Oscillators – Automatic frequency stabilization using a phase or frequency... – Afc with logic elements
Patent
1986-02-06
1987-03-31
Grimm, Siegfried H.
Oscillators
Automatic frequency stabilization using a phase or frequency...
Afc with logic elements
331 2, 331 10, 331 17, 331 20, 331 25, 358158, H03L 718, H03L 722, H04N 512
Patent
active
046546049
DESCRIPTION:
BRIEF SUMMARY
This invention relates to frequency controlled oscillators and particularly, though not exclusively, to voltage controlled oscillators (VCO's). The invention finds particular application to VCO's fabricated in integrated circuit form.
In a VCO an oscillator circuit is provided whose oscillation frequency is dependent on an applied voltage. In order to tune the VCO accurately to a particular desired frequency and in order to maintain this desired frequency in operation of the circuit, reference is conventionally made to a reference frequency external to the circuit (e.g. derived from an external crystal).
However, where a VCO is to be made in an integrated circuit, the use of such a reference external to the integrated circuit requires the use of one pin of the integrated circuit. It will, of course, be understood that in integrated circuits the number of pins available is strictly limited and so the use of one pin for an external reference frequency to tune an on-chip VCO may necessitate compromises in input/output functions and circuit design elsewhere in the integrated circuit.
It is an object of the present invention to provide a frequency controlled oscillator suitable for fabrication in integrated circuit form wherein the above disadvantage may be overcome or at least alleviated.
In accordance with a first aspect of the present invention a frequency controlled oscillator arrangement for fabriction in integrated circuit form comprises:
at least one primary frequency controlled oscillator; and
a secondary frequency controlled oscillator comprising:
a frequency controllable oscillator circuit;
A reference frequency source; counter means arranged periodically to count pulses of the reference frequency source to produce a first output signal if the count is less than a predetermined value and to produce a second output signal if the count is greater than a predetermined value; and
control means for providing a bias control signal in dependence on the output signals of the counter means for tuning the oscillation frequency of both the secondary frequency controlled oscillator and the or each primary frequency controlled oscillator.
In a particular embodiment of the invention the control means comprises: an up/down counter arranged to be decremented by the first output signal of the counter means and arranged to be incremented by the second output signal of the counter means; and digital to analogue converter means for generating the control signal representative of the count of the up/down counter.
Preferably the predetermined value is changeable between a plurality of predetermined values.
In accordance with a second aspect of the present invention, a frequency controlled oscillator arrangement for fabrication in integrated circuit form comprises:
A reference frequency source;
a frequency controllable oscillator circuit;
counter means arranged to sample the output of the frequency controllable oscillator circuit in a first mode when the output is not required and to periodically count pulses of the reference frequency source and to produce a first output signal if the count is less than a predetermined value and a second output signal if the count is greater than the predetermined value; and
control means for producing a bias control signal in dependence on the output signals of the counter means for tuning the oscillation frequency of the frequency controlled oscillator.
It will be appreciated that such a frequency controlled oscillator in accordance with the second aspect of the invention is particularly suited to applications where the oscillator is required to produce its output to drive additional circuitry only periodically, e.g. as a VCO in generating timebase signals in a television receiver.
Two voltage controlled oscillators in accordance with the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
FIG. 1 shows a block-schematic diagram of a first voltage controlled oscillator system;
FIG. 2 shows a block-schematic diagram of a second vo
REFERENCES:
patent: 3651422 (1972-03-01), Underhill
patent: 4105946 (1978-08-01), Ikeda
patent: 4122488 (1978-10-01), Mikado
patent: 4131861 (1978-12-01), Malaviya
patent: 4380742 (1983-04-01), Hart
patent: 4543661 (1985-09-01), Defeuilly et al.
Newton Anthony
Smith Robert
Grimm Siegfried H.
Ingrassia Vincent B.
Motorola Inc.
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