US 4,728,906 AGranted

Tuning and calibration circuits for CW and sweep frequency signal generators

AssigneeWiltron Measurements Limited

InventorsChristopher B. D. Turl, Geoffrey J. Hurst

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Abstract

A signal generating device and method of control thereof for producing a desired output frequency, the generator having coarse and fine tuning controls capable of producing frequency changes over a limited range, wherein the output of the device is combined in a mixing device with a multi-component reference signal produced from an oscillatory generator circuit, a beat signal is detected by processing circuitry as the frequency controls are adjusted and the values of the frequencies of the control signals occurring on such detection are stored, and using a look-up table or algorithm the value of a correction signal is determined which, when combined with the stored values, will cause the output frequency of the device to be adjusted to the desired value via the fine tuner.

Claims16

Dependent claims

A method of setting up a signal generating device to deliver an output frequency of F MHz which may lie anywhere in a range extending up to hundreds and thousands of MHz, and which includes the input of coarse and fine frequency controlling signals, wherein the fine frequency controlling signal is capable of producing linear changes in output frequency for corresponding changes in the parameter of an electric signal supplied thereto, but only over a small range of N MHz, according to which:

the output of the device is combined with a multicomponent reference signal containing at least a component having a frequency of L MHz, which is within N MHz of the desired frequency F MHz,
the frequency controlling signals supplied to the device are adjusted to yield an output signal having a frequency also within N MHz of F MHz,
the frequency of the fine frequency controlling signal is then adjusted until a correspondence signal is detected and indicates a one to one relationship of the output signal and the said component of the reference signal,
the values of the frequency controlling signals at which a correspondence signal is detected are stored,
using at least one of an algorithm and look-up table the value of a correcting signal requried for the fine frequency control to shift the frequency of the device by (F-L) MHz is determined and the desired output signal of F MHz is obtained by adding the correcting signal to the stored signals and using the combined signal as the control signal for the device.

2 more elements

A signal generating device whose output frequency is to be set at a frequency F, comprising:

(1) a master oscillator having an output at which a radio frequency signal appears when the oscillator is operating and having, in addition to a large bandwidth frequency controlling element, a small bandwidth controlling element by which changes in the frequency of oscillation over a small band of frequencies can be obtained by making linear changes in a parameter of an electrical signal supplied thereto,
(2) a control system adapted to generate, from information entered therein, electrical signals for controlling the frequency of the master oscillator,
(3) means for deriving a sample signal from the output of the master oscillator,
(4) a stable fixed frequency oscillator signal source for producing a reference signal F(ref),
(5) circuit means for producing from the reference signal F(ref) a harmonic spectrum ("comb") signal of signals F(ref);
2F(ref);
3F(ref);
. . . n.F(ref), at least one component of which is within the said small band of frequencies from F,
(6) mixing circuit means for combining the sample signal with the harmonic spectrum signal to produce beat signals, i.e. signals having frequencies which are inter alia the arithmetic difference between the frequency of the sample signal and the component in the said harmonic spectrum signal, and
(7) beat signal detector circuit means responsive to the output of the mixing circuit means and adapted to identify when a beat signal is occurring:
wherein for the purpose of frequency calibration the control system is programmed to alter the frequency determining signals supplied to the master oscillator until a selected beat signal is detected (caused by the interaction of the master oscillator output signal and a component N.F(ref) of the harmonic spectrum signal) at which point the values of the frequency determining signals supplied to te master oscillator are employed in the computation of new values for the control signals for the master oscillator to give a frequency of oscillation equal to (N.F.(ref)+X), where X is the frequency shift required between N.F(ref) and the desired frequency F.

8 more elements

A method of controlling the frequency of oscillation of a master oscillator in a signal generator in which a linear frequency controlling element has a restricted frequency sweep capability comprising the steps of:

(1) generating frequency control signals which when applied to the frequency controlling element will theoretically produce a frequency F in the output of the master oscillator,
(2) sampling the master oscillator output signal and combining the sample of the master oscillator output signal with a reference signal having a component within the said restricted frequency sweep of the master oscillator,
(3) adjusting the values of the frequency control signals until a selected beat signal is detected between the master oscillator output signal and the reference signal component, and
(4) thereafter adjusting the values of the frequency control signals from the values corresponding to the selected beat signal to new values computed using at least one of an algorithm and look-up table describing the frequency response of the master oscillator to the values of the frequency control signals therefor, thereby to shift the master oscillator output to the desired frequency, wherein digital signals are generated by a microprocessor and digital to analogue convertor means serve to convert the digital signals to signal levels which are used as the frequency controlling signals for the master oscillator.

1 more element

Dependencies are inferred from the claim text.