JP4041997B1 - High frequency sensor device - Google Patents

Abstract

A high-frequency sensor device capable of detecting an object with low radiation power is provided.
A mixer circuit includes an input terminal for inputting a high-frequency signal including a transmission wave and a reflected wave, and a conversion element that is cascade-connected to the input terminal and performs frequency conversion by mixing the transmission wave and the reflected wave. A high-pass element connected in cascade to the conversion element, and one end connected to the high-pass element so as to absorb the high-frequency signal that has passed through the high-pass element, and the other end is A grounded resistive element, and an output terminal that outputs a Doppler frequency signal generated by frequency conversion by the conversion element via a branch point between the conversion element and the high-pass element, and At the input terminal, the input impedance of the mixer circuit is matched to the characteristic impedance of an external circuit connected to the input terminal.
[Selection] Figure 1

Description

  The present invention relates to a high frequency sensor device.

  The high-frequency sensor device can detect a moving object and a stationary object. Among these, the high-frequency sensor device using the Doppler effect between the transmitted wave and the reflected wave can detect a moving object and measure the speed. Such high-frequency sensor devices are widely used for human body detection in bathrooms and toilets, automatic urinal cleaning, automatic doors, automobile back sensors, and the like.

  In this case, since radio waves such as 10 GHz band and 24 GHz band are used, it is necessary to suppress the spurious emission intensity below a regulation value in order to conform to the Radio Law. That is, the sensor device is required to have a low radiated power in order to suppress the spurious emission intensity and to detect even at a low radiated power.

  For this purpose, it is important to accurately control the antenna directivity and improve the sensitivity of the receiving circuit. As a receiving circuit of a high-frequency sensor device, a mixer circuit using a conversion element having nonlinearity such as a mixer diode or FET is usually used.

  However, in the case of a high-frequency Doppler sensor device using microwaves, the Doppler frequency is low, for example, several thousand hertz or less, and a mixer circuit for a communication device having an IF frequency of several tens of megahertz has insufficient characteristics as a sensor device. is there.

There is a technical disclosure example regarding a small-sized microwave mixer circuit that can obtain stable characteristics against high frequency characteristics and mounting variations of local oscillation FETs (Patent Document 1).
JP-A-10-107549

  The present invention provides a high-frequency sensor device capable of detecting an object with low radiation power.

According to one aspect of the present invention, an oscillator for generating a transmission wave, a transmitting antenna for radiating the transmitting wave, a receiving antenna in which the transmission wave receives the reflected waves generated is reflected by the detected object, wherein A mixer circuit that inputs the transmission wave generated by an oscillator and the reflected wave received by the antenna and outputs an intermediate frequency signal having a difference frequency between them; and the mixer circuit includes the transmission wave An input terminal for inputting a high-frequency signal including the reflected wave, and a non-linearity controlled by changing a forward bias current by a DC voltage, and the transmission wave and the reflected wave. A conversion element that converts the frequency by mixing, a high-pass element that is cascade-connected to the conversion element, and one end portion so as to absorb the high-frequency signal that has passed through the high-pass element. Is connected to the pass element is grounded and the other end, a resistive element to reduce reflection of the conversion element and a high frequency signal to the input terminal, the intermediate frequency signal generated by frequency-converted by the conversion element An output terminal that outputs via a branch point between the conversion element and the high-pass element, between the input terminal and the conversion element, between the conversion element and the high-pass element, A matching circuit that is provided between the high-pass element and the resistive element and reduces the radiation of the reflected wave from the mixer circuit, and at the input terminal, the input impedance of the mixer circuit is matched to the characteristic impedance of an external circuit connected to the input terminal becomes, the reduced reflected wave toward the antenna and the oscillator from the mixer circuit, the antenna and the oscillator RF sensor device is provided, which comprises the circuit performance of the stably maintained.

  According to the present invention, a high-frequency sensor device capable of detecting an object with low radiation power is provided.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a circuit diagram showing a configuration of a mixer circuit used in the high-frequency sensor device according to the embodiment of the present invention. The high frequency signal input terminal 10, the oscillator, the reflected wave G2 from the signal wave G1 and the object through the transmission line 8 is a characteristic impedance Z ₀ from the signal source 6, such as an antenna is input. When the object does not move, the frequencies of G1 and G2 match. On the other hand, when the object is moving, the frequency of the reflected wave G2 changes depending on the moving speed.
Even when the object is stationary, the intensity of the reflected wave changes according to the distance from the object. If this characteristic is used, it is possible to detect a stationary object.

