JP3599603B2 - Data demodulation method and circuit for synchronous electromagnetic induction communication - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a demodulation method or a demodulation circuit for received data in a portable information device using synchronous electromagnetic induction communication.
[0002]
[Prior art]
A device that exchanges data with an external device, particularly a portable information device, has a characteristic communication method. The method most widely used is a method of connecting using a cable such as RS-232C. As a non-contact method, there is a method (including IRDA) using a light emitting diode (LED) in a method that has recently become widespread. As another method, there is a method of performing electromagnetic induction communication using a coil. Since the present invention relates to this electromagnetic induction communication, it will be described in more detail.
[0003]
As a method of electromagnetic induction communication, there are asynchronous (start-stop synchronization) and synchronous communication. Asynchronous operation is basically described in JP-A-59-205659-205661. Japanese Utility Model Application Laid-Open No. 63-30038 discloses a method of increasing noise resistance by asynchronous communication. As these methods, a transmission coil is intermittently turned on and off as a burst at a frequency serving as a carrier, and a waveform is generated in a receiving coil tuned to the frequency serving as a carrier, and the waveform is shaped and demodulated to obtain an NRZ signal. Is what you get.
For synchronous communication, JP-A-4-20040 describes the principle of communication, and JP-A-3-190435 mainly describes a demodulation method.
[0004]
Here, transmission and reception will be briefly described. Consider a case where two sets of portable information devices having the same coil are facing each other as shown in FIG. A capacitor is connected in parallel so that the coils L1 and L2 resonate at the same frequency to form a tuning circuit. When the transmitting coil is driven with a special waveform, a receiving waveform corresponding to the transmitting waveform appears on the receiving coil. .
[0005]
This situation will be described specifically. FIG. 6 shows a serial communication circuit. The modulation circuit 1 contains three signals of the transmission data TXD, the transmission clock TXC, and the tuning clock CLK. FIG. 7 shows this modulation circuit 1 extracted. The transmission data TXD, which is normal NRZ data, is exclusive-ORed with the transmission clock TXC by the EXOR gate 8 to obtain a Manchester signal. Here, it is further inserted into the DF / F 9 and latched by the tuning clock CLK in order to take a beard. The coil on the transmission side is driven by the obtained coil drive waveform TXP (and its inverted signal TXN).
[0006]
On the other hand, a capacitor is connected to the coil on the receiving side and resonates (tunes) so as to be twice the communication rate (ie, the same frequency as the tuning clock CLK). For example, in the case of synchronous communication having a communication rate of 1 Mbps, the tuning frequency is 2 MHz. FIG. 8 shows the signals of each section. When the signal of the transmitting coil driven by TXP is received, a waveform (signal) indicated by QX appears in the receiving coil. Since the receiving coil resonates at twice the communication rate, when the TXP is long (one transmission clock TXC period), the receiving waveform QX has two continuous peaks on one side. From this peak, two signals RXP and RXN are obtained by the transmission / reception circuit 4 of FIG. When these two are added, a received clock RCLK having the same frequency as the tuning clock CLK is generated. The specific contents of the transmission / reception circuit 4 in the serial communication circuit 7 will be described with reference to FIG. On the receiving side, there are two comparators 14 and 15, which separate the received waveform QX in FIG. 8 to obtain two signals RXP and RXN. FIG. 10 shows an embodiment of the demodulation circuit 2 in FIG. FIG. 11 shows each signal at the time of demodulation. The demodulation method of FIG. 10 will be described using the signals of FIG. The addition of RXP and RXN is performed by the OR gate 23 to generate the reception clock RCLK. At the same time, RXP and RXN enter the RSF / F (RS flip-flop) and become RDATA. On the other hand, the reception clock RCLK becomes a clock RCK having a frequency of 1/2 by the TF / F22. Here, the original signal BRXD is obtained by latching RDATA at the rising edge of RCK by the DF / F21. Thereafter, the signal BRXD is directly or inverted by the NEGA signal. This is because the signal may be inverted depending on the direction of the coil, and the state is determined by the flag check circuit 3 in FIG. 6 to obtain a correct signal.
