Radio receiver for receiving both vsb and qam digital hdtv signals

#The invention relates to radio receivers having the capability of receiving digital high-definition television (HDTV) signals, no matter whether they are transmitted using quadrature amplitude modulation (QAM) of the principal carrier wave or they are transmitted using vestigial sideband (VSB) amplitude modulation of the principal carrier wave.

#Vestigial sideband (VSB) signals that are used in certain transmissions of HDTV signal have their natural carrier wave, which would vary in amplitude depending on the percentage of modulation, replaced by a pilot carrier wave of fixed amplitude, which amplitude corresponds to a prescribed percentage of modulation. This percentage modulation can be made the same as that associated with the smallest change in symbol code level. Such VSB signals using 8-level symbol coding will be used in over-the-air broadcasting within the United States, for example, and can be used in over-the-air narrowcasting systems or in cable-casting systems. However, certain cable-casting is likely to be done using suppressed-carrier quadrature amplitude modulation (QAM) signals instead, rather than VSB signals. This presents television receiver designers with the challenge of designing receivers that are capable of receiving either type of transmission and of automatically selecting suitable receiving apparatus for the type of transmission currently being received.

#A television receiver designer of ordinary skill in the art will readily observe that processing after symbol decoding is similar in receivers for the VSB HDTV signals and in receivers for the QAM HDTV signals, since the data format supplied for symbol encoding is the same in transmitters for the VSB HDTV signals and in transmitters for the QAM HDTV signals. The data recovered by symbol decoding are supplied as input signal to a data de-interleaver, and the de-interleaved data are supplied to a Reed-Solomon decoder. Error-corrected data are supplied to a data de-randomizer which regenerates packets of data for a packet decoder. Selected packets are used to reproduce the audio portions of the HDTV program, and other selected packets are used to reproduce the video portions of the HDTV program. A television receiver designer of ordinary skill in the art will readily observe also that the tuners are quite similar in receivers for the VSB HDTV signals and in receivers for the QAM HDTV signals. The differences in the receivers reside in the synchrodyning procedures used to translate the final IF signal to baseband and in the symbol decoding procedures. A television receiver designer of ordinary skill in the art will readily deduce that a receiver that is capable of receiving either VSB or QAM HDTV signals is more economical in design if it does not duplicate the similar tuner circuitry prior to synchrodyning to baseband and the similar receiver elements used after the symbol decoding circuitry. The challenge is in optimally constructing the circuitry for synchrodyning to baseband and for symbol decoding to accommodate both HDTV transmission standards and in arranging for the automatic selection of the appropriate mode of reception for the HDTV transmission currently being received.

#FIG. 1 is a block schematic diagram of initial portions of a digital HDTV signal radio receiver of a type embodying the invention, including circuitry for detecting symbols in an HDTV signal of QAM type, circuitry for detecting symbols in an HDTV signal of VSB type, and an amplitude-and-group-delay equalizer for symbols selected from the circuitry for detecting symbols in an HDTV signal of QAM type and the circuitry for detecting symbols in an HDTV signal of VSB type.

#FIG. 2 is a block schematic diagram of the remaining portions of the digital HDTV signal radio receiver of a type embodying the invention, which are not shown in FIG. 1.

#FIG. 3 is a detailed block schematic diagram of circuitry for providing the sample clock generator, the look-up table read-only memories (ROMs) for supplying digital descriptions of the complex carriers used for synchrodyning digital QAM signals and digital VSB signals at final IF signal frequencies each to baseband, and the address generators for those ROMs, which circuitry is included in certain digital HDTV signal radio receivers of the type embodying the invention.

#In the block schematic diagrams, clock or control signal connections are shown in dashed line, where it is desired to distinguish them from connections for the signals being controlled. To avoid overcomplexity in the block schematic diagrams, some shimming delays necessary in the digital circuitry are omitted, where a need for such shimming delay is normally taken into account by a circuit or system designer.

#FIG. 1 shows a tuner 5 comprising elements 11-21 that selects one of channels at different locations in the frequency band for digital HDTV signals and performs plural frequency conversion of the selected channel to a final intermediate-frequency signal in a final intermediate-frequency band. FIG. 1 shows a broadcast receiving antenna 6 arranged to capture the digital HDTV signals for the tuner 5. Alternatively, the tuner 5 can be connected for receiving digital HDTV signals from a narrowcast receiving antenna or from a cablecast transmission system.

#More particularly, in the tuner 5 shown in FIG. 1, a channel selector 10 designed for operation by a human being determines the frequency of first local oscillations that a frequency synthesizer 11, which functions as a first local oscillator, furnishes to a first mixer 12 for heterodyning with digital HDTV signals received from the antenna 6 or an alternative source of such signals. The first mixer 12 upconverts the received signals in the selected channel to prescribed first intermediate frequencies (e. g., with 920 MHz carrier), and an LC filter 13 is used to reject the unwanted image frequencies that accompany the upconversion result supplied from the first mixer 12. The first intermediate-frequency signal resulting from the upconversion, supplied as the filter 13 response, is applied as the input signal to a first intermediate-frequency amplifier 14, which supplies amplified first IF signal for driving a first surface-acoustic-wave (SAW) filter 15. The upconversion to the rather high-frequency first intermediate frequencies facilitates the SAW filter 15 having a large number of poles and zeroes. Second local oscillations from a second local oscillator 16 are supplied to a second mixer 17 for heterodyning with the response of the first SAW filter 15, to generate second intermediate frequencies (e. g., with 41 MHz carrier). A second SAW filter 18 is used for rejecting the unwanted image frequencies that accompany the downconversion result supplied from the second mixer 17. During the period of transition from NTSC television transmissions to digital television transmissions, the second SAW filter 18 will usually include traps for sound and video carriers of adjacent-channel NTSC television transmissions. The second IF signal supplied as the response of the second SAW filter 18 is applied as input signal to a second intermediate-frequency amplifier 19, which generates an amplified second IF signal response to its input signal. Oscillations from a third local oscillator 20 are heterodyned with the amplified second IF signal response in a third mixer 21. The plural-conversion tuner 5 as thus far described resembles those previously proposed by others, except that the frequency of the oscillations from the third local oscillator 20 is chosen such that the third mixer 21 supplies a third intermediate-frequency signal response.