Digitally temperature compensated voltage-controlled oscillator

A temperature compensated oscillator (TCO) system capable of accurately generating a desired frequency which is stabilized over a selected temperature range, said TCO system comprising

• (a) a TCO comprising a voltage-controlled oscillator (VCO) with a frequency of operation controllable by a tuning voltage V.sub.c,
• means for sensing the ambient temperature of the VCO and generating a corresponding analog electrical signal,
• ADC means for converting said analog signal to a corresponding digital temperature value,
• storage means for storing a plurality of digital V.sub.c values corresponding to said digital temperature values for discrete temperature points extending across said temperature range,
• processing means for using said digital temperature values as indices to extract the corresponding digital V.sub.c values from said storage means,
• DAC means for converting the extracted digital V.sub.c value into a corresponding analog signal,
• means for feeding the analog V.sub.c signal to said VCO in order to maintain said stabilized frequency of operation,
• means for responding to a digital temperature value V.sub.D generated by said ADC means which does not have a corresponding stored digital V.sub.c value but is within said selected temperature range, by using stored digital V.sub.c values corresponding to selected ones of said digital temperature values to determine a digital V.sub.c value corresponding to said digital temperature value v.sub.D which may be converted by said DAC means and fed to said VCO,
• means for receiving an externally generated signal including a digitized offset value, and means for responding to said external signal by combining said offset value with each of said extracted digital V.sub.c values before the value is converted into a corresponding analog value and fed to said VCO;
• and
• (b) a calibration and test circuit (CTC) for the TCO comprising
• means for feeding, at each of a series of discrete temperature levels represented by corresponding digital values and extending across said selected temperature range, a plurality of tuning voltages V.sub.c to the VCO,
• means for measuring the correspondingly generated output frequencies,
• means for comparing each of said measured output frequencies to a reference frequency to determine the frequency difference between them, in order to determine an optimum V.sub.c value which produces a VCO output frequency which differs least from said reference frequency, and
• means for storing said optimum voltage values within said storage means of said TCO in a manner allowing them to be subsequently retrieved by using corresponding digital temperature values as indices.

A method for maintaining the output frequency f.sub.o of a voltage controlled oscillator (VCO) stabilized at a desired value over a selected temperature range, including the steps of:

• calibrating the VCO by determining at each of a series of discrete temperature levels represented by corresponding digital values and spread over said temperature range, the tuning voltage V.sub.c required to maintain the output frequency of said VCO at said desired value;
• digitizing and storing said determined V.sub.c values within the VCO in a manner allowing them to be subsequently retrieved by using the corresponding digital temperature values as indices,
• sensing and digitizing the ambient temperature of the VCO during its operation;
• using the sensed digital temperature value as an index to retrieve the corresponding stored digital V.sub.c value;
• converting the digital V.sub.c value to its corresponding analog voltage form;
• feeding the analog tuning voltage to the VCO in order to maintain its output frequency at the desired value;
• sensing when a digitized ambient temperature value lies within said temperature range but does not correspond to any of said stored V.sub.c values and in response thereto using stored digital V.sub.c values corresponding to selected ones of said digital temperature values to determine a digital V.sub.c value corresponding to said digitized ambient temperature value, and using said determined V.sub.c value to maintain the output frequency of the VCO at the desired value;
• and
• sensing from a location remote to said VCO, when the output frequency of the VCO at different ambient temperatures shifts by a predetermined value from said desired frequency value and in response thereto calculating and transmitting to the VCO an offset value which when added to each of the stored digital V.sub.c values before it is converted to corresponding analog form and fed to the VCO produces a predetermined shift in the VCO output frequency.

A method for maintaining the output frequency f.sub.o of a voltage controlled oscillator (VCO) stabilized at a desired value over a selected temperature range, including the steps of:

• calibrating the VCO by determining at each of a series of discrete temperature levels represented by corresponding digital values and spread over said temperature range, the tuning voltage V.sub.c required to maintain the output frequency of said VCO at said desired value;
• digitizing and storing said determined V.sub.c values within the VCO in a manner allowing them to be subsequently retrieved by using the corresponding digital temperature values as indices,
• sensing and digitizing the ambient temperature of the VCO during its operation;
• using the sensed digital temperature value as an index to retrieve the corresponding stored digital V.sub.c value;
• converting the digital V.sub.c value to its corresponding analog voltage form;
• feeding the analog tuning voltage to the VCO in order to maintain its output frequency at the desired value;
• and
• sensing from a location remote to said VCO, when the output frequency of the VCO at different ambient temperatures shifts by a predetermined value from said desired frequency value and in response thereto calculating and transmitting to the VCO an offset value which when added to each of the stored digital V.sub.c values before it is converted to corresponding analog form and fed to the VCO produces a predetermined shift in the VCO output frequency.