JP2013096904A - Signal processing circuit and signal processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a signal processing circuit for a SAW sensor in which deterioration in detection performance can be suppressed.SOLUTION: An oscillation circuit 11 outputs a signal of a predetermined frequency. The output signal is inputted to a carrier divider 13, a first divider 25 and a second divider 29. The carrier divider 13 divides the input signal in a division ratio N to generate a carrier. An antenna 21 receives a reception signal transmitted from a SAW sensor 3. At such a time, the carrier divider 13 stops operating. The first divider 25 divides the input signal in a division ratio Nto generate a first reference signal. Furthermore, the second divider 29 divides the input signal in a division ratio Nto generate a second reference signal. At such a time, the dividing ratios satisfy the conditions of N≠1, N≠N, N≠N, 1/N=|1/N-1/N|.

Description

  The present invention relates to a signal processing circuit for a SAW sensor.

  SAW sensors (surface acoustic wave sensors) that function as pressure sensors, strain sensors, temperature sensors, etc. by detecting changes in the resonance frequency or delay time of SAW devices are used.

  By configuring the SAW sensor and the signal processing circuit for sensing to communicate wirelessly, the SAW sensor can be miniaturized, and can be easily installed and used in various situations.

A wireless remote sensing system that performs wireless communication in this way is described in Patent Document 1. The system configuration of Patent Document 1 is shown in FIG.
In this system, the sensing device 13 (signal processing circuit) mixes the output signals of the carrier wave generation means 14 and the pulse generation means 15 with a mixer 16 to create a pulse-modulated signal, which is amplified by an amplifier 17 and then amplified by an antenna 12. To transmit the signal to the SAW sensor 1. The antenna 4 of the SAW sensor 1 receives a signal and inputs it to the SAW device 2. A reflected wave or transmitted wave is transmitted to the antenna 4 after a delay time T seconds unique to the SAW device, and a signal is transmitted from the SAW sensor 1 to the sensing device 13.

  Since the delay time T of the SAW sensor 1 changes depending on temperature or strain, the sensing device 13 can perform non-contact measurement of temperature or strain.

JP 2005-92490 A

  The sensing device 13 of the above-mentioned patent document 1 combines a signal returned from the SAW sensor 1 (usually −60 dB or less) and a signal in which a carrier wave leaks from the mixer 16 to detect sensor signal detection performance (detection accuracy, resolution). ) May get worse.

  In particular, when the sensing device 13 is highly integrated and intended to be a single chip of a silicon substrate, it is difficult to suppress deterioration in detection performance due to a leak signal of the mixer 16 by adjusting the gains of a plurality of switches and amplifiers 17. It is. Since the silicon substrate is conductive, it has only about 30 dB of isolation, and the detection performance tends to deteriorate.

  An object of the present invention is to propose a signal processing circuit and a signal processing method for a SAW sensor that can suppress deterioration in detection performance.

  In order to solve the above-described problem, the invention according to claim 1 transmits a carrier wave to a SAW sensor, receives a signal returned from the SAW sensor, and performs synchronous detection or quadrature detection on the received signal. A signal processing circuit that performs detection and outputs a detection signal, and includes an oscillation circuit, a carrier wave generation unit, a reference signal generation unit, and the like.

  The oscillation circuit outputs a signal having a predetermined frequency. The carrier wave generation unit divides or multiplies the signal of the oscillation circuit to generate a carrier wave. A plurality of reference signal generation units are provided, and a predetermined reference signal is generated by dividing or multiplying the signal of the oscillation circuit. A mixer provided corresponding to each of the plurality of reference signal generators mixes the reference signal and the received signal from the SAW sensor.

  The frequency of the carrier wave generated by the carrier wave generating unit and the frequency of the plurality of reference signal generated by the plurality of reference signal generating units are each set to DC when the plurality of reference signals are sequentially mixed with the carrier wave. Is the frequency to be converted to Therefore, for example, the phase of the received signal from the SAW sensor can be output as a DC output signal by passing through a low-pass filter. This phase represents the delay time T by the SAW sensor, and non-contact measurement such as temperature and strain can be performed.

