End-to-end vital sign monitoring radar system

Abstract

The invention discloses an end-to-end vital sign monitoring radar system. The system comprises a radio frequency and buffer module and an analog demodulation module. The radio frequency and buffer module completes emission, reception and signal buffer of millimeter wave signals, and comprises a radio frequency module and an IQ two-path buffer. And the analog demodulation module completes signal demodulation in an analog domain by using an improved differential and cross multiplication (MDACM) algorithm and outputs a target time-varying displacement signal. The analog demodulation module is composed of analog devices and comprises an IQ two-path direct current item extraction module, an IQ two-path differentiator, an IQ two-path multiplier, a first-stage subtractor, a second-stage subtractor, an adder and an integrator. The phase demodulation principle of the analog demodulation module follows an MDACM algorithm, and the process is completely carried out in an analog domain. The whole radar system can realize end-to-end vital sign monitoring, is high in real-time performance and low in power consumption, and can reduce the sampling rate and sampling channels.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of radar signal processing and biomedical monitoring, in particular to an end-to-end vital sign monitoring radar system. BACKGROUND

[0002] The vital sign monitoring radar can obtain vital sign information under non-contact conditions by detecting the electromagnetic wave phase changes caused by the micro physiological activities of human respiration, heartbeat, etc., and has the advantages of high comfort and small privacy invasion, etc. It has important application value in medical care, home-based care and emergency rescue, etc. One of the key technologies of this kind of radar system is to demodulate the quadrature baseband IQ signal obtained after mixing at the receiving end with high precision, so as to accurately recover the micro displacement information of the target.

[0003] In the field of digital signal processing, various algorithms have been proposed for phase demodulation of IQ signals, among which the improved differential and cross multiplication (MDACM) algorithm is widely used due to its simple mathematical form and high computational efficiency. This algorithm directly constructs a signal proportional to the phase derivative by differentiating, cross-multiplying and correlating the I and Q signals, effectively reducing the dependence of the demodulation result on signal amplitude changes, and has good anti-amplitude modulation interference capability, suitable for extraction of weak phase change signals such as vital signs.

[0004] However, the existing MDACM demodulation method based on the digital domain usually needs to sample and quantize the analog IQ signal at a high speed, and relies on digital signal processors or programmable logic devices to complete subsequent operations. This implementation not only introduces quantization noise and non-linear distortion, but also increases the system hardware complexity and power consumption level; in addition, the sampling, buffering and operation processes in the digital processing link will bring certain system delay, which restricts its application performance in real-time vital sign monitoring scenarios. Further, limited by the Nyquist sampling theorem, high sampling rate analog-to-digital converters are required for high frequency or wideband phase modulation signals, which not only increases the system cost, but also puts higher requirements on the front-end circuit design and signal integrity. SUMMARY

[0005] The present application aims to overcome the defects or deficiencies of the prior art and provides an end-to-end vital sign monitoring radar system.

[0006] The technical solution for achieving the present application is an end-to-end vital sign monitoring radar system, which comprises a radio frequency and buffering module and an analog demodulation module.

[0007] The radio frequency and buffering module is used to complete the transmission, reception and signal buffering of millimeter wave signals.

[0008] The analog demodulation module is used to demodulate the signal in the analog domain using the MDACM method and output the target time-varying displacement signal; the entire demodulation process of the analog demodulation module is carried out continuously in the analog domain without the need for digital sampling.

[0009] Furthermore, the radio frequency and buffer module includes a radio frequency module and I and Q buffers;

[0010] The radio frequency module is used to transmit and receive millimeter-wave signals, and after mixing, it generates orthogonal baseband signals I and Q;

[0011] The I and Q buffers are used to provide impedance isolation and drive for the baseband signals I and Q, respectively.

