WO2021042309A1

WO2021042309A1 - Front-end circuit and method for calibrating transmission signal

Info

Publication number: WO2021042309A1
Application number: PCT/CN2019/104453
Authority: WO
Inventors: 杨鑫
Original assignee: Oppo广东移动通信有限公司
Priority date: 2019-09-04
Filing date: 2019-09-04
Publication date: 2021-03-11
Also published as: CN114424034A; CN114424034B

Abstract

A front-end circuit and a method for calibrating a transmission signal. The method comprises: using an amplification module of a front-end circuit to convert a received optical signal into a voltage, and amplifying the voltage (S401); regulating a gain of the amplification module according to a relation between an output voltage of the amplification module and a preset threshold, and regulating a DC offset of a current of an input end of the amplification module to calibrate an output current of the amplification module (S402); and converting a calibrated analog output voltage outputted by the amplification module into a digital output voltage (S403).

Description

Front-end circuit and calibration method of transmission signal

Technical field

The embodiments of the present application relate to electronic technology, and relate to, but are not limited to, a front-end circuit and a calibration method of transmission signals.

Background technique

PPG (Photoplethysmograph, using photoplethysmograph) is widely used to detect changes in blood volume in the microvascular bed of tissues. PPG is usually obtained by using a pulse oximeter, which illuminates the skin and measures changes in light absorption, and a traditional pulse oximeter monitors the perfusion of blood to the subcutaneous tissue and dermis of the skin. By illuminating the skin with light from an LED (Light Emitting Diode), and then measuring the amount of light transmitted or reflected to the LED, the change in capacity caused by the pressure pulse is detected. Since the blood flow to the skin can be adjusted by many other physiological systems, PPG can also be used to monitor respiration, decreased blood volume, and other blood circulation conditions. In addition, the shape of the PPG waveform varies from subject to subject, and changes according to the location and manner of the pulse oximeter attached.

At present, because the PPG signal is a simple and effective non-invasive method for detecting heart rate, the PPG principle has been applied to a large number of wearable devices. However, during the user's movement, the PPG signal often receives interference from the movement signal. Take the watch as an example. If the user does not tightly tie the watch to the surface of the skin, the light emitted by the LED in the PPG will be interfered by the ambient light, and the sensor will not receive a clean usable signal, which will greatly affect the detection result. Impact. Therefore, how to make the PPG signal more robust with respect to the interference of motion and ambient light has become a technical problem to be solved by those skilled in the art.

Summary of the invention

In view of this, the embodiments of the present application provide a front-end circuit and a calibration method for transmission signals.

The technical solutions of the embodiments of the present application are implemented as follows:

In a first aspect, an embodiment of the present application provides a front-end circuit, and the front-end circuit includes:

Amplifying module, used to convert the received optical signal into voltage and amplify it;

The calibration module is used to adjust the gain of the amplifying module according to the relationship between the output voltage of the amplifying module and a preset threshold, and to adjust the DC (Direct Current) of the current at the input end of the amplifying module Adjusting the offset to calibrate the output voltage of the amplifying module;

The analog-to-digital conversion module is used to convert the calibrated analog output voltage output by the amplifying module into a digital output voltage.

In the embodiment of the present application, the amplifying module includes:

Input circuit, used to convert the received optical signal into electric current;

The amplifying circuit is used for converting the current generated by the input circuit into a voltage and amplifying it.

In the embodiment of the present application, the calibration module is configured to move the DC offset of the current at the input end of the amplifying module downward according to the relationship between the output voltage of the amplifying module and a preset threshold; and/or, Reduce the gain of the amplifying module;

The calibration module is further configured to move the DC offset of the current at the input end of the amplifying module upward according to the relationship between the output voltage of the amplifying module and a preset threshold; and/or, make the amplifying module The gain becomes larger.

In the embodiment of the present application, the preset threshold includes a first preset threshold and a second preset threshold, and the first preset threshold is greater than the second preset threshold;

The calibration module is configured to move the DC offset of the current at the input end of the amplifying module downward when the output voltage is greater than the first preset threshold; and/or, to change the gain of the amplifying module small;

The calibration module is further configured to move the DC offset of the current at the input end of the amplifying module upward when the output voltage is less than the second preset threshold; and/or, to change the gain of the amplifying module Big.

In the embodiment of the present application, the calibration module includes:

A comparator, configured to determine whether the output voltage of the amplifying module is greater than the first preset threshold or less than the second preset threshold;

A control circuit for generating a first control signal when the output voltage is greater than the first preset threshold, and generating a second control signal when the output voltage is less than the second preset threshold;

The first adjustment circuit is configured to move the DC offset of the current at the input end of the amplifying module downward according to the first control signal; and/or, reduce the gain of the amplifying module;

The second adjustment circuit is used to move the DC offset of the current at the input end of the amplifying module upward according to the second control signal; and/or to increase the gain of the amplifying module.

In the embodiment of the present application, the amplifying module includes a current source of an input stage and a feedback resistance circuit;

Correspondingly, the first adjustment circuit is configured to adjust the current source of the input stage according to the first control signal, so that the DC offset of the current at the input end of the amplifying module moves downward; and/or , Adjusting the feedback resistance circuit to make the gain of the amplifying module smaller;

Correspondingly, the second adjustment circuit is configured to adjust the current source of the input stage according to the second control signal, so that the DC offset of the current at the input end of the amplifying module moves upward; and/or, The feedback resistance circuit is adjusted to increase the gain of the amplifying module.