  The frequency of the carrier wave generated by the carrier wave generation unit is different from the frequency of each of the plurality of reference signals generated by the plurality of reference signal generation units. The carrier wave generation unit stops the generation of the carrier wave when receiving the received signal and performing synchronous detection or quadrature detection.

  In the signal processing circuit configured as described above, the carrier wave (received signal from the SAW sensor) generated by the carrier wave generation unit is generated by the signal generated by the oscillation circuit and the reference signal generation unit. Since the frequency is different from that of the signal, when the reception signal from the SAW sensor is received and synchronous detection or quadrature detection is performed, generation of the carrier wave by the carrier wave generation unit is stopped, so that the frequency of the reception signal from the SAW sensor is It is possible to prevent the detection performance from deteriorating due to the absence of the signal and synthesis of the leaked signal in the received signal.

  The carrier wave generation unit and the reference signal generation unit can be configured using one or more frequency dividers or multipliers. Further, the plurality of reference signal generation units may have a common configuration using one or more frequency dividers or multipliers. For example, the reference signal generated by one frequency divider can be divided into two to form two reference signals. In that case, the frequency divider also serves as two reference signal generators.

  Although an amplifier can be appropriately disposed in the signal processing circuit described above, the amplifier may be disposed so as to amplify the received signal before the received signal is input to any mixer. With this configuration, it is possible to improve the signal level of the received signal and suppress the deterioration of the quality of the detection signal.

  The frequency of the carrier wave and the reference signal can be various values within a range that satisfies the above-described conditions. For example, the carrier wave generation unit divides the signal of the oscillation circuit by the frequency division ratio N, and n reference signal generation units are provided, and the signal of the oscillation circuit is divided by the frequency division ratio Nx (x = 1, 2,... N ), And Nx may be configured to be a value excluding an integer multiple of N.

  In the signal processing circuit configured as described above, even if the frequency of the generated reference signal is multiplied by an integer, it does not become the frequency of the carrier wave. That is, since the harmonics of the reference signal are not the same as the reception signal from the SAW sensor, the influence of the reference signal on the reception signal is reduced, and the deterioration in the quality of the detection signal can be further suppressed.

  Higher order frequency dividers are often created by cascading frequency dividers with divisors of order divisors. The condition of the frequency division ratio described above is also a condition for preventing the same frequency component as the signal from the SAW sensor from occurring at the cascade connection point.

Further, in order to further suppress the degradation of the quality of the detection signal, the signal processing circuit may be configured as one of (i) and (ii) shown below.
(I) a plurality of reference signal generation unit includes a first reference signal generating unit to divide the signal of the oscillation circuit at a division ratio N _1, a second reference for dividing the signal of the oscillation circuit at a division ratio N ₂ And a signal generation unit. The reference signal generated by the first reference signal generation unit is mixed with the reception signal from the SAW sensor upstream of the reference signal generated by the second reference signal generation unit. The carrier wave generation unit divides the signal of the oscillation circuit by the division ratio N. The condition of 1 / N ≠ 2 / N ₁ −1 / N ₂ is satisfied.

(Ii) a plurality of reference signal generation unit includes a first reference signal generator for multiplying the signal of the oscillation circuit multiplication factor M _1, and a second reference signal generator for multiplying the signal of the oscillation circuit multiplication factor M ₂ It consists of The reference signal generated by the first reference signal generation unit is mixed with the reception signal from the SAW sensor upstream of the reference signal generated by the second reference signal generation unit. The carrier wave generation unit multiplies the signal from the oscillation circuit by a multiplication factor M. The following conditions (a) and (b) are satisfied.

(A) M ≠ 2M ₁ −M ₂
(B) When M> M ₁ M ₁ ≠ (M + 1) / 2
In the signal processing circuit having the above-described configuration, it is possible to suppress deterioration in the quality of the detection signal. FIG. 3 is a diagram illustrating the frequency of the received signal (A) from the SAW sensor, the reference signal (B) generated by the first reference signal generation unit, and the image signal (C) with respect to the received signal (A). . When the reference signal generated by the second reference signal generation unit is the same as the frequency of the image signal, the reference signal leaks and the first mixer (the reference signal generated by the first reference signal generation unit and reception) When the signal is input to a mixer that mixes the signal, the difference output frequency becomes equal to the difference frequency between the reception signal (A) and the reference signal (B), so the leaked signal affects the reception signal. Will be given. However, if the conditions (i) and (ii) are satisfied, the second reference signal does not become the same as the frequency of the image signal, and the deterioration of the quality of the detection signal can be suppressed.