[0012] Furthermore, the baseband I and Q signals output by the receiver mixer are specifically represented as follows:

[0013] In-phase I signal :

[0014]

[0015] Quadrature Q-channel signal :

[0016]

[0017] in,

[0018]

[0019]

[0020] In the formula, For the amplitude of the I-channel signal, For the DC component of the I-channel signal, For the Q-channel signal amplitude, This refers to the DC component of the Q-channel signal. For the target time-varying displacement, The carrier frequency wavelength used by the radar. , It depends on the nominal distance at which the radar reaches the target. The phase constant, It is channel phase offset.

[0021] Furthermore, both the I and Q buffers are implemented as voltage followers composed of operational amplifiers, used to receive baseband I and Q signals, realize the conversion between high input impedance and low output impedance, isolate the load effect between the front-end signal source and the subsequent circuit, and provide stable driving capability for the subsequent stage.

[0022] Further, the analog demodulation module comprises I and Q two-way direct current term extraction modules, I and Q two-way differentiators, I and Q two-way multipliers, and a first-stage subtractor, a second-stage subtractor, an adder and an integrator; outputs of the I-way buffer are respectively connected to the I-way direct current term extraction module, the I-way differentiator and the Q-way multiplier, and outputs of the Q-way buffer are respectively connected to the Q-way direct current term extraction module, the Q-way differentiator and the I-way multiplier;

[0023] The I and Q two-way direct current term extraction modules each comprise a direct current component extraction module and an analog multiplier; the direct current component extraction module is used to extract direct current information in the baseband signal, and the analog multiplier generates a direct current term interference signal to be eliminated; the analog multiplier receives output signals of the current-way direct current component extraction module and the opposite-way differentiator;

[0024] The I and Q two-way differentiators are each used to differentiate the signal to extract a signal change rate; an output of the I-way differentiator is respectively connected to the I-way multiplier and the analog multiplier in the Q-way direct current term extraction module, and an output of the Q-way differentiator is respectively connected to the Q-way multiplier and the analog multiplier in the I-way direct current term extraction module;

[0025] The I and Q two-way multipliers are each used to realize cross multiplication of the original-way signal and the opposite-way differentiator output signal;

[0026] The first-stage subtractor takes outputs of the I and Q two-way multipliers as inputs to complete channel difference;

[0027] The second-stage subtractor and the adder cooperatively constitute a direct current interference term elimination structure, wherein an input of the second-stage subtractor is the I-way direct current term extraction module and an output of the first-stage subtractor, and an input of the adder is the Q-way direct current term extraction module and an output of the second-stage subtractor;

[0028] The integrator is used to restore phase information corresponding to the vital sign according to an output of the adder.

[0029] Further, the I and Q two-way differentiators differentiate the I and Q two-way signals, and obtain:

[0030] In-phase I-way differentiated signal :

[0031]

[0032] Quadrature Q-way differentiated signal :

[0033]

[0034] wherein,

[0035]

[0036] wherein, is the differential of is the differential of is the target time-varying displacement is the differential of

[0037] Further, the I and Q two-way multipliers are used to realize cross multiplication of the original signal and the differential signal of the opposite way, and are specifically represented as:

[0038]

[0039]

[0040] The output of the first-stage subtracter is:

[0041]

[0042] The output signal comprises the differential of the signal , and two DC components caused interference terms and ;

[0043] The two analog multipliers receive the output signals of the DC component extraction module and the opposite-way differentiator, and respectively calculate: and ;

[0044] The output of the second-stage subtracter is:

[0045]

[0046] The output of the adder is:

[0047]

[0048] Further, the integrator integrates the output signal of the adder to recover the time-varying displacement information, and is specifically:

[0049]

[0050] Further, the I, Q two-way direct current term extraction module comprises a first resistor, a second resistor, a third resistor, a first capacitor, a second capacitor, a diode, an N-channel MOS tube and a buffer; the drain of the N-channel MOS tube is connected with the baseband I or Q channel signal and one end of the third resistor; the gate of the N-channel MOS tube is connected with the ground through the first resistor, and is connected with the power supply VCC through the first capacitor; the source of the N-channel MOS tube is connected with the anode of the diode; the cathode of the diode is connected with the positive input end of the buffer, and the buffer is connected with the ground through the second capacitor; the negative input end of the buffer is connected with the output end of the buffer and is connected to the analog multiplier.

