FREQUENCY-STABLE, LOW-NOISE TIMING SIGNAL GENERATOR HAVING MULTIPLE MEMS RESONATORS AND NESTED-PLL STRUCTURE
A frequency synthesizer uses an oven-controlled oscillator (“OCXO”) to generate a reference signal. A nested-PLL structure features an outer PLL loop with a divider that implements temperature correction of the output of the OCXO, to thereby form a temperature-compensated OCXO (“TCOCXO”); this divider also is dependent on information that selects a frequency for synthesis. An oscillation source of the outer PLL loop is implemented as an inner PLL loop of the nested-PLL structure; this inner PLL loop use an output of a second oscillator (“SXO”) as its reference frequency and an electronic VCO. The nested-PLL structure is designed such that phase noise from the TCOCXO dominates a synthesized frequency output for low frequencies, phase noise from the SXO dominates at mid-range frequencies, and phase noise from the electronic VCO dominates at high frequencies.
1 . A timing signal generator, comprising:
a first oscillator (FXO);
a second oscillator (SXO);
a first phase-locked loop (PLL) to receive an output of the FXO and to generate a first signal therefrom; and
a second PLL to receive an output of the SXO and to generate a second signal therefrom, wherein the second PLL comprises an oscillation source that is at least partially dependent on an electronic voltage controlled oscillator (VCO), and wherein the second PLL comprises a divider that is controlled in dependence upon the first signal;
wherein the timing signal generator is to output a timing signal dependent on the second signal.
2 . The timing signal generator of claim 1 wherein the FXO comprises at least one microelectromechanical systems (MEMS) resonator and at least one structure to serve as a temperature sensor.
3 . The timing signal generator of claim 2 wherein:
the at least one microelectromechanical systems (MEMS) resonator comprises two MEMS resonators;
the FXO is to generate the first signal dependent on a resonance frequency of a first one of the two MEMS resonators;
the at least one structure to serve as a temperature sensor is embodied as the two MEMS resonators; and
the timing signal generator further comprises circuitry to generate a temperature-dependent signal as a function of divergence of respective resonant frequencies of the two MEMS resonators.
4 . The timing signal generator of claim 3 wherein:
the FXO is an oven-controlled oscillator (OCXO); and
the OCXO comprises a heating element and circuitry to control the heating element, using the temperature-dependent signal, to urge temperature of the two MEMS resonators toward a first temperature.
5 . The timing signal generator of claim 4 wherein the timing signal generator comprises circuitry to correct a temperature-dependent variation of the resonance frequency using the temperature-dependent signal, to thereby implement a temperature-compensated OCXO (TCOCXO).
6 . The timing signal generator of claim 2 wherein:
the divider is a second divider;
the FXO is to generate the output of the FXO dependent on a resonance frequency of the at least one MEMS resonator;
the first PLL comprises a first divider;
the timing signal generator further comprises circuitry to generate a temperature-dependent signal dependent on an output of the temperature sensor; and
the first divider is to be controlled dependent on the temperature-dependent signal, to thereby implement a temperature-compensated oscillator, based on the SXO.
7 . The timing signal generator of claim 6 wherein:
the timing signal generator comprises a first die and a second die;
the FXO is on the first die; and
circuitry of the first PLL and the circuitry of the second PLL are each on the second die.
8 . The timing signal generator of claim 1 wherein the SXO comprises at least one microelectromechanical systems (MEMS) resonator.
9 . The timing signal generator of claim 8 wherein the SXO also comprises at least one structure to serve as a temperature sensor, to sense a temperature of the at least one MEMS resonator.
10 . The timing signal generator of claim 9 wherein:
the at least one microelectromechanical systems (MEMS) resonator comprises two MEMS resonators;
the SXO is to generate the output of the SXO dependent on a resonance frequency of a first one of the two MEMS resonators;
the at least one structure to serve as a temperature sensor is embodied as the two MEMS resonators;
the timing signal generator further comprises circuitry to derive a temperature-dependent signal as a function of divergence of respective resonant frequencies of the two MEMS resonators; and
the timing signal generator comprises circuitry to correct a temperature-dependent variation of the resonance frequency using the temperature-dependent signal, to thereby implement a temperature-compensated oscillator (TCXO), based on the second oscillator.
11 . The timing signal generator of claim 1 wherein the electronic VCO is a LC voltage controlled oscillator (LCVCO).
12 . The timing signal generator of claim 1 wherein:
the SXO is a first SXO and the divider is a first divider;
the oscillation source further comprises a second SXO and a third PLL, the third PLL to receive an output of the second SXO, the third PLL having a second divider controlled according to the second signal, the third PLL having an oscillator;
the oscillator of the third PLL is the electronic VCO; and
the timing signal output by the timing signal generator is dependent on an output of the third PLL.
13 . The timing signal generator of claim 1 wherein:
the first PLL has a first loop rate;
the second PLL has a second loop rate; and
the first PLL and the second PLL are part of a nested-PLL structure, such that phase noise of the timing signal output by the timing signal generator is dominated by phase noise of the FXO at a first frequency of the timing signal, less than the first loop rate, by phase noise of the SXO at a second frequency of the timing signal, between the first loop rate and the second loop rate, and by phase noise of the electronic VCO at a third frequency of the timing signal, above the second loop rate.
