JP2008227935A - Digital signal demodulating circuit, rfid system, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To demodulate the signal received from a transmission circuit side into such digital signal as is robust against noise with high reliability, using a simple circuit configuration. <P>SOLUTION: A communication unit 102 which demodulates the signal received from a wireless tag 101 comprises a coupling capacitor 1023, for coupling carrier waves from a wireless tag 101 that has been modulated for amplitude by sub carrier waves; detection diodes 1024 and 1025 for envelope detection with the carrier waves outputted from the coupling capacitor 1023; and a coil 1026 which is connected parallel to the detection diodes 1024 and 1025, between the coupling capacitor 1023 and the detection diodes 1024 and 1025, to form a resonance circuit. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a digital signal demodulating circuit, an RFID system and an image forming apparatus including the same, and more particularly to a technique for demodulating a signal received from an IC tag into a digital signal.

2. Description of the Related Art Conventionally, in communication systems employing RFID, for example, as a receiving circuit for a reader / writer that demodulates a signal received from an IC tag, a primary band filter, a primary detector, a secondary band filter, a secondary detector, a low-pass filter What is equipped with such is known. However, since the communication system having such a configuration is complicated and expensive, a reception circuit having a simple mechanism including a primary detector and a low-pass filter as shown in Patent Document 1 below. Has been proposed.
JP 2005-136944 A

  However, the receiver circuit disclosed in Patent Document 1 has a simplified configuration, but has a problem that it is easily affected by noise due to the simplified configuration, and malfunction is likely to occur. In particular, when the receiving circuit shown in Patent Document 1 is applied to an image forming apparatus such as a copying machine or a printer, for example, an IC tag is attached to a toner container that is detachably attached to the apparatus main body of the image forming apparatus, When a reader / writer including the receiving circuit is provided at a position where communication with the IC tag can be performed in the apparatus main body, and the toner type and the toner remaining amount in the toner container are transmitted to the control unit of the image forming apparatus, Since printers and the like are equipped with a high-voltage power supply and have a function of discharging in the apparatus, there is a problem that many noises are generated and malfunctions are likely to occur.

  The present invention has been made to solve the above-described problems, and enables a signal received from the transmission circuit side to be demodulated into a highly reliable digital signal having a simple circuit configuration and resistant to noise. For the purpose.

The invention according to claim 1 of the present invention is a digital signal demodulation circuit for demodulating a signal received from the transmission circuit side,
A coupling capacitor for coupling a carrier wave subjected to amplitude modulation by a subcarrier wave from the transmission circuit;
A detection diode that performs envelope detection on the carrier wave output from the coupling capacitor;
A digital signal demodulating circuit including a coil that is connected in parallel to the detecting diode between the coupling capacitor and the detecting diode and forms a parallel resonant circuit.

The invention according to claim 3 is an RFID system comprising an IC tag and a signal transmitting / receiving device for transmitting / receiving a signal to / from the IC tag,
The IC tag forms a subcarrier based on a carrier wave received from the signal transmission / reception device, and sends a signal to the signal transmission / reception device using the subcarrier,
The signal transmitting / receiving device includes a coupling capacitor that couples a carrier wave subjected to amplitude modulation by a subcarrier wave from the IC tag, a detection diode that performs envelope detection on the carrier wave output from the coupling capacitor, Between the coupling capacitor and the detection diode, there is provided a coil that forms a parallel resonance circuit with the coupling capacitance of the detection diode.

  According to these configurations, the coil is connected in parallel with the detection diode between the coupling capacitor and the detection diode, and the subcarrier is modulated in the carrier by the resonance voltage generated by the coil. Since the peak value of the portion is raised high, the envelope amplitude after envelope detection by the detection diode is increased, and the S / N ratio is improved.

The invention according to claim 2 is the digital signal demodulating circuit according to claim 1, wherein the capacitor extracts an AC component from a carrier wave detected by envelope detection by the detection diode;
A waveform shaping circuit for shaping a carrier wave from which an AC component has been extracted by the capacitor into a rectangular wave.

  According to this configuration, the capacitor extracts the AC component from the carrier wave detected by the envelope detection by the detection diode, and the waveform shaping circuit shapes the AC component extracted by the capacitor into a rectangular wave. Can be accurately demodulated into a digital signal.

