MXPA00008840A - Digital signal processor for multistandard television reception - Google Patents

Abstract

A television converter uses digital signal processing (DSP) (12, 26) to provide compatibility with different television standards including NTSC and PAL video standards and FM, BTSC, DIN, Home Theatre, NICAM and independent digital audio standards. Audio processing (26) is accomplished without passing the audio through a Nyquist filter (72) used for video. This eliminates AM to PM conversion improving luminance linearity and differential gain and phase. It also prevents video information from phase modulating the audio intercarrier, thereby eliminating video"buzz"components in the audio. The audio processing (26) includes a synchronous FM demodulator (40) and a separate synchronous FM/QPSK demodulator (44) for handling the different audio standards. Handling historical analog TV standards with DSP also enables the advantageous combination of analog and digital television reception within a single digital VLSIASIC.

Description

PROCESSOR OF DIGITAL SIGNALS FOR THE MULTIPLE RECEPTION OF TELEVISION SIGNALS Field of the Invention The present invention relates to television systems, and more particularly, to an implementation of digital signal processing (DSP), for the demodulators / receivers of video, audio and data of cable television converters (CATV). ), satellite television receivers, multipoint multi-channel distribution services (MMDS) or similar.

Antecedents of the Invention Cable television services are communicated from a section of R.F. through a cable distribution system to the homes of the subscribers. At the subscriber's home, the downlink cable that transmits the signal from, for example, a telephone pole, connects the cable television signals directly to the subscriber's television equipment or couples the signals through a converter and / or other electronic systems of the subscriber. A converter is therefore necessary if the cable system offers more channels than the television channels 2 to 13. Only "cable-capable" television sets can tune to the higher frequency cable channels, which are above of channel 13 of VHF transmission. If the cable operator offers additional channels, such as subscription channels, they should be moved downward frequency to the frequencies used by one or more channels, to which conventional television sets can be tuned. For example, a cable television converter will commonly transmit the selected cable television channel at the frequency used by the transmission channel 3 or 4, in which the subscriber's television will be tuned whenever it is receiving signals from the converter. Steerable converters are those that can make the channels available or not, according to the instructions sent in data packets from the R.F. section of the cable. The converter includes a tuner controlled by the subscriber in order to select a specific channel. If the selected service is a premium service, it is encoded and decoded only with the control of the data sent from the R.F. Each subscriber has a unique electronic address, such that the section of R.F. of the cable can provide the display authorizations to each steerable converter. A common cable television converter will include a frequency converter and a filter (to allow subscribers to tune to the desired channels), a local oscillator, control circuits, a data receiver for authorizations and a decoder. It should be appreciated that the receivers for satellite television and the MMDS will have comparable components. When analog signals must be received, usually including a down-converter for the transmitted digital signals, suitable digital components must also be provided, generally including a down-converter for the transmitted digital signals, an analog-to-digital converter, a digital demodulator, as for example, a QAM demodulator, a digital television decoder such as, for example, an MPEG decoder, an on-screen display circuitry and a video encoder for supplying television signals retrieved in an analog format for broadcast by a conventional television set. Different television transmission standards have been adopted in different parts of the world. These standards include the National Television Systems Committee (NTSC), the alternate phase line (PAL) and the SECAM standards. Both PAL and NTSC standards have different variations that are used in different parts of the world. For example, in the USA an NTSC standard is used. In Japan, a somewhat different standard is used and in Korea a variant is used. In the same way, different variants of the PAL system have been adopted in different countries. In Table 1, a summary of the different NTSC and PAL television transmission standards is given.

Table 1 It would be advantageous to offer a cable television converter, a satellite receiver, a MMDS receiver or the like, capable of processing television signals, independently of the video standard used. However, to be economical, such converters must be produced at a low cost. This was a difficult obstacle to solve in the past, because the different video standards required different circuit systems including demodulators, filters and associated components separately, which made the final cost of the product prohibitive. In this way, it was not possible to have multi-format converters for television. It would be convenient to offer a television converter, which would have the capacity to recover the video and audio signals according to different television standards. It would also be convenient to implement said apparatus using digital signal processing techniques, both for the analog and digital television signal inputs. It would also be advantageous to offer such a converter, whose production would be economical using, for example, a very wide scale integration (VLSI) at low cost, an integrated circuit for specific application (ASIC) in order to supply most of the functions of the converter. The present invention supplies a converter with the aforementioned advantages, as well as with other advantages.

