Oscillators – Automatic frequency stabilization using a phase or frequency... – Tuning compensation
Patent
1988-02-04
1989-08-29
Grimm, Siegfried H.
Oscillators
Automatic frequency stabilization using a phase or frequency...
Tuning compensation
331 25, H03L 718
Patent
active
048621099
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a processor controlled phase locked loop multi-band frequency synthesizer.
Known frequency synthesizers follow the basic architecture as shown in FIG. 1. In FIG. 1 a simple circuit concept is greatly complicated by the need for a switchable oscillator SWO which would be required for all frequency bands the oscillator must cover. The switchable local oscillator has to be controlled by an n-wire highway N which can be obtained by inputting control information to the circuit BD decoding this and outputting to the highway. The system may be further complicated by the requirement for more than one reference crystal oscillator.
In FIG. 1, the switchable oscillator SWO generates an output signal for controlling the divider chain D1, D2. The divider D2 provides an input for the signal processor PROC, which also receives programming information from the shift register SR. The programming information is generated from the input data ID. The shift register SR also generates a control signal for the band decode circuit BD which, as discussed above, controls the switchable oscillator SWO.
A reference oscillator RO is controlled by a reference crystal RX. The reference oscillator RO drives a reference divider RD, the output from which is compared with a signal from the signal processor PROC, by a comparator circuit PC. The comparator circuit PC generates an output signal which drives a loop amplifier LA. The output from the loop amplifier LA is fed back to the switchable oscillator SWO and provides a phase-locked loop. The switchable oscillator SWO generates a signal which is presented to a mixer circuit MIX, which is combined with an RF signal, to generate the output signal IF. In FIG. 1, circuits which function in a similar manner to the circuits shown in FIG. 2, described later, have been given the same identity.
If the overall system is required to cover a frequency band which has a totally different requirement for step size, comparison frequency input, frequency range etc., then the system is greatly complicated by the need for a second frequency synthesis loop, or any other method for obtaining the local oscillator.
The frequency synthesizer according to the present invention provides the advantages of a simplified design, a reduction in external components, the need for only one reference crystal, the replacement of the switchable multi-band oscillator by a single band local oscillator, and the removal of the n-wire highway.
Accordingly an aim of the present invention is to provide a frequency synthesizer of a more simple design than hitherto known frequency synthesizers.
According to the present invention there is provided a frequency synthesizer including a store for receiving and temporarily storing a data word received on a data highway, a processor circuit controllable by output signals generated by the store, a prescale divider circuit driven by a local oscillator and arranged to provide a signal for presentation to the processor circuit, a reference divider chain providing a reference signal presented to a phase comparator which also receives a signal from the processor circuit and arranged to provide an output signal for presentation to a loop amplifier which controls the local oscillator, and a control and decode circuit arranged to receive a signal from the store, characterized in that the reference divider chain is driven by a single reference oscillator, and the prescale divider circuit and processor circuit generate output signals for presentation to an output interface under the control of the control and decode circuit which generates control signals for controlling the processor circuit and the output interface, said control and decode circuit also generates a control signal which is fed-back to the reference divider chain whereby the reference signal applied to the phase comparator is altered in a manner which requires the reference divider chain to be driven by the single reference oscillator only.
An embodiment of the present invention will now be described wit
REFERENCES:
patent: 4584539 (1986-04-01), Stankey
"AM-FM Digital Tuning System", By T. B. Mills, Nov. 1978, IEEE Trans. Consumer Electronics, vol. CE-24, No. 4, pp. 507-513.
Grimm Siegfried H.
Plessey Overseas Limited
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