Abstract:
A data transmission system includes a first device and a second device communicating with each other by electromagnetic induction. The first device includes a preparing circuit that prepares data having a voltage defined related to a first threshold, and a transmitting circuit that transmits the data. The second device includes a receiving circuit that receives the data from the transmitting circuit, a bias circuit that raises the voltage of the received data by a predetermined voltage to produce a sum voltage, and a judging circuit that judges whether the voltage of the data indicates high or low by comparing the sum voltage with a second threshold that is equal to or larger than the first threshold. The second device may also include a power supply that provides electric power for the first device using a magnetic field.

Description:
This patent application claims priority based on a Japanese patent application, H11-178493 filed on Jun. 24, 1999, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a non-contact type data transmission system that electromagnetically transmits and receives data using a coil or the like but using neither a contact-type connector nor a cable. 
     2. Description of the Related Art 
     A typical non-contact type data transmission system comprises a data processing device and a data measuring device. The data measuring device may include an IC card and can be easily moved. Due to the high mobility of the data measuring device, it may be used, for example, to measure the temperature in a room that stores various foods such as vegetables, meat and fish during transport via a transport system. In contrast, the data processing device is relatively large and is usually permanently positioned in an office or a factory where it is used to process the data collected by the data measuring device. 
     During food transportation by truck, train or plane, for example, the data measuring device is able to operate independently and can measure the temperature. At the completion of transportation, the data measuring device is returned to the office or factory and is inserted into the data processing device. The temperature data collected by the data measuring device is transmitted electromagnetically to the data processing device. The data processing device then processes the received data according to the instructions of the operator of the data transmission system. 
     In order to electromagnetically transmit and receive the data, the data processing device and the data measuring device each have a coil. The data measuring device is designed to be very small and there is no space for a internal power supply, therefore, its electrical power is supplied by an alternating power supply located in the data processing device. The power supply includes a current supply circuit with numerous transistors, an oscillator that switches the current supply circuit, and a coil used for transferal of the electric power to the data measuring device. 
     Since the coil in the data measuring device is small, the amount of electromagnetic power generated by the coil is also small. Therefore, it is necessary to ensure that the distance between the coils of the data processing device and the inserted data measuring device is kept as short as possible. 
     Another potential problem involves a failure of the oscillator within the data processing device which may cause the current supply circuit to continuously apply a direct current to the coil, leading to transistor breakage. 
     SUMMARY OF THE INVENTION 
     The objective of the present invention is to provide a non-contact type data transmission system that overcomes the issues in the related art as described previously. This objective is achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention. 
     According to an aspect of the present invention, there is provided a data transmission system including a first device and a second device communicating with each other by electromagnetic induction, wherein the first device comprises a preparing circuit that prepares a data having a voltage defined related to a first threshold; and a transmitting circuit that transmits the data prepared by the preparing circuit, and the second device comprises a receiving circuit that receives the data from the transmitting circuit; a bias circuit that raises the voltage of the received data by a predetermined voltage to produce a sum voltage; and a judging circuit that judges whether the voltage of the data indicates high or low by comparing the sum voltage with a second threshold that is equal to or larger than the first threshold. It is preferable that the receiving circuit includes a coil that produces an electromotive force upon receiving the data from the transmitting circuit, and the bias circuit includes a diode that is connected to the coil in series to increase the electromotive force by a forward voltage of the diode. It is also preferable that the bias circuit further includes a capacitor that stabilizes the given voltage. 
     According to another aspect of the present invention, there is provided a data receipt device that receives data by electromagnetic induction comprising: a receiving circuit that receives data having a voltage defined related to a first threshold; a bias circuit raises the voltage of the received data by a predetermined voltage to produce a sum voltage; and a judging circuit that judges whether the voltage of the data indicates high or low by comparing the sum voltage with a second threshold that is equal to or larger than the first threshold. It is preferable that the receiving circuit includes a coil that produces an electromotive force upon receiving the data from the transmitting circuit, and the bias circuit includes a diode that is connected to the coil in series to increase the electromotive force by a forward voltage of the diode. It is also preferable that the bias circuit further includes a capacitor that stabilizes the given voltage. 
