Television – Receiver circuitry
Reexamination Certificate
1999-04-14
2003-04-08
Miller, John (Department: 2614)
Television
Receiver circuitry
C348S726000, C348S727000, C348S728000, C455S150100, C455S188100, C455S189100
Reexamination Certificate
active
06545728
ABSTRACT:
The invention relates to radio receivers having the capability of receiving digital television (DTV) signals, such as digital high-definition television (HDTV) signals.
BACKGROUND OF THE INVENTION
The first detector in a television signal receiver converts radio-frequency (RF) signal from a selected one of the television broadcast channels, which channel occupies one of specific 6-MHz-wide portions of the electromagnetic wave frequency spectrum, to an intermediate-frequency (IF) signal in one particular 6-MHz-wide portion of that spectrum above or below that in which television broadcast channels are assigned. The first detector comprises a first local oscillator for generating first local oscillations, a first mixer for mixing the selected one of the television broadcast channels with the first local oscillations to generate the IF signal and its image, and a frequency-selective filter for passing the IF signal while blocking the image. The conversion is typically carried out by superheterodyning the RF signals, which is to say mixing the RF signals with first local oscillations of a frequency substantially higher than the frequencies in the television channel of highest frequency. The first detector is used to convert a selected RF signal to an IF signal in order that up to 60 dB or more amplification can be done in that particular 6-MHz-wide portion of that spectrum using intermediate-frequency amplifiers that do not require adjustable tuning. Amplification of the received signals is necessary to raise them to power levels required for further signal detection operations, such as video detection and sound detection in the case of analog TV signals, and such as symbol decoding in the case of digital TV signals. The first detector usually includes variable tuning elements in the form of pre-selection filter circuitry for the RF signals to select one among the various 6-MHz-wide television channels and in the further form of elements for determining the frequency of the local oscillations used for super-heterodyning the RF signals. The pre-selection filter circuitry for the RF signals usually includes a radio-frequency amplifier for strengthening the signals supplied to the first mixer. In TV receivers of more recent design the first local oscillator signals are often generated using a frequency synthesizer, in which the first local oscillator signals are generated with frequency regulated in adjustable ratio with the fixed frequency of a standard oscillator.
The mixers and IF amplifiers in a digital television receiver have different design requirements than the mixers and IF amplifiers in an analog television receiver. The mixers and IF amplifiers in an analog television receiver are designed not to exhibit an overall gain response that is linear. Symbol decoding in a DTV receiver involves a procedure known as data-slicing, which determines which of a number of amplitude bins the amplitude of the baseband DTV signal currently resides in, each of which amplitude bins is associated with a particular symbol decoding result expressed as a group of successive bits of data. In order that data-slicing be carried out optimally with the current DTV broadcast standards, the mixers and IF amplifiers in a DTV receiver must exhibit an overall gain response that is linear. Where mixing is done by multiplying selected DTV signal with sinusoidal local oscillations, spectral purity of the oscillations (i. e., freedom from harmonic distortion) is important, and the mixers should be linear multipliers. The gain provided by the IF amplifiers should be very linear.
Television signal receivers for receiving digital television (DTV) signals that have been proposed by the Grand Alliance, a group of DTV proponents including Zenith Electronics Corporation, use plural-conversion radio receivers. During the first detection procedure in these plural-conversion radio receivers, DTV signal in a selected one of the ultra-high-frequency (UHF) channels is up-converted in frequency to first intermediate-frequency signal in a first intermediate-frequency band centered at 920 MHz. This puts the image frequencies above 1 GHz, making them easy to reject by fixed-tuned front-end filtering. The upconverted DTV signals are then amplified in a first intermediate-frequency amplifier that uses ceramic resonators for tuning. The resulting amplified first intermediate-frequency signal is then down-converted in frequency by mixing it with 876 MHz local oscillations, resulting in a second intermediate-frequency signal in a second intermediate-frequency band 6 MHz wide centered at 44 MHz. The overall amplitude and phase characteristics of the receiver are controlled using a surface-acoustic-wave (SAW) filter for selecting the second intermediate-frequency band. This second intermediate-frequency signal, as selected by the SAW filter, is then amplified in a second intermediate-frequency amplifier. The response of the second IF amplifier is then synchrodyned to baseband. This synchrodyning procedure can be a direct one in which the response of the second IF amplifier is synchronously detected at the frequency of the data carrier in the second IF band. Alternatively, this synchrodyning procedure can proceed by stages, with the response of the second IF amplifier being first down converted to a third and final intermediate-frequency band and then synchronously detected at the frequency of the data carrier in the final IF band. This alternative synchrodyning procedure is preferred where synchronous detection is to be done in the digital regime, rather than the analog regime, since the sampling rates required in analog-to-digital conversion can be lowered sufficiently to make such conversion practical with currently available technology.
Radio receivers for receiving digital television signals, in which receiver the final intermediate-frequency signal is somewhere in the 1-8 MHz frequency range rather than at baseband and is digitized before synchrodyning to baseband, are described by C. B. Patel et alii in U.S. Pat. No. 5,479,449 issued Dec. 26, 1995 and entitled “DIGITAL VSB DETECTOR WITH BANDPASS PHASE TRACKER, AS FOR INCLUSION IN AN HDTV RECEIVER”. The entire specification and drawing of U.S. Pat. No. 5,479,449 is incorporated herewithin by reference, particularly
FIGS. 2-5
and the specification descriptive of various ways to implement bandpass phase tracking for a vestigial-sideband signal. The use of infinite-impulse response filters for developing complex digital carriers in such receivers is described by C. B. Patel et alii in U.S. Pat. No. 5,548,617 issued Aug. 20, 1996 and entitled “DIGITAL VSB DETECTOR WITH BANDPASS PHASE TRACKER USING RADER FILTERS, AS FOR USE IN AN HDTV RECEIVER”. The design of receivers for both VSB and QAM signals in which both types of signal are processed through the same intermediate-frequency amplifiers receivers is described by C. B. Patel et alii in U.S. Pat. No. 5,506,636 issued Apr. 9, 1996 and entitled “HDTV SIGNAL RECEIVER WITH IMAGINARY-SAMPLE-PRESENCE DETECTOR FOR QAM/VSB MODE SELECTION”. U.S. Pat. No. 5,606,579 issued Feb. 25, 1997 to C. B. Patel et alii and entitled “DIGITAL VSB DETECTOR WITH FINAL I-F CARRIER AT SUBMULTIPLE OF SYMBOL RATE, AS FOR HDTV RECEIVER” further explains bandpass trackers. These patents and patent applications are all assigned to Samsung Electronics Co., Ltd., pursuant to employee invention agreements already in force at the time the inventions disclosed in these patents and patent applications were made.
The present invention concerns solutions to problems encountered in the design of the intermediate-frequency amplification portions of a digital TV receiver which supply the final intermediate-frequency signal somewhere in the 1-8 MHz frequency range.
In a digital signal receiver there is great concern in carefully controlling the overall amplitude and phase characteristics of the receiver in order to minimize intersymbol error, while at the same time rejecting interference from signals in adjacent channels. Getting flat amplitude response within ±1
Limberg Allen LeRoy
Patel Chandrakant B.
Lo Linus H.
Miller John
Samsung Electronics Co,. Ltd.
Sughrue & Mion, PLLC
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