13 . The timing signal generator of claim 1 , embodied as a frequency synthesizer, wherein:
the timing signal generator comprises a programmable register;
the first PLL also comprises a divider which is at least partially controlled dependent on content of the programmable register; and
the timing signal output by the timing signal generator has a frequency that is dependent on the content of the divider.
14 . The timing signal generator of claim 1 wherein:
the timing signal output by the timing signal generator is a first timing signal;
the timing signal generator is to output a second timing signal; and
the second timing signal and the first timing signal differ from one another in terms of at least one of phase or frequency.
15 . The timing signal generator of claim 1 wherein:
the timing signal generator comprises a first die and a second die;
at least one of the FXO and the SXO comprises a MEMS resonator;
the MEMS resonator is on the first die; and
circuitry of the first PLL and circuitry of the second PLL are each on the second die.
16 . The timing signal generator of claim 1 wherein:
the timing signal generator comprises a first die, a second die and a third die;
each of the OCXO and the SXO comprises at least one MEMS resonator;
the at least one MEMS resonator of the OCXO is on the first die;
the at least one MEMS resonator of the SXO is on the second die; and
circuitry of the first PLL, circuitry of the second PLL, circuitry to drive the at least one MEMS resonator of the OCXO, and circuitry to drive the at least one MEMS resonator of the SXO are each on the third die.
17 . A timing signal generator, comprising:
a first oscillator, wherein the first oscillator is an oven-controlled oscillator (OCXO), and wherein the first oscillator comprises at least one microelectromechanical systems (MEMS) resonator and at least one structure to serve as a temperature sensor;
a second oscillator (SXO);
a first phase-locked loop (PLL) to receive an output of the OCXO and to generate a first signal therefrom, wherein the first PLL has a divider; and
a second PLL to receive an output of the SXO and to generate a second signal therefrom, wherein the second PLL comprises an oscillation source that is at least partially dependent on an electronic voltage controlled oscillator (VCO), and wherein the second PLL comprises a divider that is controlled in dependence on the first signal;
wherein the timing signal generator is to output a timing signal dependent on the second signal.
18 . The timing signal generator of claim 17 wherein:
the timing signal generator further comprises circuitry to generate a temperature-dependent signal dependent on an output of the temperature sensor, wherein the divider of the first PLL is to be controlled responsive to the temperature-dependent signal, to thereby implement a temperature-compensated OCXO (TCOCXO).
19 . The timing signal generator of claim 18 wherein:
the at least one microelectromechanical systems (MEMS) resonator comprises two MEMS resonators;
the OCXO is to generate the first signal dependent on a resonance frequency of a first one of the two MEMS resonators;
the at least one structure to serve as a temperature sensor is embodied as the two MEMS resonators;
the circuitry to derive the temperature-dependent signal is to do so as a function of divergence of respective resonant frequencies of the two MEMS resonators; and
the OCXO comprises a heating element and circuitry to control the heating element, dependent on the temperature-dependent signal, to urge temperature of the two MEMS resonators toward a first temperature.
20 . The timing signal generator of claim 19 wherein:
the timing signal generator comprises a first die and a second die;
the OCXO is on the first die; and
circuitry of the first PLL and circuitry of the second PLL are on each the second die.
21 . The timing signal generator of claim 17 wherein the SXO also comprises at least one microelectromechanical systems (MEMS) resonator.
22 . The timing signal generator of claim 21 wherein the SXO also comprises at least one structure to serve as a temperature sensor, to sense a temperature of the at least one MEMS resonator of the SXO.
23 . The timing signal generator of claim 21 wherein:
the timing signal generator comprises a first die, a second die and a second die;
the at least one MEMS resonator of the OCXO is on the first die;
the at least one MEMS resonator of the SXO is on the second die; and
circuitry of the first PLL, circuitry of the second PLL, circuitry to drive the at least one MEMS resonator of the OCXO, and circuitry to drive the at least one MEMS resonator of the SXO are each on the third die.
24 . A timing signal generator, comprising:
a first oscillator, wherein the first oscillator is an oven-controlled oscillator (OCXO), and wherein the first oscillator comprises at least one first microelectromechanical systems (MEMS) resonator and at least one structure to serve as a temperature sensor;
a second oscillator (SXO), wherein the first oscillator comprises at least one second MEMS resonator;
a first phase-locked loop (PLL) to receive an output of the OCXO and to generate a first signal therefrom, wherein the first PLL has a divider;
circuitry to generate a temperature-dependent signal dependent on an output of the temperature sensor, wherein the divider of the first PLL is to be controlled responsive to the temperature-dependent signal, to thereby implement a temperature-compensate OCXO (TCOCXO); and
a second PLL to receive an output of the SXO and to generate a second signal therefrom, wherein the second PLL comprises an oscillation source that is an electronic voltage controlled oscillator (VCO), and wherein the second PLL comprises a divider that is controlled in dependence on the first signal;
wherein the timing signal generator is to output a timing signal dependent on the second signal.
25 . The timing signal generator of claim 24 wherein the electronic VCO is a LCVCO.