     According to still another aspect of the present invention, there is provided a data transmission system including a first device and second device communicating with each other, the first device having a power supply that provides an electric power for the second device using a magnetic field, wherein the power supply comprises an oscillator that generates an oscillation signal; a magnetic field preparing circuit that prepares the magnetic field; a current supplying circuit that supplies a current to the magnetic field preparing circuit according to the oscillation signal; a detecting circuit that detects a halt of generating the oscillation signal by the oscillator; and a switching circuit that turns off the current supplying circuit upon detecting the halt. It is preferable that the oscillation signal includes a plurality of first pulses, the detecting circuit includes a generating circuit that generates a second pulse that permits the switching circuit to keep the current supplying circuit turned on, in response to each first pulse; and a smoothing circuit that smoothes the second pulses; wherein the switching circuit turns off the current supplying circuit in an absence of the smoothed second pulses. It is further preferable that the generating circuit includes a first resistor and a first capacitor that defines a first time constant of the second pulse, and a flip-flop circuit that detects each first pulse to generate the second pulse defined by the first time constant. Similarly, it is further preferable that the smoothing circuit includes a second resistor and a second capacitor that defines a second time constant used for smoothing the second pulses. It is also preferable that the detecting circuit further includes a Schmidt trigger circuit that forbids the smoothed second pulses to force the turning off of the current supplying circuit due to chatter. 
     According to still another aspect of the present invention, there is provided a device that communicates by electromagnetic induction, comprising a power supply, wherein the power supply includes an oscillator that generates an oscillation signal; a magnetic field preparing circuit that prepares the magnetic field; a current supplying circuit that supplies a current to the magnetic field preparing circuit according to the oscillation signal; a detecting circuit that detects a halt of generating the oscillation signal by the oscillator; and a switching circuit that turns off the current supplying circuit upon detecting the halt. It is preferable that the oscillation signal includes a plurality of first pulses, the detecting circuit includes a generating circuit that generates a second pulse that permits the switching circuit to keep the current supplying circuit turned on, in response to each first pulse; and a smoothing circuit that smoothes the second pulses; wherein the switching circuit turns off the current supplying circuit in an absence of the smoothed second pulses. It is more preferable that the generating circuit includes a first resistor and a first capacitor that defines a first time constant of the second pulse, and a flip-flop circuit that detects each first pulse to generate the second pulse defined by the first time constant. It is preferable that the smoothing circuit includes a second resistor and a second capacitor that defines a second time constant used for smoothing the second pulses. It is also preferable that the detecting circuit further includes a Schmidt trigger circuit that forbids the smoothed second pulses to force the turning off of the current supplying circuit due to chatter. 
     According to still another aspect of the present invention, there is provided a data receipt method used for a data receipt device receiving data by electromagnetic induction comprising: receiving a data having a voltage defined related to a first threshold; increasing the voltage of the received data by a predetermined voltage to produce a sum voltage; and judging whether the voltage of the data indicates high or low by comparing the sum voltage with a second threshold that is equal to or larger than the first threshold. It is preferable that the increasing includes raising the voltage of the received data by the predetermined voltage defined by the firth threshold and the second threshold. 
     According to still anther aspect of the present invention, there is provided a power supplying method used for a device that communicates by electromagnetic induction comprising: generating an oscillation signal; supplying a current according to the oscillation signal; preparing a magnetic field using the current; first detecting a halt of the generating of the oscillation signal; and turning off the supplying the current upon detection of the halt. It is preferable the power supplying method further comprises second detecting the generating of the oscillation signal; and allowing the supplying of the current during detection of the oscillation signal. 
     This summary of the invention does not necessarily describe all necessary features, thus, the invention may also be a sub-combination of these described features. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a configuration of the non-contact type data transmission system of the preferred embodiment according to the present invention; 
     FIG. 2 shows an operation of the power supply in the data processing unit; and 
     FIG. 3 shows an operation of the data transferring units in the data transmission system. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will now be described based on the preferred embodiments, which are not intended to limit the scope of the present invention, but are used to exemplify the invention. All of the features and the combinations described hereafter in the embodiment are not necessarily essential to the invention. 
     A non-contact type data transmission system of a preferred embodiment according to the present invention will now be described in detail referring to the accompanying drawings. When describing elements shown in FIGS. 1,  2  and  3 , numbers and/or letters following each component facilitate easy identification. 
     The non-contact type data transmission system of the embodiment shown in FIG. 1, is designed to measure temperature in a transportation system such as a truck, train, ship or plane, in order to analyze the transportation conditions. To achieve this task, the data transmission system comprises a data processing device  1  and a data measuring device  2 . A typical data measuring device  2  includes an IC card and can be temporarily set in the transportation system to be analyzed. Meanwhile, the data processing device  1  is installed permanently in a building such as an office or a factory. After completion of temperature measurement, the data measuring device  2  is inserted into the data processing device  1  which then receives the temperature data from the data measuring device  2  by an electromagnetic transmission. In order to conserve electric power, the power voltage VDD used for the data measuring device  2  (for example +3V) is smaller than the power voltage VCC used for the data processing device  1  (for example +5V). This difference in power voltages influences the communication between the data processing device  1  and the data measuring device  2 , the details of which will be discussed later. 