[0051] Further, the buffer is realized by a voltage follower composed of an operational amplifier.

[0052] Compared with the prior art, the present application has the following advantages:

[0053] (1) Full analog end-to-end processing, high real-time performance and low delay: the phase demodulation is realized by using a full analog circuit, without the need of an analog-to-digital conversion and a digital signal processing link, so that the delay caused by sampling, quantization and digital processing is fundamentally avoided, and the present application is particularly suitable for monitoring scenes with high real-time performance requirements, such as vital sign detection and vibration measurement.

[0054] (2) Sampling rate and sampling channel can be reduced: the present application is free from the constraint of the Nyquist sampling theorem, can directly process high-frequency or rapidly changing phase signals, and does not need to worry about signal distortion caused by insufficient sampling rate, so that end-to-end signal output can be realized.

[0055] (3) Simple structure and high system integration: the complete DACM demodulation algorithm is realized by using basic analog units such as an analog multiplier, a differentiator and an integrator, without the need of complex digital logic and storage resources, so that the present application is conducive to chip-level integration and system miniaturization.

[0056] (4) Direct current bias dynamic correction, improving demodulation accuracy: the direct current bias extraction unit is combined with a fast charging circuit, so that a stable direct current bias can be quickly established after the system is started, and the error caused by the direct current component can be effectively eliminated through cross multiplication and a correction unit, so that the accuracy and stability of the phase demodulation are significantly improved.

[0057] (5) Strong anti-interference capability: the pseudo-demodulation process does not depend on the clock and the quantization accuracy, and the signal recovery quality can still be kept high in a noisy environment.

[0058] (6) Suitable for low-power vital sign continuous monitoring applications: by using a full analog implementation, the present application can significantly reduce the system power consumption while ensuring the demodulation performance, can realize end-to-end continuous monitoring from radio frequency reception to vital sign signal output, and is particularly suitable for portable, wearable and long-term health monitoring devices.

[0059] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0060] Figure 1 This is a block diagram of an end-to-end vital signs monitoring radar system in one embodiment.

[0061] Figure 2 This is an overall circuit diagram of an end-to-end vital signs monitoring radar system in one embodiment.

[0062] Figure 3 This is a circuit diagram of the radio frequency module in one embodiment.

[0063] Figure 4 This is a circuit diagram of a buffer in one embodiment.

[0064] Figure 5 This is a circuit diagram of a differentiator in one embodiment.

[0065] Figure 6 This is a circuit diagram of a multiplier in one embodiment.

[0066] Figure 7 This is a circuit diagram of a subtractor in one embodiment.

[0067] Figure 8 This is a circuit diagram of an adder in one embodiment.

[0068] Figure 9 This is a circuit diagram of an integrator in one embodiment.

[0069] Figure 10 This is a circuit diagram of the DC term extraction module in one embodiment. Detailed Implementation

[0070] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0071] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0072] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0073] In one embodiment, an end-to-end vital signs monitoring radar system is provided, the system comprising two main modules: a radio frequency and buffer module and an analog demodulation module;

[0074] The radio frequency and buffer module is used to complete the transmission, reception and signal buffering of millimeter wave signals;

[0075] The analog demodulation module is used to demodulate the signal in the analog domain using the MDACM method and output the target time-varying displacement signal; the entire demodulation process of the analog demodulation module is carried out continuously in the analog domain without the need for digital sampling.

[0076] This invention implements the MDACM demodulation method entirely through analog circuits, achieving analog phase demodulation of IQ signals.