[0007]
In this way, the transmission coil is driven by a bi-phase signal (also referred to as a Manchester method), and is received by a parallel resonance (tuning) circuit including a coil and a capacitor tuned to twice the data transmission rate, and the waveform data is obtained. Is subjected to waveform shaping using both threshold values (Shiichi) on both the + side and the-side, and is converted into two received data. This method is suitable for low power consumption, in which a synchronous clock (a clock having the same frequency as the tuning clock CLK) can be easily obtained and reception is possible even if the maximum clock of the receiving side is twice the transmission rate. Has features.
[0008]
[Problems to be solved by the invention]
However, this demodulation method is strongly affected by the electromagnetic coupling characteristics between the transmitting coil and the receiving coil and the frequency characteristics of the receiving circuit. As described in JP-A-4-20040, the tuning frequency of the coil must be suppressed to +30 and -10% for twice the transmission rate. In this case, as the transmission rate increases, the value of the inductance of the coil and the value of the tuning capacitor decrease, and the coil is easily affected by stray capacitance and variations in elements, so that fine adjustment of the circuit constant is required. Similarly, a communication coil using a high-speed transfer pot core is shown in FIG. 12 of Japanese Patent Application Laid-Open No. Hei 4-220040. However, since the communication coil is expensive and has a small shape, the relative accuracy with respect to the opposing coil becomes severe.
[0009]
Further, it is necessary to keep the influence of the magnetic field small by not placing metal parts near the coil. It is also necessary to consider the substrate. As a specific example, as shown in Japanese Utility Model Application Laid-Open No. 3-005655, a solid inner layer (power supply layer, GND) is mounted on the substrate mounted to improve the electromagnetic coupling characteristics of the coil. Layers, etc.) and cuts in the substrate. Further, the frequency characteristic up to the waveform shaping circuit of the receiving circuit is strongly affected. FIG. 12 shows a waveform at the time of abnormality. FIG. 12 is the same as FIG. 9 of JP-A-4-20040. (A) is the case where the tuning frequency of the receiving circuit is high or the response of the receiving circuit is excessive, and the receiving clock RCLK becomes extra. (C) is the reverse case where the magnetic field is interrupted, and two continuous waveforms in the same direction are connected to reduce the reception clock RCLK by one. (A) and (c) have different reception clocks as compared to (b) in the case where they are normal, and both cannot be normally received by the conventional method.
[0010]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides a signal having a pulse width and a data train equivalent to the coil drive signal TXP on the transmission side by shaping the waveform of the received signal of the coil with a waveform shaping circuit using the midpoint of the signal as a threshold. (Hereinafter, referred to as an RXA signal), and after a predetermined count (that is, after a predetermined time has elapsed) with a demodulated clock faster than the transmission clock from its rise and fall, the level of the RXA signal is latched (determined). Then, the validity / invalidity of the data is determined according to the procedure described below, and the received data is demodulated.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
After counting a certain value with a demodulation clock faster than the transmission clock from the rising and falling of the RXA signal, the level of the RXA signal is latched, validity / invalidity of data is determined according to the procedure described below, and the received data is demodulated. In addition, even if the electromagnetic coupling characteristics between the transmission coil and the reception coil are disturbed and some noise is generated in the reception waveform, the data can be demodulated. For example, a metal may be nearby on the mounting surface, and there is no restriction on the mounting surface, and the mounting density can be increased. The power supply and the ground can be strengthened because the power supply layer and the GND layer in the inner layer of the substrate do not have to be cut out or cut in the substrate in order to improve the electromagnetic coupling characteristics of the coil by being less affected by the interior of the substrate. Further, since it is not necessary to use a coil of a special pot core, a coil can be easily formed by a pattern around the substrate, thereby enabling cost reduction and strong displacement.
