JP2014154936A - Differential signal receiver, image forming apparatus including differential signal receiver, and differential signal receiving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To continue the operation of an apparatus while maintaining a signal transmission speed in a normal state even when only one side of a differential transmission line is disconnected, so as to reduce temporal loss for a user that has been seen in the prior art.SOLUTION: A differential signal receiver receives a differential signal transmitted from a differential driver, and comprises: a line open detection unit (line abnormality detection means) 126 that detects line open of a pair of transmission lines transmitting a + signal and a - signal of a differential signal; and an analog SW (signal transmission method switching means) 128 for switching, when the line open detection unit 126 detects the line open of any one of the transmission lines, a signal transmission method from a differential transmission method to a single end method by the other transmission line.

Description

  The present invention relates to a differential signal receiving apparatus, an image forming apparatus including the differential signal receiving apparatus, and a differential signal receiving method.

In order to transmit a large amount of data such as image data at a high speed, a differential signal interface such as an LVDS (Low Voltage Differential Signaling) method is currently used. However, when data is transmitted by the LVDS method, when only one side of the transmission (or signal) line for transmitting the non-inverted input signal and the inverted input signal is opened due to disconnection or the like, proper signal transmission quality is ensured. Incorrect data is transmitted.
As a countermeasure for this problem, when the receiver (reception) side detects that the differential signal line is line open, it notifies the system of an error, stops the image data transfer, or depends on the transmitted image data. It is known to perform control such as stopping the image forming operation.

  In addition, when only one side of the line is open, original signal transmission quality and transmission speed cannot be secured by devising such as switching the control of both the transmission side circuit and the reception side circuit to reduce the transmission speed. There is also known a differential signal transmission system in which signal transmission can be continued even in a state.

  However, when a line open is detected, an error is simply notified and the operation of the apparatus is stopped. For example, the line is connected to the transmission line of the image data transmission signal to the writing unit of the image forming apparatus such as a copying machine. When an open occurs, the device stops. For this reason, the apparatus is not restored until the service person repairs it, and there is a problem that the time loss is large for the user.

  Further, as described above, even when signal transmission is continued as it is, signal transmission quality and transmission speed must be reduced. Therefore, for example, if the signal transmission in the image forming apparatus is to be continued as it is, a device for reducing the image forming speed and continuing the operation is required, resulting in a problem that the productivity of the apparatus is lowered.

  In the communication bus driving device of Patent Document 1, a circuit for detecting an abnormality such as a disconnection of a transmission line is provided for the purpose of continuing signal transmission at the time of abnormality. When disconnection is detected by this circuit, a method is adopted in which the signal transmission is continued by doubling the amplitude on the transmission circuit side and further reducing the communication speed.

  This communication bus driving device is similar to the present invention in that an abnormality of a differential signal is detected and communication is continued. According to this, communication can be continued even when the transmission line on one side of the differential signal is opened. However, the problem that the productivity of the apparatus is lowered cannot be solved. Further, since it is necessary to make both the transmission and reception configurations new, there is a problem that the application range of the method is limited.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to maintain a transmission speed in a normal state even when only one side of a pair of transmission lines for image data transfer is opened. This is to reduce the time loss of the user as in the conventional case.

  The present invention is a differential signal receiving apparatus that receives a differential signal transmitted from a differential driver, and that opens a pair of transmission lines that transmit a non-inverted input signal and an inverted input signal of the differential signal. When any line open of the transmission line is detected by the line abnormality detection means to detect and the line abnormality detection means, the signal transmission method is changed from the differential transmission method to the single end method by the other transmission line. A signal transmission system switching means for switching, and when the line open of the transmission line is detected, a differential capable of continuing the reception operation without reducing the transmission speed by switching the signal transmission system in the signal transmission system switching means It is a signal receiving device.

  According to the present invention, even when only one side of a pair of transmission lines for image data transfer is opened, it is possible to continue the operation of the apparatus while maintaining the transmission speed in a normal state, thereby reducing the time loss of the user. Can do.

