JP4765672B2 - Differential transmission circuit and signal regeneration method - Google Patents

Description

  The present invention relates to a differential transmission circuit and a signal regeneration method. For example, when used in a high-speed interface, a differential transmission circuit and a signal regeneration suitable for preventing malfunction when a signal from a transmission side is not input. Regarding the method.

  With the advent of the multimedia society, the speed of transmitted data is increasing in various fields. In high-speed interfaces, a differential transmission method is generally used. In the differential transmission method, two signal lines having opposite polarities are used for transmission of 1-bit data. As a result, there is a feature that resistance to noise applied to the two signal lines in the same manner is enhanced, and high-speed operation can be facilitated.

  However, on the other hand, when differential transmission is performed, if the signal of the receiver circuit is not input as in the state where the power of the counterpart device is turned off or the cable is not connected, That is, the potential difference between the positive phase signal (true signal) of one signal line and the negative phase signal (compare signal) of the other signal line disappears, and the receiver output becomes indefinite. As a result, the device may malfunction if the signal in the indefinite state becomes an effective signal that should be transmitted.

In order to solve such a problem, various devices have been conventionally made in the receiver circuit. For example, a pull-up resistor or a pull-down resistor is added to the input of the receiver circuit to give a potential difference in advance (see, for example, Patent Document 1), or a valid signal detection circuit is provided in the internal logic of the receiver circuit to pull up the receiver circuit. There is a method of separating resistors and pull-down resistors with a switch. In addition, a method of ignoring invalid signals by providing a circuit for detecting valid signals with internal logic is also employed.
JP 2001-136057 A (paragraphs 0004 to 0006, FIG. 4).

  However, among these methods, in the method of adding a circuit such as a resistor or a switch to the input circuit portion of the receiver circuit, the waveform may be distorted by these, which may affect the signal quality. In addition, if a potential difference is previously provided by a pull-up resistor or a pull-down resistor, the amplitude of the signal is relatively reduced by the amount of the potential difference when a normal signal is transmitted. As a result, there is also a problem that long-distance transmission becomes impossible.

  Further, when a valid signal detection circuit is provided in the internal logic of the receiver circuit, a clock signal is required for this purpose, and the hardware increases accordingly. For this reason, it is difficult to provide such an effective signal detection circuit in a relay circuit such as a simple buffer circuit or a repeater.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a differential transmission circuit and a signal regeneration method capable of preventing malfunction due to input of an indeterminate signal when not normally connected to a counterpart device.

  In the present invention, (b) a differential receiver that receives a signal transmitted from a counterpart device using a differential transmission system using two signal lines; and (b) a signal obtained from the differential receiver. (C) Of the signals obtained from the differential receiver, only noise generated in a state where the signal is not properly connected to the counterpart device. And (d) a signal that is activated whenever there is an output of this bandpass filter and masks signal regeneration of the signal regeneration means for a predetermined time that is longer than the time during which noise continues. A mask means is provided in the differential transmission circuit.

  That is, in the present invention, the wavelength component of only noise generated in a state in which the device on the other side is not normally connected is detected, and the signal reproduced by the signal reproducing means is detected for a predetermined time after the detection is started. By masking, only an effective signal as a signal transmitted by the counterpart device can be reproduced. Thereby, it is possible to prevent malfunction due to an indefinite signal when no signal is input.

  In the present invention, (a) a signal receiving step for receiving a signal transmitted from a counterpart device using a differential transmission system using two signal lines, and (b) a signal receiving step. A specific wavelength determining step for determining whether the signal is a wavelength component of only noise generated in a state where the signal is not normally connected to the counterpart device, and (c) a normal wavelength with the counterpart device in this specific wavelength discrimination step. When it is determined that the wavelength component is only noise generated in a state where it is not connected, the signal received in the signal reception step is reproduced for a predetermined time that is longer than the time that the noise continues after the determination. The signal reproduction method includes a signal reproduction mask step that is not performed.

  That is, in the present invention, the wavelength component of only noise generated in a state in which the other device is not normally connected is determined in the specific wavelength determining step, and the signal receiving step is performed for a predetermined time after the determination is performed. In this case, only the valid signal can be reproduced by not reproducing the signal received in (1). Thereby, it is possible to prevent malfunction due to an indefinite signal when no signal is input.

