Television – Receiver circuitry – Tuning
Reexamination Certificate
1999-03-10
2001-10-23
Eisenzopf, Reinhard J. (Department: 2614)
Television
Receiver circuitry
Tuning
C348S731000, C348S732000, C348S733000, C348S554000, C348S558000, C348S725000, C455S150100, C455S188200, C455S189100, C455S190100, C455S180100, C455S180200
Reexamination Certificate
active
06307600
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a tuner for tuning an input signal, having an input for receiving the input signal, a UHF section coupled to the input for handling UHF signals, a VHF section coupled to the input for handling VHF signals, the UHF section and the VHF section being coupled, with outputs, to a mixer oscillator stage which comprises UHF oscillation means with a UHF tuning circuit, and VHF oscillation means with a VHF tuning circuit, said mixer oscillator stage being coupled to an output of the tuner. The invention further relates to a mixer oscillator stage.
The invention further relates to a receiver, more particularly, but not exclusively to a television receiver.
2. Description of the Related Art
Such a tuner is used in, for example television receivers. For such a tuner, different solutions are known. As is known, television signals comprise signals in the so-called UHF and VHF band, which are tuned with a UHF section and a VHF section. Tuning can, for example be accomplished by the change in capacitance with an applied dc voltage to varicap diodes. One diode is used in each tuned circuit. Tuning the signals of the UHF band can be covered by a single varicap diode, whereas the tuning of the signals of the VHF band has to be split into at least two ranges and at least two varicap diodes are necessary. The most straight forward solution is to use a so-called 3-band concept (UHF, VHFL and VHFH) having, for each band, its own path: a tuned input circuit, a so-called RF amplifier and a bandpass filter. The UHF, VHFL and VHFH sections are then followed by a mixer oscillator (and PLL) stage.
As the above solution is quite complex, nowadays, to reduce the costs of three separate bands, a switching between the low and high VHF signals (channels) is used. A solution to perform this is to simply short-circuit, with a switching diode, a part of the tuning coil in the relevant resonant circuit to change the tuning frequency range. To obtain the off state of the switching diode, it is well known in the art to supply a negative voltage to the anode of the switching diode. Further, it is known that when the negative voltage is not connected to the switching diode, the switching diode in the oscillator circuit operates as a detector and provides a negative voltage for the other tuned circuits.
See for example “Television and Audio Handbook, page 9.22, Figure. 9.15”.
One of the disadvantages of the use of a diode detector is that a good switching diode is a poor detector. Sometimes the switching diode for the oscillator circuit is selected using a so-called detector test.
SUMMARY OF THE INVENTION
An object of the invention is to provide a tuner, a mixer oscillator stage and a receiver that do not have the disadvantages of the prior art, and, further, to improve the performance and to lower the costs of a tuner. To this end a first aspect of the invention provides a tuner as described in the opening paragraph, characterized in that the VHF oscillation means comprises a first and a second VHF oscillator, with, respectively, a first and a second VHF tuning circuit for, respectively, a first and a second VHF frequency range, and the tuner comprises detecting means for detecting which VHF oscillator is operating, the detecting means being arranged to supply a switching signal to the switchable elements of the VHF section. A second aspect of the invention provides a mixer oscillator stage for use in such a tuner. A third aspect of the invention provides a receiver compromising such as a tuner.
The invention is based on the recognition that by using two separate oscillators for the VHF signals, less parallel capacitance on the lower band VHF oscillator circuit exists than with a biased switching diode in a combined VHF tuning circuit of one VHF oscillator. Further, the tuner is much less complex as the known 3-band concept and as the known switched version. By detecting the VHFL oscillator signal when this oscillator is switched on, the detecting means provides a negative voltage to switch-off the switching diodes of the other tuned circuits.
An embodiment of a tuner according to the invention characterized in that the VHF section comprises a series arrangement of a switchable tuned input circuit, an amplifier stage, a switchable primary high frequency band filter and a switchable secondary high frequency band filter, these switchable circuits being under switching control of the detecting means.
All tuned circuits of the VHF section are supplied with the switching signal of the detecting means.
An embodiment of a tuner according to the invention characterized in that the detecting means comprises a diode detector coupled to the first VHF tuning circuit, the detecting means being part of the mixer oscillator stage.
Normally, capacitance can be added to further improve tracking in the lower VHF band, but by adding a diode detector as detecting means instead, a negative voltage can be generated. This negative voltage can then be used as switching signal for the other switchable tuned circuits of the VHF section.
REFERENCES:
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patent: 4322856 (1982-03-01), Ohta et al.
patent: 4352098 (1982-09-01), Stephen et al.
patent: 4385315 (1983-05-01), George et al.
patent: 4403346 (1983-09-01), Ogawa
patent: 4982444 (1991-01-01), Matsuura
patent: 5204645 (1993-04-01), Hohmann
patent: 5731841 (1998-03-01), Rosenbaum et al.
patent: 5859674 (1999-01-01), Chevallier
patent: 6091943 (2000-07-01), Nyenhuis
patent: 6151488 (2000-11-01), Brekelmans
“Television and Audio Handbook for Technicialns and Engineers” by K. Blair Benson et al., in Television Reception, Chapter Nine, pp. 9.20-9.23.
Biren Steven R.
Eisenzopf Reinhard J.
Natnael Paulos M.
U.S. Philips Corporation
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