Summary of the Invention According to the present invention, a digital signal processor is provided for the recovery of video and audio signals, in accordance with different standards of analogue and digital television. The signal processor comprises a video demodulator with a first path for coupling a video signal modulated with a mixer through a Nyquist filter, and a second path for coupling the video signal modulated with a carrier recovery circuit, without going through the Nyquist filter. The modulated video signal conforms to a particular television standard, for example, any of the standards indicated in Table 1. The carrier recovery circuit (i) recovers a frequency signal from the carrier to be used by the mixer in order to supply a baseband video signal (ii) detects an audio intercarrier present in the video signal modulated A programmable sound band filter is provided to filter the audio components, from the baseband video signal, in accordance with the particular television standard to provide a demodulated video output. The audio intercarrier is supplied as an output from the carrier recovery circuit, for the subsequent recovery of audio in accordance with the particular television standard. In an illustrated embodiment, the digital signal processor receives the video signal modulated at an intermediate frequency (Fl).

An analog to digital digital converter is provided to sample the modulated intermediate frequency signal at a sampling frequency Fs to digitize the signal for input into the video demodulator. In a preferred embodiment, the sampling frequency Fs is an integer multiple of the intermediate frequency. For example, the sampling frequency Fs, may be 27MHz with the intermediate frequency of 6.75 MHz or 9.0 MHz. This arrangement is convenient, since both 6.75 MHz and 9 MHz are equally divided in the frequency 27 MHz sampling. The demodulated video output can be a sample of a digital signal at an Fs frequency of 13.5 MHz. The sampling frequency can be synchronized in phase with a horizontal synchronization component of the video signal of baseband. The digital signal processor may further comprise a tuner for recovering the modulated video signal from a signal band. The particular television standard to which the modulated video signal corresponds can be identified by a channel map that acts in response to the tuner. Alternatively, the modulated video signal may transmit identifier data, indicative of the particular television standard to which the modulated video signal corresponds. The digital signal processor may further comprise means for delaying the frequency signal of the carrier, before the mixer to compensate for a delay introduced by the Nyquist filter.

An audio demodulator is provided in the digital signal processor to process the audio intercarrier. In an illustrated embodiment, the audio demodulator comprises a first synchronous demodulator to demodulate, selectively, a first modulated FM audio signal or a QPSK modulated audio signal transmitted by the audio intercarrier. A second synchronous demodulator demodulates a second modulated FM audio signal transmitted by the audio carrier. The first and second synchronous demodulators may comprise linear phase synchronized circuits, which allow the demodulation of the audio intercarrier with preliminary bandpass filtering. The video demodulator, the carrier recovery circuit, the programmable sound band filter and the audio demodulator can all be implemented on an individual integrated circuit chip. In an embodiment in which the particular television standard to which the modulated video signal corresponds is identified by a channel map that responds to a tuner, the first synchronous demodulator responds to the channel map to selectively demodulate , the first modulated FM audio signal, or the QPSK modulated audio signal. In an embodiment in which the modulated video signal transmits the identifier data, indicative of the particular television standard to which the modulated video signal corresponds, the first synchronous demodulator responds to the identifier data to demodulate, in the form selective, to the first modulated FM audio signal or to the QPSK modulated audio signal. The present invention also considers a digital signal processor for the recovery of video and audio signals according to different analogue or digital television standards in which an audio demodulator is supplied to process an audio intercarrier. The audio demodulator includes a first synchronous demodulator to demodulate, selectively, a first modulated FM audio signal or a QPSK modulated audio signal, transmitted by the audio intercarrier. A second synchronous demodulator is supplied in the audio demodulator, to demodulate a second modulated FM audio signal transmitted by the audio intercarrier. The first and second demodulators can comprise synchronized circuits in linear phase that allow the modulation of the audio carrier with preliminary bandpass filtering. The first synchronous demodulator may comprise a QPSK demodulator, with first and second output stages. One of the output stages is an output stage I and the other is an output stage Q, where I or Q are constellation axes offset by 90 degrees. A variable oscillator supplies the first and second outputs of the shifting oscillator in phase, with a frequency dictated by a demodulation control signal. The first oscillator output is related to the first output stage, and the second output of the oscillator is related to the second output stage of the QPSK demodulator. A phase-synchronized circuit controls the variable oscillator in response to an output from the first or second output stages. A selector is provided to selectively emit a QPSK from the first or second output stages or an FM signal from the phase-synchronized circuit. An apparatus is provided to recover the video and audio signals according to different analogue and digital television standards. The apparatus includes a tuner for selecting a TV channel signal. The TV channel signal conforms to a particular television standard. Means are provided for digitizing the intermediate frequency signal of the television channel. Intermediate frequency scanning is effective to demodulate both analog and digital modulation formats. Means are provided to identify the particular television standard to which the signal of the TV channel is adjusted. A digital video signal processor (DSP), which acts in response to the identification means, demodulates the signal of the selected digitized TV channel to supply a video output signal. The identification, digitization, video DPS and audio DPS means are located together in an integrated circuit chip. A data DPS can be provided on the integrated circuit chip to demodulate the auxiliary data transmitted on the TV channel signal in order to supply an auxiliary data output signal. The apparatus may further comprise a data modulator in the integrated circuit chip. The data modulator modulates the return path data to be communicated from the device to a remote location.

