Telecommunications – Receiver or analog modulated signal frequency converter – Signal selection based on frequency
Patent
1987-04-09
1989-08-29
Griffin, Robert L.
Telecommunications
Receiver or analog modulated signal frequency converter
Signal selection based on frequency
455264, 455317, H04B 110
Patent
active
048625159
DESCRIPTION:
BRIEF SUMMARY
This invention relates to frequency dividing arrangements, and in particular to frequency dividing arrangements which are suitable for use in tuners.
Frequency dividing arrangements, and in particular frequency dividing arrangements suitable for use in television tuning equipment typically comprise an input radio frequency amplifier followed by cascaded divide by two and divide by four elements which are realised in Emitter Coupled Logic (ECL) technology. The final dividing stage drives an output stage which interfaces with external circuitry. The output stage may be of ECL or transistor transistor logic (TTL) format, the ECL format producing balanced ECL type logic outputs by means of a differential transistor pair stage, and the TTL format being conventional TTL signal levels and circuitry. The differential transistor pair stage, by virtue of its gain, toggles rapidly and so produces a substantially square wave output which is very rich in harmonics.
Such frequency dividing arrangements are problematic in that they radiate electromagnetic signals at the harmonic frequencies of the square wave produced by the frequency dividing arrangement, which electromagnetic signals interfere with other circuitry in the vicinity of the frequency dividing arrangement.
The radiation of such electromagnetic signals is particularly disadvantageous when the frequency dividing arrangement is incorporated in a television tuner which also contains some intermediate frequency (IF) circuitry. This is because radiated signals having frequencies at harmonic frequencies at or near to the intermediate frequencies (such as 40 MHz) can be received by the IF circuitry within the tuner which leads to interference in the IF signal and distortion of the video picture.
It is an intention of the present invention to provide a frequency dividing arrangement which may be incorporated into a circuit arrangement and which reduces interference caused by electromagnetic signals radiated by the frequency dividing arrangement.
According to the present invention there is provided a frequency dividing arrangement for inclusion in a circuit arrangement, wherein the frequency dividing arrangement comprises a frequency divider coupled to an active filter, the active filter being operative to suppress output radiation from the frequency dividing arrangement.
The frequency dividing arrangement may form a whole or part of an integrated circuit.
According to the present invention there is further provided a tuner comprising a down conversion stage for providing an intermediate frequency signal in dependence upon a radio frequency signal received by the tuner and a local oscillator signal, and a frequency synthesiser means for generating the local oscillator signal, wherein the frequency synthesiser means includes a frequency dividing arrangement comprising a frequency divider coupled to an active filter, the active filter being operative to suppress output radiation from the frequency dividing arrangement.
The down conversion stage preferably comprises a mixer for mixing the radio frequency signal with the local oscillator signal to produce the intermediate frequency signal, and the frequency synthesiser means preferably comprises a voltage controlled oscillator for generating the local oscillator signal and a feedback signal which is afforded to a phase or frequency comparator via the frequency dividing arrangement, which phase or frequency comparator is arranged for providing a control signal for the voltage controlled oscillator in dependence upon a difference in phase or frequency between a reference signal and a feedback signal afforded thereto from the frequency dividing arrangement.
The invention will now be further described by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a circuit diagram of a output stage of a prior art frequency dividing arrangement;
FIG. 2 is a schematic diagram of a television tuner which includes a frequency dividing arrangement according to the present invention;
FIG. 3 is a circuit diagra
REFERENCES:
patent: 4068199 (1978-01-01), Madoff
patent: 4517531 (1985-05-01), Tan et al.
patent: 4521916 (1985-06-01), Wine
patent: 4542533 (1985-09-01), Parker
patent: 4556998 (1985-12-01), Yoshisato
patent: 4679246 (1987-07-01), Jeng
"IBM Technical Bulletin", 3/85, p. 1.
"A Novel Approach to Digitally Controlled PLL Tuning Systems", 8/82, Pierce et al, FIG. 1.
Satellite TV Applications; Plessey Semiconductors; Preliminary Information; SP5050/1; pp. 43-48.
Griffin Robert L.
Kuntz Curtis
Plessey Overseas Limited
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