[0012]
There are many benefits at the time of design. Since the influence of the frequency characteristics of the receiving circuit is reduced, the designing of the receiving circuit is facilitated. Furthermore, in the development of the demodulation circuit, it was not possible to judge whether the signal could not be received because the waveform was disturbed and the demodulation circuit was bad because the signal had to be received with the waveform received by the coil. Since the coil drive signal can be directly connected to the receiving side, debugging becomes very easy.
[0013]
【Example】
A receiving circuit for synchronous communication and a demodulation method thereof according to an embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows an embodiment of a transmission / reception circuit for synchronous communication to which the present invention is applied. FIG. 2 shows signal waveforms at various parts on the transmission side and the reception side. To be precise, the devices on the transmitting side and the receiving side are different, but the same device has been described for the sake of explanation. The transmitting part and the coil receiving waveform are basically the same as those shown in FIG. 10 of JP-A-4-20040, but the receiving part is different, and the coil receiving waveform is directly shaped by the comparator 20 and is the same as the signal TXP or TXN of the transmitting side circuit. An RXA signal having a waveform is obtained. The comparator 30 has a hysteresis. Although the transmission data TXD and the TXP signal are originally shifted in time due to the whisker removal circuit, they are treated as the same timing for the sake of simplicity.
[0014]
Next, an actual demodulation method will be described. As described in the prior art, the tuning clock CLK on the transmitting side is twice the transmission rate. For example, when the transmission rate is 1 Mbps, the tuning clock CLK becomes 2 MHz. On the other hand, the receiving side requires a high demodulation clock RXCLK for data demodulation. Here, the transmission rate is set to eight times for explanation. That is, when the transmission rate is 1 Mbps, the demodulated clock RXCLK is 8 MHz. Of course, the transmission rate may be higher, but if the transmission rate is not at least four times as high, the demodulation clock RXCLK on the transmitting side cannot be correctly demodulated when a phase shift occurs between the clock CLK and the demodulation clock RXCLK.
Actual demodulation is performed by the following procedure.
[0015]
Procedure 1 Measure the level of the RXA signal at the 4th and 13th clock edges of the demodulated clock RXCLK counted from the rising or falling of the RXA signal.
Step 2 When the level of the RXA signal at the fourth clock edge of the demodulated clock RXCLK is “L” with respect to the rising edge of the RXA signal, the data is invalidated and the rising edge of the RXA signal is ignored.
[0016]
Step 3 When the level of the RXA signal at the fourth clock edge of the demodulated clock RXCLK is “H” with respect to the fall of the RXA signal, the data is invalidated and the fall of the RXA signal is ignored.
Step 4 When the level of the RXA signal at the fourth and thirteenth clock edges of the demodulated clock RXCLK is both “H” with respect to the rising edge of the RXA signal, the data is recognized as “H” and “H” as valid and the RXA The falling and rising edges of the RXA signal between the rising edge of the signal and the thirteenth clock edge of the demodulated clock RXCLK are ignored.
[0017]
Step 5 When the level of the RXA signal at the fourth and 13th clock edges of the demodulated clock RXCLK is both "L" with respect to the falling edge of the RXA signal, the data is recognized as "L" and "L" as valid, The rising and falling edges of the RXA signal between the falling edge of the RXA signal and the thirteenth clock edge of the demodulated clock RXCLK are ignored.
[0018]
Step 6 When the level of the RXA signal at the fourth and thirteenth clock edges of the demodulated clock RXCLK becomes “H” and “L” with respect to the rise of the RXA signal, only the first “H” is made valid, and the RXA signal is made valid. The falling and rising edges of the RXA signal between the rising edge and the fourth clock edge of the demodulated clock RXCLK are ignored.
[0019]
Step 7 When the level of the RXA signal at the fourth and thirteenth clock edges of the demodulated clock RXCLK becomes “L” and “H” with respect to the falling edge of the RXA signal, only the first “L” is made valid, and the RXA The rising and falling edges of the RXA signal between the falling edge of the signal and the fourth clock edge of the demodulated clock RXCLK are ignored.
