TW200939764A - Demodulator and corresponding demodulating method - Google Patents

Abstract

The present invention relates to a demodulator used in the standard systems, such as ATSC, NTSC, PAL, SECAM, VSB and SSB, etc. The demodulator includes an antenna configured for receiving RF (radio-frequency) signals, a low noise amplifier connected to the antenna, a first mixer, a second mixer, a low-pass filter, and a digital signal processor. The first mixer and the second mixer are respectively connected to the low noise amplifier to produce a first output signal and a second output signal. The low-pass filter is connected to the first mixer and the second mixer respectively to filter the first output signal and the second output signal for producing a first baseband signal and a second baseband signal. The digital signal processor process the first baseband signal and the second baseband signal to recover a video signal.

Description

200939764 IX. Description of the Invention: [Technical Field of the Invention] The present invention relates to a demodulator and its corresponding demodulation method, and more particularly to an ATSC (Advanced Television Systems Committee), NTSC (ATSC) National Television System Committee, PAL (Phase Alternating Line), VSB (Vestigial Side Band 'Residual Sideband System)' SECAM (Sequential Couleur Avec ❹ Memoire, Secon) And a demodulator in a standard system such as SSB (Single Side Band) and its corresponding demodulation method. [Prior Art] Digital Television is a television system developed to be able to feel the strong atmosphere of a theater in the home. Compared with the widely used analog TVs, it greatly improves the sharpness and width of the face, and provides multi-channel sound with CD (Compact Disc) level. For digital TV, countries such as the United States, Europe, and Japan are each setting standards that meet their own standards. At present, the standards established in the world are ATSC, NTSC, PAL, SECAM, VSB, SSB standard, QAM (Quadrature Amplitude Modulation), QPSK (Quadrature Phase Shift Keying), OFDM (Orthogonal Frequency Division Multiplexing), GSM (Global System for Mobile Communications), CDMA (Code Division Multiple Access) standards, and the like. For example, the VSB standard adopted in the United States can be found in Wayne et al. 7 200939764. The VSB Modem Subsystem Design for Grand Alliance Digital Television Receivers published in the IEEE Transactions on Consumer Electronics, Vol. 41, No. 3 in August 1995. - Text. In the prior art, for the ATSC, NTSC, PAL, SECAM, VSB and SSB standards, the SUper heterodyne method for demodulation is generally used, and the signal only occupies one part of the double sideband, and the superheterodyne demodulation method A sharp passband (IF) filter is required to remove the signal in the adjacent path before recovering the modulated signal. Since the superheterodyne demodulation method requires a sharpened bandpass (intermediate frequency) filter to filter out unwanted RF signals, the sharpband bandpass (intermediate frequency) filter has a high requirement. Standard, rather complex circuits, which require a large number of electronic components' and consume more energy. In order to reduce the high requirement standard for the sharpening bandpass (intermediate frequency) filter, an imaging rejection circuit can be added to the system, but it is also required to sharpen the bandpass (intermediate frequency). The filter can meet the limits. And the image rejection circuit is also a complex circuit' especially for wide channel applications, such as 40 MHz to 800 MHz video transmission paths. In view of this, it is necessary to provide a demodulator for ATSC, NTSC, PAL, SECAM, VSB and SSB standards and a corresponding demodulation method, which can reduce the required electronic components and simplify the corresponding circuit. SUMMARY OF THE INVENTION Hereinafter, a demodulator and corresponding demodulation method for ATSC, NTSC, PAL, 8 200939764 SECAM 'VSB and SSB standards will be described by way of example, which can reduce the required electronic components and simplify the corresponding Circuit.