In the embodiment of the present application, the feedback resistor circuit includes a feedback capacitor resistor array formed by capacitors, resistors, and switches;

Correspondingly, the first adjustment circuit or the second adjustment circuit adjusts the gain of the amplifying module by using the feedback capacitor resistor array.

In the embodiment of the present application, the front-end circuit further includes:

The output module is used to read and write the digital output voltage according to the first-in first-out principle.

In a second aspect, an embodiment of the present application provides a method for calibrating a transmission signal. The method is applied to a front-end circuit, and the method includes:

Use the amplifying module of the front-end circuit to convert the received optical signal into voltage and amplify it;

Adjusting the gain of the amplifying module according to the relationship between the output voltage of the amplifying module and the preset threshold, and adjusting the DC offset of the current at the input end of the amplifying module;

Convert the calibrated analog output voltage to digital output voltage.

In the embodiment of the present application, the amplifying module using the front-end circuit to convert the received optical signal into a voltage and amplify it includes:

Using the input circuit of the amplifying module to convert the received optical signal into current;

The amplifying circuit of the amplifying module converts the current generated by the input circuit into a voltage, and amplifies it.

In the embodiment of the present application, the gain of the amplifying module is adjusted according to the relationship between the output voltage of the amplifying module and a preset threshold, and the DC offset of the current at the input of the amplifying module is adjusted The adjustment includes: moving the DC offset of the current at the input end of the amplifying module downward according to the relationship between the output voltage of the amplifying module and a preset threshold; and/or, changing the gain of the amplifying module small;

The adjusting the gain of the amplifying module according to the relationship between the output voltage of the amplifying module and the preset threshold value, and adjusting the DC offset of the current at the input end of the amplifying module, further includes: According to the relationship between the output voltage of the amplifying module and the preset threshold, the DC offset of the current at the input of the amplifying module is moved upward; and/or the gain of the amplifying module is increased.

The embodiments of the present application provide a front-end circuit and a method for calibrating a transmission signal, wherein the front-end circuit includes: an amplifying module for converting the received optical signal into a voltage and amplifying it; The relationship between the output voltage of the amplifying module and the preset threshold value, the gain of the amplifying module is adjusted, and the DC offset of the current at the input end of the amplifying module is adjusted to adjust the output of the amplifying module The voltage is calibrated; the analog-to-digital conversion module is used to convert the calibrated analog output voltage output by the amplifying module into a digital output voltage, so that the DC offset in the signal can be eliminated, and the gain of the amplifying module The adjustment of the signal will not overflow, so that no single signal will be lost, and the signal will become more robust with respect to motion and ambient light interference.

Description of the drawings

Figure 1A is a waveform diagram 1 of PPG signals of AFE equipment in the related art;

Figure 1B is the second waveform diagram of the PPG signal of the AFE device in the related art;

2A is a schematic diagram 1 of the composition structure of a front-end circuit according to an embodiment of the application;

2B is a second schematic diagram of the composition structure of the front-end circuit according to the embodiment of the application;

2C is the third schematic diagram of the composition structure of the front-end circuit according to the embodiment of the application;

FIG. 2D is a fourth schematic diagram of the composition structure of the front-end circuit according to the embodiment of the application; FIG.

3A is a schematic diagram 5 of the composition structure of the front-end circuit according to the embodiment of the application;

3B is a PPG signal waveform diagram of the front-end circuit in an embodiment of the application;

FIG. 4A is a first schematic diagram of the implementation process of the method for calibrating transmission signals according to an embodiment of the application;

FIG. 4B is a second schematic diagram of the implementation process of the method for calibrating a transmission signal according to an embodiment of this application.

detailed description

At present, the most widely used related technology is the AFE4400 device (AFE4400 is an integrated analog front end for heart rate monitors and low-cost pulse oximeters developed by Texas Instruments). AFE4400 is a fully integrated analog front end, perfect It is suitable for pulse oximeter application. The equipment includes a low-noise receiver channel integrated with ADC (Analog-to-Digital Converter), an LED transmission section, a debugger for sensor and LED fault detection, and a time controller whose time can be freely adjusted and configured. In order to alleviate time control requirements and provide AFE4400 with a low jitter clock, an oscillator running from an external crystal is also integrated. In addition, the device uses an SPI (Serial Peripheral Interface) interface to communicate with an external microcontroller or main processor.

In the analog signal chain of the device, first light is converted into current through PD (Photo-Diode), and then through TIA (Trans-Impedance Amplifier) and gain stage amplification, low-pass filtering, and finally guided to ADC and get digitized output. Due to different applications and ambient light interference, the input of the PD is unknown, so a large deviation can be seen at the PD current output. When a saturated or too small signal is detected at the ADC output, the calibration feedback loop of the device (that is, the loop control filter and the feedback loop of the ADC) is used to adjust the TIA gain and ADC compensation current to be within the entire ADC dynamic range Obtain the optimal AC (Alternating Current, alternating current) amplitude and remove the DC component.

However, in traditional AFE (Active Front End), such as the above-mentioned AFE4400 equipment, the calibration feedback is adjusted based on the digitized signal at the ADC output. Therefore, the ADC needs a long stabilization time to obtain a reliable signal. The reference signal is compared to determine whether the signal is too large or too small. Because when the signal in the ADC is detected to be saturated, a lot of data is needed to determine whether the ADC is working in the saturation stage. Moreover, since the decimator following the digital filter requires a lot of time to obtain reasonable data through a smaller clock frequency, it will lead to an even longer settling time required for the ADC. In addition, in the PPG signal processing of the AFE4400 device, because the DC component in the PD current is useless, the ADC also needs to estimate the DC offset and eliminate the offset at the TIA or gain stage. Therefore, in the traditional structure, stability and fast tracking need to be weighed.