Brief Description of the Drawings. Figure 1 is a block diagram of a digital signal processing implementation of a baseband television converter according to the present invention; Figure 2 is a more detailed block diagram of the video demodulator section of the video DSP portion of the Figure 1; and Figure 3 is a more detailed block diagram of the FM and QSPK / FM demodulators used in the audio DSP portion of Figure 1.

Detailed Description of the Invention The present invention combines the demodulator / receiver functions of video, audio and data of a television converter into an economical package. In a preferred embodiment, these functions are implemented in an individual integrated circuit such as, for example, an ASIC circuit. The implementation of the invention of television converter functions using DSP techniques eliminates the need for multiple filters and fixed bandpass discriminators to perform multinormal processing. In this way, you can have multiple different television standards through an individual converter. The sampling frequencies are selected in such a way as to allow the simple and cost-effective use of a normalized main clock frequency, such as the 27 MHz clock used by the Group of Motion Picture Experts standard (Motion). Picture Experts Group - MPEG) and specified in ITU-R BT. 601 Hardware requirements are significantly reduced using, for example, a demodulator for both FM signals and QPSK signals. In Figure 1 a complete block diagram of the television converter is illustrated. The converter includes a video DSP 12, an audio DSP of 26 and data recovery and synchronization circuits 24. The video DSP demodulates and decodes the video from the intermediate frequency carrier (Fl). The carrier may comprise, for example, a low frequency carrier Fl such as, for example, a carrier centered at 9 MHz plus minus 100 KHz. The DSP of a video is formed by an analog-to-digital (A / D) converter 14, a video demodulator 16 and a video decoder 18. Samples of the low-frequency input F1 through the terminal 10 are taken with the A / D converter 14. The sampling rate Fs can be, for example, 27 MHz. This speed is convenient because it adjusts to the main time rate used in the MPEG standard and in ITU-R BT. 601 The video demodulator 16 (which is illustrated in greater detail in Figure 2) receives the sample video of the A / D converter 14 and supplies several outputs. A band-based video output is provided without sound carriers to the video decoder 18. It is convenient to supply the baseband video at a sampling frequency of 13.5 MHz. The video decoder 18 decodes the band video according to the known techniques for supplying a decoded baseband video output on line 22 of the sampling frequency Fs of, for example, 13.5 MHz. The automatic gain control frequencies of RF and Fl. (AGC), are also transmitted from the video DSP 12 through the line 20. In addition to transmitting to the baseband video, the video demodulator 16 transmits a fine automatic tuning control (AFT) voltage on the line 108 and an audio intercarrier on line 100. Before transmitting the audio intercarrier, a phase mixer / detector 94 (Figure 2) cancels the AM modulated video components. For example, the audio intercarrier can be supplied at a sampling frequency of 27 MHz. The video decoder 18 also transmits a synchronization detection signal on the line 19 which is derived from the recovered video. This signal is transmitted to a Gen-Lock Timing and Clock Recovery circuit 28, which is part of the data synchronization and recovery block 24. The circuit 28 recovers the horizontal synchronization, the vertical synchronization, the beam extinction, and the inversion restoration synchronization (used to decode the inverted video signals) that are sent to the video decoder via line 29 to be used to decode the video output by video demodulator 16. Circuit 28 also transmits a Gen-Lock synchronization signal on line 34 to be used by the circuit On-screen display of the converter. The on-screen display circuit supplies the text and graphics to be displayed on the subscriber's television in a conventional manner. The data synchronization and recovery block 24 also includes an identifier color burst decoder 30 that transmits identifier data and a clock on line 36. The identifier data is that data encoded in the color burst of the video and those used for different control functions of the converter, including decoding. The in-band data (IBD) transmitted in the luminance portion of the video signal are decoded by an IBD 32 luminance decoder, and are transmitted through the line 38 together with an associated clock signal. In a preferred embodiment, the clock signals having identifier data and IBD data will be integers with respect to the main clock frequency of, for example, 27 MHz. The audio DSP portion 26 of the converter includes a digital demodulator. audio and baseband processing functions. The audio portion of a video signal may be formed by one or more carriers. The carrier may have one or more subcarriers. When an individual FM carrier is present, said carrier is modulated by an FM demodulator 40. The ability to demodulate a second FM carrier is supplied by a combined QPSK / FM demodulator 44. If a QPSK channel is supplied and an FM channel, the FM demodulator 40 will be used to demodulate the FM channel and the QPSK / FM demodulator 44 will be used to demodulate the QPSK channel. In the case where two FM channels are supplied, the demodulated signals are decoded in a double FM decoder 42 to supply a digital output to a MUX control circuit / stereo digital audio volume 56. This circuit processes the signals decoded to provide left and right stereo channel outputs for input to a digital interface circuit 58 (e.g., Sony-Phillips Digital Interface - SPDIF) and a high-fidelity digital-to-analog converter 60. Circuit 58 transmits a signal from digital audio (for example, SPDIF). The digital-to-analog converter 60 transmits the left and right analog audio signals for input to a conventional audio amplifier. In the case where the QPSK / FM demodulator 44 retrieves a carrier with an audio subcarrier from the Broadcast Television Systems Committee (BTSC), the subcarrier is decoded in the decoder 50 for the input to the circuit 56 Similarly, when the demodulator 44 retrieves a NICAM audio signal, said signal is decoded in a decoder 52. When present, an AC1 Dolby audio signal, retrieved by the demodulator 44, said signal is decoded by the decoder 54. Prior to decoding, any NICAM or Dolby AC1 signal is divided into sections in a disconnector 46 and demultiplexed in a bitstream demultiplexer 48 in order to recover the digital data supplied by the N ICAM or Dolby AC1 signals. As previously indicated, the audio DSP 26 can process various audio modalities. Table 2 indicates the different types of audio carriers that can be processed.