  By the way, at least one of the carrier wave generation unit and the reference signal generation unit may be configured by a cascade connection of a plurality of frequency dividers or multipliers. In this case, one frequency divider or multiplier may be a component of the carrier wave generation unit and two or more reference signal generation units.

  The invention according to claim 7, which has been made to solve the above-mentioned problem, generates a carrier wave by dividing or multiplying an output signal of a predetermined signal frequency output from the oscillation circuit, Steps of pulse modulation and transmission to the SAW sensor, reception of the reception signal returned from the SAW sensor in a state where the generation of the carrier wave is stopped, and frequency division of the output signal in a state where the generation of the carrier wave is stopped Or a step of generating a plurality of reference signals by multiplication and mixing the plurality of reference signals with a received signal to perform synchronous detection or quadrature detection, and the frequency of the carrier wave includes a plurality of reference The frequency of the signal is different from each of the signal frequencies, and the frequency of the carrier wave and the frequency of each of the plurality of reference signals are sequentially mixed with a plurality of reference signals with respect to the carrier wave. Characterized in that when the frequency of the carrier frequency is converted to DC.

  With such a signal processing method, it is possible to prevent the detection performance from deteriorating, as in the signal processing circuit of claim 1.

It is a conceptual diagram of the whole sensing system comprised from the signal processing circuit of Example 1, and a SAW sensor. FIG. 6 is a diagram illustrating a signal processing circuit according to a second embodiment. It is a figure explaining the image signal output from the mixer which mixes the received signal from a SAW sensor, a 1st reference signal, and those signals. FIG. 10 is a diagram illustrating a signal processing circuit according to a third embodiment. FIG. 10 is a diagram illustrating a signal processing circuit according to a fourth embodiment. FIG. 10 is a diagram illustrating a signal processing circuit according to a fifth embodiment. It is a figure explaining the signal processing circuit of a modification. It is a conceptual diagram of the whole sensing system comprised from the conventional signal processing circuit and a SAW sensor.

Embodiments of the present invention will be described below with reference to the drawings.
[Example 1]
(1) Overall Configuration The signal processing circuit 1 according to the present embodiment performs wireless remote sensing in cooperation with the parasitic SAW sensor 3. A conceptual diagram of the entire sensing system is shown in FIG. In the present embodiment, when the frequency has a value after the decimal point, the value rounded to the first decimal place is shown. The same applies to other embodiments described later.

  The SAW device 2 is a sensing device in which a comb electrode for exciting a surface acoustic wave and a reflective electrode for reflecting the surface acoustic wave are formed on a piezoelectric substrate, and the comb electrode is used for both input and output. Is illustrated. Needless to say, an electrode having separate comb electrodes on the input side and the output side may be used, and can be appropriately changed according to the measurement object.

  The signal processing circuit 1 includes an oscillation circuit 11, a carrier frequency divider 13, a first amplifier 15, a switch element 17, a pulse generator 19, an antenna 21, a second amplifier 23, a first frequency divider 25, and a first mixer 27. The second frequency divider 29, the second mixer 31, and the low-pass filter 33 are connected to a substrate (not shown) as shown in FIG.

The operation of each component will be described along the signal flow.
The oscillation circuit 11 outputs a signal having a frequency of 400 MHz. The output signal is input to the carrier frequency divider 13, the first frequency divider 25, and the second frequency divider 29.

  The carrier divider 13 divides the input signal by a division ratio of 2 to generate a 200 MHz carrier. The generated carrier wave is amplified by the first amplifier 15 and input to the switch element 17. The carrier frequency divider 13 can be switched ON / OFF.

  The pulse generator 19 generates a pulse signal, and the switch element 17 performs pulse modulation on the carrier wave. The pulse-modulated carrier wave is wirelessly transmitted to the SAW sensor 3 via the antenna 21.

  The SAW sensor 3 receives a carrier wave via the antenna 5. The signal is converted into a surface acoustic wave by the comb electrode of the SAW device 2, reaches the comb electrode after a delay time, and is transmitted from the antenna 5.