     In addition to transmission of data to and reception of data from the data measuring device  2 , the data processing device  1  is required to supply electric power for the data measuring device  2 . The data processing device  1  therefore includes the data transferring unit  10 , the data processing unit  20  and the power supply  30 . The data measuring device  2  includes the data transferring unit  40 , the controller  50 , the power supply  60 , the display unit  70 , the storage unit  80 , the temperature detecting unit  90 , and the clock  100 . 
     In the data processing device  1 , the data processing unit  20  includes a CPU or MPU, which prepares the transmission data SD 1 , processes the receipt data RD 1  and controls the data transferring unit  10  using the control signal CON 1 . 
     The data transferring unit  10  includes the tri-state buffer  11 , the capacitor  12 , the coil  13 , the pair of diodes  14 A and  14 B, the AND circuit  15 , the monostable multivibrator  16  and the bias circuit  17 . The tri-state buffer  11  is used for transmission of the data SD 1 , whereas the AND circuit  1 S is used for receipt of the data RD 1 . The data processing unit  20  applies the control signal CON 1  to both the tri-state buffer  11  and the AND circuit  15  to provide half-duplex communication. The “low” signal CON 1  specifically allows the tri-state buffer  11  to output transmission data but prevents the AND circuit  15  from a simultaneous output of receipt data. Conversely, the “high”signal CON 1  prevents the tri-state buffer  11  from outputting transmission data but allows the AND circuit  15  to output receipt data. If an additional coil or another signal frequency is used, other communication is possible, including full-duplex communication. 
     The capacitor  12  is positioned behind the tri-state buffer  11  and allows the alternating component of the signal output from the tri-state buffer  11  to pass through. Next to the capacitor  12  exists the coil  13 , which transmits and receives the data SD 1  and RD 1 . The coil  13  is a pattern printed on the circuit board; five millimeters in diameter and approximately  12  turns without a core. One end of the coil  13  forms the node N 12 . The diodes  14 A and  14 B, used for overvoltage protection, are in series between the voltage VCC and the node N 12 . The bias circuit  17  is connected to the node N 12  and includes the diode  17 A, the capacitor  17 B, and the resistor  17 C. The diode  17 A is designed to be in series with both the coil  13  and the resistor  17 C, and is in parallel with the capacitor  17 B. The resistor  17 C provides a current to the diode  17 A which subsequently uses forward voltage to increase the voltage of the node N 12 . The capacitor  17 B stabilizes the level of change to the voltage of the node N 12 . As will be discussed, the increase in voltage facilitates the receipt of data from the data measuring device  2 . 
     The other end of the coil  13  forms the node N 11  which is connected to the AND circuit  15 . The monostable multivibrator  16  is connected to the AND circuit  15  and includes the flip-flop circuit  16 A, the resistor  16 B, and the capacitor  16 C. The resistor  16 B and the capacitor  16 C define a pulse width which is used by the flip-flop circuit  16 A to output the signal RD 1  to the data processing unit  20 . The monostable multivibrator  16  acts in response to the increase in receipt data from the AND circuit  15 . 
     The power supply  30  comprises the oscillator  31 , the INVERT circuit  32 , the NAND circuits  33 A and  33 B, the NMOS circuits  34 A and  34 B, the coil  35 , the AND circuits  36 A and  36 B, the monostable multivibrator  37 , the LPF circuit  38 , and the buffer  39 . The oscillator  31  oscillates a continuous signal CK (8MHz for example) Which is fed to the INVERT circuit  32 , the NAND circuit  33 B, and the monostable multivibrator  37 . 
     The INVERT circuit  32  inverts the signal CK and feeds the inverted signal CK into the NAND  33 A. The output of the NAND circuit  33 A is fed to the NAND circuit  33 B which also feeds output back to the NAND circuit  33 A. 
     The outputs of the NAND circuits  33 A and  33 B are also fed into the AND circuits  36 A and  36 B, respectively. Subsequently, the outputs of the AND circuits  36 A and  36 B are provided to the NMOS circuits  34 A and  34 B, respectively. The sources of the NMOS  34 A and  34 B are connected to ground and the drains of the NMOS  34 A and  34 B are connected to the coil  35 . The coil  35  has a centertap which is connected to the voltage VCC. The coil  35  is a pattern printed on the wiring board; 10 millimeters in diameter and approximately 40 turns without a core. 
