JP2010118765A - Transmission method, transmitter, receiver, and transmission and reception system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce degradation in the signal/noise ratio (SNR) of a clock signal to be modulated, when the clock signal is modulated with a data signal for transmission. <P>SOLUTION: When the pass-band width of a band-limiting element in a receiver 20, through which a clock signal to be modulated passes is set to W, so that a modulator 13 in a transmitter 10 modulates the original clock signal to change with a data signal at an interval of 1/W or larger, and the clock signal to be modulated is generated. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a transmission method and transmitter that modulates a clock signal with a data signal and transmits the signal, a receiver that receives the transmitted signal, and a transmission / reception system, and more particularly to a technique for improving the accuracy of a modulated clock signal. .

  A method is known in which a clock signal is modulated with a data signal to multiplex and transmit the data signal to the clock signal. Here, modulation is to multiplex the data signal by changing the original clock signal by the data signal. For example, on-off-keying (OOK), which is one of the simplest modulations, is on when the clock signal is left as it is, and the signal amplitude of the clock signal is below a certain value or 0. Is defined as OFF, thereby transmitting a 1-bit data signal. Patent Document 1 discloses a method for generating a transmission signal by subjecting an original clock signal to OOK modulation with a data signal, and a method for receiving this with high accuracy.

In more complicated modulation, a clock signal is changed in several patterns, and information is assigned to each signal, whereby a data signal having a plurality of bits can be transmitted simultaneously. For example, by changing the amplitude of the modulated clock signal to 1 times, 3/4 times, 2/4 times, and 1/4 times the amplitude of the original clock signal, four-value information, that is, a data signal for 2 bits. Can be sent.
JP 2006-261826 A

    However, when the original clock signal is modulated with the data signal, there is a problem that the accuracy of the modulated clock signal deteriorates. That is, the modulated clock signal changes with respect to the original clock signal. This change can be interpreted as a distortion of the clock signal. The greater the amount of signal change, the more distortion, resulting in a lower signal-to-noise ratio (SNR) of the modulated clock signal. As described above, the method of multiplexing and transmitting the data signal by modulating the clock signal has a problem that the SNR of the modulated clock signal deteriorates instead of transmitting the data signal simultaneously with the clock signal. It was.

  The present invention provides a transmission method, a transmitter, a receiver, and a transmission / reception system capable of reducing the SNR degradation of a modulated clock signal when the clock signal is modulated with a data signal for transmission. With the goal.

  According to one aspect of the present invention, when the pass bandwidth of the band limiting element through which the modulated clock signal passes is W, modulation is performed so that the original clock signal is changed by the data signal at intervals of 1 / W or more. There is provided a transmission method comprising the steps of generating the modulated clock signal and transmitting the modulated clock signal.

  According to another aspect of the present invention, W is a pass bandwidth of a clock signal generator that generates an original clock signal, a data signal generator that generates a data signal, and a band limiting element through which the modulated clock signal passes. A modulator that generates the modulated clock signal by modulating the original clock signal according to a data signal at an interval of 1 / W or more, and a transmitter that transmits the modulated clock signal. A transmitter is provided.

  According to another aspect of the present invention, modulation is performed so that the original clock signal is changed by the data signal at intervals of 1 / W or more, where W is the pass bandwidth of the band limiting element through which the modulated clock signal passes. A receiving unit that receives the modulated clock signal generated in response to receiving the modulated clock signal, a clock recovery unit that recovers a component of the original clock signal from the received signal to obtain a recovered clock signal, and the recovered clock signal And a sampler for sampling the received signal and extracting the data signal.

  According to still another aspect of the present invention, the above-described transmitter provided in a detection device that detects a physical quantity signal and the above-described receiver provided in an analysis device that analyzes the detected physical quantity signal are provided. A transmission / reception system is provided.

  Here, the detection device includes, for example, a probe unit configured to detect a magnetic resonance signal as the physical quantity signal, and the analysis device analyzes the magnetic resonance signal and performs image reconstruction processing to perform magnetic resonance. An imaging unit for obtaining a video signal is included.

  According to the present invention, by modulating the data signal so that the original clock signal is changed by the data signal at an interval of 1 / W or more with respect to the pass bandwidth W of the band limiting element through which the modulated clock signal passes, Degradation of the SNR of the modulated clock signal due to multiplexing can be avoided. As a result, it is possible to generate a highly accurate recovered clock signal on the receiving side, or to perform timing detection with a matched timing with high accuracy.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
<Transmission / reception system>
FIG. 1 shows a transmission / reception system, that is, a transmitter 10 and a receiver 20 according to a first embodiment of the present invention. The transmitter 10 includes a clock signal generation unit 11, a data signal generation unit 12, and a modulator 13.

  The clock signal (original clock signal) generated by the clock signal generation unit 11 and the data signal generated by the data signal generation unit 12 are input to the modulator 13. The data signal is generally a multi-bit sequence (referred to as a data signal sequence). In the modulator 13, the original clock signal is modulated by the data signal, and a modulated clock signal 31 is generated. That is, the data signal is multiplexed in the modulated clock signal. Here, when the pass bandwidth of the band limiting element through which the modulated clock signal 31 passes in the receiver 20 is W, the modulator 13 changes the original clock signal by the data signal at intervals of 1 / W or more. Modulation is performed to generate a modulated clock signal 31.