A mediator for ATSC, NTSC, PAL, SECAM, VSB and SSB standard systems, comprising: an antenna for receiving an RF signal; a low noise amplifier electrically connected to the antenna, the low noise amplifier Amplifying the RF signal received by the antenna; a first mixer electrically connected to the low noise amplifier to mix the RF signal with a first local oscillator signal to generate a first output a second mixer, electrically coupled to the low noise amplifier to mix the RF signal with a second local oscillator signal to generate a second output signal, the second local oscillator signal and the first The local oscillator signal is orthogonal; a low pass filter is electrically connected to the first mixer and the second mixer to perform low-pass filtering on the first output signal and the second output signal, respectively Generating a first baseband signal and a second baseband signal; and a signal processor electrically connecting with the low pass filter to process the first-band signal and the second baseband signal to recover Original video signal. A demodulation method suitable for ATSC, NTSC, PAL, SECAM, VSB and ssb standard systems, comprising: using an "antenna" (four) frequency signal, the RF signal is generated by modulating a video signal with a carrier; The low noise amplifier amplifies the RF signal received by the antenna; mixes the amplified RF signal with the first local oscillator signal to generate a first output signal; and the amplified RF signal and a second The local oscillator signal is mixed to generate a second output signal, the second local oscillator signal is orthogonal to the first local oscillator signal; the first output signal is low-pass filtered to generate a 200939764 first baseband signal; The second output signal is low-pass filtered to generate a second baseband signal; the first baseband signal and the second baseband signal are processed by a signal processor to restore the original video signal. Compared with the prior art, the mediator and the corresponding demodulation method applicable to the ATSC, NTSC, PAL, SECAM, VSB and SSB standard systems provided by the present invention convert the radio frequency signal into a zero intermediate frequency signal, so the mediation of the present invention The demodulation method uses a low-pass filter to restore the original video signal without sharpening the bandpass (intermediate frequency) filter. The low-pass filter is simpler than the sharpened bandpass (intermediate frequency) filter. It requires less electronic components, consumes less energy, and can be integrated on an integrated chip or integrated circuit. It is suitable for the current high integration of integrated circuits. [Embodiment] Hereinafter, embodiments of the present invention will be further described in detail with reference to the accompanying drawings. The present invention relates to a demodulator for standard systems such as ATSC, NTSC, PAL, SECAM, ❹VSB and SSB, and corresponding demodulation methods. However, for a better understanding of the present invention, a brief introduction will be made first for ATSC. , NTSC, PAL, SECAM, VSB and SSB standard system video signal modulation process. In this embodiment, the video signal of the SSB standard system is used as an example for modulation and demodulation. Of course, the video signals of the standard systems such as ATSC, NTSC, PAL, and SECAM 'VSB can also be as described in this embodiment. It performs modulation and demodulation. First, 'the video signal of the SSB standard system ^ (0 is simulated by the analysis method. Please refer to Figure 1, according to the Fourier principle, if the video signal 200939764 #) is a real baseband signal, then the video signal w) is in the spectrum Upper line - Hermitian Symmetrical at 0 frequency. Referring to FIG. 2, a Hilbert transform is performed on the video signal Deng to obtain an analytic signal \(ί) of the video signal #). The analytic signal s«(i) is: Λ sa(t) = s(t) + Js(t)

A, which is the video signal 5 (the Hilbert transform form. Because the analytic signal & (the 得到 is the Hilbert transform of the video signal will be obtained, therefore, the analytic signal & (1) is a The positive frequency signal, and because the video signal is a baseband signal, the analytic signal 乂 (〇 is also a baseband signal, which is not easy to wirelessly transmit. In order to wirelessly transmit the analytic signal ^0, It needs to be correlated to obtain a modulation signal z(f). Referring to FIG. 3, the modulation signal z is obtained by mixing the analytic signal with a carrier having a positive frequency fc, that is, the modulation Signal z (〇 is the analytic signal multiplied by # : ZQ) = (0eM< = (〇[c〇s(®c〇+ jcos(act)] ❹ Since the analytic signal is a positive frequency signal, it has a positive The modulated signal 2 obtained by multiplying the carrier of the frequency fc (the 〇 is also a positive frequency signal, the modulated signal Z (〇 does not have any negative frequency component, and the modulated signal is also a analytic signal, which is a complex signal, Can be expressed as: Λ z(0 = ^(0 + /^(0 Λ The center (7) is the RF signal, which is used for path transmission; it is the Hilbert conversion form of the RF signal. Since the modulation signal ZW is a Complex Number, it cannot be used for the path. Transmission, therefore, 11 200939764 takes the modulation signal z (the real part u) as the RF signal for channel transmission and transmission. The RF signal heart is shown in Figure 4, which contains the carrier of the fc frequency. 'It is: ' ^(〇= Re{Z(〇} = Re{Sfl(〇*e^} Λ -Re{[5(i) + js(t)] · [cos(<yc〇+ jsin (act)]}

