Abstract:
A microwave motion sensor including a transmitting device, a signal processing device, a signal processing device, and a path switching device is disclosed. The transmitting device transmits a microwave signal to a space under detection. The receiving device receives a reflected microwave signal reflected from the space under detection. The signal processing device processes the reflected microwave signal received by the receiving device to judge whether there is a disturbance in the space under detection, wherein the signal processing device generates the microwave signal. The path switching device is coupled to the signal processing device and the transmitting device and results in different phase shifts to a plurality of transmission paths travelled by the microwave signal.

Description:
[0001]    This is a continuation-in-part application of U.S. application Ser. No. 13/484,732, filed May 31, 2012, which is a continuation-in-part Application of application Ser. No. 12/886,522, filed Sep. 20, 2010, which claims the benefit of Taiwan application Serial No. 100139869, filed Nov. 1, 2011. This application claims the benefit of Taiwan application Serial No. 101138273, filed Oct. 17, 2012. The disclosure of which is incorporated by reference herein in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The disclosure relates in general to a microwave motion sensor. 
       BACKGROUND 
       [0003]    Motion sensor is normally used in security surveillance or on-site identification. In general, the motion sensor is realized by infrared technology. However, the infrared technology is susceptible to environmental temperature and may even result in detection error or failure. 
         [0004]    Based on the Doppler principle, the microwave motion sensor compares the phase shift between the transmitted signal and the received signal. If phase shift occurs, this indicates that there is disturbance source in the environment. 
         [0005]    Conventional microwave motion sensor has the advantage of simple architecture but needs to resolve the problem arising from sensing zero points. Referring to  FIG. 1 , a curve chart showing sensitivity of a conventional microwave motion sensor is shown. As indicated in  FIG. 1 , the horizontal axis denotes distance and the vertical axis denotes sensing sensitivity. When the signal transmitted from the sensor  100  hits the object under detection  110 , the transmitted signal will be reflected as a reception signal.  FIG. 1  shows that the radar cannot detect motion at sensing zero points (that is, the sensing sensitivity is zero). That is, when the object under detection  110  is located at sensing zero points, the sensor  100  cannot sense the object under detection  110 . The phenomenon of sensing zero points is a common problem to the single-frequency Doppler architecture. The sensing zero points periodically occur at an interval of one quarter wavelength of an electromagnetic wave. Points with largest sensing sensitivity are best sensing points. 
         [0006]    Moreover, the microwave motion sensor performs detection with continuous wave radar that transmits and receives signals simultaneously. For Doppler shift detection, a mixer is used to down-convert the carrier frequency, hence resulting in DC offset due to co-frequency reflected wave from environmental clutters. As a result, the receiver is saturated by strong DC signals and thus system sensitivity is considerably reduced. 
       SUMMARY 
       [0007]    According to one exemplary embodiment, a microwave motion sensor including a transmitting device, a signal processing device, a signal processing device, and a path switching device is disclosed. The transmitting device transmits a microwave signal to a space under detection. The receiving device receives a reflected microwave signal reflected from the space under detection. The signal processing device processes the reflected microwave signal received by the receiving device to judge whether there is a disturbance in the space under detection, wherein the signal processing device generates the microwave signal. The path switching device is coupled to the signal processing device and the transmitting device and results in different phase shifts to a plurality of transmission paths which the microwave signal passes through. 
         [0008]    According to another exemplary embodiment, a microwave motion sensor including a transmitting device, a receiving device, a path switching device and a signal processing device is disclosed. The transmitting device transmits a microwave signal to a space under detection. The receiving device receives a reflected microwave signal reflected from the space under detection. The path switching device is coupled to the receiving device and results in different phase shifts to a plurality of reception paths which the reflected microwave signal passes through. The signal processing device processes the reflected microwave signal received by the receiving device to judge whether there is a disturbance in the space under detection, wherein the signal processing device generates the microwave signal. 
         [0009]    According to an alternative exemplary embodiment, a microwave motion sensor including a transceiving device, a signal processing device, and a path switching device is disclosed. The transceiving device transmits a microwave signal to a space under detection and receives a reflected microwave signal reflected from the space under detection. The signal processing device processes the reflected microwave signal received by the transceiving device to judge whether there is a disturbance in the space under detection, wherein the signal processing device generates the microwave signal. The path switching device is coupled to the signal processing device and the transceiving device and results in different phase shifts to a plurality of paths which the microwave signal and the reflected microwave signal pass through. 
         [0010]    The above and other disclosures of the application will become better understood with regard to the following detailed description of the preferred but non-limiting embodiment(s). The following description is made with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  (PRIOR ART) is a curve chart showing sensitivity of a conventional microwave motion sensor; 
           [0012]      FIG. 2  shows a functional block diagram of a microwave motion sensor according to an embodiment of the disclosure; 
           [0013]      FIG. 3A  shows an exemplary example of a delay path switching unit according to an embodiment of the disclosure; 
           [0014]      FIG. 3B  is a curve chart showing sensitivity according to an embodiment of the disclosure; 
           [0015]      FIG. 4A  and  FIG. 4B  respectively are a path switching control timing diagram according to an embodiment of the disclosure; and 
           [0016]      FIG. 5A  and  FIG. 5B  respectively are a functional block diagram of a microwave motion sensor according to other embodiments of the disclosure. 
       
