JPH0983462A - Interface circuit and its noise correction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the noise proof at a low cost even in an unbalanced interface circuit without increasing the number of cores of a cable to keep miniaturization. SOLUTION: One of idle signal wires of an unbalanced transmission cable 12 is used for a noise detection line Ld and a low pass filter consisting of a noise detection resistor Rd and a capacitor cd is connected to a receiver side (printer) 13 of the noise detection wire to detect a noise level superimposed on the signal line of the cable. Ground terminals g1 - gn of each of reception elements rec1 - recn are connected to the resistor Rd via an operational amplifier op and an analog switch 15 to cancel an input noise level of each signal line corresponding to the detected noise level. Furthermore, a wavelength measurement circuit (counter) 14 controlling the changeover of the analog switch 15 is connected to an input section (b) of the operational amplifier op to correct the signal level for a prescribed time when the noise level is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a signal line having an unbalanced line configuration (hereinafter referred to as an unbalanced signal line),
The present invention relates to an interface circuit used in a transmission circuit that communicates digital data and a noise correction method thereof, and in particular, an interface circuit called an unbalanced type among parallel interfaces for digital data transfer connected between a host computer and a printer. The present invention relates to a correction technique for improving resistance to external noise input when used.

[0002]

2. Description of the Related Art Conventionally, for external noise, a signal line and a signal return line are used for each signal line, and a so-called balanced type interface circuit provided with a transmission element and a reception element is used, or unbalanced. Type interface circuit, try to form a low-pass filter by the time constant of so-called CR parts such as capacitors and resistors, or try to remove external noise by covering with a braided wire.
Alternatively, each signal line is provided with a wavelength measurement counter that separates a signal and noise from each other to prevent external noise.

[0003]

However, in the balanced type interface circuit as described above, the number of cable cores and a dedicated driver and a dedicated receiver are required, which causes a cost increase and an increase in the number of core wires. The loss of flexibility also hindered miniaturization. Further, in the case of measures against external noise in the above-mentioned CR circuit of the unbalanced type interface circuit, if the superposed width of external noise, that is, if the noise application time to the signal line is long, the effect of the low-pass filter decreases, so that noise is converted into a signal It may be processed and cause a malfunction. In addition, it is extremely costly to install a wavelength measurement counter circuit on each signal line.
It was a factor of improvement.

FIG. 1 shows a conventional unbalanced interface circuit. Here, 1 is a host computer, 2 is a transmission line (cable), and 3 is a printer. The host computer 1 has drv1-drv as a signal output driver.
n are provided. Further, the printer 3 is provided with receivers rec1-recn, low-pass filter resistors rl-rn, and capacitors c1-cn as receiving elements.

FIG. 2 shows an example of the receiving line of the printer 3. For the receiving line of FIG. 2, an example in which a noise input having a time constant or less is superimposed on a signal line of normal Hi is shown in (1) of FIG. 3, and an input element due to external noise is shown in (2) of FIG. The functions of the input potential of the (reception element) and the time constant of the receiving section are shown. (3) of FIG. 3 shows noise superimposition on the signal line having a width exceeding the time constant, and (4) of FIG. The change of the receiving element input point and output at the time of input of (3) of FIG. 3 is shown.

FIG. 1 shows a typical configuration example of a conventional unbalanced type interface circuit which is most suitable for application of the present invention. Signals are sent from the transmitter of the host computer 1 to the printer 3 through the interface cable 2. Reach the interface receiver. In this interface receiver, a reception signal shaping circuit corresponding to the signal lines L1-Ln is composed of a capacitor c and a resistor r, and this reception signal shaping circuit is
It is a noise removal circuit called a so-called CR low-pass filter circuit.

First, superimposition of noise on a signal line will be described. The noise that has flown from the outside to the signal cable, so-called radiated noise, reaches the grounding braided wire, grounding wire, and signal wire of the cable. It However, the flying noise that has passed through the braided wire is applied to the signal lines L1-Ln having high ground impedance, and the potentials V1-Vn of the signal lines are increased by the variation dv due to the noise [+ d
v] or descend [-dv].

However, as shown in FIG. 2, a capacitor c and a resistor r are provided on the input side of the receiver of the printer interface.
3) and the noise length is less than or equal to the time constant of the input of (1) of FIG. 3, as shown in (2) of FIG.
The signal at the point does not reach the threshold value of VinLo, which is the transition point of Lo of the input signal, and the output does not change as indicated by out, so the signal reception output is not affected.

However, when the noise variation dv is large,
That is, if it exceeds the time constant c * r, the changing part of dv is transmitted to the receiving element. That is, all or part of the potentials V1 to Vn of the signal line transition to Hi or Lo at the input element level depending on the state. The output corresponding to the transitioned level is transmitted to the output of the input element, which causes a malfunction.

