ELECTRICAL SIGNAL PROCESSING DEVICE

Abstract

When frequencies used in the two-frequency measurement of a SAW sensor are represented by f.sub.1 and f.sub.2 (f.sub.2>f.sub.1), an electrical signal processing device is provided without use of oversampling at a frequency higher than twice the frequency f.sub.2 or a two-system low-frequency conversion circuit, in which temperature compensation with the same accuracy as the case where these are used can be realized. Narrow band frequency filtering is applied to a waveform after roundtrips in a delay line type SAW sensor capable of transmitting and receiving multiple frequencies, the two frequencies f.sub.1 and f.sub.2 (f.sub.2>f.sub.1) are extracted, and a delay time is determined utilizing an aliasing obtained by applying undersampling at a frequency lower than twice the frequency f.sub.1.

Claims

1-8. (canceled)

9. An electrical signal processing device, wherein with respect to two frequencies f.sub.1 and f.sub.2, f.sub.2=3f.sub.1, the electrical signal processing device includes an ADC (analog-to-digital converter) which samples a signal from a delay line type SAW (surface acoustic wave) sensor that can transmit the two frequencies f.sub.1 and f.sub.2 and receive two frequencies one of which is equal to or more than f.sub.1 (1−1/10) but equal to or less than f.sub.1 (1+1/10) and the other of which is equal to or more than f.sub.2 (1−1/10) but equal to or less than f.sub.2 (1+1/10), a sampling frequency f.sub.S of the ADC is f.sub.S=5f.sub.1/4 and among signals sampled by the ADC, signals of two frequencies f.sub.u1=f.sub.1/4 and f.sub.u2=f.sub.1/2 are used for measurement of a response.

10. The electrical signal processing device according to claim 9, wherein a sampling clock of the ADC is synchronized with a transmitted signal to the SAW sensor.

11. The electrical signal processing device according to claim 9, comprising: band-pass filters whose center frequencies are f.sub.1 and f.sub.2 and whose band widths are equal to or less than 20% of the center frequencies so as to process a received signal from the SAW sensor and to extract components of f.sub.1 and f.sub.2, wherein the ADC is configured so as to sample a signal extracted by the band-pass filters.

12. The electrical signal processing device according to claim 9, comprising: a digital filter which can interrupt aliasing of a frequency other than the two frequencies f.sub.u1 and f.sub.u2 from the signals sampled by the ADC.

13. The electrical signal processing device according to claim 9, wherein the SAW sensor is a delay line type SAW sensor which uses a SAW that makes roundtrips around a substrate.

14. The electrical signal processing device according to claim 9, wherein the SAW sensor is a ball SAW sensor.

15. The electrical signal processing device according to claim 9, wherein relative delay time changes Δt.sub.u1 and Δt.sub.u2 at the two frequencies f.sub.u1 and f.sub.u2, respectively, are determined among the signals sampled by the ADC, and a temperature-compensated delay time change is obtained by a calculation formula Δt.sub.u2/6+Δt.sub.u1/4.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0033] FIG. 1 a block diagram showing the first example in a TFM system which shows a concept of an electrical signal processing device according to an embodiment of the present invention;

[0034] FIG. 2 is a graph showing waveforms measured at positions A to C in FIG. 1;

[0035] FIG. 3(a) is a power spectrum of the waveform A in FIG. 2, and FIG. 3(b) is those of the waveforms B and C in FIG. 2;

[0036] FIG. 4(a) is a graph showing relative delay time changes in a TFM performed from oversampled waveforms, where a sequence of trace moisture variation is measured, and FIG. 4(b) is a graph showing the relative delay time change when temperature compensation is further performed;

[0037] FIG. 5(a) is a graph showing relative delay time changes in a TFM performed from undersampled waveforms, where a sequence of trace moisture variation is measured with the TFM system shown in FIG. 1, and FIG. 5(b) is a graph showing the relative delay time change when temperature compensation is further performed;

[0038] FIG. 6 a block diagram showing the second example in the TFM system which includes the electrical signal processing device according to the embodiment of the present invention;

[0039] FIG. 7(a) is a graph showing a waveform measured at position A in FIG. 6, and FIG. 7(b) is a graph showing a spectrum (solid curve) obtained by the waveform in FIG. 7(a) processed by FFT and that (broken curve) obtained by the waveform resulting from wavelet transform at position B in FIG. 6 processed by FFT;

[0040] FIG. 8(a) is a graph showing the waveform measured at position A in FIG. 6, and FIG. 8(b) is a graph showing the waveforms resulting from wavelet transform at position B in FIG. 6, where a real part value is indicated by a solid curve and an absolute value is indicated by a broken curve; and

[0041] FIG. 9(a) is a graph showing the relative delay time changes in the signal of an aliasing frequency f.sub.u1 when trace moisture is measured with the TFM system shown in FIG. 6, FIG. 9(b) is a graph showing the relative delay time change in the signal of an aliasing frequency f.sub.u2 when trace moisture is measured with the TFM system shown in FIG. 6 and FIG. 9(c) is a graph showing the relative delay time change when temperature compensation is performed.