Fig. 1A is a waveform diagram 1 of the PPG signal of an AFE device in the related art, as shown in Fig. 1A, which shows a typical example of how the PPG behaves during a user's exercise. Since PPG signals are highly sensitive to motion, how to overcome motion artifacts has become the most challenging problem. A common method in the related art is to eliminate adaptive noise by detecting the ADC output signal (such as AFE4400 equipment). However, due to the propagation delay, the calibration feedback loop cannot quickly react to signal changes, resulting in large deviations in the TIA output signal. In Figure 1A, the horizontal axis is time and the vertical axis is voltage. The dashed line 11 represents the upper limit of the response range, that is, the upper limit of the threshold. The lower limit of the response range, that is, the lower limit of the threshold coincides with the horizontal axis, and the solid line 12 is the measured voltage. It can be seen from the figure that due to the interference of motion and ambient light, the PPG signal has overflow or underflow at some time points or time periods as the PPG signal changes over time. This will cause part of the PPG signal to be lost, thereby detecting Inaccurate.

Figure 1B is the second waveform diagram of the PPG signal of the AFE device in the related technology. As shown in Figure 1B, when the ADC dynamic range is not fully used to keep the input signal within the ADC linear dynamic range, the full SNDR (Signal- to-Noise Distortion Ratio, signal-to-noise distortion ratio) to measure ADC performance. Although in this case, no signal overflow or underflow will occur, the quality of the signal obtained at the ADC output is poor. In Fig. 1B, the horizontal axis is time and the vertical axis is voltage. The dashed line 13 represents the upper limit of the response range, that is, the upper limit of the threshold. The lower limit of the response range, that is, the lower limit of the threshold coincides with the horizontal axis, and the solid line 14 is the measured voltage. It can be seen from the figure that although the signal does not overflow or underflow in any period of time, the signal change output by the ADC is very small and does not conform to the actual situation. In this way, the detection will still be inaccurate.

The technical solution of the present application will be further elaborated below with reference to the drawings and embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present application.

The embodiment of the application provides a new sensor front-end structure, which uses automatic correction technology of gain and DC signal. Compared with the traditional sensor front end, the structure of this solution does not require a digitized signal to detect whether the ADC of the sensor front end is in a saturated state or the SNR (Signal-to-Noise Ratio, signal-to-noise ratio) is too low. In this solution, the signal of the analog front end is automatically adjusted directly on the TIA. Therefore, the sensor in the embodiment of the present application has a strong anti-interference effect on the movement of the user and the pollution of external light.

An embodiment of the present application provides a front-end circuit. FIG. 2A is a first schematic diagram of the composition structure of the front-end circuit of the embodiment of the present application. As shown in FIG. 2A, the front-end circuit 200 includes:

The amplifying module 201 is used for converting the received optical signal into a voltage and amplifying it;

Here, the amplifying module can realize the functions of converting the received optical signal into current, converting the current into voltage, and amplifying the voltage signal.

In the embodiment of the present application, the amplifying module may be composed of a PD and a TIA, where the PD may convert the received optical signal into an electrical signal, that is, into a current. TIA can convert the current into voltage and amplify it. Of course, the amplifying module can be composed of other components, but as long as it can convert the received optical signal into a voltage and perform the amplifying function, it is within the protection scope of the present application.

The calibration module 202 is configured to adjust the gain of the amplifying module 201 according to the relationship between the output voltage of the amplifying module 201 and a preset threshold, and to adjust the DC offset of the current at the input end of the amplifying module 201 Adjust the output voltage to calibrate the output voltage of the amplifying module 201;

Here, the calibration module is connected between the amplifying module and the analog-to-digital conversion module, and is used to determine whether the output voltage of the amplifying module is within a linear range. If the output voltage of the amplifying module is not in the linear range, the gain of the amplifying module is adjusted, and the DC offset of the current at the input end of the amplifying module is adjusted to ensure that no single signal is lost And eliminate the DC offset.

The analog-to-digital conversion module 203 is configured to convert the calibrated analog output voltage output by the amplifying module 201 into a digital output voltage.

In the embodiment of the present application, the signal is adjusted and calibrated by the calibration module before the analog-to-digital conversion is performed. Then, the calibrated signal, that is, the analog output voltage, is converted into a digital voltage and output through the analog-to-digital conversion module.

In the embodiment of the present application, a front-end circuit is provided. The front-end circuit includes: an amplifying module for converting the received optical signal into a voltage and amplifying it; a calibration module for converting the received optical signal into a voltage and amplifying it; Adjust the gain of the amplifying module and adjust the DC offset of the current at the input end of the amplifying module to calibrate the output voltage of the amplifying module; The digital conversion module is used to convert the calibrated analog output voltage output by the amplifying module into a digital output voltage. In this way, the DC offset in the signal can be eliminated, and by adjusting the gain of the amplifying module, the signal There is no overflow, so no single signal is lost, and the signal becomes more robust with respect to motion and ambient light interference.