     Within monostable multivibrator  37 , the resistor  37 B and the capacitor  37 C define a pulse width which is used by the flip-flop  37 A to output a pulse in response to the output CK of the oscillator  31 . The LPF  38  defines a time constant using the resistor  38 A and the capacitor  38 B. The time constant is defined such that the LPF  38  is capable of detecting a missing pulse in the clock output CK. The LPF  38  smoothes the pulses output by the monostable multivibrator  37  and functions like “a retrigger circuit”. The time constant can be defined to be 0.1 microsecond, for example. The buffer  39 , which may be designed to include two INVERT circuits, drives the AND circuits  36 A and  36 B. Preferably, the buffer  39  should also include a Schmidt trigger circuit which prevents chattering of the output. 
     In summary: under normal operating conditions the NMOS  34 A and  34 B are driven by the outputs of the oscillator  31 , however, in the case of malfunction or irregular operation, the NMOS  34 A and  34 B are controlled by the outputs of the monostable multivibrator  37 , the LPF  38 , and the buffer  39 . 
     Within the data measuring device  2 , the data transferring unit  40  includes the tri-state buffer circuit  41 , the capacitor  42 , the coil  43 , the pair of diodes  44 A and  44 B, the AND circuit  45 , and the monostable multivibrator  46 . The tri-state  41 , the capacitor  42 , the coil  43 , the diodes  44 A and  44 B, the AND circuit  45 , and the monostable multivibrator  46  function in a similar way to the previously described roles of the tri-state  11 , the capacitor  12 , the coil  13 , the diodes  14 A and  14 B, the AND circuit  15 , and the monostable multivibrator  16 , respectively. In order to efficiently transmit and receive data, the coil  43  is positioned such that it faces the coil  13  when the data measuring device  2  is inserted into the data processing device  1 . As mentioned previously, the voltage VCC is higher than the voltage VDD and therefore, the threshold in the data measuring device  2  is lower than that in the data processing device  1 . Although the highest possible data output level from the data processing device  1  is relatively low, the data measuring device  2  is able to recognize the level as being high. Thus, the data measuring device  2  does not require the incorporation of a circuit corresponding to the bias circuit  17  of the data processing device  1 . 
     Following the electromagnetic transmission of electric power from the power supply  30  to the power supply  60 , power is conveyed to all units within the data measuring device  2 . The power supply  60  includes the coil  61 , the rectifier  62  and the battery  63 . In order to allow electromagnetic transmission of power, the coil  61  is designed to face the coil  35  upon insertion of the data measuring device  2  into the data processing device  1 . The coil  61  is a pattern printed on a wiring board; 10 millimeters in diameter and approximately 40 turns without a core. The rectifier  62  is a bridge circuit including four diodes. The rechargeable battery  63  provides electric power for the data measuring device when being used independently and is recharged when the data measuring device  2  is inserted into the data processing device  1 . 
     The operation of the power supplies  30  and  60  will now be explained referring to FIG.  2 . It is assumed that an internal or external power supply (not shown) designed to generate the voltage VCC is already switched on. First, the data measuring device  2  is inserted into the data processing device  1 . Next, the power supply  30  is turned on allowing the oscillator  31  to provide the 8 MHz clock CK for the INVERT circuit  32 , the NAND circuit  33 B, and the monostable multivibrator  37 . 
     During regular operation, the oscillator  31  continuously generates the oscillation signal CK and the monostable multivibrator  37  outputs a pulse with the defined pulse width, in, response to the rising edge of the clock CK. As shown in FIG. 2, the output duty ratio of the monostable multivibrator  37  is larger than the output duty ratio of the oscillation signal CK and subsequently, the falling curve of the output of the LPF  38  is significantly sharper. In other words, if the output duty ratio of the monostable multivibrator  37  and the oscillation signal CK were similar, the falling curve of the output of the LPF  38  is required to be dull enough to keep the output level of the monostable multivibrator  37  high, over a given period of time, in expectation of the next incoming pulse. 
     In response to each incoming pulse, the LPF  38  outputs an “H” signal specifically like a saw tooth wave as long as the oscillator  31  continuously generates the clock CK. Similarly, the buffer  39  also outputs an “H” signal to both the AND circuits  36 A and  36 B as long as the output of the LPF  38  does not fall below the low level threshold VIL. The AND circuits  36 A and  36 B are thus allowed to turn on/off the respective NMOS  34 A and  34 B only under control of the oscillator  31 . Since the INVERT circuit  32  inverts the clock CK, the incoming signals of the NAND circuits  33 A and  33 B are complementary and their outgoing signals are also complementary. Accordingly, the AND circuits  36 A and  36 B alternately switch on the corresponding NMOS circuits  34 A and  34 B in turn. The active NMOS circuit (either  34 A or  34 B) actuates the coil  35 , which produces an alternating magnetic field. The magnetic field provides an electromotive force for the coil  61  in the power supply  60 . The electromotive force produces an alternating current in the coil  61 , which is converted to a direct current by the rectifier  62 . The direct current is provided to all units within the data measuring device  2  as well as recharging the battery  63 . 