  The modulated clock signal 31 output from the modulator 13 in this way is transmitted from the transmitter 10 via a wired transmission path or a wireless transmission path and is received by the receiver 20. When using a wired transmission path, the transmitter 10 and the receiver 20 may be arranged in the same system (for example, the same computer device). That is, the receiver 20 does not necessarily have to be remote from the transmitter 10.

  The receiver 20 includes a sampler 21 and a phase locked loop (PLL) 22. The modulated clock signal 31 transmitted from the transmitter 10 is input to the sampler 21 and the PLL 22. In the PLL 22, the clock signal 32 is reproduced. The recovered clock signal 32 is supplied to the sampler 21 in order to extract a data signal in the sampler 21. The PLL 22 is assumed to have a frequency characteristic of the pass bandwidth W around the frequency of the original clock signal. More specifically, the PLL 22 has a filter having a pass bandwidth W.

  When wireless transmission is used, the transmitter 10 and the receiver 20 may be arranged in the same system (for example, the same computer apparatus) as described above, but two apparatuses that need to synchronize clocks. It may be installed in each of the above.

  For example, as shown in FIG. 2, when it is desired to synchronize the clock between the detection device 40 that detects a physical quantity signal and the analysis device 50 that analyzes the physical quantity signal detected by the detection device 40, either The transmitter 10 may be installed, and the receiver 20 may be installed on the other side. In general, the transmitter 10 tends to have a larger device scale than the receiver 20, and therefore it is desirable to install the receiver 20 on the device side where a smaller scale is desirable. For example, when comparing the detection device 40 and the analysis device 50, it is generally desirable that the detection device 40 has a smaller device scale, so that it is desirable to install the receiver 20 on the detection device 40 side as shown in FIG. .

  Specific examples of the detection device 40 and the analysis device 50 include a magnetic resonance signal (echo signal) detection coil (probe unit) and an echo signal in a magnetic resonance imaging apparatus (MRI apparatus) as shown in FIG. An imaging unit that obtains a magnetic resonance image by analyzing data and performing data processing including image reconstruction. At this time, for example, the clock signal generated by the clock signal generation unit 11 in FIG. 1 may be replaced with a clock signal generated in the analysis device 50. Further, the data signal generation unit 12 in FIG. 1 may generate a data signal based on information generated in the analysis device 40.

  On the other hand, the receiver 20 may supply the clock signal 32 output from the PLL 22 to the detection device 40 together with the data signal 33 output from the sampler 21 in FIG. In this case, as an example of the data signal 33 multiplexed and transmitted to the clock signal 32 from the analysis device 50 to the detection device 40, information indicating timing for starting signal detection, gain adjustment and frequency at the time of signal detection are performed. For example, information indicating detection parameters such as adjustment may be used.

<About PLL>
FIG. 3 shows a typical example of the PLL 22, which includes a phase comparator 221, a loop filter 222, a voltage controlled oscillator (VCO) 223, and an N divider 224. The modulated clock signal 31 is input to the first input terminal of the phase comparator 221 as a reference signal. A clock signal (reproduced clock signal) 32 generated by the VCO 223 is input to the second input terminal of the phase comparator 221 via the N frequency divider 224. Therefore, the phase comparator 221 outputs a phase difference detection signal corresponding to the phase difference between the reference signal input to the first input terminal and the clock signal input to the second input terminal. This phase difference detection signal is filtered by a loop filter 222 using, for example, a low-pass filter. As a result, a control voltage for controlling the oscillation frequency of the VCO 223 is generated in the loop filter 222 and applied to the control input terminal of the VCO 223.

  As a result, the VCO 223 outputs a recovered clock signal 32 that is synchronized with the modulated clock signal 31 that is a reference signal. Here, the recovered clock signal 32 is improved in SNR by reducing distortion caused by modulation by the modulator 13. That is, the reproduction clock signal 32 is a highly accurate clock signal. The sampler 21 can reliably extract the data signal 33 by sampling the modulated clock signal 31 using the recovered clock signal 32 thus obtained.

<About the original clock signal>
Next, a clock signal (original clock signal) used in the present embodiment will be described. The clock signal represents a signal that periodically repeats rising and falling of a waveform as shown in FIGS. 4 and 5, for example.

  The clock signal shown in FIG. 4 is a so-called unbalanced signal having a reference level (for example, zero level) and a value of one polarity, for example, a positive value. In this case, for example, the section 101 shown in FIG. 4 from the minimum level (reference level) to the next minimum level is defined as one cycle of the clock signal. The period from the positive value of the clock signal in FIG. 4 to the next positive value may be one cycle.