  The antenna 21 receives the reception signal transmitted from the antenna 5 of the SAW sensor 3. At this time, the carrier frequency divider 13 stops its operation and stops generating a 200 MHz carrier wave. The received reception signal is amplified by the second amplifier 23 and input to the first mixer 27. The carrier divider 13 is an example of the carrier generator of the present invention.

  The first frequency divider 25 divides the input signal by a frequency division ratio of 3, and generates a first reference signal of 133 MHz. The second frequency divider 29 divides the input signal by a frequency division ratio of 6 to generate a 67 MHz second reference signal. Each of the first frequency divider 25 and the second frequency divider 29 is an example of the reference signal generation unit of the present invention.

  The first mixer 27 receives the first reference signal generated by the first frequency divider 25 and the received signal from the SAW sensor 3 amplified by the second amplifier 23, and the frequency of the difference therebetween. A 67 MHz signal is output. Since the signal having the sum frequency is removed by the low-pass filter 33 described later, the description thereof is omitted. The same applies to the following description.

  The signal output from the first mixer 27 is input to the second mixer 31. That is, the first mixer 27 is disposed upstream of the second mixer 31. The second reference signal generated by the second frequency divider 29 is input to the second mixer 31, and a signal having a difference frequency is output. In this signal, the frequency of the carrier wave is converted to direct current. The signal passes through the low pass filter 33, and the phase of the received signal from the SAW sensor 3 is output as a DC output signal.

(2) Effect In the signal processing circuit 1 described above, the frequency of the carrier wave (received signal from the SAW sensor 3) is different from the frequencies of the signal generated by the oscillation circuit 11, the first reference signal, and the second reference signal. It is. Then, when detecting the reception signal from the SAW sensor 3, the operation of the carrier frequency divider 13 is stopped to stop the generation of the carrier wave.

  Therefore, a signal having the same frequency as that of the reception signal from the SAW sensor 3 does not exist, and a signal leaked from the oscillation circuit 11 or the like is combined with the reception signal, so that it is possible to suppress deterioration in detection performance by synchronous detection.

  A similar effect is that the frequency division ratio of the carrier frequency divider 13 is different from the frequency division ratios of the first frequency divider 25 and the second frequency divider 29, that is, the carrier wave is different from each reference signal. It can be obtained by setting the frequency so as to satisfy that the frequency is different and that the frequency of the carrier wave is converted to DC by sequentially mixing each reference signal with the received signal.

As described above, when two reference signals are generated from the signal of the oscillation circuit 11 and synchronous detection is performed, the frequency division ratio of the carrier frequency divider 13 is N, and the frequency division ratio of the first frequency divider 25 is N _1. If the frequency division ratio of the second frequency divider 29 is N ₂ , the frequency division ratio may be set so as to satisfy all of the following conditions.

N ≠ 1, N ≠ N ₁ , N ≠ N ₂ , 1 / N ₂ = | 1 / N−1 / N ₁ |
Each of the dividers used to generate the signal with the above dividing ratio may be one as in the above embodiment, but a plurality of dividers are connected to obtain a desired dividing ratio. It may be configured as follows.

Note that the frequency division ratio and the multiplication factor used in the examples described later are positive integers.
[Example 2]
(1) Overall Configuration The signal processing circuit 41 of the second embodiment basically has the same configuration as that of the first embodiment, but the output frequency of the oscillation circuit and the frequency divider ratio are different. The difference will be described, and the description of the same points as in the first embodiment will be omitted.

A signal processing circuit 41 of the present embodiment is shown in FIG. The oscillation circuit 43 outputs a 1200 MHz signal. The carrier frequency divider 45 has a frequency division ratio N = 6, the first frequency divider 47 has a frequency division ratio N ₁ = 2, and the second frequency divider 49 has a frequency division ratio N ₂ = 3.

  An output signal of the oscillation circuit 43 is input to the carrier frequency divider 45, the first frequency divider 47, and the second frequency divider 49. The carrier frequency divider 45 divides the input signal to generate a 200 MHz carrier wave. The first frequency divider 47 divides the input signal and generates a first reference signal of 600 MHz. The second frequency divider 49 divides the input signal and generates a second reference signal of 400 MHz.

