Patent Application
20090003503
A voltage controlled oscillator (VCO) is an oscillator that generates a signal at a frequency determined by an input voltage. A major design parameter in VCOs is the gain (Hz/V) that converts the input voltage to the frequency. In high performance VCOs it may be desirable to have lower gain while maintaining wide frequency coverage. In order to accomplish this, the VCO frequency coverage may be divided into several sub bands, where each band covers part of the whole range. Since the frequency coverage is reduced (per band), the VCO gain can be reduced without limiting the total frequency coverage.
The multi-band VCO is hooked up with a phase locked loop (PLL) which locks the VCO to a reference frequency. The correct sub-band must be selected before the PLL can lock the VCO. Multi-band VCOs may have a significant amount of bands to support wide frequency coverage. The frequency coverage of each band varies due to process, temperature, and dynamic loading variations so that the selection of the appropriate band needs to be take into account all process and/or system level variation.
The features and advantages of the various embodiments will become apparent from the following detailed description in which:
The ABS 120 may be utilized (e.g., in the VCO) to find the correct band in the VCO 100 to produce the desired frequency. The ABS 120 calculates an expected value (the number of VCO clock periods within the time frame) for the desired frequency of the VCO 100. The VCO input voltage control is fixed to a predetermined value. The ABS 120 selects an initial band and counts the number of VCO clock periods that occur during the given time period (generated from the reference clock) with the counter. The ABS 120 compares the counter value to the expected value to determine how the frequency of the band selected compares to the desired frequency. If the counter value is greater than the expected value the frequency for that band is greater than the desired frequency so a next band selected should have a lower frequency range (e.g., lower band). If the counter is less than the expected value the frequency for that band is less than the desired frequency so a next band selected should have a higher frequency range (e.g., higher band).
The next band selected may be based on any number of search criteria (e.g., linear, binary, complex). Eventually the ABS 120 will converge on the band that is guaranteed to cover the desired frequency. The amount of time that it takes to converge on the desired frequency is dependent on various parameters including the number of VCO bands, the search criteria used, and the desired frequency resolution (time period).
It should be noted that the count may never actually equal the estimated value as the count for selected bands may bounce back and forth between higher and lower. A decision may then be made that the search is over and that you are close enough and select one of the bands.
The flow is not limited to the steps or the order illustrated. Rather steps could be added, removed, combined or broken out and the order can be changed without departing from the current scope, as long as the flow resulted in a determination of the band by counting the clock cycles for a predefined time.
Although the disclosure has been illustrated by reference to specific embodiments, it will be apparent that the disclosure is not limited thereto as various changes and modifications may be made thereto without departing from the scope. Reference to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described therein is included in at least one embodiment. Thus, the appearances of the phrase “in one embodiment” or “in an embodiment” appearing in various places throughout the specification are not necessarily all referring to the same embodiment.
The various embodiments are intended to be protected broadly within the spirit and scope of the appended claims.
