CN114424034B - Front-end circuit and calibration method of transmission signal - Google Patents
Front-end circuit and calibration method of transmission signal Download PDFInfo
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- G—PHYSICS
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- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J1/00—Photometry, e.g. photographic exposure meter
- G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
- G01J1/44—Electric circuits
Abstract
A front-end circuit and a method of calibrating a transmission signal, wherein the method comprises: converting the received optical signal into a voltage by using an amplifying module of the front-end circuit, and amplifying (S401); according to the relation between the output voltage of the amplifying module and a 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 so as to calibrate the output voltage of the amplifying module (S402); the calibrated analog output voltage output by the amplifying module is converted into a digital output voltage (S403).
Description
Technical Field
The embodiment of the application relates to an electronic technology, in particular to a front-end circuit and a calibration method of a transmission signal.
Background
PPG (photoplethysmosraph) is widely used to detect changes in blood volume in the microvascular bed of tissue. PPG is typically obtained by using a pulse oximeter that illuminates the skin and measures the change in light absorption, and a conventional pulse oximeter monitors the perfusion of blood to the subcutaneous tissue and dermis of the skin. The change in volume caused by the pressure pulse is detected 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. PPG can also be used to monitor respiration, hypovolemia, and other blood circulation conditions, as blood flow to the skin can be regulated by many other physiological systems. In addition, the shape of the PPG waveform varies from subject to subject and varies depending on the location and manner in which the pulse oximeter is attached.
Currently, PPG principles have been applied on a large number of wearable devices, as PPG signals are a simple, effective, non-invasive means of detecting heart rate. However, during the motion of the user, the PPG signal is often disturbed by the motion signal. Taking a wristwatch as an example, if the user does not tightly bind the wristwatch to the skin surface, the light emitted by the LEDs in the PPG will be disturbed by ambient light, and the sensor will not receive a clean usable signal, which will have a significant impact on the detection result. Therefore, how to make the PPG signal more robust against interference of motion and ambient light is a technical problem to be solved by the person skilled in the art.
Disclosure of Invention
In view of the above, the embodiment of the application provides a front-end circuit and a calibration method of a transmission signal.
The technical scheme of the embodiment of the application is realized as follows:
in a first aspect, an embodiment of the present application provides a front-end circuit, including:
the amplifying module is used for converting the received optical signal into voltage and amplifying the voltage;
the calibration module is used for adjusting the gain of the amplification module according to the relation between the output voltage of the amplification module and a preset threshold value, and adjusting the DC (Direct Current) offset of the Current at the input end of the amplification module so as to calibrate the output voltage of the amplification module;
And the analog-to-digital conversion module is used for converting the calibrated analog output voltage output by the amplification module into a digital output voltage.
In an embodiment of the present application, the amplifying module includes:
an input circuit for converting a received optical signal into a current;
and the amplifying circuit is used for converting the current generated by the input circuit into voltage and amplifying the voltage.
In the embodiment of the application, the calibration module is used for enabling DC offset of current at the input end of the amplifying module to move downwards according to the relation between the output voltage of the amplifying module and a preset threshold value; and/or, reducing the gain of the amplifying module;
the calibration module is further used for enabling DC offset of current at the input end of the amplifying module to move upwards according to the relation between the output voltage of the amplifying module and a preset threshold value; and/or, the gain of the amplifying module is increased.
In the embodiment of the application, the preset threshold comprises a first preset threshold and a second preset threshold, and the first preset threshold is larger than the second preset threshold;
the calibration module is used for enabling DC offset of current at the input end of the amplifying module to move downwards when the output voltage is larger than the first preset threshold value; and/or, reducing 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 when the output voltage is less than the second preset threshold; and/or, the gain of the amplifying module is increased.
In an embodiment of the present application, the calibration module includes:
a comparator for determining whether the output voltage of the amplifying module is greater than the first preset threshold or less than the second preset threshold;
the control circuit is used for generating a first control signal when the output voltage is larger than the first preset threshold value and generating a second control signal when the output voltage is smaller than the second preset threshold value;
the first adjusting circuit is used for enabling the DC offset of the current at the input end of the amplifying module to move downwards according to the first control signal; and/or, reducing the gain of the amplifying module;
the second adjusting circuit is used for enabling the DC offset of the current at the input end of the amplifying module to move upwards according to the second control signal; and/or, the gain of the amplifying module is increased.
In the embodiment of the application, the amplifying module comprises a current source and a feedback resistance circuit of an input stage;
correspondingly, the first adjusting circuit is used for adjusting the current source of the input stage according to the first control signal so as to enable the DC offset of the current at the input end of the amplifying module to move downwards; and/or adjusting the feedback resistance circuit to reduce the gain of the amplifying module;
Correspondingly, the second adjusting circuit is used for adjusting the current source of the input stage according to the second control signal so as to enable the DC offset of the current at the input end of the amplifying module to move upwards; and/or adjusting the feedback resistance circuit to make the gain of the amplifying module larger.
In the embodiment of the application, the feedback resistor circuit comprises a feedback capacitor resistor array formed by a capacitor, a resistor and a switch;
correspondingly, the first adjusting circuit or the second adjusting circuit adjusts the gain of the amplifying module by using the feedback capacitance-resistance array.
In an embodiment of the present application, the front-end circuit further includes:
and the output module is used for reading, writing and outputting the digital output voltage according to the first-in first-out principle.