  As described above, according to the present invention, the wavelength component of only noise generated in a state where it is not normally connected to the counterpart device is detected, and the signal received for a predetermined time is masked based on the detected wavelength component. As a result, unnecessary signals can be removed from signals transmitted by the differential transmission method by adding a simple configuration of a filter and a time measuring means, thereby preventing malfunction.

  Hereinafter, the present invention will be described in detail with reference to examples.

  FIG. 1 shows an outline of a receiving side of a differential transmission circuit in an embodiment of the present invention. The differential transmission circuit 10 receives a differential receiver 13 that receives signals 11 and 12 sent from two devices via an unillustrated counterpart device and an output 14 of the differential receiver 13. The internal logic circuit 15 is provided. A mask signal generation circuit 17 for supplying a mask signal 16 for masking a predetermined signal to the internal logic circuit 15 is connected to the output side of the differential receiver 13. The mask signal generation circuit 17 includes a reset line 18 for resetting the mask operation inside the circuit.

  FIG. 2 specifically shows a mask signal generation circuit for the main part of the differential transmission circuit. The mask signal generation circuit 17 includes a band rejection filter (BRF) 21 that receives the output 14 of the differential receiver 13 and attenuates only the specific component. The output 22 of the band rejection filter 21 is input to a set / reset flip-flop (S / R FF) 23. The Q output 24 of the set / reset flip-flop 23 is input to the mask period setting circuit 25, one input terminal of the 2-input AND circuit 26, and one input terminal of the exclusive OR (EOR) circuit 27, respectively. It has become.

  The mask period setting circuit 25 includes a resistor 31 for inputting the Q output 24 to one end thereof, a capacitor 32 having one end connected to the other end of the resistor 31 and the other end grounded, and both ends of the capacitor 32 being turned on / off. The switch 33 is configured to be turned off. A signal 35 appearing at the connection point 34 between the other end of the resistor 31 and the capacitor 32 and the switch 33 is supplied to the other input terminal of the two-input AND circuit 26 and becomes the other input of the exclusive OR circuit 27. . The output 36 of the two-input AND circuit 26 serves as a control input for the switch 33 and is input to the reset terminal side of the set / reset flip-flop 23. Further, the mask signal 16 is supplied from the exclusive OR circuit 27 to the internal logic circuit 15 as a logic output.

  FIG. 3 specifically shows the internal logic circuit. The internal logic circuit 15 receives a buffer 41 that receives the output 14 of the differential receiver 13 shown in FIG. 2, and an AND circuit 43 that inputs a negative logic state of the output 42 of the buffer 41 and the mask signal 16 to obtain a logical product. It is composed of This internal logic circuit 15 does not require input of a clock signal. Even if an undefined asynchronous signal of several bits is input to the internal logic circuit 15 via the buffer 41, it is masked by the mask signal 16 so that the output 44 of the AND circuit 43 has a predetermined bit length (usually several tens of bits). This is because the valid signal of) is not output.

  By the way, in a high-speed interface, it is general to employ a coding method represented by 8B10B. Here, 8B10B is an encoding method in which 8-bit information is converted into 10-bit information in which “0” is not continuous for a certain amount or more and transmitted. When the signal is encoded, the frequency component of the effective signal is limited. For example, in the case of 8B10B, only signals in the range of 1T to 5T are valid signals. Here, “T” represents a 1-bit width. For example, in the case of a signal having a speed of 1 Gbps (gigabit / second), 1T is 1 ns (nanosecond). For this reason, in the case of 8B10B, frequency components other than 1T to 5T are indefinite signals. In this embodiment, the mask signal generation circuit 17 masks this indefinite signal.

  <Normal circuit operation>

  First, the operation when a counterpart device (not shown) is normally connected to the differential transmission circuit 13 shown in FIG. 2 will be described. Here, an 8B10B encoding method will be described as an example. In this case, since the counterpart device is normally connected, the input of the differential receiver 13 has a potential difference. As a result, only the 1T to 5T effective signals are output from the differential receiver 13. The band rejection filter 21 has a characteristic of rejecting all the signals of 1T to 5T. Therefore, the output 22 holds “0”. As a result, the Q output 24 of the set / reset flip-flop 23 also holds “0”, and the signal 35 appearing at the connection point 34 of the mask period setting circuit 25 also remains “0”. As a result, the other input terminal of the exclusive OR circuit 27 also maintains the “0” state.

  In the exclusive OR circuit 27, if one of the two inputs is “1”, the mask signal 16 as its output becomes “1”. Since the mask signal 16 output from the mask signal generation circuit 17 is always “0”, the internal logic circuit 15 is always enabled. For this reason, the output 14 of the differential receiver 13 is treated as a valid signal and passes through the internal logic circuit 15 as it is.