  The clock signal shown in FIG. 5 is a so-called balanced signal that takes a positive value and a negative value around a reference level (for example, zero level). In this case, for example, the section 102 shown in FIG. 5 from the rising edge of the waveform to the next rising edge is defined as one cycle of the clock signal. Further, the period from the falling edge of the waveform to the next falling edge may be one cycle of the clock signal. In either case, the time length of one cycle is the same and constant.

  The reciprocal of the time length of one cycle of the clock signal defined in this way is called the frequency of the clock signal. For example, when the cycle of the clock signal is 1 msec, the frequency is 1 kHz.

<Modulation to clock signal>
Next, a specific example of modulation of the original clock signal by the data signal will be described with reference to FIGS.

  The modulation of the original clock signal by the data signal is generally performed in units of one cycle of the original clock signal or in units of integer multiples of one cycle. For example, a modulated clock signal generated by performing modulation in units of N times one cycle is a data signal in which the same data signal is repeated N times in units of the number of bits that can be transmitted in units of one cycle of the original clock signal. This is the same as the modulated clock signal generated by modulating the original clock signal in units of one period by the series. That is, even by a method of modulating the original clock signal in units of one cycle, processing equivalent to performing modulation in units of N times one cycle is possible.

  In the following description, unless otherwise specified, modulation of the original clock signal in units of one cycle will be described as an example. However, the present invention is equally applied to the case where modulation is performed in units of N times of one cycle. Obviously it is possible.

(In the case of OOK modulation)
A method for transmitting a data signal by modulating an original clock signal using OOK as a modulation method will be described with reference to FIGS. FIG. 6 shows an example in which the original clock signal which is an unbalanced signal shown in FIG. 4 is used, and FIG. 7 shows an example in which the original clock signal which is a balanced signal shown in FIG. 5 is used.

  In FIG. 6, the data signal sequence is transmitted in the section 220. In the section 220, the signal amplitude of the original clock signal is reduced in the sections 201 to 205, and the original signal amplitude of the original clock signal is maintained in the other sections. When OOK ON is 1 and OFF is 0, the data signal sequence transmitted in the interval 220 is {1, 0, 1, 0, 1, 1, 0, 0, 1, 0, 1}. I understand.

  Similarly, in FIG. 7, the data signal sequence is transmitted in the section 320. In the section 320, the signal amplitude of the original clock signal is reduced in the sections 301 to 305, and the original signal amplitude of the original clock signal is maintained in the other sections. If OOK is on and off is 0, the data signal sequence transmitted in section 320 is {1, 0, 1, 0, 1, 1, 0, 0, 1, 0, 1}. I understand.

  In the sections 201 to 205 in FIG. 6 and the sections 301 to 305 in FIG. 7, the original clock signal is distorted by the modulation, and as a result, the SNR of the modulated clock signal deteriorates. The intervals at which the clock signal is changed due to the modulation in this way are represented by the intervals of the start points of the modulated section, that is, the intervals 211 to 214 in FIG. 6, and the intervals 311 to 314 in FIG. .

(In the case of AM modulation)
Next, a method for transmitting a data signal by modulating an original clock signal using amplitude modulation (AM) as a modulation method will be described with reference to FIGS. FIG. 8 shows an example in which the original clock signal which is an unbalanced signal shown in FIG. 4 is used, and FIG. 9 shows an example in which the original clock signal which is a balanced signal shown in FIG. 5 is used.

  In FIG. 8, the data signal sequence is transmitted in a section 420. In the sections 401 to 405, the signal amplitude of the original clock signal changes, and in the other sections, the original signal amplitude of the original clock signal is maintained. In the example of FIG. 8, there are a total of four signal amplitudes of 1/4 times, 2/4 times, 3/4 times, and 4/4 times (that is, the same amplitude as the original) of the original signal amplitude. By using these four signal amplitudes, four-stage information, that is, 2-bit information can be transmitted. For example, if 1/4, 2/4, 3/4, and 4/4 times the original signal amplitude of the original clock signal represent 00, 01, 10, and 11, respectively, they are transmitted in section 420. The data signal sequence is {1, 1, 0, 0, 1, 1, 1, 0, 1, 1, 1, 1, 0, 1, 0, 0, 1, 1, 0, 1, 1, 1}.

  Similarly, in FIG. 9, the data signal sequence is transmitted in section 520. In the sections 501 to 505, the signal amplitude of the original clock signal is changed, and in the other sections, the original signal amplitude of the original clock signal is maintained. In the example of FIG. 9, there are a total of four signal amplitudes of 1/4 times, 2/4 times, 3/4 times, and 4/4 times (that is, the same amplitude as the original) of the original signal amplitude. By using these four signal amplitudes, four-stage information, that is, 2-bit information can be transmitted. Similarly to FIG. 8, for example, when 1/4, 2/4, 3/4, and 4/4 times the original signal amplitude of the original clock signal represent 00, 01, 10, and 11, respectively. The data signal sequence transmitted in the section 520 is {1, 1, 0, 0, 1, 1, 1, 0, 1, 1, 1, 1, 0, 1, 0, 0, 1, 1, 0. , 1, 1, 1}.