In a second aspect, an embodiment of the present application provides a calibration method for a transmission signal, where the method is applied to a front-end circuit, and the method includes:
converting the received optical signal into voltage by using an amplifying module of the front-end circuit, and amplifying the voltage;
according to the relation between the output voltage of the amplifying module and a 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;
The calibrated analog output voltage is converted into a digital output voltage.
In an embodiment of the present application, the amplifying module using the front-end circuit converts a received optical signal into a voltage and amplifies the voltage, including:
converting the received optical signal into a current by using an input circuit of the amplifying module;
and converting the current generated by the input circuit into voltage by using an amplifying circuit of the amplifying module, and amplifying the voltage.
In the embodiment of the present application, the adjusting the gain of the amplifying module according to the relation between the output voltage of the amplifying module and the preset threshold value, and the adjusting the DC offset of the current at the input end of the amplifying module includes: according to the relation between the output voltage of the amplifying module and a preset threshold value, the DC offset of the current at the input end of the amplifying module is downwards moved; and/or, reducing the gain of the amplifying module;
the method for adjusting the gain of the amplifying module according to the relation between the output voltage of the amplifying module and a preset threshold value, adjusting the DC offset of the current at the input end of the amplifying module, and further comprises the following steps: according to the relation between the output voltage of the amplifying module and a preset threshold value, the DC offset of the current at the input end of the amplifying module is moved upwards; and/or, the gain of the amplifying module is increased.
The embodiment of the application provides a front-end circuit and a calibration method of transmission signals, wherein the front-end circuit comprises the following components: the amplifying module is used for converting the received optical signal into voltage and amplifying the voltage; the calibration module is used for adjusting the gain of the amplification module according to the relation between the output voltage of the amplification module and a preset threshold value, and adjusting the DC offset of the current at the input end of the amplification module so as to calibrate the output voltage of the amplification module; and the analog-to-digital conversion module is used for converting the calibrated analog output voltage output by the amplification module into a digital output voltage, so that DC offset in the signal can be eliminated, and the signal cannot overflow through adjusting the gain of the amplification module, so that a single signal cannot be lost, and the signal becomes more robust relative to motion and ambient light interference.
Drawings
FIG. 1A is a waveform diagram of a PPG signal of an AFE device in the related art;
FIG. 1B is a second waveform diagram of the PPG signal of an AFE device in the related art;
FIG. 2A is a schematic diagram of a front-end circuit according to an embodiment of the present application;
FIG. 2B is a schematic diagram of a front-end circuit according to a second embodiment of the present application;
FIG. 2C is a schematic diagram of a front-end circuit according to an embodiment of the present application;
fig. 2D is a schematic diagram of a front-end circuit according to an embodiment of the present application;
FIG. 3A is a schematic diagram showing a front-end circuit according to an embodiment of the present application;
fig. 3B is a PPG signal waveform diagram of the front-end circuit according to an embodiment of the present application;
fig. 4A is a schematic diagram of an implementation flow of a calibration method for transmitting signals according to an embodiment of the present application;
fig. 4B is a schematic diagram illustrating a second implementation flow of the calibration method of the transmission signal according to the embodiment of the present application.
Detailed Description
Currently, a relatively wide range of AFE4400 devices (AFE 4400 is an integrated analog front end developed by texas instruments for heart rate monitors and low cost pulse oximeters) are used in the related art, and AFE4400 is a fully integrated analog front end perfectly suited for pulse oximeter applications. The device comprises a low-noise receiver channel integrated with an ADC (Analog-to-Digital Converter, an LED transmission section, a sensor and a debugging instrument for LED fault detection, and a time controller with time freely controllable and configurable. To alleviate the time control requirements and provide the AFE4400 with a low jitter clock, an oscillator running from an external crystal is also integrated. Also, the device communicates with an external microcontroller or host processor using an SPI (Serial Peripheral Interface ) interface.
In the analog signal chain of the device, light is first converted into current by a PD (Photo-Diode), then amplified and low-pass filtered by TIA (Trans-Impedance Amplifier, transimpedance amplifier) and gain stages, and finally guided into an ADC and digitized output is obtained. Large deviations can be seen at the PD current output due to different applications and ambient light disturbances, which render the input of the PD unknown. When a saturated or too small signal is detected at the ADC output, the calibration feedback loop of the device (i.e., the loop control filter and the feedback loop of the ADC) is used to adjust TIA gain and ADC compensation current to obtain optimal AC (Alternating Current ) amplitude and remove DC components throughout the ADC dynamic range.
However, in conventional AFE (Active Front End), such as the above-described AFE4400 device, the calibration feedback is adjusted based on the digitized signal at the ADC output, so the ADC requires a long settling time to obtain a reliable signal to determine whether the signal is too large or too small compared to the reference signal. Since when saturation of the signal in the ADC is detected, a plurality of data is required to determine whether the ADC is operating in the saturation phase. Also, since the decimator that follows in the digital filter requires much time to obtain reasonable data with a smaller clock frequency, it will result in an even longer settling time required for the ADC. In addition, the AFE4400 device is not useful in PPG signal processing, since the DC component in the PD current is not useful, the ADC also needs to estimate the DC offset and cancel it at the TIA or gain stage. Thus, in conventional arrangements, stability and fast tracking are required to be weighed.