1 is a block diagram illustrating an image forming apparatus. It is a block diagram which shows roughly the structure of the differential signal transmission part which performs the differential signal transmission by LVDS. 3A is a diagram illustrating a signal waveform of a differential signal in the differential signal transmission unit of FIG. 2, and FIG. 3B is a diagram illustrating a reception signal of the differential receiver. FIG. 3 is a diagram on the receiving circuit side in FIG. 2 showing that a disconnection has occurred in the differential signal transmission unit. It is a figure which shows the signal waveform of the differential signal in the disconnection state of FIG. It is a block diagram which shows the circuit structure of the differential signal receiver which concerns on embodiment of this invention. It is a figure which shows the signal waveform of the differential signal input into a differential receiver when the constant voltage supply means is connected when only one side of the differential signal is line open.

Next, embodiments of the present invention will be described. Prior to that, it will be explained that normal transmission cannot be performed when a transmission line is opened in transmission of differential signals, and then the present invention for solving this problem will be described. This embodiment will be described by taking a differential signal receiving apparatus in an image forming apparatus as an example.
FIG. 1 is a block diagram illustrating an image forming apparatus.
The image forming apparatus includes a main control unit 10 and a writing unit 20 as illustrated. The main control unit 10 includes a CPU 101 and an IPU (image processing unit) 102, and an LD control unit 201 that controls lighting of a writing LD (Laser Diode) 202 in the writing unit 20 that is an image forming unit. Is provided.

  Here, when image data is transferred from the IPU 102 of the main control unit 10 to the LD control unit 201 of the writing unit 20, high-speed data transfer is required in response to a request for speeding up the apparatus. Thus, for image data transfer, currently, differential signal transmission with a small amplitude by LVDS is generally used.

FIG. 2 is a block diagram schematically showing the structure of a differential signal transmission unit that performs differential signal transmission by LVDS of the image forming apparatus of FIG.
The differential signal transmission circuit 110 includes a differential driver 112 that outputs a transmission signal. The differential driver 112 outputs a transmission signal as a pair of a differential (+) side signal (non-inverted input signal) and a differential (−) side signal (inverted input signal).
The reception circuit 120 includes a differential receiver 122 that receives the pair of signals (differential signals). In addition, a terminating resistor 124 is connected between the transmission lines in the receiving circuit 120 for impedance matching of the transmission lines. In the case of LVDS, a termination resistor 124 of about 100Ω is connected according to the standard of the LVDS transmission signal.

  3A is a diagram illustrating a signal waveform of a differential signal in the differential signal transmission unit of FIG. 2, and FIG. 3B is a diagram illustrating a reception signal of the differential receiver. 4 is a diagram on the receiving circuit side in FIG. 2 showing that a line open (disconnection) has occurred in the differential signal transmission unit, and FIG. 5 is a signal waveform of the differential signal in the disconnection state in FIG. FIG.

  In FIG. 3, the differential driver 112 on the transmission circuit 110 side outputs a pair of potential difference (Vdiff) signals so that the + side signal and the − side signal are in opposite phases to each other. As shown in FIG. 3A, the differential receiver 122 of the reception circuit 120 uses the voltage near the center of the + side voltage and the − side voltage as a reference voltage (Vref), and the received signal transitions at a point where both signals cross. It works to be a point. Here, the signal (reception data) shown in FIG. 3B is received with the timing (H) when the signal voltage on the + side is large as positive logic and the reverse as negative logic (L).

  By the way, when performing signal transmission using differential signals, even if only one transmission line is disconnected due to disconnection, etc., the other signal is connected, so the signal is received by ON / OFF of the remaining signal. In the circuit 120, a potential difference occurs between the positive side signal and the negative side signal of the differential signal, and a timing at which the reception condition of the differential signal is satisfied occurs.

  For example, as shown in FIG. 4, when only the signal on the + side of the differential signal is disconnected, the signal is not correctly transmitted due to the influence of the termination resistor 124 or the capacitance component of the circuit, and as shown in FIG. The signal on the side is also input to the + side. At this time, due to the influence of the termination resistor 124 and the like, the − side signal and the + side signal do not have predetermined waveforms, and signal transmission is not performed correctly. Therefore, normal image formation is not performed.

