APPARATUS AND METHOD FOR MEASURING PHYSIOLOGICAL SIGNAL

A method for measuring a physiological signal is provided. The method is applicable to optical physiological measurement with at least two types of light sources. The method includes a processing for adjusting amplitudes of signals of the at least two types of light sources to a predetermined ratio by adjusting intensities of the light sources, so as to increase a signal dynamic range as well as a signal-to-noise ratio.

DETAILED DESCRIPTION

Compared to infrared light, red light has a less transmission ability on a human body and thus renders lower signals. Assuming that an optimal driving ratio between energies of two light sources can be achieved with appropriate light source energies, amplitudes of the two sets of signals can be approximated to increase a signal dynamic range as well as a signal-to-noise ratio (SNR).

First Embodiment

FIG. 1shows a schematic diagram of a physiological signal measurement apparatus1in an initialization period according to a first embodiment. The physiological signal measurement apparatus1, such as the blood oxygen measurement apparatus, at least comprises a first light source11, a second light source12, an optical detector13, a light source driver14, and a signal processing circuit15a. The signal processing circuit15aat least comprises an analog-to-digital converter (ADC)151and a processor152. For example, the processor152is a field programmable gate array (FPGA). For example, the first light source11is an invisible light source and the second light source12is a visible light source. Alternatively, the first light source11may be a visible light source, and the second light source12may be an invisible light source. For example, the invisible light source is an infrared light light-emitting diode (LED), and the visible light source is a red light LED. For illustration purposes, in the first embodiment, the first light source11is a visible light source exemplified by a red light, and the second light source12is an invisible light source exemplified by an infrared light. The physiological signal may include blood oxygen concentration, blood sugar, carbon monoxide in blood, carbon dioxide in blood, oxidized hemoglobin (methemoglobin), hemoglobin, a heart rate, a respiratory rate, a body movement and a body temperature.

FIG. 2shows a flowchart of a physiological signal measurement method according to the first embodiment.FIG. 3shows a timing diagram of first initialization signals and second initialization signals according to the first embodiment.FIG. 4shows a timing diagram of first reception signals and second reception signals.FIG. 5shows a schematic diagram of the physiological signal measurement apparatus in a measurement period according to the first embodiment. Referring toFIGS. 2 to 5, the physiological signal measurement method, applicable to the physiological signal measurement apparatus1, comprises the following steps.

In the initialization period, a plurality of a signal of at least two types of initialization signals and a plurality of one other signal of the at least two types of the initialization signals are provided. The signals of one of the at least two types of initialization signals may be first initialization signals RT(1) to RT(n), and the signals of the other of the at least two types of initialization signals may be second initialization signals IRT(1) to IRT(n). Referring toFIG. 2, as shown in step21, in the initialization period, the signal processing circuit15aprovides the first initialization signals RT(1) to RT(n) and the second initialization signals IRT(1) to IRT(n). Referring toFIG. 3, for example, the first initialization signals RT(1) to RT(n) and the second initialization signals IRT(1) to IRT(n) are sequentially incremental, and the first initialization signals RT(1) to RT(n) are respectively equal to the second initialization signals IRT(1) to IRT(n). For example, the signal processing circuit15aalternately provides the first initialization signals RT(1) to RT(n) and the second initialization signals IRT(1) to IRT(n).

According to the plurality of the signal of the at least two types of initialization signals and the plurality of the other signal of the at least two types of initialization signals, at least two types of light sources are driven such that at least one light source driver correspondingly outputs a plurality of a signal of at least two types of reception signals and a plurality of one other signal of the at least two types of receptions signals. The at least two types of light sources may be the first light source11and the second light source12. The signals of one of the at least two types of reception signals may be first reception signals RR(1) to RR(n), and the signals of the other of the at least two types of reception signals may be IRR(1) to IRR(n). As shown in step22, the light source driver14drives the first light source11and the second light source12according to the first initialization signals RT(1) to RT(n) and the second initialization signals IRT(1) to IRT(n), such that the optical detector13correspondingly outputs the first reception signals RR(1) to RR(n) and the second reception signals IRR(1) to IRR(t). It should be noted that, light beams produced by the first light source11and the second light source12transmit through a physiological tissue2to reach the optical detector13. Alternatively, the light beams produced by the first light source11and the second light source12are reflected by the physiological tissue2to reach the optical detector13.

A signal of at least two types of candidate signals for rendering one of the at least two types of light sources to enter saturation is selected from the plurality of the signal of the at least two types of reception signals, and one other signal of the least two types of candidate signals is selected from the plurality of the signal of the at least two types of reception signals. A ratio of the signal of the at least two types of candidate signals to the other signal of the at least two types of candidate signals (the signal of the at least two types of candidate signals/the other signal of the at least two types of candidate signals) is approximate to a predetermined ratio. The signal of the at least two types of candidate signals may be a first candidate signal, and the other signal of the at least two types of candidate signals may be a second candidate signal. As shown in step23, from the reception signals RR(1) to RR(n), the signal processing circuit15aselects a first reception signal RR(i) for correspondingly rendering the first light source11to enter saturation as a first candidate signal; from the second reception signals IRR(1) to IRR(n), the signal processing circuit15aselects a second reception signal IRR(i−1) as a second candidate signal. A ratio of the second candidate signal IRR(i−1) to the first candidate signal RR(i) is most approximate to a predetermined ratio, e.g., 0.5 to 2. In an alternative embodiment, the predetermined ratio may be 0.8 to 1.2.