Fig. 1A is a PPG signal waveform diagram of an AFE device in the related art, as shown in fig. 1A, which shows a typical example of how PPG behaves during user exercise. Since PPG signals are highly sensitive to motion, how to overcome motion artifacts becomes one of the most challenging problems. One common approach in the related art is to eliminate adaptive noise (e.g., AFE4400 devices) by detecting the ADC output signal. However, due to propagation delay, the calibration feedback loop cannot react quickly to signal variations, resulting in large deviations in the TIA output signal. In fig. 1A, the horizontal axis represents time, the vertical axis represents voltage, the broken line 11 represents the upper limit of the response range, i.e., the upper limit of the threshold, wherein the lower limit of the response range, i.e., the lower limit of the threshold coincides with the horizontal axis, and the solid line 12 represents the measured voltage. It can be seen from the figure that, due to motion and interference of ambient light, the PPG signal changes over time, and at some point or period of time, overflow or underflow occurs, which will result in partial PPG signal loss, thus inaccurate detection.
Fig. 1B is a PPG Signal waveform diagram of an AFE device in the related art, as shown in fig. 1B, when the ADC dynamic range is not fully used to keep the input Signal within the ADC linear dynamic range, the performance of the ADC cannot be measured using the overall SNDR (Signal-to-Noise Distortion Ratio) of the ADC. Although in this case no signal overflow or underflow will occur, the signal quality obtained at the ADC output is poor. In fig. 1B, the horizontal axis represents time, the vertical axis represents voltage, the broken line 13 represents the upper limit of the response range, i.e., the upper limit of the threshold, wherein the lower limit of the response range, i.e., the lower limit of the threshold coincides with the horizontal axis, and the solid line 14 represents the measured voltage. As can be seen from the figure, although the signal does not overflow or underflow during any period of time, the signal output from the ADC varies very little and is not practical, which still results in inaccurate detection.
The technical scheme of the application is further elaborated below with reference to the drawings and examples. It will be apparent that the described embodiments are only some, but not all, embodiments of the application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to fall within the scope of the application.
The embodiment of the application provides a novel structure of the front end of a sensor, which uses the automatic correction technology of gain and DC signals. Compared with the traditional sensor front end, the structure of the scheme does not need a digitized Signal to detect whether the ADC of the sensor front end is in a saturated state or has an excessively low Signal-to-Noise Ratio (SNR). In the scheme, the signal of the analog front end is directly and automatically adjusted on the TIA, so that the sensor in the embodiment of the application has strong anti-interference effect on the movement of a user and the pollution of external light.
An embodiment of the present application provides a front-end circuit, fig. 2A is a schematic diagram of a composition structure of the front-end circuit, as shown in fig. 2A, and the front-end circuit 200 includes:
an amplifying module 201, configured to convert a received optical signal into a voltage, and amplify the voltage;
Here, the amplifying module may implement a function of converting a received optical signal into a current, converting the current into a voltage, and amplifying the voltage signal.
In the embodiment of the present application, the amplifying module may be formed by a PD and a TIA, where the PD may convert a received optical signal into an electrical signal, that is, into a current. The TIA may convert the current to a voltage and amplify it. Of course, the amplifying module may be formed of other components, but it is within the scope of the present application as long as the function of converting the received optical signal into voltage and amplifying the voltage can be achieved.
The calibration module 202 is configured to adjust a gain of the amplifying module 201 according to a relationship between an output voltage of the amplifying module 201 and a preset threshold, and adjust a DC offset of a current at an input end of the amplifying module 201 to calibrate the output voltage of the amplifying module 201;
the calibration module is connected between the amplifying module and the analog-to-digital conversion module and is used for judging whether the output voltage of the amplifying module is in a linear range or not. 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 a single signal is not lost and the DC offset is eliminated.
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 application, the signal is regulated and calibrated by the calibration module before analog-digital conversion. Then, the calibrated signal, namely the analog output voltage, is converted into digital voltage through an analog-to-digital conversion module and is output.
In an embodiment of the present application, by providing a front-end circuit, the front-end circuit includes: the amplifying module is used for converting the received optical signal into voltage and amplifying the voltage; the calibration module is used for adjusting the gain of the amplification module according to the relation between the output voltage of the amplification module and a preset threshold value, and adjusting the DC offset of the current at the input end of the amplification module so as to calibrate the output voltage of the amplification module; and the analog-to-digital conversion module is used for converting the calibrated analog output voltage output by the amplification module into a digital output voltage, so that DC offset in the signal can be eliminated, and the signal cannot overflow through adjusting the gain of the amplification module, so that a single signal cannot be lost, and the signal becomes more robust relative to motion and ambient light interference.
Based on the foregoing embodiments, the embodiment of the present application further provides a front-end circuit, fig. 2B is a schematic diagram of a second component structure of the front-end circuit according to the embodiment of the present application, as shown in fig. 2B, and the front-end circuit 200 includes:
an input circuit 211 for converting the received optical signal into a current;
here, the input circuit may be a PD, which is capable of receiving an optical signal (e.g., an optical signal emitted by an LED, and an interference signal of ambient light) and converting the received optical signal into a current.
An amplifying circuit 212 for converting the current generated by the input circuit 211 into a voltage and amplifying the voltage;
here, the amplifying circuit may be a TIA, and the amplifying circuit may be capable of converting a current generated by the PD into a voltage and amplifying the voltage within a certain gain range.