FIG. 6 is a block diagram showing a circuit configuration of the differential signal receiving apparatus according to the embodiment of the present invention.
That is, here, the line open detecting unit 126 which is a line abnormality detecting unit capable of detecting that the differential signal is line open is added to the differential signal receiving circuit 120 of the differential signal transmitting unit shown in FIG. Is provided. In addition, an analog SW (switch) 128 serving as a signal transmission system switching unit is connected to the termination resistor 124 between the connection points of the differential + side and the − side line.
Here, the analog SW 128 uses the output signal (termination circuit control signal) when the line open detection unit 126 detects the line open to determine the line where the line open is detected as a termination circuit for the GND (referred to as a second termination circuit). Switch to. That is, the analog SW 128 switches the signal transmission method from the differential transmission method using a differential signal to the single end method using a single end signal.

That is, the line open detection unit 126 in FIG. 6 outputs a termination circuit control signal when line open is detected on only one side of the differential signal. The analog SW 128 switches the termination circuit for both signals (referred to as a first termination circuit) to a termination circuit (second termination circuit) for GND suitable for single-end signal reception according to the termination circuit control signal.
Thus, the transmission signal on the transmitted side is received as a single-ended signal in which H and L in FIG. 3 of the signal are determined with reference to GND while maintaining a transmission speed equivalent to the transmission speed of a normal differential signal. be able to.
The line open detection unit 126 may have any configuration as long as it can detect the open of one or both of the + signal and the − signal among the differential signals.

By the way, if the transmission line in which the differential signal line open is detected is switched to the termination circuit (second termination circuit) for GND by the analog SW 128 of the termination circuit, the transmission line is at the GND level as it is. For this reason, the differential receiver 122 does not satisfy a predetermined reception condition.
Therefore, in the present embodiment, the constant voltage supply means that is the reference voltage (Vref) of the differential signal is connected to the signal input side on which the connection abnormality (line open) of the differential receiver 122 is detected. As a result, a waveform shown in FIG. 7 described later is input to the differential receiver 122, and signal reception in the single-ended method is continued at a transmission speed and signal transmission quality substantially equal to those of the differential signal in the normal state.

That is, FIG. 7 is a diagram illustrating a signal waveform of the differential signal input to the differential receiver 122 when the constant voltage supply unit is connected when only one side of the differential signal is line open.
In this case, as shown in the figure, the − side signal and the + side signal have predetermined waveforms, indicating that signal transmission is performed correctly and normal image formation is performed.

As described above, according to the present embodiment, the differential driver side circuit (transmission circuit) 110 transmits the signal reception in the single end system only by the reception circuit 120, while continuing the normal differential output. It is possible to continue without substantially reducing the speed, that is, under conditions close to the normal state.
It should be noted that signal transmission becomes impossible when both transmission lines for differential signals are opened. In this case, when the line open detection unit 126 detects the line open of both transmission lines, the line open detection unit 126 sends the detection signal to the system control unit which is a control unit of the image forming apparatus. The system control unit that has received the detection signal stops the signal transmission and the image forming operation. Thereby, for example, in the image forming apparatus, it is possible to prevent abnormal image formation.

Incidentally, an image forming apparatus originally attempts to realize high-speed image forming operation by performing high-speed signal transmission using differential signals. However, signal transmission using only one side signal is inferior to signal transmission quality using a differential signal. Therefore, strictly speaking, there remains a problem that the signal transmission quality is deteriorated and the formed image is slightly deteriorated.
For example, an ordinary text document handled in an office or the like has little or no influence on an image, but this embodiment is not sufficient when it is desired to form a high-quality image such as a photographic image. .

Therefore, in this embodiment, when the line open on one side is detected, the signal transmission on the remaining one side is continued. In this case as well, the abnormality of the (differential signal) receiving circuit 120 is detected by the system control unit of the apparatus. To inform.
Accordingly, it is possible to notify the user of the apparatus, the maintenance staff, etc. of the abnormal state of the differential signal while continuing the image formation. That is, since the maintenance staff can grasp the abnormal state at an early stage, it is possible to perform the early maintenance and restore the normal state. As a result, the downtime of the apparatus at the time of abnormality can be reduced.

