frequency (fosc) A signal is generated, the RF signal is mixed with the oscillation signal, and also with the oscillation signal delayed by 90 degrees to produce an I and Q signal, and then converted into the I and Q signals. Baseband by shifting the frequency to zero on the spectrum, extracting only the I and Q signals of the target signal with a W / 2 lowpass filter, and then shifting them by W / 2 opposite the previously shifted direction It is characteristic to get the target signal of

The direct conversion demodulation method and demodulation device using the frequency shifter according to the present invention operating as described above is effective even if the signal having the effective signal component in the center of the band is demodulated by the direct conversion method. This eliminates the need to use intermediate frequency (I / F) conversion stages. Therefore, it is easy to design and manufacture the high frequency processing circuit portion and lower the manufacturing cost of the RF module.

The configuration of the quadrature demodulator according to the present invention is shown. The quadrature demodulator of FIG. 3 includes a local oscillator 23, a 90/0 phase delay 24 for delaying 90/0 phase oscillation of the local oscillator 23, a received RF signal and the 90/0 phase delay. Two mixers 21 and 22 for mixing the output signals of the machine 24, two low-pass filters 25 and 26 for filtering the output signals of the mixers 21 and 22 and passing the low-pass signal, and Two A / D converters 27 and 28 for sampling the low-pass signals, a first frequency shifter 29 for shifting the frequency band of the A / D converted digital signal, and a desired basis in the frequency shifted digital signal. And two low pass filters 30 and 31 for passing only signals in the band and a second frequency shifter 32 for shifting the frequency band of each signal in the base band again. The I and Q signals having the spectrum pass through the low pass filters 25 and 26, respectively, and are sampled by the A / D converters 27 and 28 and converted into digital signals. The low pass filters 25 and 26 are larger than Wi / 2, which is half of the band Wi including the temporary signal, and also aliasing signals by digital conversion of the A / D converters 27 and 28 at the rear end. Have a filtering band lower than half of the sampling frequency fs.

Unlike the demodulator of FIG. 3, the quadrature demodulator is a configuration in which a frequency shifter and a low pass filter) are processed by an analog circuit, and are demodulated to a baseband signal and then converted into digital data. For this purpose, the A / D converters 27 and 28 are located at the rear of the quadrature demodulator. Only the arrangement of the A / D converters 27 and 28 is different, and the arrangement of the other components is the same as that of the embodiment of FIG.

However, in the configuration of the embodiment of FIG. 4, the frequency shifter is made by a computation with digitized signal data. However, in the configuration of the embodiment of FIG. 5A, the frequency shift is performed in a circuit.

Claims

And a first mixer for mixing the oscillation signal and the RF signal to output the I signal, and a second mixer for mixing the 90 degree phase delayed oscillation signal and the RF signal to output the Q signal. Direct conversion demodulation device using a frequency shifter.