    
    
       [0017]    In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing. 
       DETAILED DESCRIPTION 
       [0018]    A microwave motion sensor architecture using Doppler principle is disclosed in an embodiment of the disclosure. In an embodiment of the disclosure, output phase or frequency of the oscillator varies when the self-injection-locked voltage-controlled oscillator with high sensitivity receives a Doppler phase modulation signal reflected from an object under detection. By locking the output frequency of the injection-locked voltage-controlled oscillator with a phase-locked loop, external disturbance information is reflected on the control voltage of the injection-locked voltage-controlled oscillator, such that both bandwidth requirement and electromagnetic interference could be reduced. 
         [0019]    In an embodiment of the disclosure, the transmission/reception paths with different phase shifts are switched, such that the sensing zero points in the transmission/reception paths do not overlap (the sensing zero points in the transmission/reception paths are even interlaced), and the phenomenon of sensing zero points in single-frequency Doppler radar are eliminated. The sensing sensitivities of these transmission/reception paths are complementary to each other. That is, none of other paths will not be at a sensing zero point when one of the paths is at a sensing zero point, and the disturbance of the object under detection could thus be stably sensed. 
         [0020]    In an embodiment of the disclosure, in detecting low frequency motion/disturbance signals, the transmission signal paths are closed at non-sampling points, so as to reduce the average microwave transmission power. 
         [0021]    In an embodiment of the disclosure, a dual-control voltage-controlled oscillator is utilized to adjust the DC level and to eliminate the DC offset, because adding another voltage control port and another varactor changes the resonant frequency of the oscillator resonant cavity, so that the DC level of the output signal of the phase- and self-injection-locked dual-control voltage-controlled oscillator is adjusted to the original predetermined value. 
         [0022]      FIG. 2  shows a functional block diagram of a microwave motion sensor according to an embodiment of the disclosure. As indicated in  FIG. 2 , the microwave motion sensor  200  includes at least one transmitting antenna  210 , a delay path switching unit  220 , a phase-locked loop  225  and at least one receiving antenna  270 . The phase-locked loop  225  includes a phase frequency detector (PFD)  230 , a charge pump (CP)  240 , a low pass filter (LPF)  250  and a dual-control voltage-controlled oscillator  260 . In the present embodiment of the disclosure, the phase-locked loop is also referred as a signal processing device. The microwave motion sensor  200  may selectively include a path switching controller  280 . 
         [0023]    The transmitting antenna  210  transmits a microwave signal, and the receiving antenna  270  receives the reflected microwave signal reflected from the object under detection. 
         [0024]    The delay path switching unit  220  switches different delay paths and results in different phase shifts to multiple paths (that is, there are phase shifts existing between multiple paths). Thus, different delay paths can be selected as signal transmission paths. Here below, the switching between two different delay paths is used as an exemplification, but the present disclosure is not limited thereto. In the present disclosure, multiple delay paths can be formed, and the switching can occur between the multiple delay paths. 
         [0025]    Referring to  FIG. 3A , an exemplary example of a delay path switching unit  220  according to an embodiment of the disclosure is shown. As indicated in  FIG. 3A , the delay path switching unit  220  includes a delay unit D, and switches SW 1  and SW 2 . The switches SW 1  and SW 2  may be realized by a single-pole double-throw (SPDT) switch. The delay unit D delays the signal phase by for example but not limited to 90 degrees. That is, the phase shift between the paths P 1  and P 2  is 90 degrees. 