  The received signal from the SAW sensor 3 received by the antenna 21 is amplified by the second amplifier 23, then mixed with the first reference signal by the first mixer 27, and the output is output by the second mixer 31. 2 mixed with the reference signal. By passing through the low-pass filter 33, the carrier wave component is converted to direct current, and synchronous detection is possible.

(2) Effects In the signal processing circuit 41 described above, the same effects as those of the signal processing circuit 1 of the first embodiment can be obtained.

  Further, in the signal processing circuit 41 described above, even if the frequency of the generated first and second reference signals is multiplied by an integer, it does not become the frequency of the carrier wave. That is, since the harmonics of the reference signal are not the same as the received signal from the SAW sensor 3, the influence of the reference signal on the received signal is reduced, and the deterioration in the quality of the detection signal can be suppressed.

  FIG. 3 is a diagram for explaining the frequency of the image signal with respect to the reception signal from the SAW sensor 3, the first reference signal, and the reception signal. When the frequency of the second reference signal is the same as the frequency of the image signal, when the second reference signal leaks and is input to the first mixer 27, the output frequency of the difference between the received signal and the first reference signal Therefore, the leaked signal affects the received signal.

However, in the configuration of the present embodiment, the second reference signal does not become the same as the frequency of the image signal, and the deterioration of the quality of the detection signal can be suppressed. Such an effect is exhibited when the following division ratio condition 1 / N ≠ 2 / N ₁ -1 / N ₂ is satisfied.

[Example 3]
(1) Overall Configuration The signal processing circuit 51 of the present embodiment is the same as the signal processing circuit 1 of the first embodiment in that wireless remote sensing is performed in cooperation with the parasitic SAW sensor 3, but the arrangement of the frequency dividers Therefore, the difference will be described, and the description of the same points as in the first embodiment will be omitted.

A signal processing circuit 51 of the present embodiment is shown in FIG. The oscillation circuit 53 outputs a 1200 MHz signal. The first carrier frequency divider 55 has a frequency division ratio Na = 3, the second carrier frequency divider 57 has a frequency division ratio Nb = 2, and the reference frequency divider 59 has a frequency division ratio N ₁ = 2.

  The output signal of the oscillation circuit 53 is input to the first carrier frequency divider 55 and the reference frequency divider 59. The first carrier frequency divider 55 divides the input signal to generate a 400 MHz signal. This signal is input to the second carrier frequency divider 57 and the second mixer 31. The second mixer 31 is input as a second reference signal.

The second carrier frequency divider 57 divides the input signal to generate a 200 MHz carrier wave. The reference frequency divider 59 divides the input signal and generates a first reference signal of 600 MHz.
The received signal from the SAW sensor 3 received by the antenna 21 is amplified by the second amplifier 23, then mixed with the first reference signal by the first mixer 27, and the output is output by the second mixer 31. 2 mixed with the signal generated.

  That is, in this embodiment, based on the output signal of the oscillation circuit 53, a carrier wave is generated by the first carrier frequency divider 55 and the second carrier frequency divider 57, and a first reference signal is generated by the reference frequency divider 59, A second reference signal is generated by the first carrier frequency divider 55. Further, when receiving a reception signal from the SAW sensor 3, the second carrier frequency divider 57 is stopped.

(2) Effect In the signal processing circuit 51 described above, the same effect as that of the signal processing circuit 1 of the first embodiment can be obtained. This configuration generates a carrier wave and a reference signal having substantially the same frequency as that of the signal processing circuit of the second embodiment. Like the second embodiment, each of the frequency dividers has a common divisor other than 1. Is possible if you have Specifically, in Example 2, the frequency division ratio N of the carrier frequency divider 45 is 6, and the frequency division ratio N ₂ of the second frequency divider 49 is 3, so 3 is a common divisor. Therefore, the carrier frequency divider 45 can be divided into two frequency dividers with a frequency dividing ratio of 3 and 2, and one can be used as a frequency divider for generating a reference signal. Thereby, the circuit configuration can be simplified.

  In the present embodiment, the first carrier frequency divider 55 and the second carrier frequency divider 57 are an example of the carrier wave generation unit of the present invention, and the reference frequency divider 59 and the first carrier frequency divider 55 are respectively It is an example of the reference signal generation unit of the present invention.