  <Circuit operation at the time of abnormality>

  Next, a case where the differential transmission circuit 10 loses the input signal of the differential receiver 13 for some reason will be described. As an example of such a cause, there is a case where the power supply of the counterpart device is turned off, or a case where a cable (not shown) connecting the counterpart device and the differential transmission circuit 10 of the present embodiment is not connected. be able to. Thus, in the state where the input signal of the differential receiver 13 disappears, the output 14 outputs an indefinite signal. The frequency component of the indefinite signal is not output limited to a predetermined frequency range. For this reason, frequency components other than 1T to 5T are also output.

  Frequency components other than 1T to 5T are invalid signals. The band rejection filter 21 reflects only signals in the 1T to 5T band, and transmits invalid signals having frequencies other than 1T to 5T.

  FIG. 4 shows signal waveforms at various parts of the differential transmission circuit. Of these, FIG. 5A shows a state in which the indefinite signal 46 is output. A pulse-like indefinite signal 46 that has passed through the band rejection filter 21, which is a type of bandpass filter, is input to the set / reset flip-flop 23. The set / reset flip-flop 23 is set when it rises to "1" due to the arrival of the indefinite signal 46, and its Q output changes to "1" as shown in FIG. 4B. As a result, one input terminal of the 2-input AND circuit 26 is also held at “1”.

When the Q output changes to “1”, the contact of the switch 33 is turned off. Therefore, both ends of the capacitor 32 are not short-circuited at this time. Therefore, the capacitor 32 starts charging through the resistor 31 from the time when the Q output changes to “1”. As a result, the potential of the connection point 34 (charge voltage of the capacitor 32) is as shown in FIG. To gradually rise. When the potential at the connection point 34 becomes “1”, both inputs of the 2-input AND circuit 26 become “1” at the time t ₁ , and the output 36 (FIG. 4D) changes to “1”. . As a result, the switch 33 is turned on while the output 36 is “1”. When the switch 33 is turned on, the capacitor 32 is discharged and the potential at the connection point returns to “0”. The output 36 serves as a reset input of the set / reset flip-flop 23.

  Thus, the mask period setting circuit 25 has a role as a timer for measuring the mask period 38 (FIG. 4) as a fixed time after the Q output 24 of the set / reset flip-flop 23 becomes “1”. Yes. During the mask period 38, the mask signal 16 (FIG. 4E) as the output of the exclusive OR circuit 27 becomes “1”.

  The mask signal 16 is supplied to the internal logic circuit 15 to mask the output of the indefinite signal 46 shown in FIG. Since the rising edge of the mask signal 16 is when the Q output changes to “1”, the indefinite signal 46 is masked by the mask period 38.

  FIG. 4A shows various generation modes of the indefinite signal 46. The indefinite signal 46 that appears third in this figure is included in the mask period 38 of the second indefinite signal 46. Therefore, the same mask period 38 is masked together with the second indefinite signal 46. On the other hand, for the indefinite signal 46 shown in the fourth (last) in FIG. 4, since the previous mask period 38 has ended, the mask period 38 is newly set. Thus, even when the indefinite signal 46 appears continuously, the mask of the indefinite signal 46 is surely performed.

  The length of the mask period 38 only needs to cover the longest time width assumed as the indefinite signal 46. If the indefinite signal 46 is too long, an effective signal sent after the counterpart apparatus is normally connected is masked during the mask period 38, which is not preferable.

  In general, in a transmission system that transmits encoded data, a specific pattern of about several tens of bits is repeatedly transmitted several times from the counterpart device, and the subsequent data is transmitted as valid data. Therefore, in preparation for a case where a valid signal is transmitted from the counterpart device, the counterpart device is repeated by repeating the operation of masking this invalid signal and the operation of releasing the mask for several tens of T after detecting the invalid signal. Thus, malfunction due to the indefinite signal 46 in a state where no signal is input is prevented, and at the same time, a situation in which valid data is transmitted is prepared.

  In the embodiment described above, monitoring is performed for detection of an invalid signal having a frequency that cannot be generated in normal transmission. When an invalid signal is detected, the signal is detected at a certain time interval from the start of the detection. Decided to mask. Also, once the mask is started, the mask is released after a certain period thereafter. As a result, the internal logic circuit 15 prevents passage of the indefinite signal 46 that occurs when no signal is input, and it is possible to prevent malfunctions in the subsequent circuit portion.