Next, the details of the actual operation will be described with reference to FIGS. 1, 2 and 3 (1) to (4). The noise transmitted to each of the signal lines L1-Ln shown in FIG. 1 reaches the input IN in the abbreviated circuit diagram showing one circuit of the receiving unit of FIG. An example of the waveform diagram is shown in (1) of FIG. 3, and this state is an example in the case where the level of the signal line is Hi and noise is superimposed. 3B shows the state of the input point a of the receiving element rec. The output of the receiving element rec drops along the broken line that can be shown by the time constant T of the capacitor c and the resistance r, but since the superimposed pulse width is short, it becomes the state shown by the solid line and reaches VinLo which is the transition point of the signal. Without output [o
ut] does not change.

Next, an example in which the superimposed noise width is large will be described with reference to (3) and (4) in FIG. (3) in FIG.
Is an example of a waveform diagram in which noise is superimposed on the signal line as described above. The signal transition at the point a is shown in (4) of FIG.
The signal at the point [a] falls along the discharge curve of the time constant T, continues to fall at ViLo at the input transition point of the receiving element [rec], and from the point of no noise, this time follows the charge curve of the time constant T. And rises again and crosses the signal transition point VinHi again. Therefore, the output [out] of the receiving element rec makes a transition each time it passes through the transition point. That is, for noise with a width exceeding the time constant T, C in FIG.
The configuration of the R low pass filter circuit is invalid.

FIG. 4 shows a conventional balanced type interface circuit. Driver drvl- of the host computer 1
drvn and receiver rec1-rec of printer 3
n has a balanced type, and the cable 2 also has a return line for each signal line.

In the balanced interface circuit shown in FIG. 4, noise of the same voltage is superimposed on both the signal line and the signal return line, so that the voltage difference between the signal line and the return line of the receiving element cancels out the noise component. , Therefore, stable input can be obtained. However, in such a conventional example, the necessity of dedicated parts for the driver and the receiver and the number of cores of the transmission line include the return line of each signal line. The increase in the number has also been an obstacle to the flexibility of cables and miniaturization.

The present invention has been made in view of the above points, and an object thereof is to keep the size small, so that even in an unbalanced interface circuit in which the number of cores of the cable does not increase, noise resistance can be reduced at low cost. An object of the present invention is to provide an interface circuit and a noise correction method for the interface circuit that can be improved.

[0015]

In order to achieve the above object, the interface circuit of the present invention provides a transmission cable for transmitting digital data using unbalanced signal lines together with other signal lines. A noise detection signal line, a noise detection unit connected to the noise detection signal line in the digital data receiving unit to detect noise superimposed on the signal line, and the noise detection unit. An interface circuit, comprising: a signal line noise correction unit that cancels an input noise level superimposed on all the other signal lines in the transmission cable in correspondence with the noise level detected in step 1). As one form thereof, the present invention is characterized by having control means for causing the signal line noise correction means to execute correction for canceling the input noise level for a certain period of time in accordance with the wavelength of noise detected by the noise detection means. can do.

As another aspect of the present invention, the noise detecting means may be a filter circuit having the same characteristics as a low-pass filter of the other signal line including a resistor and a capacitor.

As another aspect of the present invention, the signal line noise correction means generates an in-phase correction output from the output of the noise detection means, and the correction output of the operation amplifier is set to all the other outputs. And an analog switch connected to the ground terminal of each receiving element of the signal line.

In another aspect of the present invention, the control means measures the wavelength of noise detected by the noise detection means, and controls the analog switch from the ground side for a certain period of time according to the measured wavelength. It can be characterized in that it has a wavelength measuring circuit for outputting a switching signal for switching to the operational amplifier side.

In another aspect of the present invention, the signal line noise correction means includes an inverting amplifier that generates an inverted output of an opposite phase from the output of the noise detection means as a correction output, and all the other signal lines. A plurality of signal level correcting resistors each having one end connected to each input line of the receiving element; and a plurality of analog switches respectively connecting the correction outputs of the inverting amplifier to the plurality of signal level correcting resistors. It can be characterized by having.

As another aspect of the present invention, the control means measures the wavelength of the noise detected by the noise detection means, and opens the plurality of analog switches for a predetermined time according to the measured wavelength. It can be characterized in that it has a wavelength measuring circuit for outputting a switching signal for switching from to the closing side.

As another aspect of the present invention, the noise detection signal line may be an empty signal line of the transmission cable.

As another mode of the present invention, the wavelength measuring circuit may include a counter for measuring the wavelength.