Based on the foregoing embodiment, the embodiment of the present application further provides a front-end circuit. FIG. 2B is a second schematic diagram of the composition structure of the front-end circuit of the embodiment of the present application. As shown in FIG. 2B, the front-end circuit 200 includes:

The input circuit 211 is used to convert the received optical signal into electric current;

Here, the input circuit may be a PD, and the input circuit can receive light signals (for example, light signals emitted by LEDs and interference signals of ambient light), and convert the received light signals into electric current.

The amplifying circuit 212 is configured to convert the current generated by the input circuit 211 into a voltage, and amplify it;

Here, the amplifying circuit may be a TIA, and the amplifying circuit can convert the current generated by the PD into a voltage, and amplify it within a certain gain range.

The calibration module 213 is used to adjust the gain of the amplifying circuit 212 according to the relationship between the output voltage of the amplifying circuit 212 and a preset threshold, and to adjust the DC offset of the current at the input end of the amplifying circuit 212 Adjust the output voltage to calibrate the output voltage of the amplifying circuit 212;

Here, the calibration module is connected between the amplifying circuit and the analog-to-digital conversion module, and is used to determine whether the output voltage of the amplifying circuit is within the linear range. If the output voltage of the amplifying circuit is not within the linear range, the gain of the amplifying circuit is adjusted to ensure that no single signal is lost, and the DC offset of the current at the input of the amplifying circuit is adjusted , To eliminate DC offset.

The analog-to-digital conversion module 214 is configured to convert the calibrated analog output voltage output by the amplifying circuit 212 into a digital output voltage.

In the embodiment of the present application, the analog-to-digital conversion module may be an ADC, which can convert the analog output voltage calibrated by the calibration module into a digital output voltage.

In the embodiment of the present application, by providing a front-end circuit, the front-end circuit includes: an input circuit for converting a received optical signal into a current; an amplifier circuit for converting a current generated by the input circuit into a voltage, And amplify; the calibration module is used to adjust the gain of the amplifying circuit according to the relationship between the output voltage of the amplifying circuit and a preset threshold, and to adjust the DC offset of the current at the input of the amplifying circuit The output voltage of the amplifying circuit can be adjusted to calibrate the output voltage of the amplifying circuit; the analog-to-digital conversion module is used to convert the calibrated analog output voltage output by the amplifying circuit into a digital output voltage. In this way, the signal can be eliminated. DC offset, and by adjusting the gain of the amplifying module, the signal will not overflow, so that a single signal will not be lost, and the signal becomes more robust with respect to motion and ambient light interference.

Based on the foregoing embodiment, an embodiment of the present application further provides a front-end circuit, and the front-end circuit includes:

The calibration module is configured to move the DC offset of the current at the input end of the amplifying module downward according to the relationship between the output voltage of the amplifying module and a preset threshold; and/or, make the amplifying module The gain is reduced to calibrate the output voltage of the amplifying module;

Here, when the amplifying module includes TIA, the calibration module can be used to adjust the current source of the TIA input stage to make the TIA input when the output voltage of the TIA is not within the linear range. The DC offset of the current at the terminal goes down to eliminate the DC offset. It is also possible to reduce the gain of the TIA by adjusting the feedback resistance of the TIA to ensure that no single signal is lost.

The calibration module is further configured to move the DC offset of the current at the input end of the amplifying module upward according to the relationship between the output voltage of the amplifying module and a preset threshold; and/or, make the amplifying module Increase the gain to calibrate the output voltage of the amplifying module;

Here, when the amplifying module includes TIA, the calibration module can be used to adjust the current source of the TIA input stage to make the TIA input when the output voltage of the TIA is not within the linear range. The DC offset of the current at the end goes upward to eliminate the DC offset. It is also possible to increase the gain of the TIA by adjusting the feedback resistance of the TIA to ensure that no single signal is lost.

In some embodiments, the preset threshold includes a first preset threshold and a second preset threshold, and the first preset threshold is greater than the second preset threshold;

The calibration module is configured to move the DC offset of the current at the input end of the amplifying module downward when the output voltage is greater than the first preset threshold; and/or, to change the gain of the amplifying module Small to calibrate the output voltage of the amplifying module;

The calibration module is further configured to move the DC offset of the current at the input end of the amplifying module upward when the output voltage is less than the second preset threshold; and/or, to change the gain of the amplifying module Large to calibrate the output voltage of the amplifying module.

In the embodiment of the present application, the preset threshold may be the response range of the signal. Correspondingly, the first preset threshold may be the upper limit of the response range, and the second preset threshold may be Is the lower limit of the response range. When the output voltage of the amplifying module is greater than the first preset threshold value, it indicates that the signal is overflowing, and when the output voltage of the amplifying module is less than the second preset threshold value, it indicates that the signal is underflowing. When the signal overflows or underflows, it will lead to inaccurate detection results of physiological parameters such as heart rate.

Therefore, when there is an overflow, the calibration module can adjust and calibrate the DC offset of the current at the input end of the amplifying module to move downward, and to reduce the gain of the amplifying module. When underflow occurs, the calibration module can adjust and calibrate the DC offset of the current at the input end of the amplifying module to move upward, and to increase the gain of the amplifying module.

Based on the foregoing embodiment, the embodiment of the present application further provides a front-end circuit. FIG. 2C is a schematic diagram of the composition structure of the front-end circuit according to the embodiment of the present application. As shown in FIG. 2C, the front-end circuit 200 includes:

The amplifying module 221 is used for converting the received optical signal into a voltage and amplifying it;

The comparator 222 is configured to determine whether the output voltage of the amplifying module 221 is greater than the first preset threshold or less than the second preset threshold;

Here, a comparator can be used to realize the function of determining whether the output voltage of the amplifying module is greater than the first preset threshold or less than the second preset threshold, that is, the comparator can be used to determine whether the output voltage of the amplifying module is Beyond the linear range, an overflow of the signal occurred.