DESCRIPTION OF EMBODIMENTS

[0042] An embodiment of the present invention will be described below with reference to drawings.

[0043] As the first example, it is indicated that undersampling performed with a simplified electrical signal processing device is useful for temperature compensation performed in a TFM using a sensor in which a sol-gel SiOx film for measurement of trace moisture is formed on a harmonic ball SAW device. Here, it is indicated that it is possible to clearly measure a response to trace moisture of 20 nmol/mol which is conventionally difficult to measure without use of a CRDS (cavity ring-down spectroscopy), and that temperature-compensated sensor response with undersampling agrees with that with oversampling with a correlation coefficient of 0.9999.

[0044] FIG. 1 shows a block diagram of a TFM system. Here, f.sub.S is the sampling frequency of an ADC, f.sub.1 and f.sub.2 (f.sub.2>f.sub.1) are two frequencies which are transmitted and received by a delay line type SAW sensor and f.sub.0 represents a frequency which is a common multiple of f.sub.1 and f.sub.2. Furthermore, f.sub.u1 and f.sub.u2 represent two aliasing frequencies utilized for measurement of a response among outputs obtained by undersampling, which are respectively caused by f.sub.1 and f.sub.2.

[0045] First, with a synthesizer 11 which utilizes a temperature-compensated crystal oscillator (TCXO) 11a as the reference oscillator, the continuous signal of f.sub.0 synchronized with f.sub.S is generated. The signal of f.sub.0 is divided in frequency with a frequency divider (FDIV) 12 so as to be converted into the signals of f.sub.1 and f.sub.2, and the signals of f.sub.1 and f.sub.2 are respectively processed with low-pass filters (LPF) 16a and 16b and are thereafter combined with an adder 17a such that a transmitted signal Tx is generated. The transmitted signal Tx is amplified by an amplifier 17b, is passed through a rf switch 17c and is input to a SAW sensor 1. A reflected signal Rx from the SAW sensor 1 is passed through the rf switch 17c, is amplified by an amplifier 17d, is thereafter processed with narrow band-pass filters (BPF) 13a and 13b whose center frequencies are f.sub.1 and f.sub.2 and are recorded in ADCs 14a and 14b. Among the signals recorded in the ADCs 14a and 14b, signals whose frequency components are not f.sub.u1 and f.sub.u2 are interrupted with BPFs 15a and 15b, and a delay time is measured with a computer 18.

[0046] In the present example, a case where the SAW sensor 1 is a ball SAW sensor, f.sub.S=5f.sub.1/4, f.sub.2=3f.sub.1, f.sub.u1=|f.sub.1−f.sub.S|=f.sub.1/4 and f.sub.u2=|3f.sub.1−2f.sub.S|=f.sub.1/2 will be described. For the measurement of the delay time, a wavelet analysis was utilized.

[0047] In a verification experiment, first, a sol-gel SiOx film for measurement of trace moisture was formed on a harmonic ball SAW device (made of quartz with a diameter of 3.3 mm, f.sub.1=80 MHz) and thus a sensor was produced, and a roundtrip waveform was measured with a broadband pulsar receiver and was recorded using a digital oscilloscope with averaging processing of 1024 times by oversampling (5 GHz).

[0048] Then, BPFs whose center frequencies were f.sub.1 and f.sub.2 and whose band widths were 5% of the individual frequencies were applied to this waveform by FFT and thereafter the waveform was sampled with a sampling frequency f.sub.S in order to simulate the situation in which f.sub.S was synchronized with a transmitted signal.

[0049] Then, in order to measure the delay time, a wavelet transform was performed where a Gabor function (γ=50) was used as a mother wavelet. Here, the wavelet transform was performed at f.sub.1 and f.sub.2 in the case of oversampling whereas it was performed at f.sub.u1 and f.sub.u2 in the case of undersampling. The delay time was measured from a propagation time difference between the roundtrip waves of the third turn and the seventh turn.