[0020]
Step 8 Combine valid data of the RXA signal two by two to obtain a valid data combination. The valid data of the RXA signal is always combined in the order of "L""H" or "H""L". When there is a combination of "H", "H" or "L" and "L", if the combination is divided in the middle, the order is automatically changed to "L", "H", "H" and "L".
[0021]
Step 9 Thereafter, the direction of the coil is determined by the flag check circuit. As a result, it is decided whether to take only the first valid data or only the last valid data (which is the inverse of the case where only the first valid data is taken). This becomes reception data (NRZ data equivalent to transmission data TXD).
The determination procedure will be specifically described with reference to FIG. (A) is transmission data TXD (NRZ). Here, the data is 10110. (B) is a signal obtained by modulating the transmission data TXD (A) on a Manchester, that is, a coil drive signal TXP (inversion of TXN). Depending on the modulation method, the rise may be "1", but here the fall is "1". For simplicity, the time delay of the beard removal circuit was ignored. Next, the signal of the receiving system will be described. [Example 1] includes waveforms (C) to (H). (C) is a reception waveform QX of the coil, and the waveform is distributed above and below the center and has an ideal shape in characteristics. The RXA signal of (D) is obtained by shaping the received waveform (C) by the comparator of FIG. (E) is a demodulation clock RXCLK. (A) One bit of transmission signal transmission data TXD includes eight clocks (= 16 edges).
[0022]
According to the procedure 1, the fourth and thirteenth edges of the demodulated clock RXCLK are counted from the rising of the first RXA signal (D), and the value of each RXA signal (D) is latched. The value of the RXA signal (D) at the fourth edge is "H". This value becomes effective by the procedure 2. Next, the value at the thirteenth edge is "L". Therefore, only the fourth data becomes valid and the value at the thirteenth becomes invalid by the procedure 6. Next, the falling of the RXA signal D will be described. From this fall, the values of the RXA signal (D) at the fourth and thirteenth edges of the demodulated clock RXCLK (E) are both "L". From step 5, these two "L" data are valid. Hereinafter, this procedure is repeated to obtain latch data (F). The latch data (F) is in the order of "HLLHLHLHL", but the combination of "HH" and "LL" is prohibited in step 8, so cut in the middle of "HH" and make the following two combinations. . This is the combination (G). The flag was determined based on the direction of the coil in the same manner as in the prior art, and received data (H) was obtained. Here, the first level of the combination is assumed to be valid. The received data (H) is “HLHH ··” (1011 ··), and the same NRZ data as the transmission data TXD (A) could be obtained.
[0023]
Next, [Example 2] will be described.
The coil reception waveform QX (I) is considerably disturbed, and the waveform is disturbed near the center when the polarity of the peak changes as compared with the coil reception waveform QX (C), and the midpoint of two consecutive peaks Has the opposite polarity. In this state, an extra clock is put on RXP and RXN in the conventional demodulation method, so that correct judgment cannot be made. In the present invention, this case can also be correctly determined. The fourth and thirteenth edges of the demodulated clock RXCLK are counted from the rising edge of the RXA signal (J), and the value of each RXA signal (D) is latched. The results are "H" and "L", respectively, and only the fourth "H" is valid from the procedure 6. Although the falling and rising edges are continuous immediately after the rising edge of the RXA signal (J), these are also ignored in the procedure 6.