  Also in the sections 401 to 405 in FIG. 8 and the sections 501 to 505 in FIG. 9, the SNR of the modulated clock signal deteriorates because the original clock signal is distorted by the modulation. The intervals at which the clock signal is changed by the modulation in this way are represented by intervals 411 to 414 in FIG. 8, and are represented by intervals 511 to 514 in FIG.

  Similarly to OOK and AM, the data signal can be multiplexed with the clock signal and transmitted by modulating the clock signal with the data signal using phase shift keying (PSK) or quadrature amplitude modulation (QAM). Is possible. In the case of PSK, the data signal can be multiplexed by changing the phase of the original clock signal. In QAM, it is possible to multiplex data signals by changing both the phase and amplitude of the original clock signal. In either case, in the section in which the original clock signal is changed by the data signal, the clock signal is distorted and the SNR of the modulated clock signal is deteriorated. Further, the interval at which the clock signal is changed by the modulation is expressed as the interval between the start points of the sections subjected to the modulation, like OOK and AM.

<About data signal series>
The data signal sequence will be described with reference to FIG. In FIG. 6, the data signal sequence is transmitted in section 220. When the timing is synchronized on the receiving side and the section in which the data signal sequence is inserted is known, information may be transmitted using all the data signals in the section 220.

  On the other hand, when the timing is not synchronized on the receiving side and the length of the data signal is known, for example, information may be sent in the section 222 with the section 221 as a known signal. In this way, since the head of the data signal can be detected by the data signal sent in the section 221, the information sent in the subsequent section 222 can be taken out. Further, for example, when aiming at imming synchronization, all the sections 220 may be known signals. These points are also the same in the examples of FIGS.

<How to set the clock signal change interval (lower limit) by modulation>
Next, a method for setting the change interval (particularly the lower limit) of the original clock signal by modulation will be described with reference to FIGS. As described above, examples of the modulation method for the original clock signal include OOK, AM, PSK, and QAM. By modulating the original clock signal, the modulated clock signal is distorted. In particular, modulation such as PSK and QAM changes not only the amplitude but also the phase, which may distort the clock signal more greatly. Therefore, when considering keeping the SNR of the clock high, modulation performed by changing the amplitude is desirable. That is, as the modulation method for the clock signal, OOK or AM is particularly desirable.

  10 and 11 show examples of transmission signals (modulated clock signals) when OOK is used as the modulation method. FIG. 10 shows an example of using the original clock signal that is an unbalanced signal shown in FIG. 4, and FIG. 11 shows an example of using the original clock signal that is a balanced signal shown in FIG. In FIG. 10, the data signal sequence is transmitted in section 620. The sections where the clock signal is distorted, that is, the sections 601 to 604 fall off OOK. Similarly, in FIG. 11, the data signal sequence is transmitted in a section 720, and a section where the clock signal is distorted, that is, the section where the OOK is turned off is the sections 701 to 704.

  Here, according to the present embodiment, when the transmission bandwidth from the transmitter 10, that is, the modulated clock signal, is W when the pass bandwidth of a band limiting element such as a filter provided in the receiver 20 is W. 10, the intervals 611 to 613 of the sections 601 to 604 where the OFF of OOK occurs, that is, the interval at which the modulated clock signal changes is set to 1 / W or more. Similarly, the intervals 711 to 713 of the sections 701 to 704 in which OOK is turned off shown in FIG. 11, that is, the intervals at which the modulated clock signal changes are set to 1 / W or more.

  12 and 13 show examples of transmission signals (modulated clock signals) when AM modulation is used as a modulation method. FIG. 12 shows an example when the original clock signal that is an unbalanced signal shown in FIG. 4 is used, and FIG. 13 shows an example when the original clock signal that is a balanced signal shown in FIG. 5 is used. In FIG. 12, the data signal sequence is transmitted in section 620. It is in sections 801 to 804 that the distortion is applied to the original clock signal, that is, the signal amplitude of the clock signal is changed by AM modulation. Similarly, in FIG. 13, the data signal sequence is transmitted in a section 720, and the part in which the clock signal is distorted, that is, the signal amplitude of the clock signal is changed by AM modulation is the sections 901 to 904. It is.

  Here, in this embodiment, when the pass band width of a band limiting element such as a filter provided in the receiver 20 with respect to the transmission signal from the transmitter 10, that is, the modulated clock signal, is W, FIG. The intervals 811 to 813 of the sections 801 to 804 in which the amplitude of the clock signal changes by AM modulation shown in FIG. Similarly, the intervals 911 to 913 in the sections 901 to 904 where the amplitude of the clock signal changes by AM modulation shown in FIG. 14, that is, the intervals where the modulated clock signal changes are set to 1 / W or more.

  Next, an effect obtained by setting the interval at which the modulated clock signal is changed by the modulation of the original clock signal by the data signal to 1 / W will be described with reference to FIG. FIG. 14 shows the spectrum of the modulated clock signal when the frequency of the original clock signal is 2 MHz, that is, the period is 0.5 μsec, and a data signal sequence in which OFF is generated three times in one period is multiplexed with the clock signal by OOK. The horizontal axis represents frequency, and the vertical axis represents signal power. As the original clock signal, a signal having a spectrum in which signal power is concentrated only at 2 MHz is used. When such an original clock signal is modulated by a data signal sequence, distortion occurs and a signal other than 2 MHz is generated. This distortion reduces the SNR of the modulated clock signal.