A = 5 ") cos(^>ci) - 5(7) sin(fi?c,) The demodulator for the ATSC, NTSC, PAL, SECAM, VSB and SSB standard systems provided by the present invention will be specifically described below. The corresponding demodulation method. In this embodiment, the video signal generated by the above method is used to perform demodulation on the video signal of the SSB standard system. Referring to FIG. 5, a demodulator 100 suitable for ATSC, NTSC' PAL' SECAM, VSB and SSB standard systems is provided in an embodiment of the present invention. The mediator 100 includes a low noise amplifier (LNA) 120 for receiving an RF signal L, and a low noise amplifier (LNA) 120 electrically connected to the antenna 110. The low noise amplifier 12 is used for the antenna. 110 receives the received RF signal heart (0 is amplified; a first mixer 130 is electrically connected to the low noise amplifier 120 to mix the RF signal with a first local oscillator signal cgsHa+OV To generate a first output signal, a second mixer 14A orthogonal to the first mixer 130, electrically connected to the low noise amplifier 120 to make the RF signal U0 and a second The vibration signal sm (-(called +ωΑ)) ί is mixed to generate a second output signal β, the second local oscillator signal 0 and the first local oscillator signal/orthogonal; a low pass filter 150, respectively Electrically connecting to the first mixer 130 and the second mixer 140 to low pass filter the 12 200939764 first output signal and the second output signal 2, respectively, to generate a first baseband signal and a a second baseband signal; - a DSP (Digital Signal Processor) 170, An electrical connection is formed with the low pass filter 150 to process the first baseband signal and the second baseband signal 2 to obtain an original signal. Preferably, the demodulator 100 further includes an analog-to-digital converter 160. The analog-to-digital converter 160 is electrically connected between the low-pass filter 150 and the signal processor 170 to form an electrical connection between the signal processor 170 and the low-pass filter device 150, and the analog-to-digital conversion The first baseband signal generated by the low pass filter 150 and the second baseband signal are digitized, and then transmitted to the signal processor 170 for processing. The signal processor 170 is a digital signal processor. The specific working principle of the mediator 100 is as follows: (1) The antenna 110 receives the RF signal heart (7), wherein the RF signal U') is:

= 5(〇cos(a>ci) - s(〇sin(iyc〇(2) The low noise amplifier 120 amplifies the RF signal. (3) The first mixer 130 pairs the amplified RF signal The heart W is mixed with the first local oscillator signal c°s (-(A+called)> to generate the first output signal, 7 = u 0) «^(-(called + ))i = (s( 〇cos〇〆)-s(i) sin(6?ci)) cos(-(fi)e + )ί) Λ Λ =j [5(ί) cos(-<»Ai) + s(t) Cos(2c)c +ωΗ)ί- s(t) sin(-aht) - s(t) sin(2<yc + ωΗ )i] where the frequency value corresponding to half the bandwidth of the RF signal 1 is called Is a baseband frequency. The first output signal / is a zero intermediate frequency signal, which has a baseband signal near the frequency and (2 A + %) near the frequency of the frequency 13 200939764. (4) the second The mixer 140 mixes the amplified RF signal with the second • local oscillator signal sin(-(4))> to generate the second output signal 2. . ' Q = ^6(〇sin(-(iyc + ah))t = (s(i)cos(<yci) - s(i)sin(iyc〇)sin(-(iyc + ah)t) Λ Λ =y[-5(i)sin(2iyc + β>Λ)ί + 5(/)sin(-fi>A)i - ^(^€08(2^ + + 5(i)cos(-c>A)i] The second output signal β is a zero intermediate frequency signal having a baseband signal near the frequency and an intermediate frequency signal near the (2α+α) frequency. (5) using the low pass filter 150 for the first output signal/and The first baseband signal I-channel and the second baseband signal Q-cMnnd are generated by the low-pass filter and the wave, and the intermediate frequency component is removed (the signal related to the vicinity of the corresponding frequency is removed here). which is

Λ A l ^channel = Y[5(i)cos(-iyA)i - s(t)sin(-&h)t] = y[5(i)coS6?fti + 5(i)sin(S&gt ;Ai]

AA Q_channel = |[5(i)sin(-6?A)/ + 5(i)cos(-^)i] = Y[-5(i)sinfi>Ai + 5(i)coS6?Ai] The first baseband signal and the second baseband signal 2-cAimnei are both baseband signals close to the chirp frequency, and the signals corresponding to the relevant frequencies (2 cents +%) are filtered by the low pass filter 150. ❹ (6) digitizing the first baseband signal 7-c/^”ei and the second baseband signal by using the analog-to-digital converter 160, and transmitting the digitized baseband signal and the second baseband signal to the digital position The signal processor 170 performs processing to restore the original video signal. Specifically, referring to FIG. 6, the first baseband signal 7-c/ww^ and the second baseband signal GC/I£mnei are first processed by the digital signal. The device 170 performs integration to generate a first processing signal, where the first processing signal is a complex signal, wherein the first baseband signal is the real part of the first processing signal * as 200939764, and the second baseband signal is used as the first The imaginary part of the processing signal (7), namely:

Sssb〇_i〇Wp〇ss (0 = ^ _ channel + jQ _ channel

AA =y {[5(0 c〇s(-iyA )t - s(t) sin(-iyA )i] + j[s(t) sin(-6?ft )t + 5(i) cos( -<a?A )i]}

AA =i{ [·ϊ(ί) cos aht + s(t) sin aht] + sin c〇ht + s(t) cos οΛί]} and the first processed signal is a baseband signal located near zero frequency . Referring to FIG. 7 , the digital processing unit 170 continues to process the first processing signal to obtain a second processing signal 0). The second processing signal W is used by the digital signal processor 170. The first processing signal is generated by mixing a complex number signal called a complex number signal, that is, the second processing signal ^ssbO _ lowpass _ shift ω Η (7) is the product of the first processed signal and the product, therefore, ^ssbO_lowpass ( 0 ^ssbO_lonpass (0 ^ A Λ ={{[-^(0 c〇s(-6?a)t - 5(i)sin(-iyfc)i] + j[s(t)8ΐη(-ωΗ) t + 5(i)cos(-iyA )i]} · (cos〇ht + jsin ωΗί) Λ Λ = +[(>s(〇cosft?Ai + «s(i)siniyAi + j.(-5 (i)sinfiy + 5(〇cosiyAi))] · (cos^y〆+ j.sinc^i) =y[5(/)(cos2 ωΗί + sin2 ωΗ1) + js(t)(cos2 &ht + Sin2 €〇ht)\=ΐΚ0+;«(〇] As shown in FIG. 7, the second processing signal-male is a complex analytic signal, and the second processing signal ~W is taken by the digital signal processor 170. The real part is calculated to restore the video signal milk that is symmetrical about the zero frequency yoke in the spectrum, ie 5 ( = 2*Re{5Mfco_ lowpass _ shift ωΗ (〇} = 2 · Re{ + j 5(i)]} = s(t) It is understood that it is also possible to generate the second processed signal W while The digital signal processor 170 performs a calculation on the real part 15 200939764 to restore the video signal < 〇, which is to say that the first processed signal is mixed with the frequency called the complex signal, and the digital signal. The processor 170 performs a real part calculation, that is, s(t) = 2·Κ6{^[(5(ί)ο〇8(-β?Λ)ί - s(t)sin(^h)t) + j(s(t)sin(^h)t + 5(i)cos(-6?A)i)] · (cos^i + jsinft)Ai)} =2 · Re{^[(5(i )coSi»Ai + s(t)sin ωΗί + j(-s(t)sin + 5(i)cosfi>Ai))] · {οο^ωΗί + j sin cokt)} =2 · Re{^[5 (i)(cos2 mht + sin2 ωΗί) + js(t)(cosz ωΗί + sin2 coht)]} = 2.i[S(〇] = 5 (〇 of course, steps (3)-(6) of the present invention It can also be understood that the RF signal ❹ passes through the first mixer 130 and the second mixer 140 to generate an intermediate processing signal *^ as shown in FIG. (〇) the RF signal is mixed with a complex signal having a frequency of -(4)+<>, that is, the intermediate processing signal 1^> (0 is the RF signal heart (the product of 0, therefore, The intermediate processing signal is