A calibration module 213, configured to adjust a gain of the amplifying circuit 212 according to a relationship between an output voltage of the amplifying circuit 212 and a preset threshold, and adjust a DC offset of a current at an input end of the amplifying circuit 212, so as to calibrate the output voltage of the amplifying circuit 212;
the calibration module is connected between the amplifying circuit and the analog-to-digital conversion module and is used for judging whether the output voltage of the amplifying circuit is in a linear range or not. 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 the 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 application, the analog-to-digital conversion module can be an ADC (analog-to-digital converter) and can convert the analog output voltage calibrated by the calibration module into the digital output voltage.
In an 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; the amplifying circuit is used for converting the current generated by the input circuit into voltage and amplifying the voltage; the calibration module is used for adjusting the gain of the amplifying circuit according to the relation between the output voltage of the amplifying circuit and a preset threshold value, and adjusting the DC offset of the current at the input end of the amplifying circuit so as to calibrate the output voltage of the amplifying circuit; and the analog-to-digital conversion module is used for converting the calibrated analog output voltage output by the amplifying circuit into a digital output voltage, so that DC offset in the signal can be eliminated, and the signal cannot overflow through adjusting the gain of the amplifying module, so that a single signal cannot be lost, and the signal becomes more robust relative to motion and ambient light interference.
Based on the foregoing embodiments, embodiments of the present application further provide a front-end circuit, where the front-end circuit includes:
the amplifying module is used for converting the received optical signal into voltage and amplifying the voltage;
the calibration module is used for enabling DC offset of current at the input end of the amplifying module to move downwards according to the relation between the output voltage of the amplifying module and a preset threshold value; and/or, reducing the gain of the amplifying module so as to calibrate the output voltage of the amplifying module;
here, when the TIA is included in the amplifying module, the calibration module may be configured to, when the output voltage of the TIA is not within a linear range, cause a DC offset of the current at the TIA input to go down by adjusting a current source of the TIA input stage, so as to cancel the DC offset. The gain of the TIA may also be made smaller by adjusting the feedback resistance of the TIA to ensure that a single signal is not lost.
The calibration module is further used for enabling DC offset of current at the input end of the amplifying module to move upwards according to the relation between the output voltage of the amplifying module and a preset threshold value; and/or, making the gain of the amplifying module larger so as to calibrate the output voltage of the amplifying module;
Here, when the TIA is included in the amplifying module, the calibration module may be configured to, when the output voltage of the TIA is not within a linear range, cause a DC offset of the current at the TIA input to go upward by adjusting a current source of the TIA input stage, so as to cancel the DC offset. The gain of the TIA may also be increased by adjusting the feedback resistance of the TIA to ensure that a single signal is not lost.
In some embodiments, the preset thresholds include a first preset threshold and a second preset threshold, the first preset threshold being greater than the second preset threshold;
the calibration module is used for enabling DC offset of current at the input end of the amplifying module to move downwards when the output voltage is larger than the first preset threshold value; and/or, reducing the gain of the amplifying module so as 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, making the gain of the amplifying module larger so as to calibrate the output voltage of the amplifying module.
In the embodiment of the present application, the preset threshold may be a response range of the signal, and correspondingly, the first preset threshold may be an upper limit of the response range, and the second preset threshold may be a lower limit of the response range. And when the output voltage of the amplifying module is smaller than a second preset threshold value, indicating signal underflow. When the signals overflow or underflow, inaccurate detection results of physiological parameters such as heart rate and the like can be caused.
Thus, when overflow occurs, the calibration module can adjust the calibration so that the DC offset of the current at the input of the amplification module moves downward and the gain of the amplification module becomes smaller. When underflow, the calibration module may cause the DC offset of the current at the input of the amplification module to move upwards and the gain of the amplification module to become larger by adjusting the calibration.
And the analog-to-digital conversion module is used for converting the calibrated analog output voltage output by the amplification module into a digital output voltage.
Based on the foregoing embodiments, the embodiment of the present application further provides a front-end circuit, and fig. 2C is a schematic diagram of a 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:
An amplifying module 221 for converting the received optical signal into a voltage and amplifying the voltage;
a comparator 222 for determining whether the output voltage of the amplifying module 221 is greater than the first preset threshold or less than the second preset threshold;
here, 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 may be implemented using a comparator, that is, whether the output voltage of the amplifying module exceeds a linear range and overflow of a signal occurs may be judged by the comparator.
A control circuit 223 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;
here, the control circuit may generate the first control signal or the second control signal according to the comparison result of the comparator, so as to adjust and calibrate the overflow and the underflow of the signal respectively.
A first adjusting circuit 224, configured to move a DC offset of the current at the input end of the amplifying module 221 downward according to the first control signal; and/or, the gain of the amplifying module 221 is made smaller;
Here, the first adjusting circuit may realize a 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 overflows.
A second adjusting circuit 225, configured to move up a DC offset of the current at the input end of the amplifying module 221 according to the second control signal; and/or, the gain of the amplifying module 221 is made larger;
here, the second adjusting circuit may realize a 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 is underflowed.
The analog-to-digital conversion module 226 is configured to convert the calibrated analog output voltage into a digital output voltage.
In the embodiment of the application, the signal is regulated and calibrated by the calibration module before analog-digital conversion. Then, the calibrated signal, namely the analog output voltage, is converted into digital voltage through an analog-to-digital conversion module and is output.
