Signal acquisition circuit for detecting a wanted signal in the presence of an unwanted signal
First Claim
1. A signal acquisition circuit for detecting a wanted signal in a composite signal containing the wanted signal and an unwanted signal, where the highest frequency in the unwanted signal is higher than the highest frequency in the wanted signal, comprising:
- a first sensor arranged to sense the composite signal, the composite signal being sensed at a rate that is at least equal to the Nyquist rate for the highest frequency in the wanted signal and less than the Nyquist rate for the highest frequency in the unwanted signal;
a second sensor arranged to sense the unwanted signal, without the wanted signal, at a rate that is at least equal to the Nyquist rate for the highest frequency in the unwanted signal;
an analog-to-digital converter arranged to receive the outputs of the first sensor and the second sensor, and sample the received outputs of the first sensor and the second sensor at a sampling rate that is at least equal to the Nyquist rate for the highest frequency in the unwanted signal;
a demultiplexer arranged to receive the output of the analog to digital converter and output a signal representative of the unwanted signal separately from a signal representative of the composite signal; and
a filter arranged to subtract the output signal representative of the unwanted signal from the signal representative of the composite signal and thereby output a signal representative of the wanted signal. containing the sum of the wanted signal and the unwanted signal sampled at a low rate at least equal to the Nyquist rate for the wanted signal but less than the high rate and a second component containing the unwanted signal sampled at the high rate.
19 Assignments
0 Petitions
Accused Products
Abstract
A signal acquisition circuit detects a wanted signal in a composite signal containing the wanted signal and an unwanted signal, where the highest frequency in the unwanted signal is higher than the highest frequency in the wanted signal. A sensor captures the composite signal and an analog-to-digital converter samples and converts the composite signal to digital format, and a filter subtracts the unwanted signal from the composite signal. The sampled signal contains a first component containing the sum of the wanted signal and the unwanted signal sampled at a first rate at least equal to the Nyquist rate for the wanted signal but less than a second rate that is at least equal to the Nyquist rate for the unwanted signal, and a second component containing the unwanted signal sampled at the second rate. The analog-to-digital converter outputs to the filter a first digital signal containing the first component sampled at the first rate and a second digital signal containing the second component at the second rate. The circuit is useful for detecting a photoplethysmograph signal in the presence of ambient light in a pulse oximetry sensor.
7 Citations
28 Claims
-
1. A signal acquisition circuit for detecting a wanted signal in a composite signal containing the wanted signal and an unwanted signal, where the highest frequency in the unwanted signal is higher than the highest frequency in the wanted signal, comprising:
-
a first sensor arranged to sense the composite signal, the composite signal being sensed at a rate that is at least equal to the Nyquist rate for the highest frequency in the wanted signal and less than the Nyquist rate for the highest frequency in the unwanted signal; a second sensor arranged to sense the unwanted signal, without the wanted signal, at a rate that is at least equal to the Nyquist rate for the highest frequency in the unwanted signal; an analog-to-digital converter arranged to receive the outputs of the first sensor and the second sensor, and sample the received outputs of the first sensor and the second sensor at a sampling rate that is at least equal to the Nyquist rate for the highest frequency in the unwanted signal; a demultiplexer arranged to receive the output of the analog to digital converter and output a signal representative of the unwanted signal separately from a signal representative of the composite signal; and a filter arranged to subtract the output signal representative of the unwanted signal from the signal representative of the composite signal and thereby output a signal representative of the wanted signal. containing the sum of the wanted signal and the unwanted signal sampled at a low rate at least equal to the Nyquist rate for the wanted signal but less than the high rate and a second component containing the unwanted signal sampled at the high rate. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
-
-
9. A method of acquiring a wanted signal in a composite signal containing the wanted signal and an unwanted signal, where the highest frequency in the unwanted signal is higher than the highest frequency in the wanted signal, comprising the steps of:
-
sensing the composite signal at a low rate that is at least equal to the Nyquist rate for the highest frequency in the wanted signal but less than the Nyquist rate for the highest frequency in the unwanted signal; sensing the unwanted signal, without the wanted signal, at a rate that is at least equal to the Nyquist rate for the highest frequency in the unwanted signal; sampling said composite and unwanted signals at a sampling rate that is at least equal to the Nyquist rate for the highest frequency in the unwanted signal; producing a signal representative of the unwanted signal separately from a signal representative of the composite signal; and subtracting the signal representative of the unwanted signal separately from the signal representative of the composite signal to produce the wanted signal; wherein said sensing includes expending energy to make said wanted signal observable. - View Dependent Claims (10, 11, 12, 13, 14, 15)
-
-
16. A pulse oximetry sensor comprising:
-
a first and a second light source; a pulse generator arrangement for sequentially pulsing said first and second light sources at a low rate that is at least equal to the Nyquist rate of a photoplethysmograph signal but less than a high rate at least equal to the Nyquist rate for the highest frequency of the ambient light to be removed; a photodetector for detecting light pulses from said first and second light sources in the presence of artificial ambient light and the ambient light in the absence of the light pulses from said light sources; an analog-to-digital converter (ADC) triggered at the high rate for acquiring and converting an output of the photodetector to digital format, wherein the analog-to-digital converter outputs a signal having a first component containing the signals from the pulsed first and second light sources in the presence of ambient light sampled at the low rate and a second component containing the ambient light signal sampled at the high rate; a demultiplexer for separating said first and second components into; a first signal representative of pulsed first light source; a second signal representative of the pulsed second light source; and a third signal representative of the ambient light; and a filter downstream of the demultiplexer for subtracting the third signal representative of the ambient light signal from each of the first and second signals light to output a first output signal representative of the pulsed first light source and a second output signal representative of the pulsed second light source. - View Dependent Claims (17, 18, 19, 20, 21, 22)
-
-
23. A method of acquiring a wanted signal in a pulse oximetry sensor comprising:
-
sequentially pulsing a first and a second light sources, having different effective wavelengths, at a first rate that is at least equal to the Nyquist rate of a photoplethysmograph signal but less than a second rate at least equal to the Nyquist rate for the highest frequency of an ambient light to be removed; detecting light pulses from said first and second light sources in the presence of the ambient light and further detecting ambient light in the absence of light pulses from the first and second light sources to produce a composite signal; acquiring and converting said composite signal to digital format in an analog-to-digital converter triggered at the second rate to produce an converted signal having a first component representative of the detected light pulses from the first light source in the presence of ambient light, a second component representative of the detected light pulses from the second light source in the presence of ambient light and a third component representative of the detected ambient light and second light sources in the absence of light pulses from the first and second light sources; separating said components of the signal; and subtracting the third component from each of the first and second components to output a first signal representative of the pulsed signal of the first light source and a second signal representative of the pulsed signal of the second light source. - View Dependent Claims (24, 25, 26, 27, 28)
-
Specification