     If a situation arises such that the oscillator  31  malfunctions or stops generating the oscillation signal CK, the output of the LPF  38  falls below the low level threshold VIL. This forces the buffer  39  to output a “L” signal, which prevents the AND circuits  36 A and  36 B from switching on the NMOS circuits  34 A and  34 B. Therefore, neither the NMOS circuit  34 A nor  34 B is able to continuously provide a current for the coil  35  when the oscillator  31  is broken or malfunctioning. 
     The operation of the transferring units  10  and  40  will now be explained in detail. First, the data measuring device  2  is inserted into the data processing device  1 . Next, the power supply  30  is switched on causing the data processing device  1  to be on standby for communication with the data measuring device  2 . The power supply  30  simultaneously provides electric power to the data measuring device  2  causing it to be on standby for communication with the data processing device  1 . 
     As shown in FIG. 3, at time T 0 , a current flows through the resistor  17 C and diode  17 A resulting in an increase in the voltage of the node N 12  by the forward voltage of the diode  17 A of approximately 0.7 volts, and more preferably by the voltage corresponding to the difference between half of the voltage VDD and half of the voltage VCC. The voltage of the node N 11  is similarly increased by the forward voltage of the diode  17 A. 
     At time T 1 , a rising edge of the transmission data SD 2  is applied to the coil  43  through the tri-state buffer  41  and the capacitor  42 . This results in a change in the magnetic field of the coil  43 . The signal of the node N 2  at time T 1  is like a differential wave and the diodes  44 A and  44 B limit the amplitude of the signal of the node N 2  within VDD+VF and GND−VF, where VF denotes the forward voltage of the diodes  44 A and  44 B. 
     The change in the magnetic field of the coil  43  provides the electromotive force for the coil  13 . The electromotive force produces a signal wave at the node N 11  similar to that observed at the node N 2 . In this case, since the voltage of the node N 11  has been raised by the forward voltage of the diode  17 A, the actual voltage of the node N 11  is the sum of the forward voltage of the diode  17 A and the electromotive force produced in the coil  13 . As a result, the actual voltage of the node N 11  at time T 1  (for example VCC/ 2 ) readily exceeds the threshold of the AND circuit  15  and forces the AND circuit  15  to output an “H” signal S 15 . Upon receipt of the “H” signal S 15 , the monostable multivibrator  16  produces a pulse RD 1  which is regulated by. the time constant defined by the resistor  16 B and the capacitor  16 C. 
     At time T 2 , a falling edge of the transmission data SD 2  is applied to the node N 2 , which produces a negative pulse. The voltage of the pulse is limited by the diode  44 B such that it does not fall below GND-VF. At time T 3 , the rising edge of the transmission data SD 2  is applied to the coil  43 , providing a similar result to that observed at time T 1 . 
     As described previously, the bias circuit  17  increases the voltage of the node N 12  using the forward voltage of the diode  17 A. Therefore, although the high level of the transmission data SD 2  is relatively. low in comparison with the threshold of the AND circuit  15 , the addition of the forward voltage of the diode  17 A boosts the level of the data SD 2  to exceed the threshold of the AND circuit  15 . This enables reliable communication between the data processing device  1  and the data measuring device  2 , even though the voltages for the two devices differ significantly from each other. 
     As discussed above, raising the voltage of an end of the coil used for receiving the receipt data enhances the reliability of communication between the two devices when compared with the conventional art. Since the reliability of communication is superior in the new. invention, the distance between the two devices may be increased, which facilitates the insertion of one device into another device. The reliability of communication decreases with the larger distance between coils, however, the distance can be limited to provide the same reliability observed in the conventional art. 
     In the above power supplies, the voltage VCC and VDD differ from each other, however, if both are the same, two bias circuits may be provided in the devices respectively. These bias circuits serve to enhance the reliability of communication or to enable the enlargement of the distance between the devices. 
     Although the present invention has been described by way of exemplary embodiments, it should be understood that many changes and substitutions may be made by those skilled in the art without departing from the spirit and the scope of the present invention which is defined only by the appended claims.