Temperature controlled acoustic resonator comprising feedback circuit

Patent metadata

Field	Value
Publication number	US-2016013771-A1
Application number	US-201514859213-A
Country	US
Kind code	A1
Filing date	Sep 18, 2015
Priority date	Jan 30, 2012
Publication date	Jan 14, 2016
Grant date	—

Abstract

An acoustic resonator device includes an annular acoustic resonator, a heater coil and a heat sensor. The annular acoustic resonator is positioned over a trench formed in a substrate of the acoustic resonator device. The heater coil is disposed around a perimeter of the annular acoustic resonator, the heater coil including a resistor configured to receive a heater current. The heat sensor is configured to adjust the heater current in response to a temperature of the heater coil. A feedback circuit is used to control a temperature of the acoustic resonator device.

First claim

1 . An acoustic resonator device, comprising:
an acoustic resonator positioned over a trench formed in a substrate; a heater disposed around at least a portion of a perimeter of the acoustic resonator, the heater configured to receive a heater current; and a heat sensor resistor disposed adjacent to the heater; a reference resistor; and an amplifier configured to receive a first input from the reference resistor and a second input from the sense resistor, and to provide an output proportional to a difference between the first input and the second input, wherein the heater current is adjusted based on the difference.

2 . The acoustic resonator device of claim 1 , wherein the sensor resistor has a temperature coefficient of resistance such that its sensor impedance (R sense ) varies in response to a temperature of the acoustic resonator.

3 . The acoustic resonator device of claim 1 , further comprising:
a plurality of tethers connected to the acoustic resonator, the plurality of tethers being configured to limit transfer of externally applied forces to the acoustic resonator.

4 . The acoustic resonator device of claim 3 , wherein a first tether of the plurality of tethers comprises a first conductive trace for providing the heater current to the heater coil, and the heater coil is disposed around an outer perimeter of the acoustic resonator.

5 . The acoustic resonator device of claim 4 , wherein a second tether of the plurality of tethers comprises a second conductive trace for providing heat sensor current to the heat sensor, a change in the temperature of the acoustic resonator device causing a corresponding change in sensor resistance of the heat sensor resistor.

6 . The acoustic resonator device of claim 5 , wherein the reference resistor has a predetermined reference resistance, and the amplifier is a transconductance amplifier configured to sense a voltage caused by a difference between the sensor impedance and the predetermined reference resistance; and the acoustic resonator device further comprises a transistor configured to receive the output from the transconductance amplifier and to provide the heater current.

7 . The acoustic resonator device of claim 6 , wherein for a predetermined temperature of the acoustic resonator, a reference voltage (Vref) across the reference resistor is set to be equal to a sensor voltage (Vsense) across the sensor resistor at the predetermined temperature.

8 . The acoustic resonator device of claim 7 , wherein the predetermined temperature is substantially equal to a turn-over-temperature (TOT), or a TOT range.

9 . The acoustic resonator device of claim 7 , wherein the transistor is a pass field effect transistor (pass FET), and the output from the TCA is an error current proportional to a difference between the reference voltage (Vref) and the sensor voltage (Vsens), the pass FET configured to change a magnitude of a current (I heat ) to the heater.

10 . The acoustic resonator device of claim 4 , wherein the first tether comprises:
a membrane, the first conductive trace being formed on a first surface of the membrane; and a second conductive trace formed on a second surface of the membrane, opposite the first surface, the second conductive trace being configured to provide a return path for the heater current, wherein the membrane defines a via through which the first conductive trace being formed on the first surface of the membrane electrically connects with the heater coil.

11 . The acoustic resonator device of claim 3 , wherein the plurality of tethers includes four tethers, each tether being approximately equal in length and having two lever arms, and each lever arm extending along approximately one quarter of a circumference of the acoustic resonator.

12 . The acoustic resonator device of claim 3 , wherein the plurality of tethers includes two tethers, each tether being approximately equal in length and having two lever arms, and each lever arm extending along approximately one half of a circumference of the acoustic resonator.

13 . The acoustic resonator device of claim 1 , wherein the acoustic resonator is annular, the acoustic resonator device further comprising:
a pillar formed in the trench, the pillar supporting the annular acoustic resonator at a central location; and a conductor wound around the pillar for providing the heater current to the heater coil, wherein the heater coil is disposed around an inner perimeter of the annular acoustic resonator.

14 . A feedback circuit configured to control a temperature of an acoustic resonator, the feedback circuit comprising:
a heater disposed around at least a portion of a perimeter of the acoustic resonator, the heater configured to receive a heater current; and a heat sensor resistor disposed adjacent to the heater; a reference resistor; and an amplifier configured to receive a first input from the reference resistor and a second input from the sense resistor, and to provide an output proportional to a difference between the first input and the second input, wherein the heater current is adjusted based on the difference.

15 . The feedback circuit of claim 14 , wherein the sensor resistor has a temperature coefficient of resistance such that its sensor impedance (R sense ) varies in response to a temperature of the acoustic resonator.

16 . The feedback circuit of claim 14 , wherein the reference resistor has a predetermined reference resistance, and the amplifier is a transconductance amplifier (TCA) configured to sense a voltage caused by a difference between the sensor impedance and the predetermined reference resistance; and the acoustic resonator device further comprises a transistor configured to receive the output from the TCA and to provide the heater current.

17 . The feedback circuit of claim 15 , wherein for a predetermined temperature of the acoustic resonator, a reference voltage (Vref) across the reference resistor is set to be equal to a sensor voltage (Vsense) across the sensor resistor at the predetermined temperature.

18 . The feedback circuit of claim 17 , wherein the predetermined temperature is substantially equal to a turn-over-temperature (TOT), or a TOT range.

19 . The feedback circuit of claim 18 , further comprising a steering digital to analog converter (DAC) configured to determine the reference voltage (Vref).

20 . The feedback circuit of claim 16 , wherein the transistor is a pass field effect transistor (pass FET), and the output from the TCA is an error current proportional to a difference between the reference voltage (Vref) and the sensor voltage (Vsens), the pass FET configured to change a magnitude of a current (I heat ) to the heater.

Assignees

• Avago Technologies General Ip

Inventors

• Sridaran Suresh
• Ruby Richard C
• Parker Reed

Classifications

• H03H3/02

  for the manufacture of piezoelectric or electrostrictive resonators or networks (H03H3/08 takes precedence) · CPC title

• H03H9/08

  Holders with means for regulating temperature · CPC title

• H03H9/172

  Means for mounting on a substrate, i.e. means constituting the material interface confining the waves to a volume · CPC title

• H03H9/02102 Primary

  of temperature influence (cutting angles H03H9/02015) · CPC title

• H05B3/06

  Heater elements structurally combined with coupling elements or holders · CPC title