According to a fourth aspect of the present invention, a toner storage body that is detachably attached to the apparatus main body, and electrophotographic image formation on a recording paper is performed using the toner stored in the toner storage body. An image forming apparatus having image forming means and the RFID system according to claim 3,
In the image forming apparatus, the IC tag is attached to the toner container, and the signal transmission / reception device is provided in a position where communication with the IC tag is possible in the apparatus main body.

  Since an electrophotographic image forming apparatus is equipped with a high voltage power source and has a function of discharging in the apparatus, noise countermeasures are important for communication in an RFID system. The peak value of the modulation part due to the subcarrier in the carrier wave is raised by the resonance voltage generated by the parallel resonance of the coil, so that the envelope amplitude after the envelope detection by the detection diode increases and the S / N ratio increases. As a result, the influence of noise caused by high-voltage power supply and discharge is reduced, and a highly reliable digital signal can be demodulated.

  According to the first and third aspects of the invention, the resonance voltage generated by the coil raises the peak value of the portion modulated by the subcarrier in the carrier wave, and after the envelope detection by the detection diode Envelope amplitude increases and the signal-to-noise ratio improves, so the signal received from the transmitter circuit has a simple circuit configuration that does not use a bandpass filter or a secondary detector, and is highly resistant to noise. It can be demodulated into a highly digital signal. Note that the cost can be reduced by simplifying the circuit configuration.

  According to the second aspect of the present invention, the information indicated by the subcarrier from the transmission circuit can be accurately demodulated into a digital signal.

  According to the fourth aspect of the present invention, the signal received from the transmission circuit can be obtained with a simple circuit configuration without being relatively affected by the high voltage power supply and noise caused by discharge in the electrophotographic image forming apparatus. Can be demodulated into a highly reliable digital signal.

  Hereinafter, a digital signal demodulation circuit, an RFID system, and an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing an internal configuration of a printer 1 as an example of an image forming apparatus according to the present invention.

  The printer 1 includes a paper feed unit 8, an image forming unit 2, a transfer unit 9, a fixing unit 11, a paper discharge tray 12, and the like.

  The image forming unit 2 includes a photosensitive drum 3, a charging unit 4, an exposure unit 5, a developing unit 6, a cleaning unit 7, and the like.

  The photosensitive drum 3 is an image carrier on which a toner image is formed. The charging unit 4 uniformly charges the photosensitive drum 3. The exposure unit 5 exposes the circumferential surface of the uniformly charged photoreceptor drum 3 to form an electrostatic latent image. The developing unit 6 visualizes the formed electrostatic latent image to create a toner image. The toner image produced in this way is transferred onto the recording paper by a transfer unit 9 described in detail later. The cleaning unit 7 cleans the toner remaining on the surface of the photosensitive drum 3 after the transfer is completed.

  The transfer unit 9 includes a transfer roller 91, and the toner image formed on the photosensitive drum 3 is transferred to the recording paper conveyed from the conveyance path 83 in a state where the transfer roller 91 is pressed against the photosensitive drum 3. Transfer.

  The paper feed unit 8 includes a paper feed cassette 81, a pickup roller 82, a transport path 83, a transport roller 84, and the like. The recording paper loaded on the paper feed cassette 81 is transferred to the image forming unit 2 and transfer unit 9 side (downstream). Paper).

  The fixing unit 11 is provided on the downstream side of the image forming unit 2 and the transfer unit 9, and includes a heat roller 11a and a pressure roller 11b. The fixing unit 11 performs fixing processing of the toner image transferred to the recording paper.

  On the further downstream side of the fixing unit 11, a conveyance roller 86, a discharge roller 87, a conveyance path 85, and the like are provided, and the recording paper subjected to fixing processing by the fixing unit 11 further passes through the conveyance path 85 by these rollers. The paper is conveyed downstream and discharged to the paper discharge tray 12 at the top of the printer 1.

  FIG. 2 is a cross-sectional view showing a detailed configuration of the developing unit 6. The developing unit 6 includes a toner cartridge (toner container) 61 including a container (container) that stores toner (or toner and carrier), a developing unit 62 including a developing roller 621, and the like. The toner of the toner cartridge 61 is supplied to the agitation unit by the rotational drive of 622 and the supply roller 623, and the toner is supplied to the agitation unit developing roller 621 by the rotational drive of the agitation roller 611 (agitation screw). A developing sleeve 6211 is provided on the outer peripheral portion of the developing roller 621, and a developing bias is applied to the developing sleeve 6211, and the toner charged positively by the agitating portion is used as the photosensitive drum 3 (FIG. 1). It is adsorbed on the exposed portion of the surface (the portion of the electrostatic latent image from which static electricity has been removed by exposure). The developing unit 6 is configured such that the toner cartridge 61 can be detachably attached to the developing unit 62.