The control circuit 223 is configured to generate a first control signal when the output voltage is greater than the first preset threshold, and generate a second control signal when the output voltage is less than the second preset threshold;

Here, the control circuit may generate a first control signal or a second control signal according to the comparison result of the comparator, so as to adjust and calibrate the overflow and underflow of the signal respectively.

The first adjustment circuit 224 is configured to move the DC offset of the current at the input terminal of the amplifying module 221 downward according to the first control signal; and/or, reduce the gain of the amplifying module 221;

Here, the first adjustment circuit can realize the function of directly adjusting the DC offset of the front-end circuit and the gain of the amplifier module when the output signal of the amplifier overflows.

The second adjustment circuit 225 is configured to move the DC offset of the current at the input end of the amplifying module 221 upward according to the second control signal; and/or, increase the gain of the amplifying module 221;

Here, the second adjustment circuit can realize the function of directly adjusting the DC offset of the front-end circuit and the gain of the amplifying module when the output signal of the amplifier underflows.

The analog-to-digital conversion module 226 is used to convert the calibrated analog output voltage into a digital output voltage.

In the embodiment of the present application, a front-end circuit is provided. The front-end circuit includes: an amplifying module for converting a received optical signal into a voltage and amplifying it; a comparator for determining the output voltage of the amplifying module Whether it is greater than the first preset threshold or less than the second preset threshold; a control circuit for generating a first control signal when the output voltage is greater than the first preset threshold, and when the output voltage is less than The second control signal is generated when the second preset threshold value; the first adjustment circuit is configured to move the DC offset of the current at the input end of the amplifying module downward according to the first control signal; and/or, The gain of the amplifying module is reduced; a second adjustment circuit is configured to move the DC offset of the current at the input end of the amplifying module upward according to the second control signal; and/or, to make the gain of the amplifying module The analog-to-digital conversion module is used to convert the calibrated analog output voltage into a digital output voltage. In this way, the DC offset in the signal can be eliminated, and the gain of the amplifying module is adjusted so that the signal will not Overflow, so that no single signal is lost, the signal becomes more robust with respect to motion and ambient light interference.

Here, the amplifying module includes a current source of an input stage and a feedback resistance circuit.

Here, the comparator is connected between the amplifying module and the analog-to-digital conversion module, and is used to determine whether the output voltage of the amplifying circuit is within a linear range.

Here, the control circuit is connected between the comparator and the adjustment circuit, and is used to generate a control signal when the comparator determines that the output voltage of the amplifying circuit is not within the linear range to control the first adjustment circuit or the second adjustment circuit. The second adjustment circuit adjusts the DC offset of the input end of the amplifier circuit, and adjusts the feedback resistance of the amplifier circuit.

The first adjustment circuit is configured to adjust the current source of the input stage according to the first control signal, so that the DC offset of the current at the input end of the amplifying module moves downward; and/or, feedback to the The resistance circuit is adjusted to make the gain of the amplifying module smaller;

Here, the first adjustment circuit is used to adjust the current source of the input stage of the amplifying circuit and the feedback resistance of the amplifying circuit when the output voltage of the amplifying circuit overflows, so as to eliminate the DC offset and ensure that no single unit is lost. signal. The current source of the input stage of the amplifying circuit may be a differential current source.

The second adjustment circuit is configured to adjust the current source of the input stage according to the second control signal, so that the DC offset of the current at the input end of the amplifying module moves upward; and/or, the feedback resistor The circuit is adjusted to increase the gain of the amplifying module;

Here, the second adjustment circuit is used to adjust the current source of the input stage of the amplifying circuit and the feedback resistance of the amplifying circuit when the output voltage of the amplifying circuit underflows, so as to eliminate the DC offset and ensure that no single unit is lost. signal.

In some embodiments, the feedback resistor circuit includes a feedback capacitor resistor array formed by capacitors, resistors, and switches;

In the embodiment of the present application, the feedback resistance circuit includes at least one capacitor, at least one resistor, and at least one switch. The adjustment circuit can control the opening and closing of multiple switches according to different control signals, so that the feedback resistance circuit has different feedback resistances in different situations, and correspondingly, the amplifying circuit has different feedback resistances in different situations. The gain. Wherein, the resistor is used to adjust the gain, and the capacitor is mainly used to cooperate with the low-pass resistor to eliminate noise.

The analog-to-digital conversion module is used to convert the calibrated analog output voltage into a digital output voltage.

Based on the foregoing embodiment, the embodiment of the present application further provides a front-end circuit. FIG. 2D is a schematic diagram of the composition structure of the front-end circuit according to the embodiment of the present application. As shown in FIG. 2D, the front-end circuit 200 includes:

The amplifying module 231 is used for converting the received optical signal into a voltage and amplifying it;

The calibration module 232 is configured to adjust the gain of the amplifying module 231 according to the relationship between the output voltage of the amplifying module 231 and a preset threshold, and to adjust the DC offset of the current at the input end of the amplifying module 231 Adjust the output voltage to calibrate the output voltage of the amplifying module 231;

The analog-to-digital conversion module 233 is configured to convert the calibrated analog output voltage output by the amplifying module 231 into a digital output voltage;

The output module 234 is used to read and write the digital output voltage according to the first-in first-out principle.

