Patent Description:
A conventional medical device generally uses large dry electrodes or wet electrodes to measure physiological signals to obtain physiological features such as bio-impedance or electrocardiography. Recently, personal biosensors such as portable/wearable medical devices become popular for providing physiological information at all time for the reference to the user. Considering the use and design of these portable medical devices, smaller dry electrodes are more appropriate. However, smaller dry electrode means worse electrode impedance, and the worse electrode impedance (i.e. large electrode impedance) may cause detection error of electrocardiography (ECG) signals. In addition, because an electrode-tissue impedance (ETI) may change greatly due to contact factors or motion artifact, it increases the difficulty of measuring ECG signals.

To solve the problem of the ECG signals in the dry electrode application, the ETI is also detected to reduce the motion artifact in the ECG signals. In the conventional art, a current for the ETI measurement is injected into the electrodes, and an ETI receiver detects the voltages at the electrodes to determine the ETI. In detail, the ETI receiver may comprise a mixer, a low-pass filter and an analog-to-digital converter (ADC), and signals from the electrodes are processed by the mixer, the low-pass filter and the ADC in sequence to generate the ETI information. However, because the ETI receiver is an analog circuit, the ETI receiver has large chip area, higher power consumption and poor mixer harmonics, and the ETI receiver is not friendly to process scaling.

<NPL>, discloses a <NUM>-channel biopotential monitoring ASIC with simultaneous electrode-tissue impedance measurements. <CIT> discloses an analogue signal processor (ASP) application-specific integrated circuit (ASIC) (<NUM>) that can be used for remotely monitoring ECG signals of a subject.

It is therefore an objective of the present invention to provide a direct sampling ETI system, which uses only one analog front-end circuit to sense the ECG signal and ETI signal simultaneously, to solve the above-mentioned problems.

Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms "including" and "comprising" are used in an open-ended fashion, and thus should be interpreted to mean "including, but not limited to. The terms "couple" and "couples" are intended to mean either an indirect or a direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections.

<FIG> is a diagram illustrating a biopotential acquisition system <NUM> according to one embodiment of the present invention. As shown in <FIG>, the biopotential acquisition system <NUM> is a two-electrode biopotential acquisition system having two electrodes <NUM> and <NUM>, and the electrodes <NUM> and <NUM> are used to connect to a right body (e.g., right hand) and a left body (e.g., left hand), respectively, to obtain biopotential signals of a human body, and the biopotential acquisition system <NUM> can process and analyze the biopotential signals to determine physiological signals such as ECG signals, and the physiological features can be displayed on a screen of the biopotential acquisition system <NUM>. In this embodiment, the biopotential acquisition system <NUM> can be built in any portable electronic device or a wearable electronic device.

The biopotential acquisition system <NUM> comprises input nodes N1 and N2, an ETI transmitter (in this embodiment, a digital-to-analog converter (DAC) <NUM> serves as the ETI transmitter), an analog front-end circuit <NUM>, a digital mixer <NUM> and digital filters <NUM>, <NUM> and <NUM>, wherein the analog front-end circuit <NUM> comprises a low-noise amplifier <NUM>, a low-pass filter <NUM> and an ADC <NUM>; and the DAC <NUM> can be implemented by any suitable DAC such as a current DAC, a capacitor DAC or a resistor DAC. When the electrodes <NUM> and <NUM> are connected to the human body, the ETI is formed so that the biopotential acquisition system <NUM> may have large input impedance, and the input impedance may change greatly due to contact factors or motion artifact. In the embodiment shown in <FIG>, the ETI with the impedance of the electrode <NUM>/<NUM> are modeled as a resistor REL and a capacitor CEL connected in parallel. In the operation of the biopotential acquisition system <NUM>, when the electrodes <NUM> and <NUM> are in contact with the human body and the biopotential acquisition system <NUM> starts to measure the ECG signals, the DAC <NUM> receives a digital input signal Din to generate a transmitter signal to the electrodes <NUM> and <NUM>. Then, the analog front-end circuit <NUM> receives the input signals VIP and VIN (biopotential signals) from the input nodes N1 and N2 that are respectively coupled to the electrodes <NUM> and <NUM> to generate information comprising the ECG signal and ETI signal. In detail, the low-noise amplifier <NUM> starts to receive input signals VIP and VIN (biopotential signals) from the input nodes N1 and N2 to generate amplified signals, wherein the input signals VIP and VIN comprise information/components of the ECG signal and ETI signal. Then, the low-pass filter <NUM> filters the amplified signals to generate filtered signals. In one embodiment, a frequency of the transmitter signal generated by the DAC <NUM> is higher than the ECG signals, for example, the ECG signals may have frequency lower than several hundred hertz, but the transmitter signal generated by the DAC <NUM> may be several kilohertz, therefore, the low-pass filter <NUM> may filter out components above several kilohertz and retain the components of the ECG signal and ETI signal within the amplified signal. Then, the ADC <NUM> performs an analog-to-digital converting operation on the filtered signal to generate a digital signal.

The digital mixer <NUM> has an in-phase path and a quadrature path, and a mixer within the in-phase path mixes an in-phase signal of the digital signal with mixer data whose phase is in-phase with the digital signal to generate an in-phase mixed signal, and a mixer within the quadrature path mixes a quadrature signal of the digital signal with mixer data whose phase is in quadrature with the digital signal to generate a quadrature mixed signal. In this embodiment, a frequency of the mixer data is close to the frequency of the transmitter signal, so that the in-phase mixed signal and the quadrature mixed signal have lower frequency. In addition, the digital mixer <NUM> may be a multi-bit digital mixer having good harmonics.

