Acoustic sensor with an acoustic object detector for reducing power consumption in front-end circuit
An acoustic object detector for detecting presence of an acoustic signal is provided. The acoustic object detector includes a number of bandpass filters. Each bandpass filter is configured to convert an input signal into an analog signal within a frequency band. The acoustic object detector also includes a number of spike generating circuits each coupled to the respective bandpass filter. Each spike generating circuit is configured to generate a series of spike signals based upon an adaptive threshold for the analog signal. The acoustic object detection further includes a decision circuit configured to generate a digital signal at a time-frequency point from the series of spike signals.
1. An acoustic sensor comprising:
an acoustic object detector for detecting presence of an acoustic signal in an input signal, the acoustic object detector comprising:
a plurality of analog bandpass filters each configured to convert an input signal into respective analog signal filtered within a frequency band;
a plurality of spike generating circuits, each spike generating circuit having an analog signal from a respective one of the analog bandpass filters as a first input and being configured to output a series of spike signals of constant amplitude and having a density proportional to a rate of change of signal energy in the analog signal, and
a decision circuit configured to generate a digital signal at a time-frequency point from the series of spike signals from the plurality of spike generating circuits;
wherein the analog front-end comprises an analog-to-digital converter coupled to digitize an output of a lowpass filter coupled to receive the input signal;
a power management apparatus adapted to control a power consumption of the analog-to-digital converter, in response to an output of the decision circuit.
2. The acoustic sensor of claim 1 , wherein, within each of the plurality of spike generating circuits, an adaptive threshold is configured to increase at a constant step until exceeding the analog signal and then decay toward the analog signal.
3. The acoustic sensor of claim 1 , wherein the decision circuit comprises:
an edge detection unit having an integrator coupled to a thresholding unit for generating an output from the series of spike signals from the plurality of spike generating circuits; and
a bandwidth encoding circuit to generate the digital signal from the output of the integrator.
4. The acoustic sensor of claim 1 wherein each spike generating circuit includes:
a comparator having hysteresis and an analog signal from a respective one of the analog bandpass filters as a first input and an adaptive threshold as a second input, the comparator configured to compare the analog signal with the adaptive threshold to output a series of constant magnitude spike signals having density corresponding to a rate of change of signal energy in the analog signal, and
a threshold generating circuit for generating the adaptive threshold, the threshold generating circuit including:
an analog lowpass filter coupled between the first and second inputs of the comparator, the analog lowpass filter including a capacitor coupled to the second input of the comparator,
a gated current source coupled to apply current to the capacitor that is coupled to the second input of the comparator, the gated current source activated by the comparator based upon a difference between the analog signal and the adaptive threshold to charge the capacitor and thereby change the adaptive threshold.
5. The acoustic sensor of claim 4 , wherein the analog lowpass filter of each threshold generating circuit further includes a transconductance amplifier coupled between the first and second inputs of the comparator of the threshold generating circuit.
6. The acoustic sensor of claim 4 , wherein the analog lowpass filter of each threshold generating circuit further includes a resistor coupled between the first and second inputs of the comparator of the threshold generating circuit.
7. The acoustic sensor of claim 4 , wherein the analog lowpass filter of each threshold generating circuit further includes a transconductance amplifier coupled between the first and second inputs of the comparator of the threshold generating circuit.
8. The acoustic sensor of claim 4 , wherein the analog lowpass filter of each threshold generating circuit further includes a resistor coupled between the first and second inputs of the comparator of the threshold generating circuit.
9. The acoustic sensor of claim 4 , wherein within each of the plurality of spike generating circuits, the an adaptive threshold is configured to increase at a constant step until exceeding the analog signal and then decay toward the analog signal.
10. An analog front-end circuit comprising the acoustic sensor of claim 1 and further comprising a low pass filter coupled to receive the input signal and to provide a signal to an analog-to-digital converter, wherein the acoustic object detector is coupled to control a power dissipation of at least one of the low-pass filter and the analog-to-digital converter based upon a maximum frequency of the input signal as detected by the acoustic object detector.
11. The analog front-end of claim 10 wherein the acoustic object detector is coupled to control a power dissipation of the analog-to-digital converter by adjusting a bandpass of the low-pass filter and a sampling rate of the analog-to-digital converter.
12. An acoustic system comprising:
an acoustic sensor for adjusting power consumption based upon an acoustic signal, comprising:
a transducer for converting an acoustic signal into an electrical signal;
a dynamically-reconfigurable analog front-end; and
an acoustic object detector, including:
a plurality of analog bandpass filters each configured to convert the electrical signal into a respective analog signal within a frequency band f i ;
a plurality of spike generating circuits, each spike generating circuit having an analog signal from a respective one of the plurality of analog passband filters as a first input and being configured to output a plurality of spike signals of constant amplitude and having a density proportional to a rate of change of signal energy in the analog signal, and
a decision circuit configured to generate a digital signal in binary form at a time-frequency point from the plurality of spike signals from the plurality of spike generating circuits;
wherein the acoustic system further comprises an analog-to-digital converter coupled to digitize an output of a lowpass filter coupled to receive the acoustic signal; and
a power management apparatus adapted to control a power consumption of the analog-to-digital converter, in response to an output of the decision circuit.
13. The acoustic sensor of claim 12 , wherein the analog front-end comprises a preamplifier coupled to amplify the electrical signal.
14. The acoustic sensor of claim 13 , wherein the analog front-end comprises a lowpass filter coupled to an output of the preamplifier.
15. The acoustic sensor of claim 12 , wherein the transducer comprises a microphone, and the acoustic signal comprises a sound signal.
16. The acoustic sensor of claim 12 , wherein the acoustic object detector is configured to serve as a speech edge detector.
17. The acoustic sensor of claim 16 , wherein the decision circuit comprises:
an edge detection unit having an integrator coupled to a thresholding unit for generating an output from the plurality of spike signals from the plurality of spike generating circuits; and
a bandwidth encoding circuit to generate the digital signal from the output of the thresholding unit.
18. A spike generating circuitry for extracting an acoustic signal and encoding the acoustic signal as a series of constant magnitude spikes, the spike generating circuitry comprises:
a comparator having a signal input and an adaptive threshold input and configured to compare the signal input with the adaptive threshold input to output a series of constant magnitude spike signals, the constant magnitude spike signals having a rate corresponding to a rate of change of the signal input; and
a threshold generating circuit for generating the adaptive threshold input, the threshold generating circuit including:
an analog lowpass filter coupled with the signal input and the adaptive threshold input of the comparator, the analog lowpass filter including a capacitor coupled to the adaptive threshold input of the comparator,
a current source, and
a transistor switch coupled between the current source and the capacitor, the transistor switch activated by the comparator based upon a difference between the signal input and the adaptive threshold input to charge the capacitor and thereby change the adaptive threshold.
19. The spike generating circuitry of claim 18 , wherein the analog lowpass filter further includes a transconductance amplifier coupled between the signal and adaptive threshold inputs.
20. The spike generating circuitry of claim 18 , wherein the analog lowpass filter further includes a resistor between the adaptive threshold input and the signal input of the comparator.
21. The spike generating circuitry of claim 18 , wherein the adaptive threshold input increases at a constant step until exceeding the signal input and then decays toward the signal input.