Television – Receiver circuitry – Tuning
Reexamination Certificate
2000-07-12
2004-05-04
Miller, John (Department: 2614)
Television
Receiver circuitry
Tuning
C348S731000, C348S536000, C455S161100, C455S180100, C455S188100, C455S193100
Reexamination Certificate
active
06731349
ABSTRACT:
The invention relates to a tuner with at least a first and a second frequency band and with a signal input terminal for the supply of a frequency information signal.
The invention further relates to an integrated circuit with a PLL circuit for controlling a tuner which comprises at least a first and a second frequency band.
Such a tuner and such an integrated circuit are known, for example, from the tuner UV 316 of the Philips company. This known tuner is manufactured in accordance with the WSP (World Standard Pinning) standard. The WSP standard lays down the mechanical dimensions, the functions of the individual connection terminals of the tuner, as well as the antenna height. Terrestrial tuners usually comprise two or three frequency bands, each comprising a tunable input filter, a controllable amplifier, a tunable band-pass filter, and a mixer circuit. Three pins are available for the supply of one control signal each for the control and selection of the frequency bands in the WSP. The control of the tuner takes place by means of the microprocessor of the TV set which is coupled to the tuner, for example, by means of a I
2
C bus. A table is stored in known TV sets for the selection of the frequency band, by means of which table the frequencies of the TV signal which can be selected are associated with the respective frequency band of the tuner. When the user of the TV set selects a TV signal frequency, for example by means of a remote control unit, the microprocessor of the TV set selects the associated frequency band of the tuner from the table and transmits the control signals defining the band selection to the tuner.
The selection of the frequency bands of the tuner by means of the microprocessor of the TV set has the disadvantage that only tuners can be used for the TV set whose frequency bands correspond to the values stored in the table of the TV set. A subsequent change in the tuner as regards the characteristics of the frequency bands, or the use of a different tuner is no longer possible.
It is an object of the invention to provide a tuner as well as an integrated circuit of the kind mentioned in the opening paragraphs which are universally applicable.
According to the invention, this object is achieved with regard to the tuner in that the tuner comprises a band selection circuit which is provided for the selection and control of one frequency band at a time, and in that the tuner comprises a frequency search function for tuning to a frequency, which function in a first step is designed to test the tuning possibility of the frequency in the first frequency band and, if tuning in the first frequency band is not possible, in a second step is designed for testing the tuning possibility of the frequency in the second frequency band.
The tuner according to the invention thus evaluates the frequency information signal supplied to it by the microprocessor of the TV set and independently selects the frequency band in dependence on this frequency information signal. To render it possible for the tuner to select the frequency band independently, this tuner comprises a frequency search function. This frequency search function is designed such that it is consecutively tested in at least two different frequency bands whether a desired frequency can be tuned in the relevant frequency band.
Each frequency band has a mixer circuit with an oscillator for driving the mixer. The oscillator preferably comprises an oscillation circuit with a controllable capacitance. The controllable capacitance is preferably implemented as a reverse-biased varicap diode whose capacitance depends on the bias voltage applied. The oscillator frequency of the oscillation circuit can be controlled through a change in the bias voltage and the resulting change in the capacitance. Terrestrial tuners are usually designed for the conversion of input frequencies in a range from 45 MHz to 863 MHz. Since the controllable or adjustable capacitance range of the varicap diodes is limited, the tuners preferably comprise three frequency bands, each with its own oscillation circuit and with its own varicap diode designed for tuning the oscillation circuit. Testing of the tuning possibility accordingly means that it is tested whether the oscillator of the relevant frequency band can be tuned to the desired frequency which is necessary for mixing to the intermediate frequency of the tuner. The oscillation circuits are preferably coupled to a quartz oscillator by means of a programmable divider circuit. To synchronize the oscillation circuit with the quartz oscillator, a phase-locked loop (PLL) is preferably provided. The test as to whether a desired frequency can be tuned in one of the frequency bands may take place by means of a latching detector which detects whether the phase control circuit latches or locks itself, i.e. whether the desired oscillator frequency of the oscillation circuit can be synchronized with the reference frequency of the quartz oscillator, a programmable divider circuit being provided between the oscillation circuit and the quartz oscillator.
The individual frequency bands usually each comprise a band-pass filter which is formed by a coil and a varicap (variable-capacitance) diode connected in parallel thereto. The barrier layer capacitance of the varicap diode is dependent on the applied bias voltage and can thus be controlled through a change in the applied bias voltage. The varicap diodes of the band-pass filter and the varicap diodes of the oscillation circuits are preferably controlled in parallel during the tuning.
When a frequency information signal with a desired frequency is supplied to the tuner, the oscillation frequency of the oscillator of the first frequency band is scanned from the lowest band frequency to the highest band frequency in a first step. It is tested during this whether the desired frequency is tunable in the first frequency band. If the desired frequency could not be tuned in the first frequency band, a switch-over to the second frequency band takes place automatically, where the respective oscillator again is scanned continuously from the lower band limit to the upper band limit for tuning to the desired frequency.
This principle may also be applied in tuners having three or more frequency bands, for example, in the case of three frequency bands, the tuning is attempted first in the first, then in the second, and finally in the third frequency band.
The independent band selection of the tuner by means of the band selection circuit and the frequency search function has the advantage that a tuner of this construction can be used in any TV set whatsoever. Neither the software of the microprocessor of the TV set nor the software of the tuner need be changed for this purpose. Such a tuner can thus be manufactured efficiently and inexpensively in very large quantities. It is in addition possible to change the physical parameters of the individual frequency bands without a change in the software of the tuner being necessary. For example, the band boundaries of the frequency bands can be shifted through the use of different varicap diodes or other inductances for the respective band-pass filters and oscillation circuits. No change in the tuner software is necessary in such a case, because the tuner changes the switch-over points between the individual frequency bands automatically.
An example embodiment of the invention renders it possible to avoid an unnecessary switching-over between the frequency bands. The band selection circuit determines a tuning mode in accordance with the frequency difference between the old and the new frequency information signal as determined by the frequency difference detection circuit, which signal is supplied to the tuner, for example, by the microprocessor of the TV set. This tuning mode influences the further band selection, i.e. it determines whether and under what conditions a band switch-over between the frequency bands will take place.
According to an example embodiment, tuning modes which can be distinguished by the frequency difference
Koninklijke Philips Electronics , N.V.
Miller John
Yenke Brian
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