  <Deformability of invention>

  FIG. 5 shows a main part of the configuration of the differential transmission circuit according to the modification of the present invention. In FIG. 5, the same parts as those in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted as appropriate. In the differential transmission circuit 10 </ b> A of this modified example, the output 22 of the band rejection filter 21 is input to the monostable multivibrator 51. The monostable multivibrator 51 is a multivibrator that outputs a mask signal 16A having a certain time width when a trigger pulse is input, and is also called a one-shot multivibrator.

  According to this modification, the indefinite signal 46 can be masked by the timer circuit of the monostable multivibrator 51 itself. Even when the indefinite signal 46 is continuously generated, the masked period can be extended with the start time of each indefinite signal 46 as a trigger.

  In the differential transmission circuit 10 of the embodiment shown in FIG. 2, the description has been made on the assumption that the capacitor 32 is incorporated in the mask signal generation circuit 17. You may make it changeable freely. Further, the capacitor 32 itself may be composed of a variable capacity type part. As a result, the mask period 38 can be freely changed by the operator.

  Although not specifically described in the embodiments and modifications, a delay element or a delay circuit may be provided in the internal logic circuit 15 that masks the indefinite signal 46 or a line portion immediately before the internal logic circuit 15. As a result, the mask processing with sufficient time by the mask signals 16 and 16A becomes possible.

  Further, in the embodiment, the band rejection filter 21 as a kind of bandpass filter is used to detect the indeterminate signal 46 by passing only the indeterminate signal 46. Conversely, only the wavelength of the effective signal is passed. A band-pass filter may be used, and when the signal does not pass from the band-pass filter for a certain time or longer, the internal logic circuit may be masked until the next signal passes.

It is a block diagram showing the outline | summary of the receiving side of the differential transmission circuit in one Example of this invention. FIG. 3 is a block diagram specifically showing a mask signal generation circuit with respect to the main part of the differential transmission circuit of the present embodiment. It is the block diagram which showed the internal logic circuit of the present Example concretely. It is a wave form diagram showing the signal waveform of each part of a differential transmission circuit in this example. It is a block diagram showing the principal part of the differential transmission circuit in the modification of this invention.

Explanation of symbols

10, 10A Differential transmission circuit 13 Differential receiver 15 Internal logic circuit 16, 16A Mask signal 21 Band rejection filter (BRF)
23 Set / Reset Flip-flop (S / R FF)
25 mask period setting circuit 26 2-input AND circuit 27 exclusive OR circuit 51 monostable multivibrator

Claims (6)

A differential receiver that receives a signal transmitted by a differential transmission method from a counterpart device using two signal lines;
A signal reproducing means for inputting a signal obtained from the differential receiver and reproducing a signal sent from the counterpart device;
Among the signals obtained from the differential receiver, a bandpass filter that transmits only a wavelength component of noise generated in a state where the differential receiver is not normally connected to the counterpart device;
And a signal masking means that is activated each time the bandpass filter outputs, and masks the signal reproduction of the signal reproduction means for a predetermined time that is longer than the duration of the noise. Dynamic transmission circuit.   The signal masking means reproduces the signal of the signal regenerating means only for a time period from the start of charging of the capacitor until the charging voltage reaches a predetermined level, with a capacitor charged by the charge of the signal that has passed through the bandpass filter. 2. The differential transmission circuit according to claim 1, further comprising mask signal generation means for blocking.   The differential transmission circuit according to claim 2, wherein the capacitor is configured as a replaceable part according to a required capacity.   2. The differential transmission circuit according to claim 1, wherein the signal masking means is a monostable multivibrator activated by an output of the bandpass filter.   2. The differential transmission circuit according to claim 1, wherein the signal mask means includes a logic circuit that takes a logical product of an output of the differential receiver and a signal for masking signal reproduction of the signal reproduction means. A signal receiving step for receiving a signal transmitted by a differential transmission method from a counterpart device using two signal lines;
A specific wavelength determining step for determining whether the signal received in this signal receiving step is a wavelength component of only noise generated in a state where the signal is not normally connected to the counterpart device;
When it is determined in this specific wavelength determination step that the wavelength component is only noise generated in a state in which the device is not normally connected to the counterpart device, it is determined that the noise continues for a time longer than the determination. And a signal reproduction mask step that does not reproduce the signal received in the signal reception step for a predetermined time.

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