Sssb〇(t)-Sssb(t)e-^t Λ Λ =Y[(5(〇cos(-<s>A)i + 5(i)cos(2ft?c + ώ)Α)ί - 5(i)sin(-^)i - 5(i)sin(2iyc + coh)t) + j (s(t) sin(-fi?A )t« s(t) sin(2<5>c + β>Α )i + s(t) cos(-6Ja )i) - s(t) cos(26?c + ωΗ )i)] © Please filter the intermediate processing signal through the low pass filter 150 (2a+a) a signal related to the frequency, thereby obtaining the first processed signal 5ssfc. - -, and then processing the first processed signal to obtain the second processed signal S ssbQ "". Wpass—shiftcok W and video signal s(f). The demodulator 100 of the standard system for ATSC, NTSC, PAL, SECAM, VSB and SSB of the present invention and the corresponding demodulation method directly convert the RF signal heart (0 to zero intermediate frequency signal (intermediate processing signal*) ^. (〇), then use the low-pass filter 150 to remove the IF signal (the signal related to the frequency near (2^+^)), and only let the baseband signal (the first processing signal ·^°). ^/)) Through the low 16 200939764 pass filter 150, the baseband signal is processed to restore the video signal. Compared with the prior art, the demodulator 100 of the standard system for ATSC, NTSC, PAL, SECAM, VSB and SSB of the present invention and the corresponding demodulation method adopt a low pass filter 150, which There is no need to sharpen the bandpass (intermediate frequency) filter, and the low pass filter 150 is simpler than the sharpened bandpass (intermediate frequency) filter, requiring fewer electronic components and less energy consumption. And can be integrated on an integrated chip or integrated circuit, suitable for the high integration of current integrated circuits. In summary, the present invention has indeed met the requirements of the invention patent, and has filed a patent application according to law. However, the above description is only a preferred embodiment of the present invention, and it is not possible to limit the scope of the patent application of the present invention. Equivalent modifications or variations made by persons skilled in the art in light of the present invention are intended to be included within the scope of the following claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram showing the frequency spectrum of video signals for the ATSC, NTSC, PAL, SECAM, VSB and SSB standard systems provided by the embodiments of the present invention. FIG. 2 is a schematic diagram of the resolution signal of the video signal shown in FIG. 1. FIG. 3 is a schematic diagram of the modulated signal generated after the modulated signal of FIG. 2 is modulated. FIG. 4 is a schematic diagram of the RF signal generated by calculating the real part of the modulated signal shown in FIG. FIG. 5 is a schematic diagram of a mediator for an ATSC, NTSC, 17 200939764 PAL, SECAM, VSB, and SSB standard system according to an embodiment of the present invention. FIG. 6 is a schematic diagram of an intermediate processing signal and a first processing signal generated by demodulating the RF signal shown in FIG. 5. FIG. 7 is a schematic diagram of the second processed signal and the restored video signal generated by processing the first processed signal shown in FIG. 6. [Key component symbol description] Demodulator 100 Antenna 110 Low noise amplifier 120 First mixer 130 Second mixer 140 Low-pass filter 150 Digital signal processor 170 Analog-to-digital converter 160 18

