KR20090035061A

KR20090035061A - Dvb -t dmodulator

Info

Publication number: KR20090035061A
Application number: KR1020070100110A
Authority: KR
Inventors: 임재원
Original assignee: (주)텔리뷰
Priority date: 2007-10-05
Filing date: 2007-10-05
Publication date: 2009-04-09

Abstract

A DVB-T direct down conversion modulator using a frequency shifter and a modulating method thereof are provided to simplify a high frequency processing circuit without an intermediate frequency conversion unit by removing influence of a leakage signal of an intermediate frequency. A high frequency receiver generates a signal of an oscillation frequency satisfying a predetermined formula. The high frequency receiver mixes the oscillation signal with an RF signal and mixes the oscillation signal with a 90 degree phase delayed oscillation signal with the RF signal. The high frequency receiver outputs I and Q signals by the mixed result. A first frequency shifter(29) preforms the frequency shift so that a band center of a target signal becomes 0 by using I and Q signals. A signal extractor extracts the I and Q signal of a target signal from a frequency shifted signal. A second frequency shifter(32) performs the frequency shift as much as 1/2 of the target signal band by using the extracted I and Q signals.

Description

Direct conversion demodulation method and demodulation device using frequency shifter {DVB -T Dmodulator}

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.

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.

A quadrature demodulator for demodulating the modulated signal as described above is configured as shown in FIG. 1. Operation of the demodulator of FIG. 1 is performed as follows.

The oscillation signal oscillated by the local oscillator 3 is the same frequency as the carrier wave fc of the signal band to be received, and this oscillation signal is applied to both mixers 1 and 2 via the 90/0 phase delay unit 4. do. At this time, the oscillation signal having a phase delay of 90 degrees is applied to one mixer 2, so that in each mixer 1, 2, the signal band centering on fc is a direct base band I, Q signal. The output is converted. Each low pass filter 5, 6 at the rear stage filters only the baseband I, Q signals and outputs them, and these signals are restored to digital data by the A / D converters 7, 8, respectively. 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, and a super hetero heteromorphism as shown in FIG. 2 is performed. Use a multi-modulator demodulator. In the demodulator of FIG. 2, the first local oscillator 12 applies an oscillation signal that is different from the center frequency fc of the received signal and a few tens to several hundred MHz, to the first mixer 11 and then outputs the output signal to a band pass filter ( 13) to first convert the desired signal band into a first intermediate frequency (I / F) signal of several hundred MHz band or more, and then oscillate of the second local oscillator 15 back to the first intermediate frequency signal. Mix the signal, pass it through a band pass filter, convert it into a second intermediate frequency signal in the tens of MHz band, and then mix the oscillation signal of the third local oscillator 20 to the second intermediate frequency signal again and pass the low pass filter. You get the desired signal in the band. However, the super heterodyne demodulator requires bandpass filters 13 and 16 to pass only the converted intermediate frequency (I / F) signals as shown in FIG. Since it should be cut off, filtering characteristics should be very good. In addition, technically, it is difficult to implement a sufficient bandpass filter at the first intermediate frequency, so that, as in the demodulator configuration of FIG. 2, a second intermediate frequency is required, which complicates the high frequency processing circuitry of the demodulator and also demodulators. There is a problem that the manufacturing cost is increased by making the design and manufacture of the substrate difficult.

The present invention has been created under the above-described background, and even in the case of a modulated signal having a valid signal component in the center of the signal band, a direct downconversion and demodulation is performed without being affected by a leakage signal of a DC frequency. It is an object of the present invention to provide a DVB-T direct conversion demodulation method and demodulation device using a frequency shifter that simplifies the processing circuit.

See specifics

The DVB-T direct conversion demodulation method and demodulation apparatus using the frequency shifter according to the present invention operating as described above is capable of detecting the leakage signal of the DC frequency even if the signal having the effective signal component in the center of the band is demodulated by the direct conversion method. Unaffected 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.

In the DVB-T direct conversion demodulation method and demodulation apparatus using the frequency shifter according to the present invention, in demodulating a target signal whose center is fc and its bandwidth is W in an RF signal, | | fosc-fc | Generate a signal of oscillation frequency (fosc) satisfying > W / 2, convert the RF signal with the oscillation signal, and also mix with the oscillation signal delayed by 90 degrees to produce an I and Q signal, and then I and Q signals are frequency shifted so that the band center of the target signal becomes zero on the spectrum, and the W / 2 low pass filter extracts only the I and Q signals of the target signal, and then the frequency shifted direction. It is characterized by obtaining the baseband target signal by redirection by the opposite direction of W / 2. Fig. 3 shows the configuration of the quadrature demodulator according to the present invention. The quadrature demodulator of FIG. 3 includes a local oscillator 23, a 90/0 phase delay 24 for delaying the oscillation signal of the local oscillator 23 by 90/0, 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. Two low pass filters 30 and 31 which pass only a band signal, and a frequency of each signal of the base band;

And a second frequency shifter 32 for shifting the band again. First, it is assumed that the target signal to be received has a spectrum as shown in Fig. 4A so that the center frequency of the band is fc and the bandwidth is W. To demodulate this signal, the local oscillator 23 | | fosc-fc | Outputs an oscillation signal having an arbitrary frequency (fosc) satisfying> = W / 2, that is, an arbitrary frequency lower than fc-w / 2 or higher than fc-w / 2. The embodiment outputs an oscillation signal having a frequency lower than fc-w / 2. The oscillation signal is simply applied to one mixer 21 by the 90/0 phase delayer 24 and is delayed by 90 ⁰ phase to the other mixer 22. (in-phase) and Q (quadrature-phase) signals are output

1 illustrates a configuration of a quadrature demodulator for demodulating a signal band having no signal component in a carrier wave,

2 illustrates a configuration of a quadrature demodulator for demodulating a signal band having a signal component at the center of the band;

Figure 3 shows an embodiment of the configuration of a quadrature demodulator according to the present invention,

4A to 4G respectively show signal spectra in the process in which the demodulator of FIG. 3 demodulates a target signal.

Claims

An apparatus for demodulating a target signal having a center of fc and a bandwidth of W in a received RF signal, the | | fosc-fc | A high frequency receiver for generating a signal having an oscillation frequency (fosc) satisfying> = W / 2, mixing the RF signal with the oscillation signal, and mixing the oscillation signal with a 90 degree phase delay and outputting I and Q signals; A first frequency shifter for frequency shifting the band center of the target signal to zero using the I and Q signals, a signal extraction unit for extracting only the I and Q signals of the target signal from the frequency shifted signal; And a second frequency shifter configured to frequency shift by 1/2 of the target signal band W in the direction opposite to the frequency shift direction in the first shifter using the extracted I and Q signals. DVB-T direct conversion demodulator using