  FIG. 3 is a partially enlarged view of a range indicated by a symbol A of the developing unit 6 in FIG. The configuration of the lower part of the mounted toner cartridge 61 is shown in detail.

  A wireless tag (transmission circuit) 101 made of an IC tag or the like is attached to one side wall portion of the toner cartridge 61. A communication unit 102 is provided on one side wall of the developing unit 62. These wireless tag 101 and communication unit 102 constitute an RF-ID system 100. When the toner cartridge 61 is mounted, the wireless tag 101 and the communication unit 102 face each other with a predetermined distance (for example, about 5 mm).

  The wireless tag 101 performs wireless communication with the communication unit 102. The wireless tag 101 includes a semiconductor chip (wireless IC chip) that can transmit and receive data using electromagnetic waves, generates an electromotive force by electromagnetic waves from the communication unit 102 (by an electromagnetic induction method), and drives the circuit by this power. Exchange control data (identification code) and the like with the communication unit 102.

  The communication unit 102 performs radio communication with the wireless tag 101 by outputting an electromagnetic wave having a predetermined frequency with a predetermined communication output.

  Next, a schematic configuration of the wireless tag 101 will be described. FIG. 4 is an explanatory diagram showing a schematic configuration of the wireless tag 101. The wireless tag 101 includes a memory 1011, a resonance capacitor 1012, and a resonance inductance (antenna) 1013.

  The memory 1011 stores information unique to the toner cartridge, that is, information such as the number of times the toner cartridge is used, the characteristics of the toner in the container, and the remaining toner amount.

  A resonant inductance (antenna) 1013 is an antenna composed of a coil configured as a loop antenna. Wireless communication with the communication unit 102 is performed via the antenna 1013.

  The antenna 1013 and the resonance capacitor 1012 constitute a resonance circuit 101f. The resonance circuit 101f functions as a filter that allows the input / output signal from the antenna 1013 to be only the resonance frequency of the resonance circuit 101f and a signal having a frequency close to the resonance frequency.

  The toner cartridge information stored in the memory 1011 is read by the communication unit 102 by communication with the communication unit 102. For example, when the antenna 1013 of the wireless tag 101 receives a carrier wave transmitted from the communication unit 102, a subcarrier generated by dividing the carrier wave by 1/32 by the semiconductor chip in the wireless tag 101 is set to a certain period. By applying to the antenna 1013, the toner cartridge information stored in the memory 1011 is expressed and sent out from the antenna 1013 to the communication unit 102.

  FIG. 5 is a circuit diagram showing a schematic configuration of the communication unit (digital signal demodulation circuit) 102. The communication unit 102 includes a transmission circuit unit 1021 and an antenna coil 1022. The transmission circuit unit 1021 applies a carrier wave for reading information such as the toner cartridge information from the memory 1011 in the wireless tag 101 to the antenna coil 1022. The transmission circuit unit 1021 transmits information to be transmitted from the communication unit 102 to the wireless tag 101 by modulating the carrier wave transmitted to the wireless tag 101.

  The antenna coil 1022 generates a magnetic field by applying a carrier wave by the transmission circuit unit 1021. The magnetic field generated by the antenna coil 1022 is electromagnetically induced by the antenna 1013 in the wireless tag 101 and used to transmit information to the wireless tag 101. Further, the magnetic field generated by the antenna coil 1022 generates electric power consumed by a circuit in the wireless tag 101 in the wireless tag 101. The antenna coil 1022 receives a carrier wave (a carrier wave amplitude-modulated by a subcarrier wave) transmitted from the wireless tag 101.

  The communication unit 102 further includes a coupling capacitor 1023, detection diodes 1024 and 1025, a coil 1026, a resistor 1027, a capacitor 1028, a transistor 1029, and a comparison circuit 1030.

  The coupling capacitor 1023 couples a carrier wave that has been amplitude-modulated by the subcarrier wave from the wireless tag 101 to the communication unit 102. Further, the coupling capacitor 1023 also functions as a high pass filter.

  The detection diodes 1024 and 1025 perform envelope detection on a carrier wave subjected to amplitude modulation with a subcarrier wave from the wireless tag 101, and extract a modulation component from the carrier wave.