[0024]
Next, the fourth and thirteenth edges of the demodulated clock RXCLK are counted with respect to the falling edge of the RXA signal (J), and the value of each RXA signal (J) is latched. The result is "L" or "L", and both data are made valid by the procedure 5. However, the RXA signal (J) is once at "H" at two places near the first and second and seventh to ninth places of the demodulated clock RXCLK (K). The falling is ignored and the determination by the demodulation clock RXCLK is not performed during this period. For the next rising edge of the RXA signal (J), the RXA signal (J) is measured at the fourth and thirteenth edges of the demodulated clock RXCLK. The results are "H" and "H", which are valid from step 4. Also at this time, the RXA signal (J) is once at "L" at two places near the first and eighth to twelfth places of the demodulated clock RXCLK (K). Is ignored and the determination by the demodulation clock RXCLK is not performed during this period. Hereinafter, data determination is performed in the same procedure. In this way, the abnormal portion of the RXA signal (J) due to the disturbance of the received waveform (I) is ignored. As a result, the same latch data (L) as in [Example 1] is obtained for [Example 2]. Thereafter, reception data is obtained in the same manner as in [Example 1].
[0025]
Although not described in the description so far, if two consecutive peaks are connected due to disturbance of the coil reception waveform QX (C or I), RXP or RXN is reduced by the conventional method and correct demodulation cannot be performed. In this method, it can be seen that the RXA signal itself can be demodulated correctly because it is the same as the case where the mountain is not connected.
[0026]
The reason why the fourth and thirteenth demodulation clocks RXCLK are taken with respect to the rise or fall of the RXA signal is as follows. Originally, if the RXA signal is completely equal to the coil drive signal TXP (B), it is better to latch (measure) the level of the RXA signal at the fourth and twelfth demodulation clock RXCLK. However, if the coil reception waveform (C or I) continues for two consecutive peaks, the second peak becomes smaller, and if the middle of the consecutive peaks has the opposite polarity, the second peak becomes timing-dependent. Be late. Therefore, it is not the twelfth but the thirteenth.
[0027]
Next, the fourth and thirteenth measurement timing of the demodulation clock RXCLK will be described in detail. Specifically, the transmission rate is 1 Mbps, and the demodulation clock RXCLK is 8 Mbps. At this time, the width of one bit of data is 1 μS, which corresponds to a long pulse width of the RXA signal. Therefore, the short pulse width of the RXA signal is 500 μS. One peak of the received waveform QX is inserted between the short pulse widths of the RXA signal. One cycle of the demodulation clock RXCLK is 125 nS, and the edge interval is half that of 62.5 nS.
[0028]
The fourth and thirteenth times of the demodulated clock RXCLK with respect to the rise or fall of the RXA signal are 187.5 to 250 nS and 750 to 812.5 nS, respectively, because of the phase shift between the transmission clock and the reception clock. . This is 18.75 to 25% and 75 to 81.25%, respectively, for the long pulse width of the RXA signal. It can be seen that the thirteenth is slightly transmitted at about 1/4, 3/4. Practical ranges for the determination timing of the RXA signal are 15 to 35% and 65 to 90%, respectively.
[0029]
FIG. 4 shows a circuit for taking in the RXA signal at the fourth and thirteenth edges of the demodulated clock RXCLK with respect to the rising or falling edge of the RXA signal. The exclusive OR EXOR has a demodulation clock RXCLK on one side and an integrated signal on the other. Therefore, pulses corresponding to the rising and falling of the demodulation clock RXCLK are extracted. The RXA signal enters the flip-flop FF11 and its output becomes "H" at the rising edge. At the falling edge, the flip-flop FF21 becomes "H". The counters 1 and 2 both count the edges of the demodulated clock RXCLK, and the outputs Q4 and Q13 become "H" at the fourth and thirteenth times of the demodulated clock RXCLK from the rising and falling edges of the RXA signal edge, respectively. The flip-flops FF12 to FF23 latch the level of the RXA signal at the moment when the output of the connected counter 1 or 2 becomes "H". Each output is connected to the arithmetic unit CPU via the input / output circuit I / O, where the validity / invalidity of the level is determined.
Here, the processing unit CPU is used for the procedure, but it can be configured by a logic circuit or the like.
[0030]
【The invention's effect】
The present invention is implemented in the form described above, and has the following effects.