  In either case, G1 and G2 pass through the transmission line 12 such as a microstrip line and are input to the conversion element 14 such as a mixer diode. The conversion element 14 has non-linearity, and G1 and G2 are mixed to generate a signal having various frequency components. A signal having a difference frequency between G1 and G2 can be taken out from the intermediate frequency (IF) signal output terminal 40 through the low pass filter (LPF) 30 from the branch point 17, and the object to be detected can be extracted. Can be detected.

Here, the configuration of the sensor using the mixer circuit will be described.
FIG. 2 shows a configuration of a high-frequency sensor device using the mixer circuit 50 of the present embodiment. FIG. 2A shows a case where a transmission antenna and a reception antenna are separated, and FIG. 2B shows a common transmission / reception antenna. This is the case.

  In the case of FIG. 2A, the frequency of the transmission wave G1 from the oscillator 52 is, for example, 10.525 or 24.15 GHz. Some are radiated from the transmission antenna 54, and others are branched by a directional coupler or the like and input to the mixer circuit 50 via the high-frequency signal input terminal 10. The reflected wave G2 from the object is input to the mixer circuit 50 via the receiving antenna 56 and the high frequency signal input terminal 10. The IF signal G10 generated in the mixer circuit 50 is output from the IF signal output terminal 40 and input to an external IF amplifier (not shown).

  2B, a part of the transmission wave G1 from the oscillator 52 is radiated from the transmission / reception antenna 58, and the other is input to the mixer circuit 50 via the high-frequency signal input terminal 10. The reflected wave G2 from the object is input to the mixer circuit 50 via the transmission / reception antenna 58 and the high-frequency signal input terminal 10. Although the configuration of FIG. 2B is simpler, a circuit for separating transmission and reception is necessary. The oscillator 52 can be reduced in size by a transistor such as a HEMT (High Electron Mobility Transistor) and a dielectric resonator.

The oscillator 52 and the antenna constitute a transmission line system having a characteristic impedance Z ₀ such as 50Ω. As a result, the impedance Zout viewed power from the high frequency signal input terminal 10 in FIG. 1 is configured so as to be Z _0. In any configuration, the IF signal G10 having a difference frequency between the signal wave G1 and the reflected wave G2 is taken out from the IF signal output terminal 40.

Next, the Doppler frequency will be described. If the frequency of G1 is f1, and the frequency of G2 is f2, an intermediate frequency (IF) signal G10 in the vicinity of the Doppler frequency as a difference (f1-f2) is generated. In the case of a moving object, f2 changes according to the moving speed, and the Doppler frequency Δf is expressed by Expression (1).

Δf = f1−f2 = 2 × f1 × v / c Equation (1)

F1: Transmission frequency (Hz)
f2: reflection frequency (Hz)
v: object moving speed (m / s)
c: speed of light (= 300 × 10 ⁶ m / s)

For example, when the high-frequency sensor is directed to a moving human body or liquid flow, an output signal in the vicinity of the Doppler frequency Δf that is proportional to the flow velocity v is output from the IF signal output terminal 40 as represented by the equation (1). . The output signal G10 has a frequency spectrum, and there is a correlation between the Doppler frequency that is the peak of the spectrum and the velocity v. Therefore, the velocity v can be obtained by measuring the Doppler frequency Δf. For example, if f1 is 24 GHz and v is 10 m / s, Δf is 1600 Hz.

  Further, the conversion element 14 having non-linearity generates spurious signals including a harmonic component having a frequency that is an integral multiple of f1 in addition to the signal having the Doppler frequency Δf. G1 is a spectrum with these spurious components added. G3 and G4 generated by adding spurious to G1 and G2 are input to the terminal resistive element 22 through the high-pass element 20 such as the transmission line 12 and the capacitor.

  G3 and G4 are consumed by the resistive element 22 and are almost converted into heat or light, and reflected very little. The reflection of the high-frequency signal to the conversion element 14 and the high-frequency signal input terminal 10 is reduced by the signals G3 and G4 being absorbed by the resistive element 22. In addition, in this specification, absorption includes what is consumed by being converted into heat or light.

  The reflected waves G5 and G4 reflected waves G6 pass through the conversion element 14, the transmission line 12, and the high-frequency signal input terminal 10 and travel in the reverse direction, and the IF signal G10 is input to the LPF 30. Since the reflected waves G5 and G6 are not attenuated unless there is a resistive element, the high-frequency signal is emitted from the transmission line 12 and the high-frequency signal input terminal 10 to the outside.

