Control circuitry
Control circuitry, comprising: first control means operable to generate a first control signal, the first control signal being indicative of a relationship between an output signal and a first reference signal, and to generate said output signal in dependence upon said first control signal, the first control means being configured to tend to maintain a first desired relationship between the output signal and the first reference signal in response to said first control signal; and second control means configured to influence operation of said first control means in response to said first control signal by way of a second control signal so as to tend to maintain a second desired relationship between said first control signal and a second reference signal.
1. Control circuitry, comprising:
first control means operable to generate a first control signal, the first control signal being indicative of a relationship between an output signal and a first reference signal, and to generate said output signal in dependence upon said first control signal, the first control means being configured to tend to maintain a first desired relationship between the output signal and the first reference signal in response to said first control signal, wherein said first control means forms a first control loop configured to compensate for the effect of hiqh-frequency disturbances in said first desired relationship; and
second control means configured to influence operation of said first control means in response to said first control signal by way of a second control signal so as to tend to maintain a second desired relationship between said first control signal and a second reference signal, wherein said second control means forms part of a second control loop configured to compensate for the effect of low-frequency disturbances in said first desired relationship by way of compensating for corresponding low-frequency disturbances in said second desired relationship.
2. Control circuitry as claimed in claim 1 , wherein:
said high-frequency disturbances are low-energy disturbances only capable, in the absence of said low-frequency disturbances, of causing a magnitude of said first control signal to fluctuate by a particular amount; and
said low-frequency disturbances are high-energy disturbances capable, in the absence of said second control means, of causing the magnitude of said first control signal to fluctuate by an amount substantially larger than said particular amount.
3. Control circuitry as claimed in claim 2 , wherein said second control means is operable to control said first control means with said second control signal such that the magnitude of said first control signal in the presence of such high-frequency and low-frequency disturbances fluctuates within a band of magnitude values defined by said particular amount.
4. Control circuitry as claimed in claim 3 , wherein said second control means comprises band-positioning means operable to controllably position said band of magnitudes relative to a datum magnitude.
5. Control circuitry as claimed in claim 4 , comprising means operable to control operation of said first control means such that, when said first desired relationship is changed, a position of said band of magnitudes relative to the Of a datum magnitude remains the same.
6. Control circuitry as claimed in claim 2 , wherein the low-frequency disturbances result from changes in ambient temperature.
7. Control circuitry as claimed in claim 1 , configured to perform the function of a phase-lock loop, wherein:
said first control means comprises a dual-input voltage-controlled oscillator; and
one of those inputs is connected to receive said first control signal and the other one of those inputs is connected to receive said second control signal.
8. Control circuitry as claimed in claim 1 , wherein said second control means is operable to generate said second control signal in dependence upon a comparison between the first control signal and the second reference signal.
9. Control circuitry as claimed in claim 8 , wherein said second control means comprises a comparator configured to carry out said comparison.
10. Control circuitry as claimed in claim 8 , wherein said second control means comprises an amplifier operable in dependence upon said comparison to generate said second control signal such that said second control signal may fluctuate over a substantially large range relative to fluctuations of said first control signal.
11. Control circuitry as claimed in claim 8 , wherein means in said second control means operable to carry out said comparison serves to DC-separate said second control signal from said first control signal.
12. Control circuitry as claimed in claim 1 , wherein said second control means comprises preset means operable, during a setup phase, to preset said second control signal to a preset value, and wherein said second control means is operable, during an operational phase, to base generation of the second control signal on said preset value.
13. Control circuitry as claimed in claim 12 , wherein said preset value is configurable in dependence upon an external factor.
14. Control circuitry as claimed in claim 13 , wherein said preset value is a value in a range of magnitude values open to said second control signal corresponding to the position of the current ambient temperature within a range of ambient temperatures over which the circuitry is adapted to operate.