Even if the reception waveform is disturbed due to the influence of the electromagnetic coupling characteristics between the transmission coil and the reception coil, demodulation can be performed, which is advantageous in mounting. For example, a metal may be nearby on the mounting surface, and it is not necessary to cut out the power supply layer and the GND layer in the inner layer of the substrate or cut the substrate in order to improve the electromagnetic coupling characteristics of the coil. As a result, the mounting density is increased and the power supply can be increased. In addition, since a coil can be easily formed with a pattern around the substrate without using a special pot core coil, the cost can be reduced and the relative accuracy is not severe. In addition, since the influence of the frequency characteristics of the receiving circuit is reduced, the designing of the receiving circuit is facilitated, and the benefit received at the time of designing is high. In the past, especially when debugging the receiver circuit, demodulator circuit, etc., it was necessary to receive the waveform received by the coil, but this time it is very easy to work by connecting the coil drive signal on the transmission side to the reception side as it is became.
[0031]
On the other hand, the need for a high demodulation clock, which has been a drawback up to now, and the corresponding increase in current, add that the recent development of batteries has become less of a problem.
[Brief description of the drawings]
FIG. 1 is an embodiment of a transmitting / receiving circuit for synchronous communication to which the present invention is applied.
FIG. 2 is a signal waveform of each unit on a transmission side and a reception side.
FIG. 3 is a diagram for explaining an actual demodulation method;
(A) is transmission data TXD (NRZ).
(B) is a signal obtained by modulating the transmission data TXD (A) to Manchester.
(C) and (I) are reception waveform QX signals of the coil.
(D) and (J) are RXA signals after waveform shaping by the comparator.
(E) is the demodulated clock RXCLK.
(F) Latch data.
(G) Combination of latch data.
(H) Received data obtained by determining the flag.
FIG. 4 is a circuit which captures the level of the RXA signal at the fourth and thirteenth edges of the demodulation clock RXCLK with respect to the rising or falling of the RXA signal.
FIG. 5 is a diagram showing two sets of opposed portable information devices having the same coil.
FIG. 6 is a diagram illustrating a serial communication circuit.
FIG. 7 is a diagram showing a modulation circuit 1 in FIG. 6;
FIG. 8 shows signals of respective units.
FIG. 9 is a diagram showing a transmission / reception circuit 4 in FIG. 6;
FIG. 10 is a diagram showing a demodulation circuit 2 in FIG. 6;
FIG. 11 is a diagram showing each signal at the time of demodulation.
FIG. 12 is a diagram showing a reception waveform at the time of abnormality.
[Explanation of symbols]
30 Comparator EXOR Exclusive OR I / O I / O circuit CPU Arithmetic unit FF11, FF12, FF13, FF21, FF22, FF23 Flip-flop counter 1, 2 Counter

Claims (6)

The transmission signal is driven by a coil by the Manchester method, and a signal having a pulse width and a data train having the same width as the coil driving signal of the transmission signal is set using a substantially middle point between the highest level and the lowest level of the reception signal as a threshold value. (Hereinafter referred to as an RXA signal).
  A level when the RXA signal is latched before a lapse of approximately half the width of one bit of non-return-to-zero (NRZ) transmission data from the rise or fall of the RXA signal (hereinafter referred to as a first level) And a level when the RXA signal is latched after a lapse of substantially half of the signal width and before a lapse of one bit width of the transmission data from the rising or falling of the RXA signal ( (Hereinafter referred to as the second level)
  If the first level is equal to or less than the threshold value (hereinafter referred to as “L”) when the RXA signal is the rising edge, the data of the RXA is invalidated,
  When the first level is equal to or higher than the threshold value (hereinafter referred to as “H”) with respect to the falling edge of the RXA signal, the data is invalidated,
  When the first level and the second level are both “H” with respect to the rising edge of the RXA signal, the data is validated;
  When both the first level and the second level are “L” with respect to the falling of the RXA signal, the data is valid,
  When the first level is “H” and the second level is “L” with respect to the rising of the RXA signal, only the first “H” is valid,
  A synchronous electromagnetic induction system wherein only the first "L" is valid when the first level is "L" and the second level is "H" with respect to the fall of the RXA signal. Data demodulation method. The valid data is the first received data, and the first level and the second level of the valid data of the RXA signal are used. Two 2. The synchronous electromagnetic induction data demodulation according to claim 1, wherein when the levels are both "H", "H" or "L", "L", the data is effective from the second level data. Method. The coil of the transmission signal is driven by the Manchester method, and a signal having a pulse width and a data train having the same width as the coil driving signal of the transmission signal is set as a threshold value at a substantially middle point between the highest level and the lowest level of the reception signal. (Hereinafter referred to as an RXA signal).