[0077] Furthermore, in one embodiment, combined with Figure 1 and Figure 2 The radio frequency and buffer module includes a radio frequency module and I and Q buffers;

[0078] The radio frequency module, such as Figure 3 As shown, it is used to transmit and receive millimeter-wave signals, and after mixing, it generates orthogonal baseband signals I and Q;

[0079] The I and Q buffers are used to provide impedance isolation and drive for the baseband signals I and Q, respectively.

[0080] Here, the baseband I and Q signals output by the receiver mixer are specifically represented as follows:

[0081] In-phase I signal :

[0082]

[0083] Quadrature Q-channel signal :

[0084]

[0085] in,

[0086]

[0087]

[0088] In the formula, For the amplitude of the I-channel signal, For the DC component of the I-channel signal, For the Q-channel signal amplitude, This refers to the DC component of the Q-channel signal. For the target time-varying displacement, The carrier frequency wavelength used by the radar. , It depends on the nominal distance at which the radar reaches the target. The phase constant, It is channel phase offset.

[0089] Preferably, in some embodiments, such as Figure 4 As shown, both the I and Q buffers are implemented as voltage followers composed of operational amplifiers. They are used to receive baseband I and Q signals, realize the conversion between high input impedance and low output impedance, isolate the load effect between the front-end signal source and the subsequent circuit, and provide stable driving capability for the subsequent stage.

[0090] Preferably, in some embodiments, the analog demodulation module includes two DC term extraction modules (I and Q channels), two differentiators (I and Q channels), two multipliers (I and Q channels), and a first-stage subtractor, a second-stage subtractor, an adder, and an integrator; the output of the I-channel buffer is connected to the I-channel DC term extraction module, the I-channel differentiator, and the Q-channel multiplier, respectively, and the output of the Q-channel buffer is connected to the Q-channel DC term extraction module, the Q-channel differentiator, and the I-channel multiplier, respectively.

[0091] Each of the I and Q DC term extraction modules includes a DC component extraction module and an analog multiplier. The DC component extraction module is used to extract DC information from the baseband signal, and the analog multiplier generates a DC term interference signal for elimination. The analog multiplier receives the output signals of the current DC component extraction module and the corresponding differentiator.

[0092] The I and Q differentiators, such as Figure 5 As shown, all are used to differentiate the signal to extract the signal rate of change; the output of the I-channel differentiator is connected to the I-channel multiplier and the analog multiplier in the Q-channel DC term extraction module, respectively, and the output of the Q-channel differentiator is connected to the Q-channel multiplier and the analog multiplier in the I-channel DC term extraction module, respectively.

[0093] Here, after differentiation, we get:

[0094] In-phase I-channel differential signal :

[0095]

[0096] Orthogonal Q-path differential signal :

[0097]

[0098] in,

[0099]

[0100] In the formula, for The differential, For the target time-varying displacement The differential.

[0101] The I and Q multipliers, such as Figure 6 As shown, these are all used to achieve cross-multiplication of the original signal and the output signal of the differentiator, specifically expressed as follows:

[0102]

[0103]

[0104] The first-stage subtractor, such as Figure 7 As shown, using the outputs of the I and Q multipliers as inputs, channel differential is performed to obtain:

[0105]

[0106] Here, the output signal China covers Differential of signal And two interference terms caused by DC components. and Two analog multipliers receive the output signals from the DC component extraction module and the output signal from the differential module, and calculate respectively: and ;

[0107] The second-stage subtractor (e.g.) Figure 7 (as shown) and adder (such as) Figure 8 As shown), they work together to form a DC interference elimination structure, where the input of the second-stage subtractor is the I-channel DC term extraction module and the output of the first-stage subtractor, and the input of the adder is the Q-channel DC term extraction module and the output of the second-stage subtractor;

[0108] Here, the second-stage subtractor eliminates... The DC-related interference term output is:

[0109]

[0110] Adder elimination The DC-related interference term output is:

[0111]

[0112] This signal is only related to Proportional signals, where Therefore, by integrating the output signal, we can obtain... Complete the phase dephase operation of the I and Q signals.