In an embodiment of the present application, by providing a front-end circuit, the front-end circuit includes: the amplifying module is used for converting the received optical signal into voltage and amplifying the voltage; a comparator for determining whether the output voltage of the amplifying module is greater than the first preset threshold or less than the second preset threshold; the control circuit is used for generating a first control signal when the output voltage is larger than the first preset threshold value and generating a second control signal when the output voltage is smaller than the second preset threshold value; the first adjusting circuit is used for enabling the DC offset of the current at the input end of the amplifying module to move downwards according to the first control signal; and/or, reducing the gain of the amplifying module; the second adjusting circuit is used for enabling the DC offset of the current at the input end of the amplifying module to move upwards according to the second control signal; and/or, making the gain of the amplifying module larger; the analog-to-digital conversion module is used for converting the calibrated analog output voltage into the digital output voltage, so that DC offset in the signal can be eliminated, and the signal cannot overflow through adjusting the gain of the amplifying module, so that a single signal cannot be lost, and the signal becomes more robust relative to motion and ambient light interference.
Based on the foregoing embodiments, embodiments of the present application further provide a front-end circuit, where the front-end circuit includes:
the amplifying module is used for converting the received optical signal into voltage and amplifying the voltage;
here, the amplification module includes a current source and a feedback resistance circuit of the input stage.
A comparator for determining whether the output voltage of the amplifying module is greater than the first preset threshold or less than the second preset threshold;
the comparator is connected between the amplifying module and the analog-to-digital conversion module and is used for judging whether the output voltage of the amplifying circuit is in a linear range or not.
The control circuit is used for generating a first control signal when the output voltage is larger than the first preset threshold value and generating a second control signal when the output voltage is smaller than the second preset threshold value;
the control circuit is connected between the comparator and the adjusting circuit and is used for generating a control signal to control the first adjusting circuit or the second adjusting circuit to adjust the DC offset of the input end of the amplifying circuit and adjust the feedback resistance of the amplifying circuit when the comparator determines that the output voltage of the amplifying circuit is not in the linear range.
The first adjusting circuit is used for adjusting the current source of the input stage according to the first control signal so as to enable the DC offset of the current at the input end of the amplifying module to move downwards; and/or adjusting the feedback resistance circuit to reduce the gain of the amplifying module;
here, the first adjusting circuit is configured to adjust a current source of an input stage of the amplifying circuit and a feedback resistance of the amplifying circuit when an output voltage of the amplifying circuit overflows, so as to eliminate a DC offset and ensure that a single signal is not lost. The current source of the amplifying circuit input stage may be a differential current source.
The second adjusting circuit is used for adjusting the current source of the input stage according to the second control signal so as to enable the DC offset of the current at the input end of the amplifying module to move upwards; and/or adjusting the feedback resistance circuit to make the gain of the amplifying module larger;
here, the second adjusting circuit is configured to adjust a current source of an input stage of the amplifying circuit and a feedback resistance of the amplifying circuit when an output voltage of the amplifying circuit overflows, so as to eliminate a DC offset and ensure that a single signal is not lost.
In some embodiments, the feedback resistive circuit comprises a feedback capacitive resistive array formed by a capacitance, a resistance, and a switch;
correspondingly, the first adjusting circuit or the second adjusting circuit adjusts the gain of the amplifying module by using the feedback capacitance-resistance array.
In the embodiment of the application, the feedback resistor circuit comprises at least one capacitor, at least one resistor and at least one switch. The adjusting circuit can control the opening and closing of the switches according to different control signals, so that the feedback resistance circuit has different feedback resistances under different conditions, and correspondingly, the amplifying circuit has different gains under different conditions. The resistor is used for adjusting gain, and the capacitor is mainly used for eliminating noise by matching with the resistor in a low-pass mode.
And the analog-to-digital conversion module is used for converting the calibrated analog output voltage into a digital output voltage.
Based on the foregoing embodiments, the embodiment of the present application further provides a front-end circuit, and fig. 2D is a schematic diagram of a 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:
an amplifying module 231 for converting the received optical signal into a voltage and amplifying the voltage;
A calibration module 232, configured to adjust a gain of the amplifying module 231 according to a relationship between an output voltage of the amplifying module 231 and a preset threshold, and adjust a DC offset of a current at an input end of the amplifying module 231, so as to calibrate the output voltage of the amplifying module 231;
an analog-to-digital conversion module 233, configured to convert the calibrated analog output voltage output by the amplification module 231 into a digital output voltage;
in the embodiment of the application, the signal is regulated and calibrated by the calibration module before analog-digital conversion. Then, the calibrated signal, namely the analog output voltage, is converted into digital voltage through an analog-to-digital conversion module and is output.
And an output module 234, configured to read, write and output the digital output voltage according to a first-in first-out principle.
Here, the output module may be a FIFO (First Input First Output, first-in first-out) circuit for outputting the received digital signal according to a first-in first-out principle.
In an embodiment of the present application, by providing a front-end circuit, the front-end circuit includes: the amplifying module is used for converting the received optical signal into voltage and amplifying the voltage; the calibration module is used for adjusting the gain of the amplification module according to the relation between the output voltage of the amplification module and a preset threshold value, and adjusting the DC offset of the current at the input end of the amplification module so as to calibrate the output voltage of the amplification module; the analog-to-digital conversion module is used for converting the calibrated analog output voltage output by the amplifying module into digital output voltage; and the output module is used for carrying out read-write output on the digital output voltage according to a first-in first-out principle, so that DC offset in the signal can be eliminated, and the signal cannot overflow through adjusting the gain of the amplifying module, so that a single signal cannot be lost, and the signal becomes more robust relative to motion and ambient light interference.