For illustration purposes, the predetermined ratio in the first embodiment is 1, for example. As the first initialization signal RT(i) already renders the first light source11to enter saturation, the first receptions signals RR(i+1) to RR(n) do not increase even if the light source driver14drives the first light source11according to the incremented first initialization signals RT(i+1) to RT(n). When the predetermined ratio is set to 1, the second candidate signal is most approximate to the first candidate signal. That is to say, an amplitude of the second reception signal IRR(i−1) is most approximate to an amplitude of the first reception signal RR(i).

The ADC151converts the first receptions signals RR(1) to RR(n) and the second reception signals IRR(1) to IRR(n) to digital signals DS, according to which the processor152selects the first candidate signal and the second candidate signal.

A signal of at least two types of operation driving signals corresponding to the signal of the at least two types of candidate signals is selected from the plurality of the signal of the at least two types of initialization signals, and one other signal of the at least two types of operation driving signals corresponding to the other signal of the at least two types of candidate signals is selected from the plurality of the other signal of the at least two types of initialization signals. The signal of the at least two types of operation driving signals may be a first operation driving signal, and the other signal of the at least two types of operation driving signals may be a second operation driving signal. As shown in step24, from the first initialization signals RT(1) to RT(n), the signal processing circuit15aselects the first initialization signal RT(i) corresponding to the first candidate signal as the first operation driving signal; from second initialization signals IRT(1) to IRT(n), the signal processing circuit15aselects the second initialization signal IRT(i−1) corresponding to the second candidate signal as the second operation driving signal.

In a measurement period, at least two light sources are driven according to the signal of the at least two types of operation driving signals and the other signal of the at least two types of operation driving signals. As shown in step25, in the measurement period, the signal processing circuit15adrives the first light source and the second light source according to the first operation driving signal and the second operation driving signal. Before the measurement period, the signal processing circuit15ahas already identified the first operation driving signal and the second operation driving signal most appropriate for respectively driving the first light source11and the second light source12, so that a limited dynamic range of the ADC15in subsequent processes is avoided.

FIG. 6shows a timing diagram of a digital signal outputted by an ADC in a delay period, an initialization phase and a measurement phase.FIG. 7shows an enlarged partial view of T3inFIG. 6.FIG. 8shows a schematic diagram of a ratio of a second reception signal to a first reception signal. Referring toFIGS. 1,2,6,7, and8, the ADC151sequentially outputs the digital signal DS in a delay period T1, an initialization phase T2and a measurement period T3. After powering on and the delay period T1, the physiological signal measurement apparatus1enters a ready state. To identify the most appropriate first operation driving signal and second operation driving signal, the physiological signal measurement apparatus1first performs the above steps21and24in the initialization phase T2. To further ensure the correctness of the identified first operation driving signal and second operation driving signal, steps21and24can be repeated several times. InFIG. 3, steps21and24are repeated for three times, for example.

Referring toFIG. 7, when the physiological signal measurement apparatus1is in the measurement phase T3, the amplitude of the digital signal DS outputted by the ADC151appears consistent. That is to say, when the processor152drives the first light source11and the second light source12according to the first operation driving signal and the second operation driving signal, the signal amplitude outputted correspondingly to the first operation driving signal and the second operation driving signal by the optical detector13is also consistent. When the physiological signal measurement apparatus1is in the measurement phase T3, the signal ratio outputted correspondingly to the first light source and the second light source by the optical detector13is maintained between 1.07 and 1.14, as shown inFIG. 8. Thus, the ADC151is prevented from a limited dynamic range.

Second Embodiment

FIG. 9shows a schematic diagram of a physiological signal measurement apparatus in an initialization period according to a second embodiment. Referring toFIGS. 1 and 9, a main difference of the second embodiment from the first embodiment is that, the signal processing circuit15ain the first embodiment is replaced by a signal processing circuit15bin a physiological signal measurement apparatus3. In addition to the ADC151and the processor152, the signal processing circuit15bfurther comprises an auto-gain control circuit153and an amplifier154. The amplifier154is controlled by the auto-gain control circuit153, and amplifies the first reception signals RR(1) to RR(n) and the second reception signals IRR(1) to IRR(n) to analog signals AS. The ADC151converts the analog signals AS to the digital signals DS. The processor152selects the first candidate signal and the second candidate signal according to the digital signals DS, and selects the first operation driving signal and the second operation driving signal according to the first candidate signal and the second candidate signal. The processor152subsequently determines an auto-gain value of the auto-gain control circuit153according to the first operation driving signal and the second operation driving signal.