[0113] The integrator, such as Figure 9 As shown, this is used to recover the phase information corresponding to vital signs based on the output of the adder, specifically:

[0114] .

[0115] Furthermore, in one embodiment, combined with Figure 10 Both the I and Q DC term extraction modules include a first resistor R. 22 Second resistor R 23 Third resistor R 24 The system includes a first capacitor C6, a second capacitor C7, a diode D1, an N-channel MOSFET SW1, and a buffer OP9; the drain of the N-channel MOSFET SW1 is connected to the baseband I or Q signal and a third resistor R. 24 At one end, the gate of the N-channel MOS transistor SW1 is connected to a first resistor R. 22 The circuit is grounded and connected to the power supply VCC through the first capacitor C6. The source of the N-channel MOSFET SW1 is connected to the positive terminal of the diode D1, the negative terminal of the diode D1 is connected to the positive input terminal of the buffer OP9, and grounded through the second capacitor C7. The negative input terminal of the buffer OP9 is connected to its output terminal and connected to the analog multiplier.

[0116] Preferably, the buffer OP9 is implemented by a voltage follower composed of an operational amplifier.

[0117] Analog signal processing offers advantages such as continuous-time response, zero quantization error, low power consumption, low latency, and freedom from sampling theorem limitations. Building upon the excellent phase extraction capabilities of the MDACM algorithm, this invention utilizes basic analog functional units such as analog differentiators, analog multipliers, analog adders, analog subtractors, and integrators to complete the entire phase demodulation process in the analog domain, effectively simplifying the system structure and reducing power consumption. Therefore, the end-to-end radar system proposed in this invention features a simple structure, eliminates the need for complex digital signal processing units, and is particularly suitable for vital sign monitoring applications with high requirements for real-time performance, energy efficiency, and reliability. This system enables high-precision, low-power, and high-real-time non-contact vital sign monitoring.

[0118] In summary, this invention, while inheriting the excellent phase extraction capabilities of the MDACM algorithm, achieves high real-time performance, low power consumption, wide bandwidth, and high precision phase demodulation through a fully analog design. It is particularly suitable for embedded sensing and monitoring systems with stringent requirements for real-time performance, power consumption, and integration.

Claims

1. An end-to-end vital signs monitoring radar system, characterized by, The system comprises a radio frequency and buffer module and an analog demodulation module; The radio frequency and buffer module is used for transmitting and receiving millimeter wave signals and buffering signals; The analog demodulation module is used for demodulating signals in an analog domain by using an MDACM method and outputting a target time-varying displacement signal.

2. The end-to-end vital signs monitoring radar system of claim 1, wherein, The radio frequency and buffer module comprises a radio frequency module and I and Q two-way buffers; The radio frequency module is used for transmitting and receiving millimeter wave signals and generating orthogonal baseband signals I and Q after frequency mixing; The I and Q two-way buffers are used for respectively performing impedance isolation and driving on the baseband signals I and Q.

3. The end-to-end vital signs monitoring radar system of claim 2, wherein, In the radio frequency module, the baseband I and Q two-way signals output by a receiver mixer are specifically represented as: In-phase I-path signal : ； Quadrature Q-path signal : ； wherein, ； ； In the formula, For the amplitude of the I-channel signal, For the DC component of the I-channel signal, For the Q-channel signal amplitude, This refers to the DC component of the Q-channel signal. For the target time-varying displacement, The carrier frequency wavelength used by the radar. , It depends on the nominal distance at which the radar reaches the target. The phase constant, It is channel phase offset.

4. The end-to-end vital signs monitoring radar system of claim 3, wherein, The I and Q two-way buffers are both realized by voltage followers composed of operational amplifiers, are used for receiving the baseband I and Q signals, realizing conversion of high input impedance and low output impedance, isolating load effects between a front-stage signal source and a subsequent circuit, and providing stable driving capability for a rear stage.