FIG. 3 is a diagram illustrating the input impedance of the mixer circuit 50. 3 (a) is a Smith diagram and impedance display the S _11, FIG. 3 (b) construction of this embodiment, FIG. 3 (c) is a configuration of the comparative example. FIG. 3A shows an impedance locus viewed from the high-frequency signal input terminal 10 in a frequency range of 9 to 11 GHz. In the present embodiment, the VSWR (Voltage Standing Wave Ratio) is within 1.4 or less, which is a good match. For this reason, the radiation of the reflected waves G5 and G6 inside and outside the mixer circuit 50 can be reduced.

  On the other hand, in the comparative example of FIG. 3C, the conversion element 14 is connected to the quarter-wavelength transmission line 14 having an open end, but is not connected to the resistive element. In the quarter-wavelength open termination transmission line, the impedance is set to near zero near the conversion element 14, and a large high-frequency current flows through the conversion element 14. However, in this configuration, the VSWR of the mixer circuit 50 is as high as 5 to 10, and the reflected waves G5 and G6 are large. In the configuration shown in FIG. 3C, a signal having a frequency higher than the high cutoff frequency of the LPF 30 is not absorbed. In such a state, radiation of the reflected waves G5 and G6 to the outside is large inside and outside the mixer circuit 50, which becomes a noise source and degrades the detection characteristics of the sensor device.

  In addition, the reflected wave toward the signal source 6 including the antenna and the oscillator via the input terminal 10 and the transmission line 8 deteriorates the performance of the signal source 6 and is different from the design value. In this embodiment, since the reflected wave is reduced, the performance of the circuit outside the input terminal 10 such as the signal source 6 can be stably maintained.

  Next, the IF signal G10 will be described. In the case of detecting the movement of the human body and the liquid flow such as washing water at 10.525 GHz or 24.15 GHz, Δf is considered to be 3000 Hz or less from the equation (1). Therefore, the LPF 30 in FIG. 1A may have a frequency passband of, for example, 3000 Hz or less.

  When the reflected waves G5 and G6 including distortion enter the conversion element 14 again, the IF signal G10 further changes due to nonlinearity in the conversion element 14. Further changes in the IF signal caused by the reflected waves G5 and G6 are preferably reduced because they disturb the IF signal that should be detected by the transmitted wave G1 and the reflected wave G2 from the moving object.

  4A and 4B are graphs showing noise characteristics. FIG. 4A shows this embodiment, and FIG. 4B shows a comparative example. In either case, the output of the oscillator is 8 mW, and represents an IF signal obtained by detecting a moving object at a constant speed at a constant distance. The vertical axis represents amplitude value (V), and the horizontal axis represents time (s). In the comparative example, a noise component of 0.025V is generated. However, in the present embodiment, since there is no unnecessary reflection of a high frequency signal, a noise component of 0.014V or less can be obtained.

  5A and 5B are graphs showing IF signal characteristics. FIG. 4A shows this embodiment, and FIG. 4B shows a comparative example. Similarly to FIG. 3, the output of the oscillator is 8 mW, and represents an IF signal obtained by detecting a moving object at a constant speed at a constant distance. The vertical axis represents amplitude value (V), and the horizontal axis represents time (s). In the comparative example, the amplitude value is minus 0.2 to plus 0.28V. On the other hand, in this embodiment, since there is no unnecessary reflection of the high frequency signal, attenuation of the signal to the local oscillator and the high frequency signal input from the input terminal 10 can be reduced, and these high frequency signals are efficiently input to the conversion element 14. The amplitude can be as large as minus 0.4 to plus 0.4 V or more.

  The IF signal in the comparative example in which the reflected waves G5 and G6 are large, that is, the VSWR is large, has a large noise and a small amplitude value. As a result, it is necessary to increase the radiated power for obtaining the lower limit value of the IF signal amplitude for detecting the object, but there is a limit to make it less than the spurious emission intensity regulation by the Radio Law. Also, increasing the transmission wave increases power consumption. On the other hand, in this embodiment, an IF signal in which the influence of spurious is reduced can be obtained at a lower radiation power, and an object can be detected with high accuracy. Further, power consumption can be reduced.

  Next, description will be supplemented for each component of the mixer circuit 50 of FIG. The high-pass element 20 can be a capacitor or a stripline type pattern filter. In the case of the 10 GHz band, the lumped constant capacitor can be reduced in size. On the other hand, in the case of the 24 GHz band, by using a high-precision etching process, the pattern filter has uniform characteristics and can be easily downsized.

  In a high frequency sensor device for detecting a human body or measuring a liquid flow, the IF frequency is 3000 Hz or less, and the IF signal G10 can be output from the output terminal 40 when the band of the high-pass element 20 is greater than 3000 Hz. In this case, it is easy to steeply attenuate the high-frequency characteristics of the low-pass filter 30 having a pass band of 3000 Hz or less at 3000 Hz or more. In this way, only the IF signal to be detected among the signals generated in the conversion element 14 can be efficiently output from the output terminal 40.

