Transconductance and current modulation for resonant frequency control and selection
View Patent ↗In various embodiments, the invention provides a frequency controller and a temperature compensator for frequency control and selection in a clock generator and/or a timing and frequency reference. The various apparatus embodiments include a resonator adapted to provide a first signal having a resonant frequency; an amplifier; a temperature compensator adapted to modify the resonant frequency in response to temperature; and a process variation compensator adapted to modify the resonant frequency in response to fabrication process variation. In addition, the various embodiments may also include a frequency divider adapted to divide the first signal having the resonant frequency into a plurality of second signals having a corresponding plurality of frequencies substantially equal to or lower than the resonant frequency; and a frequency selector adapted to provide an output signal from the plurality of second signals. The output signal may be provided in any of various forms, such as differential or single-ended, and substantially square-wave or sinusoidal.
1. An apparatus for frequency control of a reference signal, the apparatus comprising:
a reference resonator to provide the reference signal having a selectable resonant frequency;
a negative transconductance amplifier coupled to the reference resonator;
a frequency controller to maintain a selected resonant frequency within a predetermined range in response to a variation of a parameter.
2. The apparatus of claim 1 , wherein the parameter is one or more of the following parameters: temperature, fabrication process, voltage, and frequency.
3. The apparatus of claim 1 , wherein the frequency controller further is to modify a current through the negative transconductance amplifier in response to a temperature variation.
4. The apparatus of claim 3 , wherein the frequency controller further comprises a current source responsive to temperature.
5. The apparatus of claim 4 , wherein the current source has at least one CTAT, PTAT, or PTAT 2 configuration.
6. The apparatus of claim 1 , wherein the frequency controller further is to modify a current through the negative transconductance amplifier to select the resonant frequency.
7. The apparatus of claim 1 , wherein the frequency controller further is to modify a transconductance of the negative transconductance amplifier to select the resonant frequency.
8. The apparatus of claim 1 , wherein the frequency controller further is to modify a current through the negative transconductance amplifier in response to a voltage variation.
9. The apparatus of claim 1 , wherein the frequency controller further is to modify a transconductance of the negative transconductance amplifier when calibrated for a fabrication process variation.
10. The apparatus of claim 1 , wherein the frequency controller further is to modify a current through the negative transconductance amplifier when calibrated for a fabrication process variation.
11. The apparatus of claim 1 , wherein the frequency controller further comprises a voltage isolator coupled to the reference resonator to substantially isolate the reference resonator from a voltage variation.
12. The apparatus of claim 11 , wherein the voltage isolator comprises a current mirror.
13. The apparatus of claim 12 , wherein the current mirror has a cascode configuration.
14. The apparatus of claim 1 , wherein the reference resonator is at least one of the following resonators: an inductor (L) and a capacitor (C) configured to form an LC-tank resonator; a ceramic resonator, a mechanical resonator, a microelectromechanical resonator, or a film bulk acoustic resonator.
15. The apparatus of clime 1 , further comprising:
at least one variable capacitor coupled to the reference resonator and responsive to a control voltage to modify the effective reactance of the reference resonator.
16. The apparatus of claim 15 , wherein the frequency controller provides the control voltage and wherein the control voltage is variable in response to temperature variation.
17. The apparatus of claim 1 , wherein the reference resonator further comprises at least one variable capacitor responsive to a control voltage provided by the frequency controller.
18. The apparatus of claim 1 , wherein the resonant frequency is selectable through calibration to a second reference signal.
19. The apparatus of claim 1 , wherein the predetermined range is plus or minus twenty-five hundredths of a percent (±0.25%).
20. An apparatus, comprising:
a reference resonator, the reference resonator to provide a reference signal having a selectable resonant frequency;
a negative transconductance amplifier coupled to the reference resonator; and
a temperature compensator coupled to the negative transconductance amplifier or to the reference resonator, the temperature compensator to maintain a selected resonant frequency substantially within a predetermined range in response to a temperature variation.
21. The apparatus of claim 20 , wherein the temperature compensator further is to modify a current through the negative transconductance amplifier in response to the temperature variation.
22. The apparatus of claim 21 , wherein the temperature compensator further comprises a current source responsive to temperature.
23. The apparatus of claim 22 , wherein the current source has a CTAT, PTAT, or PTAT 2 configuration.
24. The apparatus of claim 22 , further comprising a plurality of current sources having at least two different CTAT, PTAT, or PTAT 2 configurations.
25. The apparatus of claim 22 , wherein the current source is coupled though one or more current mirrors to the negative transconductance amplifier.
26. The apparatus of claim 20 , further comprising:
a coefficient register embodied as one or more memory circuits to store a first plurality of calibration coefficients.