Table 2: As indicated in Table 2, various modalities including the BTSC, DIN Germany, DIN Korea, PAL I, PAL B modalities include a primary carrier as well as a secondary carrier. When two FM carriers are supplied, as in the private BTSC, German DIN and DIN Korean modes, one will be processed by the FM 40 demodulator and the other by the 44 demodulator. All QPSK demodulation is provided by the QPSK demodulator / FM 44. The QPSK modulation provided in the secondary carrier of the two PAL modes represents a digital NICAM audio signal that is subsequently processed by the NICAM 52 decoder. In the "home theater" audio mode, the QPSK modulation of the carrier Primary provides a Dolby AC1 digital audio signal, which is decoded AC1 54. More details of the FM demodulator 40 and the QPSK / FM 44 demodulator are provided in the description in Figure 3.

Figure 2 illustrates the video demodulator 16 in greater detail. This demodulator can process both a large carrier (vestigial sideband "VSB") of modulated amplitude and the suppressed carrier of amplitude modulated with AM pilot signals. The only difference between the two demodulation systems is in the carrier recovery block 74. More particularly, the phase mixer / detector 94 supplied in the carrier recovery block can be implemented as a Coastal circuit, such as a synchronized circuit in quadrature phase, both well known in technology. A Coastal circuit can recover the carrier, both for the large carrier (vestigial sideband) and the suppressed carrier with AM pilot signal sources. The quadrature phase synchronized circuit (QPLL) is only capable of demodulating signals from large carriers. The input to the video demodulator is a signal of intermediate video frequency from which samples can be taken, for example, at 27 MHz. This is the signal output from the A / D converter 14 of Figure 1, and is transmitted. to the video demodulator through the terminal 70 illustrated in Figure 2. This signal is transmitted to a Nyquist 72 filter mixer and block and to the carrier recovery block 74. In the Nyquist 72 filter mixer and block, the frequency intermediate video is first filtered by Nyquist through the Nyquist 80 filter and then converted, in descending order, to the baseband by mixing it with the carrier recovered in the mixer 82. The recovered carrier first passes through the Nyquist delay 84 that compensates for the delay of the Nyquist 80 filter. The Nyquist filter is a low pass filter that provides additional adjacent channel filtering as well as dual-individual base band VSB equalization. For NTSC signals, the individual sideband component is 0.75 to 4.2 MHZ. The Nyquist filter 80 can be implemented as a finite impulse response low pass filter (FI R) with a sampling frequency of, for example, 27 MHz, a bandpass edge of 7.75 MHz, a band attenuation. 0.5 dB pitch, a 10.25 MHz stop band edge, a 40 dB stopping band attenuation, 3.3953 beta, and a -6 dB cutting frequency of 9 MHz. The FIR filter it can be implemented as a derivation filter 27 with fixed coefficients. The output of the mixer 82 is transmitted to a sound band filter 76. A baseband video output is generated (for example, with a sampling frequency Fs of 13.5 MHz) from the demodulated video by eliminating the signal components of Audio. The audio components are eliminated by the sound band filter. The filtering is carried out in a two-stage filtering process using a down-converter, down-converter 86 and a low-pass filter, sound elimination 92. A reduction of two circuits 90 is provided between the two low-pass filters . The use of a two-stage filtering process in the sound-band filter 76 reduces the hardware requirements. The first stage supplied by the LPF 86 and the reducer 90 reduce by two the modulated sample video from 27 MHz to 13.5 MHz. The filter 86 is an anti-spurious low pass filter which may comprise, for example, a FIR half-band low pass filter. For example, the sampling removal frequency of the filter 86 may be 27 MHz with an operating frequency of 13.5 MHz, a bandpass edge of 5.5 MHz, a passband attenuation of 0.5 dB , an 8 MHz stop band edge, a stop band attenuation of 60 dB, and the filter may have, for example, 37 taps with fixed coefficients. A half-band filter is used to reduce the gate count. Considering the 2: 1 reduction, this filter operates at 13.5 MHz because it ignores one out of every two samples. Since a medium band filter is used, the pass band and the stop band are centered at a quarter of the sampling frequency (27 MHz) or 6.75 MHz. The last stage of sound band filter 76 is a FIR low pass filter 92. This filter can be designed, for example, to supply the sound carrier at 50 dB below the video on the sound carrier, and at 25 dB below the video on the sound carrier + 50 KHz . The coefficients of this filter are programmed to adjust all the different video standards that can be processed by the television converter. The number of filter derivations can be determined by the video standard with the smallest step-to-transition bandwidth. The NTSC standards have the smallest transition bandwidth, which is 696 KHZ. As previously indicated, block 74 provides for the recovery of the carrier. The intermediate video frequency from the terminal 70 is transmitted to a phase mixer / detector 94, whose output is filtered through the circuit filter 96 which controls a numerically controlled oscillator (NCO) 98. The NCO functions as a controlled oscillator of voltage (VCO) and can be synchronized in phase