         [0026]    Referring to  FIG. 3B , a curve chart showing sensitivity change according to an embodiment of the disclosure is shown. In the curve chart, the horizontal axis denotes distance, and the vertical axis denotes sensing sensitivity.  FIG. 3B  shows that there are two different delay paths whose sensing zero points are different from each other. In the prior art, the sensing zero points incapacitate the sensor of sensing the object under detection. However, the failure of sensing the object under detection is resolved in the embodiment of the disclosure. To put it in greater details, if the object under detection  310  is located at a sensing zero point in one of the paths of the sensor  300 , the object under detection  310  will not be located at the sensing zero point on another path. 
         [0027]    Referring to  FIG. 2 . The phase-locked loop  225  controls the dual-control voltage-controlled oscillator  260 . The phase-locked loop  225  is also referred as a signal processing device. Details of the phase-locked loop  225  are disclosed below. The phase frequency detector  230  detects an output phase shift (or frequency shift) between an output signal of the dual-control voltage-controlled oscillator  260  and a reference signal REF. 
         [0028]    The charge pump  240  outputs a voltage signal according to the detection results of the phase frequency detector  230 . The output voltage signal of the charge pump  240  is filtered by the low pass filter  250  as a first control voltage VCO_CN 1 . The first control voltage VCO_CN 1  controls the frequency of the output signal of the dual-control voltage-controlled oscillator  260 . 
         [0029]    The dual-control voltage-controlled oscillator  260  is realized by an injection-locked voltage-controlled oscillator architecture. The dual-control voltage-controlled oscillator  260  may output and receive a signal at the same time. In other possible embodiments, the output signal of the dual-control voltage-controlled oscillator  260  may be connected to an input end of the delay path switching unit  220  and an input end of the phase-locked loop  225  via a power distributor (not illustrated). After the microwave signal generated from the dual-control voltage-controlled oscillator  260  passes through the delay path switching unit  220 , the output microwave signal is transmitted to the object under detection and/or space under detection by the transmitting antenna  210 . 
         [0030]    If there are disturbance signals existing in the space under detection (disturbance is such as heart beat, breath, or window vibration), when the transmission signal is reflected, the phase or frequency of the reflected signal will change (relative to the transmission signal) due to the Doppler effect. After the reflected signal is received by the receiving antenna  270 , the reflected signal can be amplified (the amplifier not illustrated) and injected to the dual-control voltage-controlled oscillator  260 . Due to the influence of the reflected signal, the phase or frequency of the output signal of the dual-control voltage-controlled oscillator  260  will change. After the phase variation or frequency variation of the output signal of the dual-control voltage-controlled oscillator  260  is detected by the phase-locked loop  225 , the phase-locked loop  225  generates a corresponding first control voltage VCO_CN 1  in response to the phase variation or frequency variation, so as to adjust the output frequency of the dual-control voltage-controlled oscillator  260  to the reference frequency. The external disturbance information can be obtained from the observation of the first control voltage VCO_CN 1 . 
         [0031]    In an embodiment of the disclosure, the second control voltage VCO _CN 2  of the dual-control voltage-controlled oscillator  260  may eliminate the DC offset. The oscillation frequency of the dual-control voltage-controlled oscillator  260  is determined by the two control voltages VCO_CN 1  and VCO_CN 2 . If the dual-control voltage-controlled oscillator  260  is affected by an external disturbance signal and a DC offset occurs in the primary first control voltage VCO_CN 1 , variation in the second control voltage VCO_CN 2  which is used to eliminate the DC offset of the first control voltage VCO_CN 1  is obtained according to equation (1), wherein Kv1, Kv2 are system constants that are determined by the designer. 
         [0000]        Kv 1 *ΔVCO   —   CN 1 +Kv 2 *ΔVCO   —   CN 2=0   (1)
 