[0050] In A of FIG. 2, the waveform obtained by performing oversampling at position A in FIG. 1 is indicated. On the other hand, in B and C of FIG. 2, the waveforms (waveforms at positions B and C in FIG. 1) obtained by performing undersampling after the application of the BPFs are indicated.

[0051] FIG. 3 shows power spectra corresponding to the waveforms of FIG. 2. As shown in FIG. 3(a), the components of f.sub.1 and f.sub.2 were confirmed in the spectrum of the waveform obtained by performing oversampling and, as shown in FIG. 3(b), the components of f.sub.u1 and f.sub.u2 were confirmed in the spectrum of the waveform obtained by performing undersampling.

[0052] FIG. 4 shows results of a TFM on f.sub.1 and f.sub.2 performed from the waveform obtained by oversampling, when moisture concentration (H.sub.2O concentration) was generated by step sequence from 4 to 790 nmol/mol with a trace moisture generator. In FIG. 4(a), a broken curve and a solid curve respectively indicate relative delay time changes at f.sub.1 and f.sub.2. FIG. 4(b) is a result showing a difference between the output of f.sub.2 and the output of f.sub.1 with a coefficient of 1.0. A moisture response became clear by the temperature compensation, and thus a response to 4 to 17 nmol/mol was measured with a signal-to-noise ratio S/N=44.8.

[0053] As in the case of FIG. 4, FIG. 5 shows results obtained when undersampling was simulated. In FIG. 5(a), a broken curve and a solid curve respectively represent the outputs of f.sub.u1 and f.sub.u2. A difference between the output of f.sub.u2 and the output of f.sub.u1 was obtained with a coefficient of −1.5 taking the enlargement rate of the output of undersampling into account as shown in FIG. 5(b), where the same temperature compensation as shown in FIG. 4(b) was achieved. This response agreed with the response in oversampling by a linear function with a correlation coefficient of |R|=0.9999.

[0054] Although in the first example, the oversampling and the simulated undersampling within the computer were used, an electrical signal processing device was applied to a trace moisture sensor formed with a ball SAW sensor as the second example, where oversampling is not used, that is, a burst waveform is transmitted and received signal was processed with narrow BPFs, and undersampling was applied to BPF-processed waveforms. Specifically, a ball SAW sensor with a diameter of 3.3 mm in which an amorphous silica film synthesized by a sol-gel method was used as a sensitive film was installed in an ultra-high vacuum cell, and the flow of N.sub.2 gas (1 L/min) generated using a trace moisture generator utilizing a diffusion tube method was measured.

[0055] A block diagram of a TFM system here is shown in FIG. 6. Here, f.sub.S is the sampling frequency of an ADC, f.sub.1 and f.sub.2 (f.sub.2>f.sub.1) are two frequencies which are transmitted and received by a delay line type SAW sensor and f.sub.0 represents a frequency which is a common multiple of f.sub.1 and f.sub.2. Furthermore, f.sub.u1 and f.sub.u2 represent two aliasing frequencies which are utilized for measurement of a response among outputs obtained by undersampling, and they are respectively caused by f.sub.1 and f.sub.2.

[0056] In the measurement, first, an output (f.sub.0=2.4 GHz) of a synthesizer (Syn) 21 utilizing a temperature-compensated crystal oscillator (TCXO) 21a as the reference oscillator is divided in frequency with frequency dividers (FDIV1,2,3) 22a, 22b and 22c so as to respectively generate the signals of f.sub.S=100 MHz, f.sub.2=240 MHz and f.sub.1=80 MHz. The signals of f.sub.1 and f.sub.2 are processed with low-pass filters (LPF1,2) 26a and 26b and are thereafter combined with an adder 27a. A switch signal of a timing controller (TC) 27b synchronized with the signal of f.sub.S is used for controlling an rf switch (SW) 27c for generating a transmitted burst signal Tx. The transmitted burst signal Tx is amplified by an amplifier (Amp1) 27d, is passed through a directional coupler (DC) 27e, and is input to the SAW sensor 1. A reflected signal Rx from the SAW sensor 1 is passed through the directional coupler 27e, is amplified by an amplifier (Amp2) 27f, is thereafter processed with narrow band-pass filters (BPF) 23a and 23b whose Q values are respectively 20 and 40 and whose center frequencies are respectively f.sub.1 and f.sub.2, and is recorded in ADCs 24a and 24b. The input of the transmitted burst signal Tx to the SAW sensor 1 and the output of the reflected signal Rx from the SAW sensor 1 are switched with the directional coupler 27e. Among the signals recorded in the ADCs 24a and 24b, signals whose frequency components are not f.sub.u1 and f.sub.u2 are interrupted with BPFs 25a and 25b, and a delay time is measured with a computer 28. Here, the wavelet transform using a Gabor function (γ=50) is applied to the BPFs 25a and 25b in order to extract the outputs of undersampling frequencies (f.sub.u1=20 MHz, f.sub.u2=40 MHz) which satisfy a sampling theorem.