Here, the output module may be a FIFO (First Input First Output) circuit, which is used to output the received digital signal on a first-in first-out principle.

In the embodiment of the present application, a front-end circuit is provided. The front-end circuit includes: an amplifying module for converting a received optical signal into a voltage and amplifying it; a calibration module for converting a received optical signal into a voltage according to the output voltage of the amplifying module Adjust the gain of the amplifying module and adjust the DC offset of the current at the input end of the amplifying module to calibrate the output voltage of the amplifying module; The digital conversion module is used to convert the calibrated analog output voltage output by the amplifying module into a digital output voltage; the output module is used to read and write the digital output voltage according to the first-in-first-out principle. The DC offset in the signal is eliminated, and the gain of the amplifying module is adjusted so that the signal does not overflow, so that a single signal is not lost, and the signal becomes more robust with respect to motion and ambient light interference.

Based on the foregoing embodiment, the embodiment of the present application further provides a front-end circuit to implement a TIA-level automatic gain and DC offset calibration analog front end. The digitized signal in the front-end circuit does not participate in the calibration loop. The entire AFE is based on a completely different architecture. The TIA converts the PD current into a voltage, and the voltage is directly guided to the threshold detection circuit. FIG. 3A is a schematic diagram of the composition structure of the front-end circuit according to the embodiment of the application. As shown in FIG. 3A, the front-end circuit 300 includes: PD 301, TIA 302, comparator 303, controller 304, regulator 305, and A/D conversion 306 (ie ADC) and FIFO 307, where:

The PD 301 converts the received optical signal into electric current. The TIA 302 converts the current generated by the PD 301 into voltage. The high-level threshold V _TH and the low-level threshold V _TL in the comparator 303 are used to detect whether the output voltage of the TIA 302 is within the linear range. When an overflow or underflow occurs, the controller 304 generates a control signal and transmits it to the regulator 305, and the regulator 305 uses the control signal to adjust the current source 3051 of the input stage of the TIA 302. For example, when the output voltage of the TIA 302 is greater than V _TH , the current will be adjusted so that the DC offset input by the TIA 302 is reduced, thereby forming an effective negative feedback. Wherein, the regulator 305 includes a current source 3051 and a feedback resistor circuit 3052.

The overflow and underflow thresholds (ie, the high-level threshold V _TH and the low-level threshold V _TL ) are programmable, and usually still leave some margin for the saturation voltage of the ADC (ie, the A/D converter 306 ). Therefore, no single signal is lost during any movement. The same principle can be used to eliminate DC offset. The digital signal output by the A/D converter 306 passes through the FIFO 307 for reading and writing output.

On the other hand, the front-end circuit 300 adjusts the gain of the TIA 302 by using different capacitors and resistor arrays, so that the optimal dynamic range of the ADC can be used. The capacitor and resistor arrays are the feedback resistor circuit 3052 of the TIA 302. Arrays of capacitors and resistors.

Fig. 3B is a PPG signal waveform diagram of the front-end circuit in the embodiment of the application. As shown in Fig. 3B, the horizontal axis is time, the vertical axis is voltage, and the dashed line 31 represents the upper limit of the response range, that is, the upper limit of the threshold. The lower limit, that is, the lower limit of the threshold coincides with the horizontal axis, and the solid line 32 is the measured voltage. Without any help from the digital domain, the front-end circuit in the embodiments of the present application can automatically adjust and calibrate the pure analog signal, so that the PD current can be directly and quickly adjusted within the detectable range.

The embodiment of the application provides a new front-end circuit, which makes the PPG signal more robust with respect to motion and ambient light interference, and can overcome when the user wears loosely, the peripheral ambient light will enter, thereby affecting the DC of the TIA input terminal. The problem. At the same time, it can also overcome the problem that when the user's detection device is close to the skin for a while and away from the skin for a while, the PPG signal strength is different. Therefore, in a typical use case such as jogging, the user does not need to tighten the wearable watch to the skin, but can still obtain a reliable PPG signal. At the same time, in the case of high acceleration such as throwing or falling, the PPG signal can be quickly adjusted in the analog domain so that a single signal will not be lost.

Based on the foregoing embodiment, an embodiment of the present application provides a method for calibrating a transmission signal, which is applied to a front-end circuit. FIG. 4A is a schematic diagram 1 of the implementation flow of the calibration method for a transmission signal according to an embodiment of this application, as shown in FIG. 4A. As shown, the method includes:

Step S401: Use the amplifying module of the front-end circuit to convert the received optical signal into a voltage, and amplify it;

In some embodiments, the step S401, using the amplifying module of the front-end circuit to convert the received optical signal into a voltage, and amplify it, can be implemented in the following manner:

Step S4011, using the input circuit of the amplifying module to convert the received optical signal into a current;

Step S4012, using the amplifying circuit of the amplifying module to convert the current generated by the input circuit into a voltage, and amplify it.

Step S402: Adjust the gain of the amplifying module according to the relationship between the output voltage of the amplifying module and the preset threshold, and adjust the DC offset of the current at the input end of the amplifying module to adjust Calibrating the output voltage of the amplifying module;

In some embodiments, in step S402, the gain of the amplifying module is adjusted according to the relationship between the output voltage of the amplifying module and a preset threshold, and the DC of the current at the input of the amplifying module is adjusted. The adjustment of the offset can be achieved in the following manner: step S402a, according to the relationship between the output voltage of the amplifying module and a preset threshold, move the DC offset of the current at the input of the amplifying module downward; and/ Or, make the gain of the amplifying module smaller;

In some embodiments, in step S402, the gain of the amplifying module is adjusted according to the relationship between the output voltage of the amplifying module and a preset threshold, and the DC current at the input of the amplifying module is adjusted. The adjustment of the offset can also be achieved in the following manner: step S402b, according to the relationship between the output voltage of the amplifying module and a preset threshold, move the DC offset of the current at the input of the amplifying module upward; and/ Or, make the gain of the amplifying module larger.