         [0000]    Wherein, ΔVCO_CN 1  and ΔVCO_CN 2  respectively denote the variation in the first control voltage VCO_CN 1  and the second control voltage VCO_CN 2 . 
         [0032]    Equation (2) is from equation (1) and expressed as: 
         [0000]    
       
         
           
             
               
                 
                   
                     Δ 
                      
                     
                         
                     
                      
                     VCO_CN 
                      
                     
                         
                     
                      
                     2 
                   
                   = 
                   
                     - 
                     
                       
                         
                           K 
                           
                             V 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                          
                         Δ 
                          
                         
                             
                         
                          
                         VCO_CN 
                          
                         
                             
                         
                          
                         1 
                       
                       
                         K 
                         
                           V 
                            
                           
                               
                           
                            
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0033]    When it is detected that the DC average value of the primary first control voltage VCO_CN 1  varies, the required variation in the second control voltage VCO_CN 2  can be obtained from the above equations (1) and (2). Exemplarily but not restrictively, the constant Kv1 is equal to 2 MHz/V and the constant Kv2 is equal to 20 MHz/V. When the system detects that DC average variation of the primary first control voltage VCO_CN 1  is 1V, the variation in the second control voltage VCO_CN 2  is −0.1V, as from the above equations (1) and (2). That is, the DC offset of the first control voltage VCO_CN 1  can be eliminated by stepping down the second control voltage VCO_CN 2  by 0.1V. That is, the DC offset of the external disturbance information denoted by the first control voltage VCO_CN 1  has been eliminated. 
         [0034]    In practice, the dual-control voltage-controlled oscillator  260  can be realized by adding a voltage control port and a varactor to a conventional VCO. By changing the resonant frequency of the resonant cavity, the DC level of the first control voltage controlling the phase- and self-injection-locked oscillator (the dual-control voltage-controlled oscillator  260 ) is adjusted to the original predetermined value, and there is no need to add any complicated control loops or radio-frequency circuit components. This effectively resolves the problem of saturation in the dynamic range of the conventional radar receiver (this problem is caused by DC offset), so that the detection of the microwave sensor is more stable and the detection failure due to change in external environment will not occur easily. 
         [0035]    Referring to  FIG. 4A  and  FIG. 4B , path switching control timing diagrams according to an embodiment of the disclosure are respectively shown. As indicated in  FIG. 4A , by switching between the paths P 1  and P 2 , transmission or reception of the sensing signals on the paths P 1  and P 2  is in different time slots, and the problem arising from sensing zero points in the paths could thus be avoided. 
         [0036]    Besides, if the disturbance of the object under detection under detection is a low frequency signal (for example, the heart beat rate of human is about 72 beats/minute in the frequency of 1.2 Hz), then the transmission power can further be reduced in an embodiment of the disclosure. As indicated in  FIG. 4B , exemplarily but not restrictively, the transmission time of the paths P 1  and P 2  is about 1 ms. If the non-transmission period (during which time no microwave signal is transmitted) is 48 ms, then the average frequency is 20 Hz, which is far higher than the frequency of the disturbance of the object under detection. In an embodiment of the disclosure, the transmission paths can be turned-off at non-sampling time periods of the two paths to reduce the average transmission power and almost without deteriorating the detection sensitivity. The switching timing of  FIG. 4A  and  FIG. 4B  can be controlled by a path switching controller ( FIG. 2 ). The path switching controller transmits multiple switch control signals to control the multiple switches in the delay path switching unit. 
         [0037]      FIG. 5A  and  FIG. 5B  respectively are functional block diagrams of a microwave motion sensor according to other embodiments of the disclosure. The comparison between  FIG. 5A  and  FIG. 2  shows that in the microwave motion sensor  500 A of  FIG. 5A , the delay path switching unit  520 A is used for switching between different transceiving paths. The comparison between  FIG. 5B  and  FIG. 2  shows that in the microwave motion sensor  500 B of  FIG. 5B , an antenna  510  is capable of receiving and transmitting microwave signals. The delay path switching unit  520 B of  FIG. 5B  is different from the delay path switching unit  220  of  FIG. 2  is that the path phase shift is 45 degrees for example. 
         [0038]    Besides, anyone who is skilled in the technology of the present disclosure will understand that any combinations of the above embodiments are still within the spirit of the present disclosure. For example, in other possible embodiments of the present disclosure, delay path switching units may be disposed in both the transmission paths and the reception paths for switching the transmission paths and the reception paths respectively. Details of the disposition of the delay path switching units are obtained from the above disclosure and the similarities are not repeated here. 
         [0039]    The embodiments of the disclosure may be used for detecting such as but not limited to breaths, heartbeat, disturbance and vibration (such as the vibration of windows). 
         [0040]    In the embodiments of the disclosure, path delay switching is with a self-injection-locked Doppler radar. However, in other embodiment of the disclosure, the path delay switching may also be with other architecture of single-frequency Doppler radar. 
         [0041]    As disclosed in the above embodiments, the disclosure at least has many advantages exemplified below: 
         [0042]    In an embodiment of the disclosure, to resolve the problem arising from sensing zero points (that is, external disturbances cannot be sensed in some positions), the transmission/reception paths with different phase shifts are switched, such that the sensing zero points in the transmission/reception paths do not overlap (the sensing zero points in the transmission/reception paths are even interlaced). By doing so, object are has under excellent sensing sensitivity in every position and the phenomenon of sensing zero points is eliminated. That is, the sensing sensitivities of these transmission/reception paths are complementary to each other. 
         [0043]    In an embodiment of the disclosure, in detection low frequency motion/disturbance signal, a lower sampling frequency would suffice to detect the low frequency motion/disturbance signal. Furthermore, there is no need to transmit electromagnetic wave at non-sampling time, so that the average transmission power is effectively reduced, and the concern of microwave exposure to human body can thus be relieved. 
         [0044]    In an embodiment of the disclosure, a dual-control voltage-controlled oscillator is utilized to adjust the DC level to eliminate the DC offset, and there is no need to add any complicated control loops or radio frequency circuit components. The detection result of the microwave sensor is even more stable, and the detection failure due to change in external environment will not occur easily. 
         [0045]    It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.