As mentioned above, although embodiment of this invention was described, the characteristic is as follows.
That is, the differential signal receiving circuit 120 can detect that only one transmission line is open. When it is detected that the line is open on only one side, only the terminating circuit on the receiving circuit 120 side is switched so that only the signal on the connected side can operate as a single-end transmission line.
That is, when the line is opened only on one side, the termination circuit connected between the differential signal lines is cut by an analog switch circuit or the like. Thereby, it is possible to eliminate the influence of the mutual signal lines and perform signal transmission by the single-ended method using only the signal on the line side where the line is not open.

In addition, by supplying a constant voltage (reference voltage) to the receiving circuit 120 for the line in which line open is detected, the signal transmission can be continued and the receiving operation of the device can be continued without reducing the communication speed. It was.
In other words, for a transmission line that has been opened, the receiving circuit 120 side receives a constant voltage so that it is exactly halfway between H (high level) and L (low level) of a normal transmission line. The circuit 120 is a condition for receiving a differential signal, and the change of the differential signal on the receiving circuit 120 side can be minimized. In addition, data transmission can be continued with signal transmission quality close to normal, and the operation of the apparatus can be continued.

  Conventionally, when an abnormality is detected, it is necessary to switch the circuit configuration between both the transmission circuit 110 and the reception circuit 120. On the other hand, according to the present embodiment, only the configuration on the receiving side of the conventional differential signal transmission system needs to be replaced, and the convenience and economy are greatly improved. Therefore, its application range has been expanded.

  In the above description, the differential signal transmission system between the main control unit and the writing unit of the image forming apparatus, particularly the image data receiving unit is taken as an example. However, the present invention is not limited to this, and can also be applied to a receiving circuit unit and a receiving apparatus for differential signals such as LVDS in apparatuses other than the image forming apparatus or between apparatuses.

  DESCRIPTION OF SYMBOLS 10 ... Main control part, 20 ... Writing part, 101 ... CPU, 102 ... IPU, 110 ... Transmission circuit, 112 ... Differential driver, 120 ... Reception circuit, 122: Differential receiver, 124: Terminating resistor, 126: Line open detector, 128: Analog SW

Japanese Patent Application Laid-Open No. 07-222256

Claims (7)

A differential signal receiving device for receiving a differential signal transmitted from a differential driver,
A line abnormality detecting means for detecting a line open of a pair of transmission lines for transmitting a non-inverting input signal and an inverting input signal of a differential signal;
When any one of the transmission lines is detected by the line abnormality detection means, the signal transmission system switching means for switching the signal transmission system from the differential transmission system to the single-ended system by the other transmission line;
Have
A differential signal receiving apparatus capable of continuing a receiving operation without lowering a transmission speed by switching a signal transmission method in the signal transmission method switching means when detecting a line open of the transmission line. The differential signal receiving device according to claim 1,
A reception circuit, the reception circuit having a first termination circuit for differential signals and a second termination circuit for single-ended signals that receive signals only on one side, and switching the signal transmission method The means is a differential signal receiving apparatus which is means for switching from the first termination circuit to the second termination circuit. In the differential signal receiver according to claim 1 or 2,
A constant voltage supply means for supplying a constant reference voltage, and when a line open of the transmission line is detected, a difference in which a constant voltage is supplied from the constant voltage supply means to the signal input side where the line open is detected; Motion signal receiver. The differential signal receiving device according to any one of claims 1 to 3,
A differential signal receiving apparatus comprising control means for stopping a receiving operation when an abnormality of both lines of a pair of transmission lines is detected by the line abnormality detecting means.   An image forming apparatus comprising the differential signal receiving apparatus according to claim 1. The image forming apparatus according to claim 5.
An image processing unit and an image forming unit;
The differential signal receiving device is an image forming device provided in the image forming unit that receives image data transferred from the image processing unit. A differential signal receiving method in a differential signal receiving apparatus for receiving a differential signal transmitted from a differential driver,
A line abnormality detection step of detecting a line open of a pair of transmission lines that transmit a non-inverting input signal and an inverting input signal of a differential signal;
In the line abnormality detection step, when any one of the transmission lines is detected to be open, the signal transmission method switching step of switching the signal transmission method from the differential transmission method to the single-ended method using the other transmission line;
Have
A differential signal receiving method capable of continuing a receiving operation without lowering a transmission speed by switching a signal transmission method in the signal transmission method switching step when detecting a line open of the transmission line.

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