Correspondingly, in step S402a, according to the relationship between the output voltage of the amplifying module and the preset threshold, the DC offset of the current at the input end of the amplifying module is moved downward; and/or, the amplifying module is The decrease in the gain of the amplifier includes: when the output voltage is greater than the first preset threshold, the DC offset of the current at the input end of the amplifying module is moved downward; and/or the gain of the amplifying module is changed small;

Correspondingly, in step S402b, according to the relationship between the output voltage of the amplifying module and the preset threshold, the DC offset of the current at the input end of the amplifying module is moved upward; Increasing the gain includes: when the output voltage is less than the second preset threshold, moving the DC offset of the current at the input end of the amplifying module upward; and/or increasing the gain of the amplifying module.

Step S403: Convert the calibrated analog output voltage output by the amplifying module into a digital output voltage.

Based on the foregoing embodiment, the embodiment of the present application further provides a method for calibrating a transmission signal, and the method is applied to a front-end circuit. FIG. 4B is a second schematic diagram of the implementation process of the calibration method for a transmission signal according to the embodiment of this application, as shown in FIG. 4B As shown, the method includes:

Step S411: Use the amplifying module of the front-end circuit to convert the received optical signal into voltage, and amplify it;

Step S412: Determine whether the output voltage of the amplifying module is greater than the first preset threshold or less than the second preset threshold;

Step S413: Generate a first control signal when the output voltage is greater than the first preset threshold, and generate a second control signal when the output voltage is less than the second preset threshold;

Step S414: According to the first control signal, the DC offset of the current at the input end of the amplifying module is moved downward; and/or, the gain of the amplifying module is reduced to reduce the output voltage of the amplifying module. Carry out calibration;

Step S415: According to the second control signal, the DC offset of the current at the input end of the amplifying module is moved upward; and/or the gain of the amplifying module is increased so as to adjust the output voltage of the amplifying module. calibration;

In some embodiments, the amplifying module includes a current source of an input stage and a feedback resistance circuit;

Correspondingly, the step S414, moving the DC offset of the current at the input end of the amplifying module downward according to the first control signal; and/or reducing the gain of the amplifying module, includes: The first control signal adjusts the current source of the input stage to move the DC offset of the current at the input end of the amplifying module downward; and/or adjusts the feedback resistance circuit so that the The gain of the amplifying module becomes smaller;

Correspondingly, in step S415, moving the DC offset of the current at the input end of the amplifying module upward according to the second control signal; and/or increasing the gain of the amplifying module includes: according to the The second control signal adjusts the current source of the input stage to move the DC offset of the current at the input end of the amplifying module upward; and/or adjusts the feedback resistance circuit so that the amplifying module The gain becomes larger.

Correspondingly, the front-end circuit adjusts the gain of the amplifying module by using the feedback capacitor resistor array.

Step S416: Convert the calibrated analog output voltage output by the amplifying module into a digital output voltage.

In some embodiments, the method further includes: step S41, reading and writing the digital output voltage according to the first-in-first-out principle.

The description of the above method embodiment is similar to the description of the above circuit embodiment, and has similar beneficial effects as the circuit embodiment. For technical details not disclosed in the method embodiment of this application, please refer to the description of the circuit embodiment of this application for understanding.

It should be noted that, in the embodiments of the present application, if the above-mentioned transmission signal calibration method is implemented in the form of a software function module and sold or used as an independent product, it can also be stored in a computer readable storage medium. Based on this understanding, the technical solutions of the embodiments of the present application can be embodied in the form of a software product in essence or a part that contributes to the prior art. The computer software product is stored in a storage medium and includes several instructions for An electronic device (which may be a personal computer, a server, etc.) executes all or part of the methods described in the various embodiments of the present application. The aforementioned storage media include: U disk, mobile hard disk, ROM (Read Only Memory), magnetic disk or optical disk and other media that can store program codes. In this way, the embodiments of the present application are not limited to any specific combination of hardware and software.

In the several embodiments provided in this application, it should be understood that the disclosed circuit and method can be implemented in other ways. The circuit embodiments described above are merely illustrative. For example, the division of the units is only a logical function division, and there may be other divisions in actual implementation, such as: multiple units or components can be combined, or It can be integrated into another system, or some features can be ignored or not implemented. In addition, the coupling, or direct coupling, or communication connection between the components shown or discussed may be indirect coupling or communication connection through some interfaces, devices or units, and may be in electrical, mechanical or other forms. of.

The units described above as separate components may or may not be physically separate, and the components displayed as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units; Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of the embodiment.

In addition, the functional units in the embodiments of the present application can be all integrated into one processing module, or each unit can be individually used as a unit, or two or more units can be integrated into one unit; the above-mentioned integration The unit can be implemented in the form of hardware, or in the form of hardware plus software functional units. A person of ordinary skill in the art can understand that all or part of the steps in the above method embodiments can be implemented by a program instructing relevant hardware. The foregoing program can be stored in a computer readable storage medium. When the program is executed, it is executed. It includes the steps of the above method embodiment.