Claims (1)

200939764 X. Patent application scope: * A mediator for ATSC, NTSC, PAL, SECAM, VSB and SSB standard systems, the mediator includes: an antenna for receiving RF signals; a low noise amplifier for amplifying the RF signal received by the antenna; a first mixer ' electrically connected to the low noise amplifier to make the amplified RF signal and a first The local oscillator signal is mixed to generate a first output signal. A second mixer is electrically connected to the low noise amplifier to mix the amplified RF signal with a second local oscillator signal. Generating a second output signal, the second local oscillator signal is orthogonal to the first local oscillator signal; and a low pass filter electrically connected to the first mixer and the second mixer respectively to the first The output signal and the second output signal are low-pass filtered to generate a first baseband signal and a second baseband signal, respectively; and a signal processor that is electrically connected to the low-pass filter to the first baseband The second number is processed baseband signal to restore the video signal of the original obtained. 2. The demodulator of claim 1, further comprising an analog-to-digital converter electrically coupled between the low pass chopper and the signal processor An electrical connection is formed between the processor and the low-pass filter, and the analog-to-digital converter digitizes the baseband 5 and the second baseband signal generated by the low-pass filter, and transmits the signal to the signal processor. Process it. 200939764 3Cry the demodulator as described in claim 2, wherein the signal processing is a digital signal processor. A demodulation method for the ATSC, NT SC, PAL, SECAM, VSB and SSB standard systems, the mediation method comprising: receiving an RF signal by using an antenna, the RF signal modulating a video signal and a carrier to generate Amplifying the RF signal received by the antenna by using a low noise amplifier; mixing the amplified RF signal with a first local oscillator signal to generate a first output signal; and the amplified RF signal and a second local oscillator signal is mixed to generate a first output signal, the second local oscillator signal is orthogonal to the first local oscillator signal; low-pass filtering the first output signal to generate a first baseband signal The second output signal is low-pass chopped to generate a second baseband signal; the first baseband signal and the second baseband signal are processed by a signal processor to restore the original video signal. 5. The demodulation method of claim 4, wherein the carrier has a positive frequency fc. 6. The demodulation method of claim 4, wherein the first local oscillator signal and the second local oscillator signal have a frequency of _team + call, and the % corresponds to a frequency of half of the bandwidth of the RF signal. Value, which is a baseband frequency. 7. The demodulation method of claim 4, wherein the first output signal is a zero intermediate frequency signal having a baseband signal and an intermediate frequency signal, and the second output signal is also a zero. The IF signal also has a 200939764 baseband signal and an IF signal. 8. The demodulation method of claim 7, wherein the low pass filter filters out intermediate frequency components of the first output signal and the second output signal to generate the first baseband Signal and the second baseband signal. 9. The demodulation method of claim 6, wherein the signal processor processes the first baseband signal and the second baseband signal to = a first processing signal, the first processing The signal has a first baseband signal of 0 4 and a second baseband signal of an imaginary part. =·If the application of the scope of the application of the scope of the ninth reliance on the method of financing, where the signal device ^ will be the first processing signal and a frequency of the called complex signal mixed, to get a second processing signal, The second processing signal performs a calculation to restore the video signal. twenty one