[Example 4]
(1) Overall configuration The signal processing circuit 61 of the fourth embodiment basically has the same configuration as that of the first embodiment, but differs in that a multiplier is used instead of a frequency divider. The difference will be described, and the description of the same points as in the first embodiment will be omitted.

A signal processing circuit 61 of this embodiment is shown in FIG. The oscillation circuit 63 outputs a 33 (33.3...) MHz signal. The carrier multiplier 65 has a multiplication factor M = 6, the first multiplier 67 has a multiplication factor M ₁ = 4, and the second multiplier 69 has a multiplication factor M ₂ = 2.

  The output signal of the oscillation circuit 63 is input to the carrier multiplier 65, the first multiplier 67, and the second multiplier 69. The carrier multiplier 65 multiplies the 33 MHz input signal to generate a 200 MHz carrier. The first multiplier 67 multiplies the input signal and generates a first reference signal of 133 MHz. The second multiplier 69 multiplies the input signal and generates a 67 MHz second reference signal.

  The received signal from the SAW sensor 3 received by the antenna 21 is amplified by the second amplifier 23 and then mixed with the signal generated by the first multiplier 67 by the first mixer 27, and the output thereof is the second. The mixer 31 mixes the signal generated by the second multiplier 69.

(2) Effect In the signal processing circuit 51 described above, the same effect as that of the signal processing circuit 1 of the first embodiment can be obtained. In addition, the maximum frequency in the signal processing circuit can be reduced.

  The same effect is that the multiplication factor of the carrier multiplier 65 is different from the multiplication factors of the first multiplier 67 and the second multiplier 69, that is, the carrier has a frequency different from each reference signal. And by setting each frequency so as to satisfy that the frequency of the carrier wave is a frequency converted into a direct current by sequentially mixing each reference signal with the received signal.

As described above, when two reference signals are generated from the signal of the oscillation circuit 63 and synchronous detection is performed, the multiplication factor may be set so as to satisfy all of the following conditions.
M ≠ 1, M ≠ N ₁ , M ≠ N ₂ , M ₂ = | M−M ₁ |
In the present embodiment, the received signal from the SAW sensor 3 and the first reference signal are changed by switching the multiplication factors of the first multiplier 67 and the second multiplier 69 as shown in the parentheses of FIG. The image signal output from the first mixer 27 that mixes the second reference signal and the second reference signal are no longer the same, and similarly to the signal processing circuit 51 of the second embodiment, it is possible to suppress deterioration in the quality of the detection signal.

Such an effect is exhibited when the following multiplication rate condition is satisfied.
(A) M ≠ 2M ₁ −M ₂
(B) When M> M ₁ M ₁ ≠ (M + 1) / 2
[Example 5]
(1) Overall Configuration The signal processing circuit 51 of the present embodiment is the same as the signal processing circuit 1 of the first embodiment in that wireless remote sensing is performed in cooperation with the parasitic SAW sensor 3, but the signal processing circuit 51 is changed to a frequency divider. Therefore, the difference is described, and the description of the same points as in the first embodiment is omitted.

A signal processing circuit 71 of this embodiment is shown in FIG. The oscillation circuit 73 outputs a 33 MHz signal. The first carrier multiplier 75 has a multiplication factor Ma = 2, the second carrier multiplier 77 has a multiplication factor Mb = 3, and the reference multiplier 79 has a multiplication factor M ₁ = 2.

  The output signal of the oscillation circuit 73 is input to the first carrier multiplier 75. The first carrier multiplier 75 multiplies the 33 MHz input signal to generate a 67 MHz signal. This signal is input to the second carrier multiplier 77 and the first mixer 27. The first mixer 27 is input as a first reference signal.

  The second carrier multiplier 77 multiplies the output signal of the first carrier multiplier 75 to generate a 200 MHz carrier. The reference multiplier 79 multiplies the output signal of the first carrier multiplier 75 to generate a second reference signal of 133 MHz.

  The received signal from the SAW sensor 3 received by the antenna 21 is amplified by the second amplifier 23, then mixed with the first reference signal by the first mixer 27, and the output is output by the second mixer 31. 2 mixed with the reference signal.