The methods disclosed in the several method embodiments provided in this application can be combined arbitrarily without conflict to obtain new method embodiments.

The features disclosed in the several product embodiments provided in this application can be combined arbitrarily without conflict to obtain new product embodiments.

The features disclosed in the several method or device embodiments provided in this application can be combined arbitrarily without conflict to obtain a new method embodiment or device embodiment.

The above are only specific implementations of this application, but the protection scope of this application is not limited to this. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed in this application. Should be covered within the scope of protection of this application. Therefore, the protection scope of this application should be subject to the protection scope of the claims.

Claims

A front-end circuit, wherein the front-end circuit includes:

Amplifying module, used to convert the received optical signal into voltage and amplify it;

The calibration module is used to adjust the gain of the amplifying module according to the relationship between the output voltage of the amplifying module and a preset threshold, and to adjust the DC offset of the current at the input end of the amplifying module, To calibrate the output voltage of the amplifying module;

The analog-to-digital conversion module is used to convert the calibrated analog output voltage output by the amplifying module into a digital output voltage.
The front-end circuit according to claim 1, wherein the amplifying module comprises:

Input circuit, used to convert the received optical signal into electric current;

The amplifying circuit is used for converting the current generated by the input circuit into a voltage and amplifying it.
The front-end circuit according to claim 1, wherein the calibration module is configured to make the DC offset of the current at the input end of the amplifying module downward according to the relationship between the output voltage of the amplifying module and a preset threshold. Move; and/or make the gain of the amplifying module smaller;

The calibration module is further configured to move the DC offset of the current at the input end of the amplifying module upward according to the relationship between the output voltage of the amplifying module and a preset threshold; and/or, make the amplifying module The gain becomes larger.
The front-end circuit according to claim 3, wherein the preset threshold includes a first preset threshold and a second preset threshold, and the first preset threshold is greater than the second preset threshold;

The calibration module is configured to move the DC offset of the current at the input end of the amplifying module downward when the output voltage is greater than the first preset threshold; and/or, to change the gain of the amplifying module small;

The calibration module is further configured to move the DC offset of the current at the input end of the amplifying module upward when the output voltage is less than the second preset threshold; and/or, to change the gain of the amplifying module Big.
The front-end circuit according to claim 4, wherein the calibration module comprises:

A comparator, configured to determine whether the output voltage of the amplifying module is greater than the first preset threshold or less than the second preset threshold;

A control circuit for generating a first control signal when the output voltage is greater than the first preset threshold, and generating a second control signal when the output voltage is less than the second preset threshold;

The first adjustment circuit is configured to move the DC offset of the current at the input end of the amplifying module downward according to the first control signal; and/or, reduce the gain of the amplifying module;

The second adjustment circuit is used to move the DC offset of the current at the input end of the amplifying module upward according to the second control signal; and/or to increase the gain of the amplifying module.
The front-end circuit according to claim 5, wherein the amplifying module includes a current source of an input stage and a feedback resistor circuit;

Correspondingly, the first adjustment circuit is configured to adjust the current source of the input stage according to the first control signal, so that the DC offset of the current at the input end of the amplifying module moves downward; and/or , Adjusting the feedback resistance circuit to make the gain of the amplifying module smaller;

Correspondingly, the second adjustment circuit is configured to adjust the current source of the input stage according to the second control signal, so that the DC offset of the current at the input end of the amplifying module moves upward; and/or, The feedback resistance circuit is adjusted to increase the gain of the amplifying module.
7. The front-end circuit according to claim 6, wherein the feedback resistor circuit comprises a feedback capacitor resistor array formed by capacitors, resistors and switches;

Correspondingly, the first adjustment circuit or the second adjustment circuit adjusts the gain of the amplifying module by using the feedback capacitor resistor array.
The front-end circuit according to claim 1, wherein the front-end circuit further comprises:

The output module is used to read and write the digital output voltage according to the first-in first-out principle.
A calibration method for transmission signals, wherein the method is applied to a front-end circuit, and the method includes:

Use the amplifying module of the front-end circuit to convert the received optical signal into voltage and amplify it;

According to the relationship between the output voltage of the amplifying module and the preset threshold, the gain of the amplifying module is adjusted, and the DC offset of the current at the input end of the amplifying module is adjusted to adjust the amplifying The output voltage of the module is calibrated;

The calibrated analog output voltage output by the amplifying module is converted into a digital output voltage.
The method according to claim 9, wherein the conversion of the received optical signal into a voltage by the amplifying module of the front-end circuit and amplifying it comprises:

Using the input circuit of the amplifying module to convert the received optical signal into current;

The amplifying circuit of the amplifying module converts the current generated by the input circuit into a voltage, and amplifies it.
The method according to claim 9, wherein the gain of the amplifying module is adjusted according to the relationship between the output voltage of the amplifying module and a preset threshold, and the current at the input of the amplifying module is adjusted Adjusting the DC offset of the amplifying module includes: moving the DC offset of the current at the input end of the amplifying module downward according to the relationship between the output voltage of the amplifying module and a preset threshold; and/or, making the The gain of the amplifying module becomes smaller;

The adjusting the gain of the amplifying module according to the relationship between the output voltage of the amplifying module and the preset threshold value, and adjusting the DC offset of the current at the input end of the amplifying module, further includes: According to the relationship between the output voltage of the amplifying module and the preset threshold, the DC offset of the current at the input of the amplifying module is moved upward; and/or the gain of the amplifying module is increased.