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JP-7855859-B2 - Electronic equipment and systems

JP7855859B2JP 7855859 B2JP7855859 B2JP 7855859B2JP-7855859-B2

Inventors

  • 岡田 敦

Assignees

  • 株式会社リコー

Dates

Publication Date
20260511
Application Date
20211227

Claims (6)

  1. It is an electronic device, A controller mounted on the main circuit board of the aforementioned electronic device for controlling external devices, A level conversion IC mounted on the main board converts the signal voltage level of the controller to the signal voltage level of the external device, It has, The GND terminal of the controller is connected to the first GND, which is the GND of the main board. The GND terminal of the level conversion IC is not connected to the first GND within the main board, but is connected to the second GND, which is the GND of the external device, when the external device is connected to the main board. The first GND is connected to the frame GND of the electronic device, The second GND is connected to the frame GND of the electronic device when the external device is connected to the main board. electronic equipment.
  2. The electronic device according to claim 1, wherein the power terminal of the level conversion IC is connected to the power terminal of the controller within the main board.
  3. The electronic device according to claim 1, wherein the power terminal of the level conversion IC is configured to be at the same potential as the power terminal of the controller within the main board.
  4. It is mounted on the main board and has an interface that electrically connects the main board and the external device, The level conversion IC is provided between the controller and the interface, The electronic device according to any one of claims 1 to 3, wherein when the external device is connected to the interface, the GND terminal of the level conversion IC is connected to the GND of the external device via the interface.
  5. The electronic device according to any one of claims 1 to 4, wherein the level conversion IC further converts the signal voltage level of the external device to the signal voltage level of the controller.
  6. A system comprising the electronic equipment described in any one of claims 1 to 5.

Description

This invention relates to electronic devices and systems. For example, electronic devices such as image forming apparatuses, projectors, or electronic whiteboards are configured to allow connection of various external devices, such as wireless LAN (Local Area Network) devices, authentication devices, or USB (Universal Serial Bus) memory. Furthermore, in electronic devices including circuit components and external devices, a technique is known in which a level shifter is provided between the processing circuit and the physical layer circuit of the circuit component, and the potential difference of the ground is corrected by the level shifter based on the measurement results of the signal voltage (see, for example, Patent Document 1). This figure shows an example configuration of a system including electronic equipment according to the first embodiment.This figure shows the equivalent circuit of the system according to the first embodiment.This figure shows an example of the voltage level of a transmitted signal according to the first embodiment.This figure shows an example of the voltage level of a received signal according to the first embodiment.This figure shows an example configuration of a system including electronic equipment according to the second embodiment.This diagram illustrates communication failures caused by leakage current.This figure shows an example of the signal voltage level when no leakage current is occurring.This figure shows an example of the signal voltage level when leakage current is occurring. The embodiments of the present invention will be described in detail below with reference to the drawings. <Communication failure due to leakage current> Before describing the electronic device and the system including the electronic device according to this embodiment, we will explain the communication failure caused by leakage current, which is the problem of this application. Figure 6 illustrates communication failure due to leakage current. In electronic devices with connected external devices, the main unit of the electronic device and the external device transmit and receive signals, such as control signals or data signals, via an interface such as a connector or cable. In the example in Figure 6, the main board 10, which is equipped with a controller IC 11 that controls the device IC (Integrated Circuit) 12, and the device board 20, which is equipped with the device IC 12, transmit and receive signals such as control signals 14 and data signals 15 via cable 13. Note that the device IC 12 and the device board 20 are examples of external devices. To match the signal voltage levels of the main board 10 and the device board 20, for example, the frame ground FG of the electronic device equipped with the main board 10 is used as a common GND, and this frame ground FG is used as the reference potential for circuit operation. However, in reality, there is a small resistive component (hereinafter referred to as parasitic resistance Rp1) between the GND of the main board 10 and the frame ground FG, and there is a small resistive component (hereinafter referred to as parasitic resistance Rp2) between the GND of the device board 20 and the frame ground FG. Therefore, for example, when a leakage current occurs in controller IC 11, a current I1 flows through the parasitic resistor Rp1, generating a voltage V1 between the GND of controller IC 11 and the frame ground FG. Similarly, when a leakage current occurs in device IC 12, a current I2 flows through the parasitic resistor Rp2, generating a voltage V2 between the GND of device IC 12 and the frame ground FG. Here, leakage current is the current that flows to GND when an IC (Integrated Circuit), etc., is operating. As a result, the GND of controller IC 11 and the GND of device IC 12 are no longer at the same potential, causing the GND level reference to become misaligned. This can lead to the incorrect transmission and reception of control signals 14 and data signals 15, potentially resulting in communication failures. Figure 8 shows an example of signal voltage levels when no leakage current is occurring. For illustrative purposes, controller IC 11 is assumed to output a HIGH level within an output voltage range 801 of 2.64V to 3.3V, and a LOW level within an output voltage range 811 of 0V to 0.66V. Meanwhile, device IC 12 is assumed to recognize signals above a HIGH voltage threshold of 2.31V as HIGH, and signals below a LOW voltage threshold of 0.99V as LOW. In this case, the HIGH voltage threshold of device IC 12 (2.31V) is lower than the lower limit of the HIGH level of controller IC 11 (2.64V), and the LOW voltage threshold of device IC 12 (0.99V) is higher than the upper limit of the LOW level of controller IC 11 (0.66V). Therefore, device IC 12 can correctly recognize the HIGH and LOW levels of the signals output by controller IC 11. Figure 9 shows an example of signal voltage levels when leakage current is present. For illustrative purpose