In order to achieve the above-mentioned object, the noise correction method for an interface circuit according to the present invention transmits a signal along with other signal lines in a receiving section of a transmission line for communicating digital data using an unbalanced type signal line. A noise detection step for detecting noise superimposed on a signal line for noise detection provided in the cable, and superposed on all the other signal lines in the transmission cable corresponding to the noise level detected in the noise detection step And a signal line noise correction step for canceling the input noise level.

As one form of the method of the present invention, the wavelength measuring step of measuring the wavelength of the noise detected in the noise detecting step, and the signal line noise according to the wavelength measured in the wavelength measuring step The control step may further include a control step of performing correction for canceling the input noise level in the correction step for a certain period of time.

In the present invention, one of the empty signal lines of the unbalanced transmission cable is used as a signal line for noise detection,
As a noise detection means, for example, a low-pass filter including a resistor and a capacitor for noise detection is connected to the receiving side of the signal line for noise detection, and the noise level superimposed on the signal line of the cable is detected by this low-pass filter. To do. Corresponding to the detected noise level by connecting the ground terminal (or signal level correcting resistor) of each receiving element to the noise detecting resistor as signal line noise correcting means, for example, through an operational amplifier and an analog switch. Then, correction is performed to cancel the input noise level of each signal line. Further, by connecting a wavelength measuring circuit (counter) for controlling switching of the analog switch as a control means to the input part of the operational amplifier, the signal level is corrected for a certain time when the noise level is detected. This makes it possible to realize a low-cost, compact interface circuit that is highly resistant to external noise.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings.

In the following description, a detailed description of portions common to the conventional example shown in FIGS. 1 and 2 is partially omitted. Further, it goes without saying that the printer to which the present invention is applied is not limited to the laser beam printer and may be a printer of another printer type.

(First Embodiment) FIG. 5 shows a first embodiment of the present invention.
1 shows the configuration of the embodiment. Here, 11 is a host computer, 12 is a transmission line (cable), and 13 is a printer. Drv1-drvn of the host computer 11
Is a signal export driver. In addition, the printer 13 re
c1-recn is a receiver as a receiving element, and r
1-rn is a resistor for a low-pass filter, and c1-
cn is a capacitor for a low pass filter.

Ld is one of the empty lines used as the noise detection line, and Rd is a resistance for noise detection. Cd is a noise detecting capacitor. op is an operational amplifier that adjusts the ground potential of the signal receiving elements [rec1]-[recn].

The receiving interface circuit via the connector of the cable 12 on the printer 13 side has the cable 1
Since the empty line Ld of 2 is used as a noise detection line,
A resistor Rd and a capacitor cd are connected in series to this Ld similarly to the signal line, and their connection point is an operational amplifier op.
Connected to the input of the operational amplifier op
Receiving element rec1 of each signal line via switch 15.
It is connected to the ground terminals g1-gn of -recn. 1
Reference numeral 4 denotes a wavelength measuring circuit (hereinafter referred to as a counter) that measures the noise width and controls the switching of the analog switch 15. The analog switch 15 receives the ground signal g1 of the receiving elements rec1-recn based on the control signal of the counter 14.
-Gn is switched to the operational amplifier op or the ground, and the ground potentials thereof are adjusted. The noise detection line Ld is grounded on the host computer 11 side, and the input terminal of the counter 14 is a detection section (or an input point) b between the connection point of the resistor Rd and the capacitor cd and the operational amplifier op. Connected.

FIG. 6A shows the state of the input potential of the noise [time T1] and the signal [time T2] that exceeds the specified width Ts for signal separation in the present embodiment, and FIG. ) Is the input point a1-a of the receiving elements rec1-recn
The potential change of n and the potential change of the detection part b point between resistance Rd and operational amplifier op are shown.

Next, the operation when external noise is applied to the circuit of FIG. 5 will be described with reference to (1) and (2) of FIG. By superimposing external noise, L1 of each signal line
The potential V1-Vn of -Ln is raised [+ dv] or lowered [-dv] by external noise, as in the conventional example. However, when the width (time width) of the external noise is equal to or less than the time constant, the noise is removed by the low-pass filter effect similar to the conventional example (see (1) and (2) in FIG. 3).

When the noise width exceeds the time constant,
The potential V1-V of each signal line L1-Ln depends on the superimposed voltage dv.
n rises or falls above the threshold voltage of rec1-recn of the receiving element, and transits to the level of Hi or Lo. However, at this time, the noise detection line Ld for noise detection and the capacitor cd also similarly have the voltage d of the external noise.
v is superimposed. In FIG. 6B, the noise receiving element rec1-re superimposed on the signal line and the noise detection line Ld is shown.
cn input point a (a1-an) and operational amplifier op
7 shows the waveform of the voltage ag between the input point b, the output bout of the operational amplifier op, and the a-g of the receiving elements rec1-recn.