  The coil 1026 is connected in parallel to the detection diodes 1024 and 1025 between the coupling capacitor 1023 and the detection diodes 1024 and 1025. A parallel resonance circuit is formed by the junction capacitance of the detection diode and the inductance of the coil 1026. A reflected wave is generated under the influence of the sub-carrier generated by the wireless tag 11, and a standing wave is generated on the carrier, so that amplitude modulation is applied. If the phase of the reflected wave and the carrier wave is the same phase, the added standing wave is obtained, and if the phase is opposite, the subtracted standing wave is obtained. A point A shown in FIG. 5 is connected to a low-pass filter in the transmission circuit. Point B is a connection point of a parallel resonance circuit that resonates with the frequency of the carrier wave by the inductance of the coil 1026 and the coupling capacitance of the detection diodes 1024 and 1025.

  As the inductance of the coil 1026, for example, if the coupling capacity of the detection diode is 1 PF and the frequency of the carrier wave is 13.56 MHz, 68.8 μH is used as the inductance of the coil. By forming the parallel resonance circuit, the amplitude of the carrier wave including the envelope is increased, and the non-resonant noise component is attenuated.

  Capacitor 1028, together with resistor 1027, rectifies the carrier wave detected by detection diodes 1024 and 1025 and converts it to direct current. The envelope portion subjected to amplitude modulation is extracted as an AC component.

  The envelope amplitude of the transistor 1029 is increased by a parallel resonance circuit formed by the coil 1026, and the base is driven by the alternating voltage extracted by the capacitor 1028 and the resistor 1027 to be switched. The comparison circuit 1030 performs waveform shaping by comparing the waveform generated at the collector of the transistor 1029 by the switching with a predetermined threshold.

  Next, the operation of the communication unit 102 will be described with reference to FIGS. 6 to 8 in addition to FIG. FIG. 6 is a diagram illustrating a waveform of a carrier wave amplitude-modulated by a subcarrier wave received from the wireless tag 101 by the antenna coil 1022. FIG. 7 is a diagram illustrating a waveform of a carrier wave whose peak value is increased by parallel resonance of the coil 1026. FIG. 8 is a diagram illustrating a waveform (ch2) generated at the collector of the transistor 1029 and a waveform (ch1) of a rectangular wave shaped by the comparison circuit 1030.

  When the antenna coil 1022 receives a carrier wave amplitude-modulated by the subcarrier from the wireless tag 101, the received carrier wave has the waveform shown in FIG. The coupling capacitor 1023 passes only the high frequency component of the carrier wave having the waveform as a high pass filter. Detection diodes 1024 and 1025 perform envelope detection on the carrier wave output from coupling capacitor 1023. At this time, the voltage at point B in FIG. 5 flows through the detection diode 1024 to charge the coupling capacitor 1023 during the half cycle of the negative carrier wave. On the other hand, when the voltage at point B is the positive half cycle period of the carrier wave, the detection diode 1025 charges the capacitor 1028. In the positive half cycle period of the carrier wave, the voltage at the point C is equivalent to the state where the capacitor 1028 and the coupling capacitor 1023 are connected in series, and the charge of the coupling capacitor 1023 is added to the capacitor 1031. The This is a so-called half-wave voltage doubler detection circuit.

  AC components are extracted from the carrier wave after the envelope detection by the detection diodes 1024 and 1025 by the capacitor 1028 and the resistor 1027. The base of the transistor 1029 is driven and switched by the voltage from which the AC component is extracted by the capacitor 1028 and the resistor 1027. A waveform generated at the collector of the transistor 1029 by the switching is a waveform indicated by ch2 in FIG. The waveform generated at the collector of the transistor 1029 is shaped into a rectangular wave by the comparison circuit 1030 to be a rectangular wave indicated by ch1 in FIG. The digital signal demodulated by the waveform shaping by the comparison circuit 1030 is input to a control unit (CPU) 105 that controls the operation of the printer 1.