  In the example of FIG. 14, the pass bandwidth W of a band limiting element such as a filter (for example, loop filter 222) in the receiver 20 through which the modulated clock signal transmitted from the transmitter 10 passes is 0.2 MHz. . According to the present embodiment, the OFF generation interval in the modulated clock signal is set to 1 / W or more with respect to the pass bandwidth W of the band limiting element. In this example, since W = 0.2 MHz, 1 / W = 5 μsec. That is, according to the present embodiment, the OFF generation interval in the modulated clock signal is set to 5 μsec or more. The example of FIG. 14 shows a spectrum when the off occurrence interval in the modulated clock signal is 1 μsec as a conventional example, and when the off occurrence interval is 7 μsec as an example according to the present embodiment.

  As can be seen from the example of FIG. 14, when the off-occurrence interval in the modulated clock signal is 1 μsec, it can be seen that the distortion is greatly spread around 2 MHz. On the other hand, it can be seen that when the OFF generation interval in the modulated clock signal is 7 μsec according to the present embodiment, the distortion component is once reduced in the bandwidth W. This is because, on the frequency axis of the modulated clock signal, the modulated clock signal has a reciprocal of an off generation interval of 7 μsec, that is, a periodicity of about 150 kHz. As a result, the spectrum is such that the distortion signal power is greatly reduced near both ends of the bandwidth W, and the distortion signal power generated in the bandwidth W can be reduced. In other words, when compared within the bandwidth W, if the off-occurrence interval in the modulated clock signal is 7 μsec, the distortion component can be made smaller than in the case of 1 μsec.

  As described above, the modulated clock signal transmitted according to the first embodiment can have a higher SNR than that of the conventional case when the modulated clock signal passes through the band limiting element having the pass bandwidth W. In other words, among the distortion components generated in the modulated clock signal due to the data signal being multiplexed by modulation, the signal power generated in the pass band of the band limiting element can be reduced, and as a result, the signal power is reduced as compared with the conventional case. It becomes possible to reduce the degradation of the SNR of the modulated clock signal.

<About the pass bandwidth W of the band limiting element>
Here, the pass bandwidth W of the band limiting element will be described. A filter, which is a typical example of a band limiting element, is a device that acts to weaken signal power outside a certain frequency band. For example, in FIG. 12, a filter whose passband is 2 MHz and whose bandwidth is 0.2 MHz is a device that acts to weaken signal power other than the band indicated by W in FIG.

  As is generally known, most electronic circuit devices have a frequency characteristic that enhances a signal in one frequency band but weakens signal power in another frequency band. Specifically, for example, the amplifier is designed so as to increase the signal power in a desired frequency band, and has a characteristic that the signal power cannot be sufficiently increased for other frequency bands or is weakened. In addition, for example, the PLL is designed to weaken signal power at a frequency other than the vicinity of the center of the clock frequency in order to generate a clock having a desired frequency. In the present specification, an element having such frequency characteristics is referred to as a band limiting element.

  The pass band refers to a band in which the signal power of the outer frequency can be sufficiently weakened. The degree to which the signal power is weakened varies depending on the application destination. For example, in an application where only a certain degree of accuracy is required, the signal power can be weakened by several to several tens of dB as compared with the highest gain in the passband. A passband is defined. Further, for example, in an application where very high accuracy is required, a difference of 80 dB may be required. The pass bandwidth W is defined according to the required accuracy.

When the modulated clock signal transmitted from the transmitter 10 according to the present embodiment is used after passing through a plurality of band limiting elements, for example, a plurality of filters and amplifiers, in the receiver 20, the frequency characteristics of the plurality of band limiting elements are set. A pass bandwidth W is defined based on the combined frequency characteristics. For example, there are N band limiting elements in the passage path of the modulated clock signal, and the functions representing the respective frequency characteristics, that is, the gain for each frequency, are G1 (f), G2 (f),. When represented by (f), the passband width W is defined based on the frequency characteristic of the following equation that combines these.

  In this way, by defining the pass bandwidth W and setting the OFF generation interval in the modulated clock signal to 1 / W or more, the modulated clock when used after passing through a plurality of band limiting elements The SNR of the signal can be improved.

<How to set the clock signal change interval (upper limit) by modulation>
Next, a method for setting the upper limit of the change interval of the original clock signal by modulation will be described with reference to FIGS.

  In the present embodiment, as described above, the intervals 611 to 613 of the intervals in which the modulated clock signal shown in FIGS. 10 to 13 is turned off with respect to the pass bandwidth W of the band limiting element for the modulated clock signal. 711 to 713, 811 to 813 and 911 to 913 are set to 1 / W or more, but the upper limit of the intervals 611 to 613, 711 to 713, 811 to 813 and 911 to 913 may be 2 / W or less. desirable.