  A level when the RXA signal is latched before a lapse of approximately half the width of one bit of non-return-to-zero (NRZ) transmission data from the rise or fall of the RXA signal (hereinafter referred to as a first level) And a level when the RXA signal is latched after a lapse of substantially half of the signal width and before a lapse of one bit width of the transmission data from the rising or falling of the RXA signal ( (Hereinafter referred to as a second level).
  Means for invalidating the data of the RXA when the first level is equal to or less than the threshold value (hereinafter referred to as “L”) when the RXA signal is the rising edge;
  Means for invalidating the data when the first level is equal to or higher than the threshold value (hereinafter referred to as “H”) with respect to the fall of the RXA signal;
  Means for validating the data when both the first level and the second level are “H” with respect to the rising of the RXA signal;
  Means for validating data when the first level and the second level are both "L" with respect to the falling of the RXA signal;
  Means for validating only the first "H" when the first level is "H" and the second level is "L" with respect to the rising of the RXA signal;
  A synchronous system comprising means for validating only the first "L" when the first level is "L" and the second level is "H" with respect to the fall of the RXA signal. electromagnetic Inductive data demodulation circuit. The valid data is the first received data, and the first level and the second level of the valid data of the RXA signal are used. Two 4. The synchronous electromagnetic induction system according to claim 3, further comprising means for validating from the second level data when the levels are both "H", "H" or "L", "L". Data demodulation circuit. The transmission signal is driven by a coil using the Manchester method, and a signal having a pulse width and a data train having the same width as the coil driving signal of the transmission signal is set using a substantially middle point between the highest level and the lowest level of the reception signal as a threshold. A portable information terminal having a synchronous electromagnetic induction type data demodulation circuit characterized by taking out an RXA signal).
  A level when the RXA signal is latched before a lapse of approximately half the width of one bit of non-return-to-zero (NRZ) transmission data from the rise or fall of the RXA signal (hereinafter referred to as a first level) And a level when the RXA signal is latched after a lapse of substantially half of the signal width and before a lapse of one bit width of the transmission data from the rising or falling of the RXA signal ( (Hereinafter referred to as a second level).
  Means for invalidating the data of the RXA when the first level is equal to or less than the threshold value (hereinafter referred to as “L”) when the RXA signal is the rising edge;
  Means for invalidating the data when the first level is equal to or higher than the threshold value (hereinafter referred to as “H”) with respect to the fall of the RXA signal;
  Means for validating the data when both the first level and the second level are “H” with respect to the rising of the RXA signal;
  Means for validating data when the first level and the second level are both "L" with respect to the falling of the RXA signal;
  Means for validating only the first "H" when the first level is "H" and the second level is "L" with respect to the rising of the RXA signal;
  A synchronous system comprising means for validating only the first "L" when the first level is "L" and the second level is "H" with respect to the fall of the RXA signal. An electromagnetic induction type data demodulation circuit,
  A portable information terminal with a coil that performs synchronous electromagnetic induction communication. The valid data is the first received data, and the first level and the second level of the valid data of the RXA signal are used. Two 6. A synchronous electromagnetic induction system according to claim 5, further comprising means for validating the data of the second level when the levels are both "H", "H" or "L", "L". Portable information terminal having the data demodulation circuit of FIG.

Images