with an external clock by modulating its phase error input. An output of the mixer / phase detector 94 is the audio intercarrier that is transmitted with the intermediate video frequency. The video intercarrier is transmitted through line 100 in such a way that it can be transmitted directly to the audio DSP 26 (see Figure 1). Conveniently, the video demodulator is designed in such a way that the sound tap and drop point at the output of the mixer / phase detector 94 does not require sound to pass through the Nyquist 80 filter. , a separate sound demodulator is not necessary, which would make the system more expensive. Both the 96-circuit filter and NCO 98 are programmed to allow operation with different television standards. The NCO output frequency is supplied by an automatic fine tuning circuit 78. The NCO frequency is compared in a frequency comparison circuit 102, with the actual frequency at which the intermediate video frequency signal is received. A frequency blocking circuit 104 is controlled by the output of the frequency comparison circuit 102 in order to tune in fine tuning and automatically the actual operating frequency. The output of the frequency blocking circuit is modulated by pulse width in circuit 106 to supply an automatic fine-tuning (AFT) signal through line 108. The AFT signal is used by a conventional down-converter (which is not sample) in the television converter, to supply the low intermediate frequency input to the video DSP through terminal 10 of Figure 1. Figure 3 illustrates in more detail the FM demodulator 40 the QPSK / FM demodulator 44 of the video DSP 26. The demodulator 44 is a synchronous demodulator that is configured to perform FM or QPSK demodulation. The demodulator 40 is a synchronous demodulator used only for FM demodulation. The audio intercarrier is supplied on line 100 to the demodulators 40 as 44. The intercarrier is supplied on the demodulator 4. audio through a 2: 1 multiplexer (used as a selector) to a mixer 152 that provides automatic gain control (AGC). The output of mixer 152 is transmitted to mixers 154 and 156 where the signal is mixed with appropriate frequency outputs from an oscillator 158 controlled in numerical form. The output of the interlock filter 162 also passes through a low pass filter 164 to provide the demodulated FM output. The output of the mixer 154 is integrated into the integrator 160 to supply the AGC signal. The multiplexer 150 supplies the audio intercarrier as an output to the mixer 152 when the audio mode is the DIN mode (which requires two carriers for stereo) or the PAL mode, in which case, the demodulator 40 demodulates the FM modulation of the primary carrier. For the FM stereo or second audio program (SAP) signals, the multiplexer 150 passes the "FM 1" signal from the multiplexer (ie, selector) 142 of the demodulator 144 to the mixer 152 of the demodulator 40. The demodulator FM / QPSK synchronous 44 receives a QPSK / FM selection signal at terminal 1 10 in order to establish the demodulator for QPSK or FM demodulation. The audio intercarrier is transmitted to a mixer 1 16 which supplies an AGC signal from the integrator 126. The output of the mixer 1 16 is connected to the mixers 1 18 and 120 receiving the programmable NCO outputs 122. The NCO is programmable for adjust the different standards that can be processed by the converter. A circuit filter 124 is provided to maintain the nominal frequency at which the NCO 122 operates. When a QPSK signal is demodulated, the circuit filter 124 receives the "Q" phase of the QPSK signal from the mixer 120 through the multiplexer (ie selector) 130. When the demodulator is demodulating an FM signal, the multiplexer 130 is driven through the selection signal input QPSK / FM at terminal 1 10 to pass the arc tangent (Q / I). ) from a rectangular to polar coordinate converter 136 to circuit filter 124. The selection signal QPSK / FM also controls a multiplexer (selector) 128 to supply an appropriate input to an integrator 126 in order to supply the necessary AGC signal. At the same time, the selection signal QPSK / FM operates a multiplexer (selector) 142 to transmit a demodulated FM signal from the low pass filter 144 or the component I of a demodulated QPSK signal from the low pass filter 134. The filter 132 may comprise a root-raised cosine (RRC) FI R filter and an adaptive equalizer, the counterpart of which is provided as a filter 138 for the Q component of the demodulated QPSK signal. The Q component passes through a second low pass filter 146 (which may also be an FIR filter RRC) before being transmitted from the demodulator 44. Both the output of the I and Q components from the respective low pass filters 134 and 146 are transmitted to the rectangular to polar coordinate converter 136, which also receives a sample symbol synchronization recovery output from the symbol synchronization recovery circuit 140. This circuit transmits a symbol clock signal (SYMCLK) for be used by the TV converter. When the demodulator 44 demodulates an FM signal, the FM output is taken from the output of the circuit filter 124, passes through the multiplexer (selector) 138 and is filtered by low pass in the low pass filters 138 and 144 before to be transmitted through the multiplexer 142. It should be clear from Figure 3 that an audio signal transmitted by the audio signal intercarrier may comprise FM modulation, QPSK modulation, or both when separate carriers are supplied. In this way, any of the audio modalities