Periodic signal generators having microelectromechanical resonators therein that support generation of high frequency low-TCF difference signals
View Patent ↗A periodic signal generator is configured to generate high frequency signals characterized by relatively low temperature coefficients of frequency (TCF). A microelectromechanical resonator, such as concave bulk acoustic resonator (CBAR) supporting capacitive and piezoelectric transduction, may be geometrically engineered as a signal generator that produces two periodic signals having unequal resonant frequencies with unequal temperature coefficients. Circuitry is also provided for combining the two periodic signals using a mixer to thereby yield a high frequency low-TCF periodic difference signal at an output of the periodic signal generator.
1. A periodic signal generator, comprising:
an oscillator comprising a microelectromechanical bulk acoustic resonator having a piezoelectric layer therein and drive and sense electrodes on the piezoelectric layer, said oscillator configured to generate first and second periodic signals having unequal first and second frequencies (f 1 , f 2 ), said first and second periodic signals characterized by respective first and second temperature coefficients of frequency (TCf 1 , TCf 2 ) that differ by at least about 10 ppm/° C.;
a frequency multiplier responsive to the first periodic signal, said frequency multiplier configured to generate a periodic output signal having a frequency equal to N times a frequency of the first periodic signal, where N is a real number greater than one; and
a mixer circuit configured to generate a periodic beat signal in response to the second periodic signal and the periodic output signal, said periodic beat signal having a frequency f b equal to f 2 −Nf 1 and a temperature coefficient of frequency (TCf b ) of less than a smaller of the absolute value of TCf 1 and TCf 2 .
2. The generator of claim 1 , wherein said mixer circuit comprises a low pass filter configured to pass the periodic beat signal.
3. The generator of claim 1 , wherein:
TCf b =TCf 1 +μ f ( TCf 2 −TCf 1 ), where μ f =f 2 /f b .
4. The generator of claim 3 , wherein said microelectromechanical bulk acoustic resonator is configured to support capacitive and piezoelectric transduction.
5. The generator of claim 3 , wherein said microelectromechanical bulk acoustic resonator is a combined capacitively and piezoelectrically transduced CBAR.
6. The generator of claim 1 , wherein said microelectromechanical bulk acoustic resonator is configured to support capacitive and piezoelectric transduction.
7. The generator of claim 1 , wherein said microelectromechanical bulk acoustic resonator is a combined capacitively and piezoelectrically transduced CBAR.
8. A periodic signal generator, comprising:
an oscillator comprising at least one microelectromechanical bulk acoustic resonator having a piezoelectric layer therein and drive and sense electrodes on the piezoelectric layer, said oscillator configured to generate first and second periodic signals having unequal first and second frequencies (f 1 , f 2 ), said first and second periodic signals characterized by respective first and second temperature coefficients of frequency (TCf 1 , TCf 2 ) that differ by at least about 5 ppm/° C.;
a frequency multiplier responsive to the first periodic signal, said frequency multiplier configured to generate a periodic output signal having a frequency equal to N times a frequency of the first periodic signal, where N is a positive real number; and
a mixer circuit configured to generate a periodic beat signal in response to the second periodic signal and the periodic output signal, said periodic beat signal having a frequency f b equal to f 2 −Nf 1 and a temperature coefficient of frequency (TCf b ) of less than a smaller of the absolute value of TCf 1 and TCf 2 .
9. The generator of claim 8 , wherein said mixer circuit comprises a low pass filter configured to pass the periodic beat signal.
10. The generator of claim 8 , wherein:
TCf b =TCf 1 +μ f ( TCf 2 −TCf 1 ), where μ f =f 2 /f b .
11. The generator of claim 10 , wherein said microelectromechanical bulk acoustic resonator is configured to support capacitive and piezoelectric transduction.
12. The generator of claim 10 , wherein said microelectromechanical bulk acoustic resonator is a combined capacitively and piezoelectrically transduced CBAR.
13. The generator of claim 8 , wherein said microelectromechanical bulk acoustic resonator is configured to support capacitive and piezoelectric transduction.
14. The generator of claim 8 , wherein said microelectromechanical bulk acoustic resonator is a combined capacitively and piezoelectrically transduced CBAR.