  As described above, in the communication unit 102, when the antenna coil 1022 receives the carrier wave amplitude-modulated by the sub-carrier wave from the wireless tag 101, the coil 1026 resonates with the carrier wave, and the peak value of the carrier wave portion that has been amplitude-modulated. Is increased, and the envelope amplitude after the envelope detection by the detection diodes 1024 and 1025 is increased. Therefore, the transistor without using an amplifier or the like can be obtained by using the voltage passed through the detection diodes 1024 and 1025, the capacitor 1028 and the resistor 1027. 1029 can be driven. Further, since the envelope amplitude after the envelope detection is increased by the resonance voltage of the coil 1026, the carrier wave amplitude-modulated by the sub-carrier wave is affected by noise due to discharge or the like by the high-voltage power source in the printer 1. Hateful. Therefore, it is possible to accurately demodulate the carrier wave transmitted from the wireless tag 101 into a digital signal while simplifying the configuration of the amplifier, the filter, and the like in the communication unit 102.

  The present invention is not limited to the configuration of the above embodiment, and various modifications can be made. For example, in the above embodiment, the digital signal demodulation circuit according to the present invention is applied to communication by RFID using the communication unit 102 as the communication unit 102, but the digital signal demodulation circuit according to the present invention is applicable to communication by RFID. The present invention is not limited, and can be applied to other communication methods (for example, UWB (Ultra Wide Band)).

  Further, the application of the RFID system 100 described above is not limited to the application to the printer 1 and can be widely applied to other electric devices.

  The image forming apparatus according to the present invention is not limited to the printer 1 described above, and may be a copier, a facsimile machine, or a multifunction machine having a copy function, a facsimile function, a printer function, and the like.

1 is a cross-sectional view schematically showing an internal configuration of a printer as an example of an image forming apparatus according to the present invention. It is sectional drawing which shows the detailed structure of a image development part. FIG. 3 is a partially enlarged view of a range indicated by a symbol A of a developing unit in FIG. 2. It is explanatory drawing which shows schematic structure of a wireless tag. It is a circuit diagram which shows schematic structure of a communication unit (digital signal demodulation circuit). It is a figure which shows the waveform of the carrier wave amplitude-modulated by the subcarrier which the coil for antennas received from the wireless tag. It is a figure which shows the waveform of the carrier wave by which the peak value was raised by the induced voltage of a coil. It is a figure which shows the waveform (ch2) which generate | occur | produces in the collector of a transistor, and the waveform (ch1) of the rectangular wave shape | molded by the comparison circuit.

Explanation of symbols

1 Printer 61 Toner Cartridge 100 RFID System 101 Wireless Tag 1011 Memory 1012 Resonant Capacitor 1013 Antenna 102 Communication Unit 1021 Transmitter Circuit Unit 1022 Antenna Coil 1023 Coupling Capacitors 1024 and 1025 Detection Diode 1026 Coil 1027 Resistor 1028 Capacitor 1029 Transistor 1030 Comparison Circuit

Claims (4)

A digital signal demodulating circuit for demodulating a signal received from the transmitting circuit side,
A coupling capacitor for coupling a carrier wave subjected to amplitude modulation by a sub-carrier wave from the transmission circuit;
A detection diode that performs envelope detection on the carrier wave output from the coupling capacitor;
A digital signal demodulating circuit comprising: a coil that is connected in parallel to the detecting diode between the coupling capacitor and the detecting diode to form a parallel resonant circuit. A capacitor for extracting an AC component from a carrier wave detected by an envelope by the detection diode;
The digital signal demodulating circuit according to claim 1, further comprising: a waveform shaping circuit that shapes the AC component extracted by the capacitor into a rectangular wave. An RFID system comprising an IC tag and a signal transmitting / receiving device for transmitting / receiving a signal between the IC tag,
The IC tag forms a subcarrier based on a carrier wave received from the signal transmission / reception device, and sends a signal to the signal transmission / reception device using the subcarrier,
The signal transmitting / receiving apparatus includes a coupling capacitor for coupling a carrier wave subjected to amplitude modulation due to an influence of a reflected wave generated by a subcarrier wave from the IC tag, and an envelope for the carrier wave output from the coupling capacitor. A detection diode that performs detection, and a coil that forms a parallel resonance circuit between the coupling capacitor and the detection diode, with a junction capacitance of the diode connected in parallel to the detection diode and the inductance of the coil; RFID system comprising: The toner storage body detachably attached to the apparatus main body, image forming means for forming an electrophotographic image on a recording paper using the toner stored in the toner storage body, and An image forming apparatus having an RFID system,
An image forming apparatus in which the IC tag is attached to the toner container, and the signal transmission / reception device is provided at a position in the apparatus main body where communication with the IC tag is possible.

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