indicated in Table 2 can be adjusted. It should now be appreciated that the present invention provides a reduced cost television converter using digital signal processing techniques. In the video demodulator section, a sampling frequency of 27 MHz is advantageous (although it is not required) in order to handle the PAL 1, PAL B and NTSC television signals without alternative name creation during the demodulation. This alternative name is avoided because the sum products are below the frequency at which they could be renamed in the DC for the 7 MHz band in question. A low intermediate frequency input is converted from an analog signal to a digital signal, which is applied to a Nyquist filter. In a preferred implementation, the Nyquist filter may comprise a filter of the 9 MHz symmetric linear inclination type, -6 dB. A gain control multiplier is used to restore the distorted video modes to a correct level. A 9 MHz NCO is synchronized in phase with the filtered Nyquist video carrier and applied to the I and Q multipliers. The difference product is the desired baseband video signal. After demodulation, the video signal may be reduced (for example, down to a sampling of 13.5 MHz) before further processing takes place. In a preferred embodiment, the video PLL (synchronized phase circuit) bandwidth is approximately 200 KHz initially during tuning and reduced to approximately 25 KHz after synchronization was detected. This multiple speed circuit in the DSP design is useful during the acquisition of tuning to accelerate the synchronization time and extend the capture range. The multiplier Q is used for the generation of AFC and the intercarrier. It is connected before the decoding gain control stage to prevent the AM modulation from being applied to the intercarrier. A delay setting of the gain control multiplier in the path must be inserted before the multiplier Q in order to maintain the correct quadrature phase relationship. Connecting the multiplier Q before the Nyquist filter with the appropriate delay reduces the conversion from AM to PM and improves the operation of the suppressed operator. The multiplier I is reduced by two and is filtered by FIR to eliminate the sound carrier (s). The FI R filter is programmable in terms of the coefficients to the video standard in use. The converter allows the reception of digital audio independent of the video (for example, for a digital audio channel only). In such a case, the NCO of the video carrier must be set to a fixed frequency mode in order to mix the desired QPSK carrier to the frequency of the desired intercarrier. The television converter can receive different modalities of audio signals. For analog FM audio, a video demodulator quadrature output is used in, for example, 27 MHz as the source of the audio intercarriers. A cancellation of approximately 40 dB can be expected from the quadrature output assuming that the image was originally modulated by a good quality analog video modulator. Video cancellation reduces the complexity of the audio filter. The processing of the intercarrier is necessary due to the noise of the up and down conversion phase. A linear PLL demodulator can be used as AGC to extract the FM modulation while providing an AM rejection of at least 40 dB. Due to the linear downward conversion, the AM video carrier is present in a sparse form. The AGC circuit eliminates hum amplitude modulation. The PLL demodulator is also used for DI N applications. For digital audio, an intercarrier PLL may include a ROM look-up table for carrier recovery when used in QPSK modes. Clock recovery is also included. The output of the I and Q multipliers is divided in descending order at a low sampling rate for an effective low-pass filtering and then to be interpolated again in ascending form before the data sampling is applied. A filter can be used for PAL 1, PALB and AC-1. Only the NCO frequency can be changed for these different modalities. The demodulated data is demultiplexed, decoded if authorized, decoded using the Dolby AC-1 mode, the volume is controlled, and transmitted through a digital to analog converter for the left and right stereo audio outputs. A digital audio output is also supplied, for example, that complies with the Sony-Phillips Digital Interface (SPDIF). Similar processing is also provided for the N ICAM data when they are present. In the illustrated embodiment, the video carrier synchronized phase circuit (PLL) is placed before Nyquist for AM-VSB, and the compensating delay is placed in the NCO path to the multiplier after the Nyquist filter. This eliminates AM to FM conversion, improving luminance linearity and differential gain and phase. This design also prevents the video information from subjecting the radio intercarrier to phase modulation, thereby eliminating the video "buzz" components in the audio. The Nyquist filter is a programmable FI R filter, either high pass or low pass, to allow the tuner oscillator to be higher or lower than the desired channel. In other words, the digitized intermediate frequency video carrier may be above the sound carrier and below the sound carrier. The frequencies of the video carrier are, for example, 6.75 MHz for high pass and 9 MHz for low pass. Although the invention has been described in relation to different specific embodiments, it should be appreciated that numerous adaptations and modifications can be made without departing from the scope of the invention, as set forth in the following claims.

