Digital microphone with over-voltage protection
The disclosure relates generally to microphone and vibration sensor assemblies ( 100 ) having a transducer ( 102 ), like a microelectromechanical systems (MEMS) device, and an electrical circuit ( 103 ) disposed in a housing ( 110 ) configured for integration with a host device. The electrical circuit includes an output driver circuit, a low drop out (LDO) regulator circuit, and an over-voltage protection circuit with improved capacity and response time.
1. A sensor assembly comprising:
a transducer configured to generate an analog signal responsive to sensing changes in an environment; and
an integrated circuit coupled to an output of the transducer, the integrated circuit comprising:
a signal processing circuit connectable to a transducer of the digital sensor assembly;
an output driver circuit coupled to the signal processing circuit;
a low drop out (LDO) regulator circuit coupled to the output driver circuit; and
an over-voltage protection circuit comprising:
a current-sink circuit coupled to the output driver circuit and configured to sink current associated with reflected energy received by the output driver circuit;
a current comparator circuit coupled to the current-sink circuit; and
a control circuit coupled to the current comparator and configured to change a state of the current comparator when a voltage of the reflected energy exceeds a threshold,
wherein the current comparator enables the current-sink circuit to sink current associated with the reflected energy upon changing state.
2. The sensor assembly of claim 1 , the control circuit configured to provide the reflected energy to the current comparator circuit as additional current when the voltage of the reflected energy exceeds the threshold, wherein the additional current due to the reflected energy increases a rate at which the current comparator circuit changes state.
3. The sensor assembly of claim 2 , the control circuit including a bandwidth control circuit configured to prevent the current comparator circuit from oscillating between states when the reflected energy received by the output driver circuit oscillates about the threshold at frequency greater than a bandwidth of the bandwidth control circuit.
4. The sensor assembly of claim 3 , the control circuit configured to increase a voltage applied to the current comparator circuit when the voltage of the reflected energy exceeds the threshold.
5. The sensor assembly of claim 2 , the control circuit comprising a variable resistance circuit coupled to the output driver circuit and to the current comparator circuit, the variable resistance circuit configured to provide the reflected energy to the current comparator circuit in a relatively low resistance state when the voltage of the reflected energy exceeds the threshold compared, wherein the variable resistance circuit is in relatively high resistance state when the voltage of the reflected energy is does not exceed than the threshold.
6. The sensor assembly of claim 5 , the control circuit comprising a switch coupled to the output driver circuit and configured to increase a voltage applied to the current comparator when the voltage of the reflected energy exceeds the threshold, wherein the current comparator circuit changes state in response to the increased voltage.
7. The sensor assembly of claim 6 , the control circuit comprising a bandwidth control circuit coupled to the output driver circuit and to the current comparator circuit, the bandwidth control circuit configured to prevent the current comparator circuit from changing state to reflected energy transients received by the output driver circuit.
8. The sensor assembly of claim 1 , wherein the over-voltage protection circuit further includes a current comparator circuit-controlled switch configured to output current from the current comparator circuit to the LDO regulator circuit, the current comparator circuit-controlled switch configured to be disabled when the current comparator enables the current-sink circuit.
9. The sensor assembly of claim 1 , the current comparator circuit comprising a first current source and a second current source isolated by a cascode circuit, wherein the cascode circuit stabilizes a current comparator circuit output signal applied to the current-sink circuit.
10. The sensor assembly of claim 1 , the LDO regulator comprising a reference buffer coupled to the over-voltage regulator circuit by a low pass filter, the reference buffer configured to output an over-voltage reference that is greater than a reference voltage of the LDO regulator, wherein the threshold is based on the over-voltage reference.
11. The sensor assembly of claim 1 is a microphone further comprising a housing having a host-interface and a sound port, wherein the transducer and the integrated circuit are disposed in the housing, the transducer is a MEMS transducer acoustically coupled to the sound port, and the integrated circuit is electrically coupled to contacts on the host-interface.
12. An integrated circuit for interfacing with a transducer of a digital sensor assembly, the integrated circuit comprising:
a signal processing circuit connectable to a transducer of the digital sensor assembly;
an output driver circuit coupled to the signal processing circuit;
a low drop out (LDO) regulator circuit coupled to the output driver circuit; and
an over-voltage protection circuit comprising:
a current-sink circuit coupled to the output driver circuit and configured to sink current associated with reflected energy received by the output driver circuit;
a current comparator circuit coupled to the current-sink circuit; and
a control circuit coupled to the current comparator and configured to change a state of the current comparator when a voltage of the reflected energy exceeds a threshold,
wherein the current comparator enables the current-sink circuit to sink current associated with the reflected energy upon changing state.
13. The integrated circuit of claim 12 , the control circuit configured to provide the reflected energy to the current comparator circuit as additional current when the voltage of the reflected energy exceeds the threshold, wherein the additional current due to the reflected energy increases a rate at which the current comparator circuit changes state.
14. The integrated circuit of claim 13 , the control circuit including a bandwidth control circuit configured to prevent the current comparator circuit from oscillating between states when the reflected energy received by the output driver circuit oscillates about the threshold at frequency greater than a bandwidth of the bandwidth control circuit.
15. The integrated circuit of claim 14 , the control circuit configured to increase a voltage applied to the current comparator circuit when the voltage of the reflected energy exceeds the threshold.
16. The integrated circuit of claim 12 , wherein the over-voltage protection circuit further includes a current comparator circuit-controlled switch configured to output current from the current comparator circuit to the LDO regulator circuit, the current comparator circuit-controlled switch configured to be disabled when the current comparator enables the current-sink circuit.
17. The integrated circuit of claim 13 , the control circuit comprising a variable resistance circuit coupled to the output driver circuit and to the current comparator circuit, the variable resistance circuit configured to provide the reflected energy to the current comparator circuit in a relatively low resistance state when the voltage of the reflected energy exceeds the threshold compared, wherein the variable resistance circuit is in relatively high resistance state when the voltage of the reflected energy is does not exceed than the threshold.
18. The integrated circuit of claim 17 , the control circuit comprising a switch coupled to the output driver circuit and configured to increase a voltage applied to the current comparator when the voltage of the reflected energy exceeds the threshold, wherein the current comparator circuit changes state in response to the increased voltage.
19. The integrated circuit of claim 18 , the control circuit comprising a bandwidth control circuit coupled to the output driver circuit and to the current comparator circuit, the bandwidth control circuit configured to prevent the current comparator circuit from changing state to reflected energy transients received by the output driver circuit.
20. The integrated circuit of claim 12 , the current comparator circuit comprising a first current source and a second current source isolated by a cascode circuit, wherein the cascode circuit stabilizes a current comparator circuit output signal applied to the current-sink circuit.
21. The integrated circuit of claim 12 , the LDO regulator comprising a reference buffer coupled to the over-voltage regulator circuit by a low pass filter, the reference buffer configured to output an over-voltage reference that is greater than a reference voltage of the LDO regulator, wherein the threshold is based on the over-voltage reference.