Television – Receiver circuitry – Television receiver adapted to receive radio broadcast or in...
Reexamination Certificate
1998-01-06
2001-10-23
Eisenzopf, Reinhard J. (Department: 2614)
Television
Receiver circuitry
Television receiver adapted to receive radio broadcast or in...
C348S725000, C348S728000, C348S720000, C348S721000, C348S555000
Reexamination Certificate
active
06307598
ABSTRACT:
The present invention relates to the radio receiver portions of television (TV) signal receivers for receiving terrestrial through-the-air television broadcasting in the United States of A America whether the received signals be digital television signals, in accordance with the Advanced Television Systems Committee (ATSC) standard, or analog television signals, in accordance with the National Television System Committee (NTSC) standard.
BACKGROUND OF THE INVENTION
The first detector in a television signal receiver converts radio-frequency (RF) signals in a selected one of the television broadcast channels, which channels occupy various 6-MHz-wide portions of the electromagnetic wave frequency spectrum, to intermediate-frequency (IF) signals in one particular 6-MHz-wide portion of that spectrum. This first conversion-is typically carried out by superheterodyning the RF signals, which is to say mixing the RF signals with local oscillations from an oscillator oscillating at 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 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 with fixed, rather than variable, 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 preselection filter circuitry for the RF signals to select 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 superheterodyning the RF signals. In. TV receivers of more recent design the local oscillator signals are often generated using a frequency synthesizer in which the local oscillator signals are generated with frequency regulated in adjustable ratio with the fixed frequency of a standard oscillator.
Television signal receivers for receiving digital television (DTV) signals that have been described in the prior art use plural-conversion radio receivers wherein DTV signal in a selected one of the ultra-high-frequency (UHF) channels is first up-converted in frequency to first intermediate-frequency signal in a first intermediate-frequency band centered at 920 MHz for amplification in a first intermediate-frequency amplifier. 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. This second intermediate-frequency signal, in a second intermediate-frequency band centered at 44 MHz, is then amplified in a second intermediate-frequency amplifier. The response of the second intermediate-frequency amplifier is then synchrodyned to baseband in DTV signal receivers developed by the Grand Alliance.
Radio receivers for receiving DTV signals, in which receivers the final intermediate-frequency signal is somewhere in the 1-8 MHz frequency range, are described by C. B. Patel and the inventor in U.S. Pat. No. 5,479,449 issued Dec. 26, 1995, entitled “DIGITAL VSB DETECTOR WITH BANDPASS PHASE TRACKER, AS FOR INCLUSION IN AN HDTV RECEIVER”, and included herein by reference. The radio receivers specifically described in U.S. Pat. No. 5,479,449 are of triple-conversion type using a 920 MHz analog IF amplifier for first detector response, the first detector being an up-converter, and using a 44 MHz analog IF amplifier for second detector response, the second detector being a down-converter. A third detector is a further down-converter, generating a 1-8 MHz final IF signal as third detector response. This final IF signal is not amplified, but is digitized by an analog-to-digital converter for use in digital circuitry for synchronizing to baseband. The resulting digital baseband signal is equalized and then data-sliced in a symbol decoder. The first intermediate-frequency amplifier in one of the DTV signal receivers described in U.S. Pat. No. 5,479,449 uses a surface-acoustic wave (SAW) filter for establishing the bandwidth of the 920 MHz IF amplifier.
The DTV signal receiver developed by the Grand Alliance is of double-conversion type using a 920 MHz analog IF amplifier for first detector response, the first detector being an up-converter, and using a 44 MHz analog IF amplifier for second detector response, the second detector being a down-converter. The amplified response of the 44 MHz analog IF amplifier is the final IF signal, which is synchrodyned to baseband in the analog regime. The resulting analog baseband response is then digitized by an analog-to-digital converter prior to being equalized and then data-sliced in a symbol decoder. The first intermediate-frequency amplifier in the DTV signal receiver developed by the Grand Alliance uses ceramic resonators for establishing the bandwidth of the 920 MHz IF amplifiers.
For a period of years while DTV broadcasting is becoming established, it is planned that the broadcasting of analog TV signals will continue in the United States in accordance with the NTSC standard using the same UHF channels as DTV signals as well as other channels in the VHF and UHF bands. While analog and digital TV signals occupy the same television channels, the requirements of radio receivers for the two types of TV signal are not particularly compatible. This is pointed out by the inventor in his U.S. patent application Ser. No. 08/825,711 filed Mar. 19, 1997, entitled “RADIO RECEIVER DETECTING DIGITAL AND ANALOG TELEVISION RADIO-FREQUENCY SIGNALS WITH SINGLE FIRST DETECTOR”, and incorporated herein by reference. In that application the inventor points out that the cost of a first detector is substantial enough that it is undesirable to use separate first detectors for analog TV signals and for digital TV signals in radio receivers designed to receive both types of signal, whether those radio receivers are included in a TV set complete with viewscreen or in a digital recording apparatus, such as one using magnetic tape as a recording medium. The use of a single first detector for both analog TV signals and digital TV signals is also desirable in that it allows more-compact radio receiver design and at the same time avoids any problems of unwanted radiation from the output of one of separate respective first detectors for analog TV signals and for digital TV signals to the other first detector. The different radio receiver requirements for analog TV signals and for digital TV signals are accommodated by using different intermediate-frequency amplification for analog TV signals and for digital TV signals.
Using different intermediate-frequency amplification for analog TV signals and for digital TV signals allows for the different radio receiver passbands required for each type of TV signal. In an analog TV signal the video carrier is located at a frequency 1.25 MHz above the lower limit frequency of the TV channel, and the vestigial sideband exhibits no gain reduction vis-a-vis the full sideband until modulating frequencies exceed 750 kHz. Accordingly, the radio receiver for an analog TV signal customarily exhibits a linear roll-off of the overall intermediate-frequency response supplied to the video detector, which roll-off is down 6 dB at the video carrier frequency and provides for an overall flat baseband video response up to 4.2 MHz or so. In a DTV signal, the data is located at a frequency only 310 kHz above the lower limit frequency of the TV channel; and roll-off down 6 dB at the data carrier frequency is provided at the transmitter, rather than at the receiver. The overall intermediate-frequency response is essentially flat over a frequency band 6 MHz-wide between 1-dB-down limit frequencies in Grand Alliance receiver designs published by Zenith Radio
Eisenzopf Reinhard J.
Lo Linus M.
Samsung Electronics Co,. Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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