  That is, in this embodiment, based on the output signal of the oscillation circuit 73, a carrier wave is generated by the first carrier multiplier 75 and the second carrier multiplier 77, a second reference signal is generated by the reference multiplier 79, and the first carrier wave is generated. A multiplier 75 generates a first reference signal. Further, when receiving a reception signal from the SAW sensor 3, the second carrier multiplier 77 stops.

(2) Effects The signal processing circuit 71 described above can achieve the same effects as the signal processing circuit 1 of the first embodiment. This configuration generates a carrier wave and a reference signal having substantially the same frequency as that of the signal processing circuit (frequency configuration shown in parentheses in FIG. 5) shown in the modification of the fourth embodiment. This is possible when the multiplication factor has a common divisor other than 1. Specifically, in the modification of the fourth embodiment, the multiplication factor M of the carrier multiplier 65 is 6, the multiplication factor M ₁ of the first multiplier 67 is 2, and the multiplication factor M ₂ of the second multiplier 69. Is 4, so 2 is a common divisor. Therefore, the signal of the oscillation circuit 73 can be multiplied by a multiplication factor of 2, and the signal can be appropriately multiplied for use. Thereby, the circuit configuration can be simplified.

  In the present embodiment, the first carrier multiplier 75 and the second carrier multiplier 77 are examples of the carrier generation unit of the present invention, and the reference multiplier 79 and the first carrier multiplier 75 are the reference of the present invention. It is an example of a signal generation part.

[Modification]
As mentioned above, although the Example of this invention was described, it cannot be overemphasized that this invention can take a various form, as long as it belongs to the technical scope of this invention, without being limited to the said Example at all.

  For example, in each of the above-described embodiments, the configuration in which synchronous detection is performed using two mixers is illustrated. However, three or more mixers may be used, and in this case, the frequency of a carrier wave and a plurality of reference signals may be used. Each frequency may be a frequency at which the frequency of the carrier wave is converted to a direct current when a plurality of reference signals are sequentially mixed with the carrier wave.

Further, in each of the above-described embodiments, the configuration in which the plurality of reference signals have different frequencies is exemplified, but the same frequency may be used as long as the frequency condition is satisfied.
In that case, the input signal from the oscillation circuit is divided or multiplied by using any one of a common frequency divider, multiplier, and those connected in cascade, and the signal is distributed to a plurality of signals. The reference signal may be generated. In this example, any one of the frequency divider, the multiplier, and those connected in cascade is an example of the reference signal generation unit in the present invention and also serves as a plurality of reference signal generation units It becomes.

  Moreover, in the said Example, although the structure which performs the detection by a synchronous detection was illustrated, the structure which detects by a quadrature detection may be sufficient. FIG. 7 shows a signal processing circuit 81 in which the signal processing circuit of the first embodiment is changed to quadrature detection.

  In the signal processing circuit 81, a part of the reception signal received from the SAW sensor 3 is amplified by the second amplifier 23, and then the first reference signal whose phase is shifted by π / 2 by the phase shifter 83 and the mixer 85. The signal is mixed by the mixer 87 with the second reference signal whose phase is shifted by π / 2 by the phase shifter 83 and passes through the low-pass filter 89. In this way, a signal necessary for quadrature detection is output.

DESCRIPTION OF SYMBOLS 1 ... Signal processing circuit, 2 ... SAW device, 3 ... SAW sensor, 5 ... Antenna, 11 ... Oscillator circuit, 13 ... Carrier frequency divider, 15 ... 1st amplifier, 17 ... Switch element, 19 ... Pulse generator, 21 ... Antenna, 23 ... Second amplifier, 25 ... First frequency divider, 27 ... First mixer, 29 ... Second frequency divider, 31 ... Second mixer, 33 ... Low pass filter, 41 ... Signal processing circuit, DESCRIPTION OF SYMBOLS 43 ... Oscillator circuit, 45 ... Carrier frequency divider, 47 ... First frequency divider, 49 ... Second frequency divider, 51 ... Signal processing circuit, 53 ... Oscillator circuit, 55 ... First carrier frequency divider, 57 ... Second carrier frequency divider 59 ... Reference frequency divider 61 ... Signal processing circuit 63 ... Oscillation circuit 65 ... Carrier frequency multiplier 67 ... First frequency multiplier 69 ... Second frequency multiplier 71 ... Signal processing circuit 73 ... Oscillator circuit 75 ... First carrier multiplier 77 ... Second carrier multiplier 7 ... reference multiplier, 81 ... signal processing circuit, 83 ... phase shifter, 85 ... mixer, 87 ... mixer, 89 ... low-pass filter