In addition, the phase lead and lag of the signal communication and processing from the DAC <NUM> to an input of the digital mixer <NUM> can be compensated by internal phase shift compensation at the analog front-end circuit <NUM> and the digital mixer <NUM> to derive practical in-phase mixed signal and quadrature mixed signal.

The digital filter <NUM> filters the in-phase mixed signal generated by the digital mixer <NUM> to output an in-phase ETI signal ETI_I, and the digital filter <NUM> filters the quadrature mixed signal generated by the digital mixer <NUM> to output a quadrature ETI signal ETI_Q.

Meanwhile, because the ECG signals has lower frequency such as several hundred hertz, the digital filter <NUM> may directly receive the digital signal outputted by the ADC <NUM>, that is the digital signal is not processed by any mixer, and the digital filter <NUM> filters out components above several hundred hertz to obtain the ECG signal.

Finally, a following processing circuit (not shown) within the biopotential acquisition system <NUM> can notify the user about the motion artifact issue or to adjust/compensate the ECG signal generated by the ECG receiver <NUM> by using the ETI signal.

In the above embodiment, because the ECG signal and the ETI signal are processed by the same analog front-end circuit <NUM> simultaneously, and the ECG signal and the ETI signal are converted to digital signal without first performing a mixing operation, the biopotential acquisition system <NUM> may have smaller chip area and lower power consumption. In addition, because the digital mixer <NUM> is used for the mixing operation of the digital signal, the mixer harmonics can be improved. Furthermore, using the digital filters <NUM>, <NUM> and <NUM> in the biopotential acquisition system <NUM> can reduce the chip area and reduce data rate.

In the embodiment shown in <FIG>, the analog front-end circuit <NUM> comprises the low-noise amplifier <NUM>, the low-pass filter <NUM> and the ADC <NUM>, but this feature is not a limitation of the present invention. <FIG> is a diagram illustrating an analog front-end circuit <NUM> according to one embodiment of the present invention, wherein the analog front-end circuit <NUM> can be used to replace the analog front-end circuit <NUM> shown in <FIG>. As shown in <FIG>, the analog front-end circuit <NUM> comprises a low-noise amplifier <NUM> and an ADC <NUM>, wherein the low-noise amplifier <NUM> is configured to receive input signals VIP and VIN (biopotential signals) from the electrodes <NUM> and <NUM> to generate an amplified signal, wherein the input signals VIP and VIN comprises information of the ECG signal and ETI signal; and the ADC <NUM> performs an analog-to-digital converting operation on the amplified signal to generate a digital signal. <FIG> is a diagram illustrating an analog front-end circuit <NUM> according to another embodiment of the present invention, wherein the analog front-end circuit <NUM> can be used to replace the analog front-end circuit <NUM> shown in <FIG>. As shown in <FIG>, the analog front-end circuit <NUM> comprises a low-pass filter <NUM> and an ADC <NUM>, wherein the low-pass filter <NUM> filters the input signals VIP and VIN (biopotential signals) from the electrodes <NUM> and <NUM> to generate a filtered signal, for example, the low-pass filter <NUM> may filter out components above several kilohertz and retain the components of the ECG signal and ETI signal within the input signals VIP and VIN; and the ADC <NUM> performs an analog-to-digital converting operation on the filtered signal to generate a digital signal.

<FIG> is a flowchart of a signal processing method of the biopotential acquisition system <NUM> according to one embodiment of the present invention. Referring to <FIG> and <FIG> together, the flowchart of the signal processing method is described as follows.

Step <NUM>: generate a transmitter signal for ETI measurement to an input node, wherein the input node is coupled to an electrode of the biopotential acquisition system, and the electrode is used to be in contact with a human body.

Step <NUM>: use an analog front-end circuit to process an input signal from an input node to generate a digital signal, wherein each of the input signal and the digital signal comprises components of an ECG signal and an ETI signal.

Step <NUM>: mix the digital signal with mixer data to generate an in-phase mixed signal and a quadrature mixed signal, wherein the mixer data corresponds to a frequency of the transmitter signal, and the in-phase mixed signal and the quadrature mixed signal comprise the components of the ETI signal.

Step <NUM>: filter the in-phase mixed signal to generate an in-phase ETI signal, filter the quadrature mixed signal to generate a quadrature ETI signal, and filter the digital signal to generate the ECG signal.

Briefly summarized, in the biopotential acquisition system of the present invention, only one analog front-end circuit is used to process two input signals to generate a digital signal comprising the components of the ECG signal and ETI signal, and the mixing operation and the filtering operation for obtaining the ETI signal are performed in digital domain. Therefore, the biopotential acquisition system has smaller chip area and lower power consumption.

Claim 1:
A circuitry of a biopotential acquisition system (<NUM>), comprising:
an input node (N1, N2), wherein the input node (N1, N2) is coupled to an electrode of the biopotential acquisition system (<NUM>), and in use the electrode is to be in contact with a human body;
an electrode-tissue impedance, ETI, transmitter (<NUM>), configured to generate a transmitter signal to the input node (N1, N2); and
an analog front-end circuit (<NUM>, <NUM>, <NUM>), coupled to the input node (N1, N2), configured to process an input signal from the input node (N1, N2) to generate a digital signal, wherein each of the input signal and the digital signal comprises components of an electrocardiography, ECG, signal and an ETI signal,
characterized by
a digital mixer (<NUM>), configured to mix the digital signal with mixer data to generate an in-phase mixed signal and a quadrature mixed signal, wherein the mixer data corresponds to a frequency of the transmitter signal, and the in-phase mixed signal and the quadrature mixed signal comprise the components of the ETI signal; and
a digital filter (<NUM>, <NUM>, <NUM>), configured to filter the digital signal to generate the ECG signal.