  Next, the effect of setting the interval at which the modulated clock signal changes due to the modulation of the original clock signal by the data signal to 2 / W or less will be described with reference to FIGS. As described with reference to FIG. 14, by setting the interval at which the modulated clock signal changes due to modulation to 1 / W or more, distortion caused by modulation can be reduced within the passband having a bandwidth of W. . In particular, a portion (called notch) in which the signal power greatly drops in the spectrum generally occurs at a reciprocal period of the interval at which the original clock signal is changed by modulation. That is, if the interval at which the modulated clock signal changes due to modulation is 1 / W, one notch is generated at each end of the passband.

  If the interval at which the modulated clock signal changes due to modulation is greater than 1 / W, the notch moves inside the passband. When the interval becomes 2 / W, notches that exist outside the passband are generated at both ends of the passband. In other words, two notches are generated in the pass band and two notches are formed at both ends of the pass band, resulting in a total of four notches.

  As is clear from FIG. 14, the signal power is reduced in the vicinity of the notch. Therefore, if the interval at which the modulated clock signal changes due to modulation is set to 1 / W, only half of the signal power drop caused by the notch falls within the pass band of the band limiting element. That is, only about half of the SNR improvement due to the drop in signal power caused by the notch can be obtained. Therefore, it can be said that it is desirable to make the position of the notch to the inside. On the other hand, if the interval at which the modulated clock signal changes due to modulation is increased to 2 / W, even the outer notch enters the pass band of the band limiting element.

  Therefore, it can be seen that the interval at which the signal power due to distortion in the pass band of the band limiting element is minimized is between 1 / W and 2 / W. This is also shown in the results of FIG. FIG. 15 compares the SNRs in the passband for data signal sequences in which OFF occurs for 2, 4, and 8 periods under the same conditions as in FIG. In FIG. 15, the horizontal axis represents the off-occurrence interval. Under this evaluation condition, 1 / W is 5 μsec and 2 / W is 10 μsec. As shown in FIG. 15, the interval at which the modulated clock signal changes due to modulation, that is, the off-occurrence interval between 1 / W and 2 / W, where the SNR is the best, exists. Since the optimum interval varies depending on the modulation method and the number of periods for changing the clock signal, it can be said that it is desirable to use the optimum interval according to the selected parameter in order to improve the SNR of the clock signal.

  As described above, in order to improve the SNR of the modulated clock signal, it is desirable to set the interval at which the modulated clock signal changes due to modulation to 1 / W or more, and further to the interval from 1 / W to 2 / It is more desirable to make it W or less. 14 and 15 show the evaluation results when the intervals at which the modulated clock signals change due to modulation are all the same. On the other hand, FIG. 16 shows the results of evaluation with different intervals for changing the modulated clock signal due to modulation.

  In the example of FIG. 16, a data signal sequence having three cycles of OFF is used under the same conditions as in FIGS. The horizontal axis represents the interval between the first off and the second off, and the vertical axis represents the interval between the second off and the third off. A region 1002 indicates a high SNR, and a region 1001 indicates a low SNR.

  As shown in FIG. 16, the SNR of the modulated clock signal becomes the highest depending on the modulation method and the parameters such as the number of periods (depending on the length of the data signal sequence) of changing the clock signal by the modulation. It can be said that an optimal interval is applied between all off-states. For this reason, when the highest priority is given to improving the SNR of the clock signal, it can be said that it is desirable that the intervals at which the original clock signal is changed by modulation are all the same. Therefore, the SNR of the clock signal can be most improved by applying the original clock signal to all the optimal intervals for changing the modulation by modulation, depending on parameters such as the modulation method and the number of periods for changing the clock signal. Become.

<About the waveform of the original clock signal>
The clock signal refers to a signal that periodically repeats rising and falling of a waveform as shown in FIG. The digital signal processing operation can be started by using the rising or falling edge of the clock signal waveform as a trigger. When considering starting the operation of the digital signal processing, it is important that the clock signal rises and falls.

  The shape of the waveform including the rising edge and the falling edge can be various. For example, the two most typical examples are the waveforms shown in FIGS. FIG. 17 shows a rectangular wave, where rise and fall occur instantaneously. In addition, the signal amplitude is constant after rising and falling. The spectrum of the rectangular wave in FIG. 17 is a spectrum in which power is distributed at an integer multiple of the frequency of the clock signal as shown in FIG.

  The waveform in FIG. 19 is called a sine wave, cosine wave, or continuous wave (CW), and has a waveform shape represented by a trigonometric function. In terms of the spectrum, unlike FIG. 18, the power concentrates only on the frequency of the clock signal as shown in FIG.

  Although it is a typical waveform of the clock signal of FIG.17 and FIG.18, it is difficult to actually produce these waveforms completely. For example, when the change in the waveform in FIG. 17 becomes gentle, the spectrum in FIG. 18 changes as shown in FIG. 22, and the signal power at a high frequency attenuates. Further, for example, if the waveform of FIG. 18 is distorted and a complete sine wave cannot be formed, the signal power is dispersed at an integer multiple of the frequency of the clock signal as shown in FIG.