Based on the foregoing embodiments, the embodiments of the present application further provide a front-end circuit to implement TIA stage 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 to a voltage, and the voltage is directed into the threshold detection circuit. Fig. 3A is a schematic diagram of a front-end circuit according to an embodiment of the present application, as shown in fig. 3A, the front-end circuit 300 includes: PD 301, TIA 302, comparator 303, controller 304, regulator 305, a/D converter 306 (i.e., ADC), and FIFO 307, wherein:
the PD 301 converts the received optical signal into a current. The TIA 302 converts the current generated by the PD 301 into a voltage. High threshold V in comparator 303 TH And a low level threshold V TL To detect if the TIA 302 output voltage is within a linear range. When an overflow or an underflow occurs, the controller 304 generates a control signal that is transmitted to the regulator 305, which regulator 305 uses to adjust the current source 3051 of the TIA 302 input stage. For example, when the output voltage of TIA 302 is greater than V TH The current is regulated such that the DC offset of the TIA 302 input is reduced, thereby creating an effective negative feedback. The regulator 305 includes a current source 3051 and a feedback resistor circuit 3052.
Overflow and underflow thresholds (i.e. high level threshold V TH And a low level threshold V TL ) Is programmable and typically still leaves some margin for the ADC (i.e., a/D converter 306) saturation voltage. Thus, no single signal is lost during any movement. The same principle can be used to cancel the DC offset. The digital signal output from the a/D converter 306 is read/written through the FIFO 307.
On the other hand, the front-end circuit 300 adjusts the gain of the TIA 302 by using different capacitive and resistive arrays, which are in the feedback resistive circuit 3052 of the TIA 302, so that the optimal dynamic range of the ADC can be used.
Fig. 3B is a PPG signal waveform diagram of a front-end circuit according to an embodiment of the present application, where, as shown in fig. 3B, the horizontal axis is time, the vertical axis is voltage, the dashed line 31 represents the upper limit of the response range, i.e., the upper limit of the threshold, and the lower limit of the response range, i.e., the lower limit of the threshold coincides with the horizontal axis, and the solid line 32 is the measured voltage. The front-end circuitry in embodiments of the present application is able to automatically adjust and calibrate a pure analog signal without any assistance from the digital domain, so that the PD current can be adjusted directly and quickly within a detectable range.
The embodiment of the application provides a novel front-end circuit, so that a PPG signal becomes more robust relative to motion and ambient light interference, and the problem that when a user wears relatively loose, peripheral ambient light enters, thereby affecting DC of a TIA input end can be solved. Meanwhile, the problem that the intensity of the PPG signals is different when the detection device of the user is close to the skin for a while and is far away from the skin for a while can be solved. Thus, in typical use cases such as jogging, the user does not need to tighten the wearable watch to the skin, but still can obtain a reliable PPG signal. At the same time, in case of high accelerations such as throwing or dropping, the PPG signal can be adjusted quickly in the analog domain so that no single signal will be lost.
Based on the foregoing embodiments, the embodiments of the present application provide a method for calibrating a transmission signal, where the method is applied to a front-end circuit, fig. 4A is a schematic implementation flow diagram of the method for calibrating a transmission signal according to the embodiment of the present application, as shown in fig. 4A, and the method includes:
step S401, converting the received optical signal into voltage by using an amplifying module of a front-end circuit, and amplifying the voltage;
in some embodiments, the step S401 of converting the received optical signal into a voltage and amplifying the voltage by using the amplifying module of the front-end circuit may be implemented by:
Step S4011, converting the received optical signal into current by using an input circuit of the amplifying module;
step S4012, converting the current generated by the input circuit into a voltage by using the amplifying circuit of the amplifying module, and amplifying the voltage.
Step S402, according to the relation between the output voltage of the amplifying module and a preset threshold value, adjusting the gain of the amplifying module, and adjusting the DC offset of the current at the input end of the amplifying module so as to calibrate the output voltage of the amplifying module;
in some embodiments, the step S402 of adjusting the gain of the amplifying module and the DC offset of the current at the input end of the amplifying module according to the relationship between the output voltage of the amplifying module and the preset threshold may be implemented by: step S402a, according to the relationship between the output voltage of the amplifying module and a preset threshold, moving the DC offset of the current at the input end of the amplifying module downward; and/or, reducing the gain of the amplifying module;
in some embodiments, the step S402 may be implemented by adjusting the gain of the amplifying module according to the relationship between the output voltage of the amplifying module and a preset threshold, and adjusting the DC offset of the current at the input end of the amplifying module by: step S402b, according to the relationship between the output voltage of the amplifying module and a preset threshold, moving the DC offset of the current at the input end of the amplifying module upwards; and/or, the gain of the amplifying module is increased.