The input impedance Zin of the mixer circuit 50, if the match with the external impedance Zout via the characteristic impedance Z ₀ is a transmission line 8, can be used a transmission line between the respective components of the mixer circuit 50 as a matching element.

  For example, the resistive element 22 is 10Ω, and the distance from the high-pass element 20 is the transmission line length L1 up to the vicinity where it intersects with the circle of r = 1 in the Smith chart. Since the line length L1 can be shorter than a quarter wavelength, the line length L1 can be reduced. Further, the high-pass element 20 is a lumped constant type capacitor so as to cancel out the reactance of the conversion element 12, and the capacitance C1 and the transmission line length L2 up to the conversion element 14 are matched with the impedance of the conversion element 14 to obtain the VSWR. Can be improved.

  As the conversion element 14, a pn junction diode made of a semiconductor, a Schottky barrier diode, an FET, a HEMT, or the like can be used. The higher the frequency, the more preferred is a compound semiconductor over silicon. In the case of such a conversion element 14 made of a semiconductor, it is possible to change the bias current in the forward direction by a DC power source to control nonlinearity and obtain a larger IF signal amplitude.

  The resistive element 22 may be a resistor that changes electrical energy into heat or light, an LED (Light Emitting Diode), or the like.

  The embodiments of the present invention have been described above with reference to the drawings. However, the present invention is not limited to these embodiments. Those skilled in the art have made various design changes with respect to the conversion elements, resistive elements, high-pass elements, transmission lines, low-pass filters, oscillators, antennas, etc. that constitute the mixer circuit and the high-frequency sensor device. Are included in the scope of the present invention without departing from the gist of the present invention.

It is a figure showing the structure of the mixer circuit used for the high frequency sensor apparatus concerning embodiment of this invention. It is a figure showing the structure of the high frequency sensor apparatus concerning embodiment of this invention. It is a figure explaining the input impedance of a mixer circuit. It is a graph showing a noise characteristic. It is a graph showing IF signal characteristics.

Explanation of symbols

8 transmission line, 10 high-frequency signal input terminal, 12 transmission line, 14 conversion element, 20 high-pass element, 22 resistive element, 30 low-pass filter, 40 IF signal output terminal, 50 mixer circuit, 52 oscillator, 54 transmission Antenna, 56 Receive antenna, 58 Transmit / receive antenna

Claims (7)

An oscillator for generating a transmission wave;
A transmitting antenna that radiates the transmitted wave;
A receiving antenna for receiving a reflected wave generated by the transmission wave being reflected by an object to be detected;
A mixer circuit that inputs the transmission wave generated by the oscillator and the reflected wave received by the antenna and outputs an intermediate frequency signal having a differential frequency thereof ;
With
The mixer circuit is
An input terminal for inputting a high-frequency signal including the transmission wave and the reflected wave;
Cascade connected to the input terminal, the nonlinearity is controlled by changing the forward bias current by a DC voltage , a conversion element that mixes the transmission wave and the reflected wave to convert the frequency,
A high-pass element cascaded to the conversion element;
One end is connected to the high-pass element so as to absorb the high-frequency signal that has passed through the high-pass element, the other end is grounded , and the high-frequency signal to the conversion element and the input terminal A resistive element that reduces reflection ;
An output terminal that outputs the intermediate frequency signal generated by frequency conversion by the conversion element via a branch point between the conversion element and the high-pass element;
Provided between the input terminal and the conversion element, between the conversion element and the high-pass element, and between the high-pass element and the resistive element, respectively, and reflected waves from the mixer circuit A matching circuit to reduce radiation;
Including
In the input terminal, the input impedance of the mixer circuit is matched to the characteristic impedance of an external circuit connected to the input terminal ,
A high-frequency sensor device that reduces a reflected wave from the mixer circuit toward the antenna and the oscillator and stably maintains the performance of the circuit of the antenna and the oscillator .   The high-frequency sensor device according to claim 1, wherein the transmitting antenna and the receiving antenna are the same. The high-frequency sensor device according to claim 1 , wherein the matching circuit includes a transmission line in which a characteristic impedance and a line length are changed. The matching circuit, a high frequency sensor device according to any one of claims 1 to 3, characterized in that they are composed of microstrip lines. The high-pass element is a high frequency sensor device according to any one of claims 1-4, characterized in that the capacitor or pattern filter. Wherein a branch point, a high-frequency sensor device according to any one of claims 1 to 5, characterized said output terminal, a further, further comprising a low-pass filter connected between the. The resistive element is a high frequency sensor device according to any one of claims 1-6, characterized in that the resistor or LED.

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