[0057] In the present example, the SAW sensor 1 is a ball SAW sensor, f.sub.S=5f.sub.1/4, f.sub.2=3f.sub.1, f.sub.u1=|f.sub.1−f.sub.S|=f.sub.1/4 and f.sub.u2=|3f.sub.1−2f.sub.S|=f.sub.1/2. For the measurement of the delay time, the wavelet analysis was utilized.

[0058] A waveform obtained by performing undersampling at position A in FIG. 6 is shown in FIG. 7(a). A spectrum obtained by performing FFT on the waveform is indicated by a solid curve in FIG. 7(b). The components of f.sub.u1 and f.sub.u2 were confirmed in the spectrum of the waveform after undersampling. The amplitude of f.sub.u2 here was about 33.8 dB larger than that of f.sub.u1.

[0059] A part of the waveform in FIG. 7(a) obtained by performing undersampling at position A in FIG. 6 is shown in FIG. 8(a). A waveform obtained by performing wavelet transform at position B in FIG. 6, that is, a waveform obtained by performing wavelet transform on FIG. 8(a) and then performing 100-point interpolation is shown in FIG. 8(b). A solid curve in FIG. 8(b) indicates a real part value, and a broken curve indicates an absolute value (envelope curve). A zero cross time (position indicated by an alternate long and short dashed line in FIG. 8(b)) closest to the peak of the absolute value was measured as the delay time. A spectrum obtained by performing FFT on the real part waveform of FIG. 8(b) is indicated by a broken curve in FIG. 7(b).

[0060] FIGS. 9(a) and 9(b) respectively show relative delay time changes in signals between the third turn and the seventh turn at aliasing frequencies f.sub.u1 and f.sub.u2 when the moisture concentration (H.sub.2O concentration) was generated by step sequence from 2.4 to 680 nmol/mol with a trace moisture generator. FIGS. 9(a) and 9(b) respectively show results obtained when relative delay time changes Δt.sub.u1 and Δt.sub.u2 at f.sub.u1 and f.sub.u2 were divided by the enlargement rate of the output in undersampling.

[0061] FIG. 9(c) shows a result of the temperature compensation which is a difference between the relative delay time change Δt.sub.u2 at f.sub.u2 and the relative delay time change Δt.sub.u1 at f.sub.u1. Although in FIGS. 9(a) and 9(b), significant variations in the output were recognized from 4 to 7 hour for the constant moisture concentration as shown in FIG. 9(c), the temperature compensation was performed by obtaining the difference, and thus such variations were able to be removed. A signal-to-noise ratio of a response to 2.4 to 18 nmol/mol was 92.1 because an rms noise was evaluated as 0.00998 ppm in the time range from 0 to 1 hour.

[0062] As described above, it was confirmed that in any of the examples, the 100 MHz ADC can be used for the measurement of 240 MHz. Hence, it can be said that according to the present invention, it is possible to simplify the TFM system which can perform practical temperature compensation on the ball SAW sensor and provide it inexpensively.

[0063] Although in the examples of the present invention, the case where the ball SAW sensor was used as the delay line type SAW sensor has been described, the present invention can also be applied to a case where a delay line type SAW sensor of a general planar substrate is used and a case where a delay line type SAW sensor using a SAW making roundtrips around a substrate is used.

REFERENCE SIGNS LIST

[0064] 1 SAW sensor

[0065] 11 synthesizer

[0066] 11a temperature-compensated crystal oscillator

[0067] 12 frequency divider

[0068] 13a, 13b narrow band-pass filter

[0069] 14a, 14b ADC

[0070] 15a, 15b band-pass filter

[0071] 16a, 16b low-pass filter

[0072] 17a adder

[0073] 17b, 17d amplifier

[0074] 17c rf switch

[0075] 18 computer

[0076] 21 synthesizer

[0077] 21a temperature-compensated crystal oscillator

[0078] 22a, 22b, 22c frequency divider

[0079] 23a, 23b narrow band-pass filter

[0080] 24a, 24b ADC

[0081] 25a, 25b band-pass filter

[0082] 26a, 26b low-pass filter

[0083] 27a adder

[0084] 27b timing controller

[0085] 27c rf switch

[0086] 27d, 27f amplifier

[0087] 27e directional coupler

[0088] 28 computer