5. The end-to-end vital signs monitoring radar system of claim 3, wherein, The analog demodulation module comprises I and Q two-way direct current term extraction modules, I and Q two-way differentiators, I and Q two-way multipliers, a first-stage subtracter, a second-stage subtracter, an adder and an integrator; Outputs of the I-way buffer are respectively connected to the I-way direct current term extraction module, the I-way differentiator and the Q-way multiplier, and outputs of the Q-way buffer are respectively connected to the Q-way direct current term extraction module, the Q-way differentiator and the I-way multiplier; Each of the I and Q two-way direct current term extraction modules comprises a direct current component extraction module and an analog multiplier; the direct current component extraction module is used for extracting direct current information in the baseband signal, and the analog multiplier generates a direct current term interference signal for elimination; the analog multiplier receives output signals of the current-way direct current component extraction module and the opposite-way differentiator; The I and Q two-way differentiators are both used for differentiating signals to extract signal change rates; an output of the I-way differentiator is respectively connected to the I-way multiplier and the analog multiplier in the Q-way direct current term extraction module, and an output of the Q-way differentiator is respectively connected to the Q-way multiplier and the analog multiplier in the I-way direct current term extraction module; The I and Q two-way multipliers are both used for realizing cross multiplication of original-way signals and opposite-way differentiator output signals; The first-stage subtracter takes outputs of the I and Q two-way multipliers as inputs to complete channel difference; The second-stage subtracter and the adder cooperatively constitute a direct current interference term elimination structure; an input of the second-stage subtracter is the output of the I-way direct current term extraction module and the first-stage subtracter, and an input of the adder is the output of the Q-way direct current term extraction module and the second-stage subtracter; The integrator is used for recovering phase information corresponding to vital signs according to an output of the adder.

6. The end-to-end vital signs monitoring radar system of claim 5, wherein, The I and Q two-way differentiators differentiate the I and Q two-way signals to obtain: In-phase I path differential signal : ； Quadrature Q path differential signal : ； wherein, ； In the formula, for The differential, For the target time-varying displacement The differential.

7. The end-to-end vital signs monitoring radar system of claim 6, wherein, The I and Q two-way multipliers are both used for realizing cross multiplication of original-way signals and opposite-way differentiated signals, and are specifically represented as: ； ； An output of the first-stage subtracter is: ； output signal encompassing the differential of the signal and two dc components resulting in interference terms and ; Two analog multipliers receive the output signals of the DC component extraction module and the differential circuit, and calculate, respectively: and ; The output of the second stage subtracter is: ； The output of the adder is: 。 8. The end-to-end vital signs monitoring radar system of claim 7, wherein, The integrator integrates the output signal of the adder to restore the time-varying displacement information, and specifically is: 。 9. The end-to-end vital signs monitoring radar system of claim 5, wherein, The I, Q two-way direct current item extraction module includes first resistance (R 22 ), second resistance (R 23 ), third resistance (R 24 ), first capacitor (C6), second capacitor (C7), diode (D1), N channel MOS tube (SW1) and buffer (OP9); the drain of the N channel MOS tube (SW1) is connected with the baseband I or Q road signal and one end of the third resistance (R 24 ), the gate of the N channel MOS tube (SW1) is grounded through the first resistance (R 22 ), and is connected with the power supply VCC through the first capacitor (C6); the source of the N channel MOS tube (SW1) is connected with the anode of the diode (D1), the cathode of the diode (D1) is connected with the positive input end of the buffer (OP9) and grounded through the second capacitor (C7), the negative input end of the buffer (OP9) is connected with the output end and connected to the analog multiplier.

10. The end-to-end vital signs monitoring radar system of claim 9, wherein, The buffer (OP9) is realized by a voltage follower composed of an operational amplifier.

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