This invention generally relates to a vital-sign radar sensor, and more particularly to a vital-sign radar sensor using a wireless frequency-locked loop.
Conventional continuous wave (CW) radar can transmit a transmission signal to a moving subject and receive a reflected signal from the moving subject, the movement of the subject may generate Doppler Effect on the transmission signal to allow the reflected signal to contain Doppler phase shifts. For this reason, the information of the movement of the subject can be extracted from the reflected signal received by CW radar. An oscillation signal output from an oscillator of CW radar is transmitted as the transmission signal and also used as a local oscillation signal for frequency down-conversion or signal demodulation, so the frequency stability of CW radar is important. The oscillator may have phase noise due to internal components or external injection signals, for example, thermal noise, shot noise or flicker noise from internal components of the oscillator (resistor, capacitor, inductor and transistor) may vary amplitude, phase or frequency of the oscillation signal. The phase noise may cover Doppler phase shifts caused by tiny movement of the subject, such as vital sign, to result in a detection error.
Self-injection-locked (SIL) radar has a good sensitivity to tiny vibration for vital-sign detection because the reflected signal from the moving subject can be injected into injection port of the oscillator of the SIL radar to vary the frequency of the oscillator. However, null point may exist if the distance from the subject to the transmit antenna of SIL radar is an integer multiple of a half-wavelength.
The present invention provides a wireless frequency-locked loop composed of voltage-controlled oscillator, antenna component, propagation delay between antenna component and subject, mixer and loop filter to allow Doppler phase shifts caused by subject's movement to modulate the voltage-controlled oscillator such that frequency shifts can present vital sign of subject. Additionally, the wireless frequency-locked loop also can reduce phase noise of the voltage-controlled oscillator to enhance sensitivity of vital-sign detection.
A vital-sign radar sensor of the present invention includes a voltage-controlled oscillator (VCO), an antenna component, a mixer, a loop filter and a frequency demodulation component. The VCO includes an output port and a tuning port and is configured to output an oscillation signal via the output port. The antenna component is coupled to the VCO and configured to receive and transmit the oscillation signal as a transmitted signal to a subject and configured to receive a reflected signal from the subject as a received signal. The mixer is coupled to the VCO and the antenna component and configured to receive and mix the oscillation signal and the received signal to output a mixed signal. The loop filter is coupled to the mixer and configured to receive and filter the mixed signal to output a filtered signal, the filtered signal is configured to be delivered to the VCO via the tuning port. The frequency demodulation component is coupled to the VCO and configured to receive and demodulate the oscillation signal to output a vital-sign signal.
A wireless frequency-locked loop composed of the VCO, the antenna component, the propagation delay between the transmit antenna and the subject, the propagation delay between the subject and the receive antenna, the mixer and the loop filter is provided to detect vital sign of the subject in the present invention. The using of the wireless frequency-locked loop can eliminate null point and reduce phase noise to improve signal-to-noise ratio of the vital-sign signal and detection range of the vital-sign radar sensor.
With reference to
The VCO 110 includes an output port 111 and a tuning port 112 and is configured to output an oscillation signal SO from the output port 111. The antenna component 120 includes a transmit antenna 121 and a receive antenna 122, the transmit antenna 121 is coupled to the output port 111 of the VCO 110 and configured to receive and transmit the oscillation signal SO as a transmitted signal ST to a subject O. While the subject O has a motion relative to the transmit antenna 121, the motion results in a Doppler Effect on the transmitted signal ST to allow a reflected signal SR from the subject O to contain Doppler phase shifts. The receive antenna 122 is configured to receive the reflected signal SR as a received signal Sr from the subject O, the received signal Sr also contains the Doppler phase shifts caused by the motion of the subject O.
The mixer 130 is coupled to the VCO 110 and the antenna component 120 for receiving the oscillation signal SO and the received signal Sr and configured to mix the two signals into a mixed signal SM. The mixed signal SM represents the phase variation from the oscillation signal SO to the received signal Sr so it contains the information of the motion of the subject O. In the first embodiment, the combination of the signal propagation from the transmit antenna 121 to the subject O and from the subject O to the receive antenna 122 and the down-conversion process of the mixer 130 constructs a frequency discriminator configured to demodulate the Doppler phase shifts caused by the motion of the subject O and the phase noise of the VCO 110.
The loop filter 140 is coupled to the mixer 130 and configured to receive and filter the mixed signal SM to output a filtered signal SF. In the first embodiment, the loop filter 140 is a low-pass filter that is configured to filter high-frequency content of the mixed signal SM so as to extract the low-frequency content from vital signs. The filtered signal SF delivered to the tuning port 112 of the VCO 110 from the loop filter 140 is configured to modulate the oscillation signal SO of the VCO 110 to generate frequency shifts on the oscillation signal SO. A wireless frequency-locked loop (FLL) is constructed of the VCO 110, the antenna component 120, the propagation delay between the transmit antenna 121 and the subject O, the propagation delay between the subject O and the receive antenna 122, the mixer 130 and the loop filter 140. The delay of delay element of the wireless FLL is positively correlated with the inhibition of the phase noise such that the wireless FLL of the first embodiment, using the propagation delay between the transmit antenna 121 and the subject O and between the subject O and the receive antenna 122 as the delay element, reveals better inhibition of the phase noise when the subject O is located at a longer distance from the antenna component 120.
In the first embodiment, the feedback of the demodulated signal having the Doppler phase shifts caused by the motion of the subject O re-modulates the VCO 110 such that the VCO 110 can trace the Doppler phase shifts to enhance the strength of vital sign sensing due to its high tuning sensitivity, and the vital-sign detection range is not restricted because there is no null point. In addition, the re-modulation of the VCO 110 by using the demodulated signal having the Doppler phase shifts also reduces the phase noise of the VCO 110 to increase signal-to-noise ratio (SNR) of the vital-sign radar sensor 100.
With reference to
The wireless FLL of the first embodiment can reduce the phase noise of the VCO 110, as a result, vital-sign sensitivity and detection range of the vital-sign radar sensor 100 are increased for long-distance detection of vital sign of the subject O.
The ILO 170 is electrically connected to the receive antenna 122 to receive the received signal Sr and injection-locked by the received signal Sr to output an injection-locked signal SIL. The injection-locked signal SIL is delivered to the mixer 130 to mix with the oscillation signal SO4. The ILO 170 can amplify the Doppler phase shifts of the received signal Sr result from the motion of the subject O to effectively enhance the SNR of the vital-sign signal SVS detected by the vital-sign radar sensor 100.
With reference to
In a third embodiment of the present invention as shown in
The present invention utilizes the wireless FLL composed of the VCO 110, the antenna component 120, the propagation delay between the transmit antenna 121 and the subject O, the propagation delay between the subject O and the receive antenna 122, the mixer 130 and the loop filter 140 to detect the vital sign of the subject O. The using of the wireless FLL can eliminate null point and reduce phase noise to enhance the SNR of the vital-sign signal SVS and increase detection range of the vital-sign radar sensor 100.
While this invention has been particularly illustrated and described in detail with respect to the preferred embodiments thereof, it will be clearly understood by those skilled in the art that is not limited to the specific features shown and described and various modified and changed in form and details may be made without departing from the spirit and scope of this invention.
Number | Date | Country | Kind |
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109110785 | Mar 2020 | TW | national |