Claims (23)

1. R E I V I N D I C A I N N E S Having described the present invention, it is considered as a novelty and, therefore, what is contained in the following REVIVALS is claimed as property. 1 . A digital signal processor for the recovery of video and audio signals according to different analogue and digital transmission standards, characterized by comprising: a video demodulator with a first path for coupling a video signal modulated to a mixer through of a Nyquist filter, and a second path for coupling said modulated video signal to a carrier recovery circuit without passing through said Nyquist filter, said modulated video signal being adjusted to a particular television standard; said carrier recovery circuit (i) retrieves a frequency signal from the carrier to be used by said mixer in order to supply a baseband video signal and (ii) detects an audio intercarrier present in said signal modulated video; and a programmable sound band filter for filtering audio components from said baseband video signal in accordance with said particular television standard to supply a demodulated video output; wherein said audio intercarrier is supplied as an output from said carrier recovery circuit for the subsequent recovery of audio in accordance with said particular television standard.
2. 2. A digital signal processor according to the Claim 1, further characterized in that said modulated video signal is supplied at an intermediate frequency (Fl), which further comprises an analog-to-digital converter for sampling the intermediate frequency modulated video signal at a sampling frequency fs for digitize said signal for its input to said video demodulator.
3. 3. A digital signal processor according to Claim 2, further characterized in that said sampling frequency fs is an integer multiple of said intermediate frequency.
4. 4. A digital signal processor according to the Claim 3, further characterized in that said intermediate frequency is 6.75 MHz or 9.0 MHz and said sampling frequency fs is 27 MHz.
5. 5. A digital signal processor according to the Claim 4, further characterized in that said demodulated video output is a digital signal whose sampling gives a frequency fs of 13.5 MHz.
6. 6. A digital signal processor according to Claim 2, further characterized in that said sampling frequency is synchronized in the phase with a horizontal synchronization component of said baseband video signal.
7. 7. A digital signal processor according to Claim 1, further characterized in that said modulated video signal is retrieved from a signal band by a tuner, and the particular television standard to which said modulated video signal corresponds is identified to through a channel map corresponding to said tuner.
8. 8. A digital signal processor according to Claim 1, further characterized in that said modulated video signal transmits indicator identifier data of the particular television standard to which the modulated video signal corresponds.
9. 9. A digital signal processor according to the Claim 1, further characterized in that it further comprises the following: means for delaying said frequency signal from the carrier before said mixer to compensate for a delay introduced by said Nyquist filter.
10. 10. A digital signal processor according to the Claim 1, further characterized in that an audio demodulator is provided for processing said audio intercarrier, said audio modulator comprising the following: a first synchronous demodulator for selectively modulating a first FM modulated audio signal or a QPSK modulated audio signal transmitted by said audio intercarrier; and a second synchronous demodulator for the demodulation of a second FM modulated audio signal transmitted by said audio intercarrier. eleven .
11. A digital signal processor according to the Claim 10, further characterized in that said first and second synchronous demodulators comprise on-line synchronized circuits allowing the demodulation of said audio intercarrier with preliminary bandpass filtering.
12. 12. A digital signal processor according to the Claim 10, further characterized in that said video demodulator, carrier recovery circuit, programmable sound band filter and audio demodulator are all implemented in an individual integrated circuit chip