In some embodiments, the preset thresholds include a first preset threshold and a second preset threshold, the first preset threshold being greater than the second preset threshold;
correspondingly, step S402a is 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 the preset threshold; and/or, reducing the gain of the amplifying module, including: when the output voltage is greater than the first preset threshold value, the DC offset of the current at the input end of the amplifying module is downwards moved; and/or, reducing the gain of the amplifying module;
correspondingly, step S402b moves the DC offset of the current at the input end of the amplifying module upwards according to the relation between the output voltage of the amplifying module and the preset threshold value; and/or, making the gain of the amplifying module larger, including: when the output voltage is smaller than the second preset threshold value, the DC offset of the current at the input end of the amplifying module is moved upwards; and/or, the gain of the amplifying module is increased.
Step S403, converting the calibrated analog output voltage output by the amplifying module into a digital output voltage.
Based on the foregoing embodiments, the embodiment of the present application further provides a calibration method for a transmission signal, where the method is applied to a front-end circuit, and fig. 4B is a schematic diagram illustrating a second implementation flow of the calibration method for a transmission signal according to the embodiment of the present application, as shown in fig. 4B, where the method includes:
step S411, converting the received optical signal into voltage by using an amplifying module of the front-end circuit, and amplifying the voltage;
step S412, determining whether the output voltage of the amplifying module is greater than the first preset threshold or less than the second preset threshold;
step S413, generating a first control signal when the output voltage is greater than the first preset threshold value, and generating a second control signal when the output voltage is less than the second preset threshold value;
step S414, according to the first control signal, moving the DC offset of the current at the input end of the amplifying module downward; and/or, reducing the gain of the amplifying module so as to calibrate the output voltage of the amplifying module;
step S415, according to the second control signal, moving the DC offset of the current at the input end of the amplifying module upwards; and/or, making the gain of the amplifying module larger so as to calibrate the output voltage of the amplifying module;
In some embodiments, the amplification module includes a current source and a feedback resistance circuit of an input stage;
correspondingly, in step S414, according to the first control signal, a DC offset of the current at the input end of the amplifying module is moved downward; and/or, reducing the gain of the amplifying module, including: adjusting a current source of the input stage according to the first control signal so as to enable a DC offset of a current at the input end of the amplifying module to move downwards; and/or adjusting the feedback resistance circuit to reduce the gain of the amplifying module;
correspondingly, in the step S415, according to the second control signal, a DC offset of the current at the input end of the amplifying module is moved upwards; and/or, making the gain of the amplifying module larger, including: adjusting a current source of the input stage according to the second control signal so as to enable a DC offset of the current at the input end of the amplifying module to move upwards; and/or adjusting the feedback resistance circuit to make the gain of the amplifying module larger.
In some embodiments, the feedback resistive circuit comprises a feedback capacitive resistive array formed by a capacitance, a resistance, and a switch;
Correspondingly, the front-end circuit adjusts the gain of the amplifying module by using the feedback capacitive resistive array.
Step S416, converting the calibrated analog output voltage output by the amplifying module into a digital output voltage.
In some embodiments, the method further comprises: and S41, reading, writing and outputting the digital output voltage according to a first-in first-out principle.
The description of the method embodiments above is similar to that of the circuit embodiments above, with similar advantageous effects as the circuit embodiments. For technical details not disclosed in the method embodiments of the present application, please refer to the description of the circuit embodiments of the present application for understanding.
It should be noted that, in the embodiment of the present application, if the calibration method of the transmission signal is implemented in the form of a software functional module, and sold or used as a separate product, the calibration method may also be stored in a computer readable storage medium. Based on such understanding, the technical solutions of the embodiments of the present application may be embodied essentially or in part in the form of a software product stored in a storage medium, including instructions for causing an electronic device (which may be a personal computer, a server, etc.) to perform all or part of the methods described in the embodiments of the present application. And the aforementioned storage medium includes: various media capable of storing program codes, such as a usb disk, a removable hard disk, a ROM (Read Only Memory), a magnetic disk, or an optical disk. Thus, embodiments of the application are not limited to any specific combination of hardware and software.
In the several embodiments provided in the present application, it should be understood that the disclosed circuits and methods may be implemented in other ways. The above described circuit embodiments are only illustrative, e.g. the division of the units is only a logical functional division, and there may be other divisions in practice, such as: multiple units or components may be combined or may be integrated into another system, or some features may be omitted, or not performed. In addition, the various components shown or discussed may be coupled or directly coupled or communicatively coupled to each other via some interface, whether indirectly coupled or communicatively coupled to devices or units, whether electrically, mechanically, or otherwise.
The units described as separate units may or may not be physically separate, and units displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units; some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.
In addition, each functional unit in each embodiment of the present application may be integrated in one processing module, or each unit may be separately used as one unit, or two or more units may be integrated in one unit; the integrated units may be implemented in hardware or in hardware plus software functional units. Those of ordinary skill in the art will appreciate that: all or part of the steps of implementing the above method embodiments may be implemented by hardware associated with program instructions, and the above program may be stored in a computer readable storage medium, which when executed, performs steps including the above method embodiments.
The methods disclosed in the method embodiments provided by the application can be arbitrarily combined under the condition of no conflict to obtain a new method embodiment.
The features disclosed in the several product embodiments provided by the application can be combined arbitrarily under the condition of no conflict to obtain new product embodiments.
The features disclosed in the embodiments of the method or the apparatus provided by the application can be arbitrarily combined without conflict to obtain new embodiments of the method or the apparatus.
The foregoing is merely illustrative of the present application, and the present application is not limited thereto, and any person skilled in the art will readily recognize that variations or substitutions are within the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.