  Thus, as the waveform of the original clock signal, there is also an intermediate waveform of FIG. 17 and FIG. 19 as shown in FIG. 21 with respect to a typical waveform of FIG. 17 and FIG. In the following description, a clock signal having a waveform close to that in FIG. 17 is referred to as a rectangular wave clock signal, and a clock signal having a waveform close to that in FIG. 19 is particularly referred to as a sine wave clock signal.

  As described above, according to the present embodiment, distortion components generated in the pass bandwidth W of the band limiting element including the frequency of the modulated clock signal can be reduced. The SNR of the modulated clock signal when it passes can be improved as compared with the prior art. In general, it can be said that the SNR of the modulated clock signal can be easily improved because the distortion component can be reduced more as the pass bandwidth W of the band limiting element is smaller. Therefore, if priority is given to improving the SNR of the modulated clock signal, it can be said that the waveform of the original clock signal is preferably a sine wave. This is because the power of the sine wave spectrum is concentrated at a certain frequency as shown in FIG.

  On the other hand, considering that the clock signal is used to activate the digital signal processing operation, it is desirable that the rising and falling edges of the clock signal are steep. This is because the sharper the change in the signal, the more accurately the start point of one cycle can be specified, and the clock can be determined with a more accurate cycle. Therefore, it can be said that the original clock signal is preferably a rectangular wave when priority is given to the accuracy when the digital signal processing operation is started. In this case, however, the spectrum spreads in the frequency direction as shown in FIG. In order to improve the SNR in such a case, for example, a band limiting element such as a filter having a pass bandwidth W around each integer multiple of the frequency of the clock signal is prepared, and the sum of the outputs of the band limiting elements is prepared. May be used as a clock signal. Even in the case of FIG. 18, the distortion caused by the modulation becomes smaller within the bandwidth W around each integer multiple of the frequency of the clock signal, so that the SNR can be improved as compared with the conventional case.

(Second Embodiment)
FIG. 24 shows a wireless transmission / reception system according to the second embodiment of the present invention. In the transmitter (wireless transmitter) 10, the modulated clock signal 31 output from the modulator 13 is further input to the amplitude modulator 14, and the amplitude of the carrier signal (local signal) output from the carrier signal generation unit 15. Modulated. The modulated clock signal after amplitude modulation, that is, the RF signal 34 is radiated as a radio wave from the transmitting antenna 16.

  On the other hand, the RF signal transmitted from the transmitter 10 via the antenna 16 is received by the receiving antenna 23 and input to the receiver (wireless receiver) 20. In the receiver 20, the reception signal output from the reception antenna 23 is demodulated corresponding to the amplitude modulation by the envelope detector 23, and a signal equivalent to the modulated clock signal 31 output from the modulator 13 is generated. The The output signal from the envelope detector 23 passes through the filter 24 and the PLL 22 having a pass band including the frequency of the clock signal, so that an accurate clock signal 32 is reproduced. The sampler 21 can reliably extract the data signal 36 by sampling the modulated clock signal 35 output from the filter 35 using the recovered clock signal 32 thus obtained.

(Third embodiment)
FIG. 25 shows a wireless transmission / reception system according to the third embodiment of the present invention, which is different from the second embodiment in that a matched filter 25 is added in the receiver 20. The modulated clock signal 31 transmitted from the transmitter 10 can also be used for timing detection in the receiver 20.

  Specifically, in the matched filter 25, the same reference signal as the modulated clock signal 31 generated by modulation in the transmitter 10 is prepared, and this reference signal and the modulated clock transmitted as the RF signal 34 from the transmitter 10. What is necessary is just to correlate with a signal. Such processing is generally called matched filter (MF) processing, and the correlation value output from the matched filter 25 is called MF output. The MF output has the highest value when the timings of two correlated signals coincide. Using this property, the timing detection signal 37 can be obtained from the MF output in FIG. That is, the peak of the MF output can be obtained as the timing detection signal 37.

  In order to improve the accuracy of timing detection using the MF output, it is desirable that the peaks of the MF output appear not at a plurality of times but at a certain timing. In order to satisfy this requirement, it is desirable that the modulated clock signal generated by modulation does not have periodicity. Therefore, when priority is given to increasing the accuracy of timing detection using the MF output, the intervals at which the original clock signal is changed by modulation may be set to different values. At this time, it is desirable to set the value as close as possible to the optimum interval. For example, when the optimum interval is 10 periods, it is desirable to use intervals such as 8, 9, 11, and 12. Further, as is apparent, when there are three intervals and the optimum interval is 10 periods, it is more preferable to set each interval to 9, 10, 11 than to 10, 11, 12. desirable. As shown in FIG. 16, by using an interval close to the optimum interval, it is possible to achieve an SNR that is close to that when the optimum interval is used.