13. 13. A digital signal processor according to Claim 10, further characterized in that: said modulated video signal is retrieved from a signal band by a tuner; the particular television standard to which said modulated video signal corresponds is identified by a channel map that responds to said tuner; and said first demodulator responds to said channel map for selective demodulation of said first modulated FM audio signal or of said QPSK modulated audio signal.
14. 14. A digital signal processor according to Claim 10, further characterized in that: said modulated video signal transmits indicator identifier data of the particular television standard to which the modulated video signal corresponds; and said first synchronous demodulator responds to said identifier data for selectively demodulating said first FM modulated audio signal, or said modulated audio signal QPSK.
15. 15. A digital signal processor for the recovery of video and audio signals according to different analogue and digital transmission standards, characterized in that it comprises the following: an audio demodulator for the processing of an audio intercarrier; a first synchronous demodulator in said audio demodulator for the selective demodulation of a first FM modulated audio signal or a QPSK modulated audio signal transmitted by said audio intercarrier; and a second synchronous demodulator in said audio demodulator for the demodulation of a second FM modulated audio signal transmitted by said audio carrier.
16. 16. A digital signal processor as described in Claim 15, further characterized in that said first and second demodulators comprise linear phase synchronized circuits that allow the demodulation of said audio intercarrier with preliminary bandpass filtering.
17. 17. A digital signal processor as described in Claim 15, further characterized in that said first synchronous demodulator comprises the following: a QPSK demodulator with first and second output stages, one of said output stages being an output stage I and being the other, an exit stage Q; a variable oscillator for the supply of first and second outputs of the oscillator displaced from the phase with a frequency dictated by a demodulation control signal, said first output of the oscillator being associated with said first output stage and said second output of the oscillator being associated with said second exit stage; a phase-synchronized circuit for controlling said variable oscillator in response to an output from a particular stage of said first and second stages; and a selector for selectively outputting a QPSK signal from a particular stage of said first and second output stage or an FM signal, from said phased circuit.
18. 18. An apparatus for the recovery of video and audio signals according to different analogue and digital transmission standards, characterized in that it comprises the following: a tuner for the selection of a TV channel signal, said TV channel signal being adjusted to a standard particular of television; means for digitizing said television signal; means for identifying the particular television standard to which said television channel fits; a digital video signal processor (DSP) in response to said identification means for demodulating the digitized TV channel signal selected to supply a video output signal; and an audio DSP in response to said identification means for demodulating the selected digitized TV channel signal in order to supply an audio output signal; said identification means being digitalization means, video DSP and audio DSP, located together in an integrated circuit chip.
19. 19. An apparatus as described in the Claim 18, further characterized in that it comprises the following on said integrated circuit chip: a data DSP for demodulating auxiliary data transmitted on said television channel signal to supply an auxiliary data output signal.
20. 20. An apparatus as described in the Claim 18, further characterized in that it comprises, in said integrated circuit chip: a data modulator for the modulation of data of the return path that must be communicated from said apparatus to a remote location. twenty-one .
21. A digital signal processor as described in Claim 1, further characterized in that: the particular transmission standard comprises a standard television standard.
22. 22. A digital signal processor as described in Claim 15, further characterized in that: the particular transmission standard comprises a standard television standard.
23. 23. An apparatus as described in Claim 18, further characterized in that: the particular transmission standard comprises a standard television standard.