Claims (10)
1. A front-end circuit, the front-end circuit comprising:
the amplifying module is used for converting the received optical signal into voltage and amplifying the voltage;
the calibration module is used for adjusting the gain of the amplification module according to the relation between the output voltage of the amplification module and a preset threshold value, and adjusting the DC offset of the current at the input end of the amplification module so as to calibrate the output voltage of the amplification module;
And the analog-to-digital conversion module is used for converting the calibrated analog output voltage output by the amplification module into a digital output voltage.
2. The front-end circuit of claim 1, wherein the amplification module comprises:
an input circuit for converting a received optical signal into a current;
the amplifying circuit is used for converting the current generated by the input circuit into voltage and amplifying the voltage;
the calibration module is used for enabling DC offset of current at the input end of the amplifying module to move downwards according to the relation between the output voltage of the amplifying module and a preset threshold value; and/or, reducing the gain of the amplifying module;
the calibration module is further used for enabling DC offset of current at the input end of the amplifying module to move upwards according to the relation between the output voltage of the amplifying module and a preset threshold value; and/or, the gain of the amplifying module is increased.
3. The front-end circuit of claim 2, wherein the preset threshold comprises a first preset threshold and a second preset threshold, the first preset threshold being greater than the second preset threshold;
the calibration module is used for enabling DC offset of current at the input end of the amplifying module to move downwards when the output voltage is larger than the first preset threshold value; and/or, reducing 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 when the output voltage is less than the second preset threshold; and/or, the gain of the amplifying module is increased.
4. A front-end circuit as recited in claim 3, wherein the calibration module comprises:
a comparator for determining whether the output voltage of the amplifying module is greater than the first preset threshold or less than the second preset threshold;
the control circuit is used for generating a first control signal when the output voltage is larger than the first preset threshold value and generating a second control signal when the output voltage is smaller than the second preset threshold value;
the first adjusting circuit is used for enabling the DC offset of the current at the input end of the amplifying module to move downwards according to the first control signal; and/or, reducing the gain of the amplifying module;
the second adjusting circuit is used for enabling the DC offset of the current at the input end of the amplifying module to move upwards according to the second control signal; and/or, the gain of the amplifying module is increased.
5. The front-end circuit of claim 4, wherein the amplification module comprises a current source and a feedback resistance circuit of an input stage;
Correspondingly, the first adjusting circuit is used for adjusting the current source of the input stage according to the first control signal so as to enable the DC offset of the current at the input end of the amplifying module to move downwards; and/or adjusting the feedback resistance circuit to reduce the gain of the amplifying module;
correspondingly, the second adjusting circuit is used for adjusting the current source of the input stage according to the second control signal so as to enable the DC offset of the current at the input end of the amplifying module to move upwards; and/or adjusting the feedback resistance circuit to make the gain of the amplifying module larger.
6. The front-end circuit of claim 5, wherein the feedback resistive circuit comprises a feedback capacitive resistive array formed by a capacitance, a resistance, and a switch;
correspondingly, the first adjusting circuit or the second adjusting circuit adjusts the gain of the amplifying module by using the feedback capacitance-resistance array.
7. The front-end circuit of claim 1, further comprising:
and the output module is used for reading, writing and outputting the digital output voltage according to the first-in first-out principle.
8. A method of calibrating a transmission signal, the method being applied to a front-end circuit, the method comprising:
converting the received optical signal into voltage by using an amplifying module of the front-end circuit, and amplifying the voltage;
according to the relation between the output voltage of the amplifying module and a 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 so as to calibrate the output voltage of the amplifying module;
and converting the calibrated analog output voltage output by the amplifying module into a digital output voltage.
9. The method of claim 8, wherein the amplifying module using the front-end circuit converts the received optical signal into a voltage and amplifies the voltage, comprising:
converting the received optical signal into a current by using an input circuit of the amplifying module;
and converting the current generated by the input circuit into voltage by using an amplifying circuit of the amplifying module, and amplifying the voltage.
10. The method of claim 8, wherein adjusting the gain of the amplifying module and adjusting the DC offset of the current at the input of the amplifying module according to the relationship between the output voltage of the amplifying module and the preset threshold value comprises: according to the relation between the output voltage of the amplifying module and a preset threshold value, the DC offset of the current at the input end of the amplifying module is downwards moved; and/or, reducing the gain of the amplifying module;
The method for adjusting the gain of the amplifying module according to the relation between the output voltage of the amplifying module and a preset threshold value, adjusting the DC offset of the current at the input end of the amplifying module, and further comprises the following steps: according to the relation between the output voltage of the amplifying module and a preset threshold value, the DC offset of the current at the input end of the amplifying module is moved upwards; and/or, the gain of the amplifying module is increased.
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| PCT/CN2019/104453 WO2021042309A1 (en) | 2019-09-04 | 2019-09-04 | Front-end circuit and method for calibrating transmission signal |
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| TWI783696B (en) * | 2021-09-27 | 2022-11-11 | 瑞昱半導體股份有限公司 | Photoplethysmography front-end receiver |
| CN115083097A (en) * | 2022-06-09 | 2022-09-20 | 南京英锐创电子科技有限公司 | Analog front-end circuit and smoke alarm |
| CN117440563A (en) * | 2022-07-22 | 2024-01-23 | 华为技术有限公司 | Light source dimming method and electronic equipment |
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