  When all the intervals at which the original clock signal is changed by modulation are set to different values, the intervals may be set so as to become larger later in time. That is, for example, when the optimal interval is 10 cycles and there are 6 OFFs, these 5 intervals may be sequentially set to 8 cycles, 9 cycles, 10 cycles, 11 cycles, and 12 cycles, respectively. In this way, distortion generated in the modulated clock signal due to modulation is biased forward in time, so that the SNR of the clock signal is improved in a section after the section in which the data signal sequence is multiplexed in the modulated clock signal. It becomes easy. This is particularly effective when a data signal sequence is used for timing detection and then processing using a clock signal is started.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The block diagram which shows the transmission / reception system which concerns on the 1st Embodiment of this invention. Block diagram showing an application example of the transmission / reception system of FIG. Block diagram showing details of PLL in FIG. Diagram showing original clock signal consisting of unbalanced signal Diagram showing original clock signal consisting of balanced signal The figure which shows the example of the OOK modulation | alteration with respect to the original clock signal of FIG. The figure which shows the example of the OOK modulation | alteration with respect to the original clock signal of FIG. The figure which shows the example of AM modulation with respect to the original clock signal of FIG. The figure which shows the example of AM modulation with respect to the original clock signal of FIG. The figure which shows the example which changes the space | interval of the original clock signal of FIG. 4 by OOK modulation | alteration The figure which shows the example which changes the space | interval of the original clock signal of FIG. 5 by OOK modulation | alteration The figure which shows the example which changes the space | interval of the original clock signal of FIG. 4 by AM modulation The figure which shows the example which changes the space | interval of the original clock signal of FIG. 5 by AM modulation Diagram showing an example of the spectrum of a modulated clock signal to be transmitted The figure which shows the example of SNR within the pass bandwidth of a band-limiting element The figure which shows the example of SNR within the pass bandwidth of a band-limiting element The figure which shows the example of the waveform of the clock signal The figure which shows the example of the spectrum of the clock signal of FIG. The figure which shows the other example of the waveform of a clock signal The figure which shows the example of the spectrum of the clock signal of FIG. The figure which shows another example of the waveform of a clock signal The figure which shows the example of the spectrum of the clock signal of FIG. The figure which shows the other example of the spectrum of the clock signal of FIG. The block diagram which shows the transmission / reception system which concerns on the 2nd Embodiment of this invention. The block diagram which shows the transmission / reception system which concerns on the 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Transmitter 11 ... Clock signal generation part 12 ... Data signal generation part 13 ... Modulator 14 ... Amplitude modulator 15 ... Carrier signal generator 16 ... Transmission antenna 20 ... Receiver 21 ... Sampler 22 ... PLL
23 ... Envelope detector 24 ... Filter 25 ... Matched filter 40 ... Analysis device 50 ... Detection device

Claims (18)

When the pass bandwidth of the band limiting element through which the modulated clock signal passes is W, modulation is performed so that the original clock signal is changed by the data signal at intervals of 1 / W or more to generate the modulated clock signal. Steps,
Transmitting the modulated clock signal;
The transmission method characterized by comprising.   The transmission method according to claim 1, wherein the interval is 2 / W or less.   The transmission method according to claim 1, wherein the intervals are all the same in one series of the data signals.   The transmission method according to claim 1, wherein the intervals are all different in one series of the data signals.   3. The transmission method according to claim 1, wherein the interval is set to be larger as an interval later in time in one sequence of the data signal. 4.   The transmission method according to claim 1, wherein the waveform of the original clock signal is a sine wave.   The transmission method according to claim 1, wherein the waveform of the original clock signal is a rectangular wave.   The transmission method according to claim 1, wherein the modulation is on-off keying.   The transmission method according to claim 1, wherein the modulation is amplitude modulation.   The transmission method according to claim 1, wherein the band limiting element includes a filter. A clock signal generator for generating an original clock signal;
A data signal generator for generating a data signal;
When the pass bandwidth of the band limiting element through which the modulated clock signal passes is W, modulation is performed so that the original clock signal is changed by the data signal at intervals of 1 / W or more to generate the modulated clock signal. A modulator,
And a transmitter that transmits the modulated clock signal.   The transmitter according to claim 11, wherein the interval is 2 / W or less. The modulated clock signal generated by performing modulation such that the original clock signal is changed by the data signal at intervals of 1 / W or more, where W is the pass bandwidth of the band limiting element through which the modulated clock signal passes. A receiving unit for receiving a received signal and
A clock recovery unit for recovering a component of the original clock signal from the received signal to obtain a recovered clock signal;
And a sampler for sampling the received signal using the recovered clock signal and extracting the data signal.   The receiver according to claim 13, wherein the clock recovery unit includes the band limiting element.   The receiver according to claim 13, wherein the clock recovery unit includes a filter as the band limiting element.   The receiver according to claim 13, wherein the clock recovery unit is a PLL including a filter having the passband width W. The transmitter according to claim 11 provided in a detection device for detecting a physical quantity signal;
14. A transmission / reception system comprising: the receiver according to claim 13 provided in an analysis device that analyzes the detected physical quantity signal.   The detection device includes a probe unit configured to detect a magnetic resonance signal as the physical quantity signal, and the analysis device analyzes the magnetic resonance signal and performs image reconstruction processing to obtain a magnetic resonance video signal The transmission / reception system according to claim 17, further comprising an imaging unit.

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