Claims (7)

A signal processing circuit that transmits a carrier wave to a SAW sensor, receives a signal returned from the SAW sensor, and performs synchronous detection or quadrature detection on the received signal;
An oscillation circuit that outputs a signal of a predetermined frequency;
A carrier generation unit that generates a carrier by dividing or multiplying the signal of the oscillation circuit;
A plurality of reference signal generators for generating a predetermined reference signal by dividing or multiplying the signal of the oscillation circuit;
A plurality of mixers that are provided corresponding to each of the plurality of reference signal generation units, and that mix the reference signal and the received signal from the SAW sensor,
The frequency of the carrier wave generated by the carrier wave generation unit is a frequency different from the frequency of each of the plurality of reference signals generated by the plurality of reference signal generation units,
Each of the frequency of the carrier wave and the frequency of the plurality of reference signals is a frequency at which the frequency of the carrier wave is converted into direct current when the plurality of reference signals are sequentially mixed with the carrier wave,
The signal processing circuit, when receiving the received signal and performing the synchronous detection or the quadrature detection, stops the generation of the carrier wave. The signal processing circuit according to claim 1, further comprising an amplifier that amplifies the reception signal before the reception signal is input to any of the mixers. The carrier wave generation unit divides the signal of the oscillation circuit by a division ratio N,
N reference signal generators are provided, which divide the signal of the oscillation circuit by a frequency division ratio Nx (x = 1, 2,... N), and Nx is a value excluding an integer multiple of N. The signal processing circuit according to claim 1, wherein: The plurality of reference signal generation units include a first reference signal generation unit that divides the signal of the oscillation circuit by a division ratio N ₁ and a second reference that divides the signal of the oscillation circuit by a division ratio N _2. A signal generator,
The reference signal generated by the first reference signal generation unit is mixed with the reception signal upstream of the reference signal generated by the second reference signal generation unit,
The carrier wave generation unit divides the signal of the oscillation circuit by a division ratio N,
The signal processing circuit according to claim 1, wherein 1 / N ≠ 2 / N ₁ −1 / N ₂ . Wherein the plurality of reference signal generation unit includes a first reference signal generator for multiplying the signal of the oscillation circuit multiplication factor M _1, and a second reference signal generator for multiplying the signal of the oscillation circuit multiplication factor M ₂ Consists of
The reference signal generated by the first reference signal generation unit is mixed with the reception signal upstream of the reference signal generated by the second reference signal generation unit,
The carrier wave generation unit multiplies the signal of the oscillation circuit by a multiplication factor M,
The signal processing circuit according to any one of claims 1 to 3, wherein the following conditions (a) and (b) are satisfied.
(A) M ≠ 2M ₁ −M ₂
(B) When M> M ₁ M ₁ ≠ (M + 1) / 2 6. The device according to claim 1, wherein at least one of the carrier wave generation unit and the reference signal generation unit includes a cascade connection of a plurality of frequency dividers or multipliers. Signal processing circuit. Dividing or multiplying the output signal of a predetermined frequency output from the oscillation circuit to generate a carrier wave;
Pulse modulating the carrier wave and transmitting to a SAW sensor;
Receiving a reception signal returned from the SAW sensor in a state where generation of the carrier wave is stopped;
With the generation of the carrier wave stopped, the output signal is divided or multiplied to generate a plurality of reference signals, and the plurality of reference signals are mixed with the reception signal to perform synchronous detection or quadrature detection; With
The frequency of the carrier wave is different from the frequency of each of the plurality of reference signals, and the frequency of the carrier wave and the frequency of each of the plurality of reference signals are different from each other with respect to the carrier wave. A signal processing method, wherein the frequency of the carrier wave is a frequency converted into a direct current when sequentially mixed.

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