27. The apparatus of claim 26 , further comprising:
a first array having a plurality of switchable capacitive modules coupled to the coefficient register and to the reference resonator, each switchable capacitive module having a fixed capacitance and a variable capacitance, each switchable capacitive module responsive to a corresponding coefficient of the first plurality of calibration coefficients to switch between the fixed capacitance and the variable capacitance and to switch each variable capacitance to a control voltage.
28. The apparatus of claim 27 , further comprising:
a second array having a plurality of switchable resistive modules coupled to the coefficient register and further having a capacitive module, the capacitive module and the plurality of switchable resistive modules further coupled to a node to provide the control voltage, each switchable resistive module responsive to a corresponding coefficient of a second plurality of coefficients stored in the coefficient register to switch the switchable resistive module to the control voltage node; and
wherein the temperature compensator comprises a temperature-dependent current source coupled through a current mirror to the second array.
29. The apparatus of claim 26 , further comprising:
an array having a plurality of switchable capacitive modules coupled to the coefficient register and to the reference resonator, each switchable capacitive module having a first fixed capacitance and a second fixed capacitance, each switchable capacitive module responsive to a corresponding coefficient of the first plurality of calibration coefficients to switch between the first fixed capacitance and the second fixed capacitance.
30. The apparatus of claim 26 , further comprising:
an array having a plurality of switchable variable capacitive modules coupled to the coefficient register and to the reference resonator, each switchable variable capacitive module responsive to a corresponding coefficient of the first plurality of calibration coefficients to switch between a first voltage and a second voltage.
31. The apparatus of claim 30 , wherein at least one of the first voltage and second voltage is a fixed voltage.
32. The apparatus of claim 30 , wherein at least one of the first voltage and second voltage is a variable voltage.
33. The apparatus of claim 20 , further comprising:
an array having a plurality of variable capacitive modules coupled to the reference resonator and to a control voltage.
34. The apparatus of claim 20 , further comprising:
at least one variable capacitor coupled to the reference resonator and responsive to a control voltage to modify the effective reactance of the reference resonator.
35. The apparatus of claim 34 , wherein the temperature compensator provides the control voltage and wherein the control voltage is variable to temperature variation.
36. An apparatus, comprising:
a reference resonator, the reference resonator to provide a reference signal having a selectable resonant frequency;
a negative transconductance amplifier coupled to the reference resonator;
a current mirror coupled to the negative transconductance amplifier; and
a current source coupled to the current mirror, the current source to maintain the resonant frequency substantially within a predetermined range by varying a current through the current mirror and the negative transconductance amplifier in response to a temperature variation.
37. The apparatus of claim 36 , wherein the current source has at least one CTAT, PTAT, or PTAT 2 configuration.
38. The apparatus of claim 36 , further comprising a plurality of current sources coupled to the current mirror, the plurality of current sources having at least two different CTAT, PTAT, or PTAT 2 configurations.
39. An apparatus, comprising:
a reference oscillator, the reference oscillator to provide a reference signal having a selectable oscillation frequency;
a negative transconductance amplifier coupled to the reference oscillator; and
a temperature compensator coupled to the reference oscillator, the temperature compensator to maintain a selected oscillation frequency substantially within a predetermined range in response to a temperature variation.
40. The apparatus of claim 39 , wherein the temperature compensator further comprises a current source responsive to temperature.
41. The apparatus of claim 40 , wherein the current source has at least one CTAT, PTAT, or PTAT 2 configurations.
42. The apparatus of claim 39 , wherein the reference oscillator is at least one of the following oscillators: an inductor (L) and a capacitor (C) configured to form an LC-tank oscillator; a resonator (R) and a capacitor (C) configured to form an RC oscillator; a ceramic oscillator; a mechanical oscillator; a microelectromechanical oscillator; a ring oscillator; a surface acoustic wave (SAW) oscillator; or a film bulk acoustic oscillator.
43. The apparatus of claim 39 , further comprising:
at least one variable capacitor coupled to the reference oscillator and responsive to a control voltage to modify the effective reactance to the reference oscillator.
44. The apparatus of claim 43 , wherein the temperature compensator provides the control voltage and wherein the control voltage is variable in response to temperature variation.
45. The apparatus of claim 43 , further comprising:
a coefficient register coupled to the temperature compensator, the coefficient register to store a plurality of coefficients, the plurality of coefficients calibrated over temperature variation and provided to the temperature compensator to generate a corresponding control voltage.
46. The apparatus of claim 39 , wherein the reference oscillator further comprises at least one variable capacitor responsive to a control voltage provided by the temperature compensator.