The noise detection line Ld is originally at the ground potential when there is no signal transition or when the noise is below the time constant. Therefore, the potential of the noise detection line Ld rises or falls by the potential dv of the noise applied due to the superposition of noise. At this time, in the case of this example, -d
Assume v.

The voltage superimposed on this noise detection line Ld-
dv is detected by the resistor Rd and the capacitor cd at the point b, becomes the input of the [-] potential of the operational amplifier op as shown in (2) of FIG. 6, and the operational amplifier op outputs an adaptive voltage, which is 1 / Output voltage doubled [-dv *
[1/2]] is supplied to the ground terminals g1-gn of the input receiving elements rec1-recn.

In this way, when the noise dv is superimposed on the input signal lines L1-Ln and the voltage change of -dv occurs in each of the receiving elements rec1-recn as described above, the ground potential of the receiving elements is also from the operational amplifier op. -Dv * at the voltage supplied
A change corresponding to 1/2 occurs. By thus lowering the ground potential, each receiving element rec1-r
The voltage ag between the ground potential of ecn and the input voltage of each of these receiving elements is relatively -dv due to the external noise of the input voltage.
This is absorbed by 1/2 * dv, and the state transition point of Hi or Lo (VinHi, H) of the output of each receiving element is absorbed.
inLo) does not pass and the stability is improved. Further, since each receiving element and the grounding portion of the element at the next stage are connected with a threshold value necessary for transition of reception appropriately, the receiving element re
The fluctuation of the potential of the ground portion of c1-recn does not change to the element (not shown) in the next stage, and noise can be removed.

When the noise width exceeds a certain time,
That is, if there is a signal input indicated by T2 that exceeds the noise time width T1 and the signal width threshold Ts, the counter 14
The analog switch 15 is switched to the ground side by the output indicating that the preset set value has been reached, the ground terminals g1-gn of the respective receiving elements rec1-recn are directly grounded, and the connection from the operational amplifier op is cut off. Therefore, the input levels of the signal lines L1-Ln are not corrected and become the output of each receiving element (that is, the inverted output in the case of this example). This counter 14 changes the signal, that is, Lo of the signal.
Restarts the operation of the width measurement in response to the passage of the threshold value from Hi to Hi,
Further, the analog switch 15 is switched to the operational amplifier op side, and after a lapse of a certain time, the analog switch 15 is switched to the ground side again to suspend the counting operation.

(Second Embodiment) FIG. 7 shows a second embodiment of the present invention.
1 shows the configuration of the embodiment. Here, 11 is a host computer, 12 is a transmission line, and 13 is a printer. Drv1-drvn of the host computer 11 are signal output drivers. In addition, rec1-rec of the printer 13
n is a receiver as a receiving element, r1-rn are resistors for a low-pass filter, and c1-cn are capacitors for a low-pass filter. Ld is one of the empty lines used as the noise detection line, and rd is a resistance for noise detection. cd is a capacitor for noise detection.

Op is an inverting amplifier, which adjusts the signal potentials of the receiving elements rec1-recn via the resistors Lbr1-Lbrn corresponding to the detection voltage. 14
Is a counter as a waveform measuring circuit, which observes the signal width and controls a plurality of analog switches an1-ann provided for each receiving element.

Resistors Lbr1-Lb for adjusting the signal potential
One end of rn is a resistor r1-r for the low-pass filter.
n and the receiving elements rec1 to recn, and the other ends thereof are connected to the output terminals of the inverting amplifier op via the respective analog switches an1 to ann. Each of the analog switches an1-ann opens and closes according to the output of the counter 14 to output the output of the inverting amplifier op to the resistor Lbr1-.
Connect to Lbrn or disconnect.

FIG. 8 shows a change state of the input potential of the input point b of the inverting amplifier op of FIG. 7 and a change state of the potential of the inverting output bout of the inverting amplifier op at that time.

Next, the operation of the input level correction circuit shown in FIG. 7 will be described with reference to the waveform chart of FIG.

First, when the external noise width is less than the time constant, the noise is removed by the low-pass filter circuit composed of r1-rn and c1-cn as in the conventional example.
When the external noise exceeds the time constant, the electric potential of the noise is superimposed on each of the signal lines L1-Ln and the noise detection line Ld as in the above-described first embodiment. This superimposed noise is detected by the resistor Rd and input to the [-] input terminal of the amplifier op. In this case, the amplifier op acts as an inverting amplifier, and the output of the amplifier op is output as the voltage bout on the opposite side to the input value shown by b in FIG. This output bout is an analog switch an1-a
nn and resistors Lbr1-Lbrn are connected to the respective signal lines L1-Ln, and the input level is corrected by supplying a reverse output to the rise or fall of the noise component dv superimposed on these signal lines. It will be.

The noise and the signal are separated by the above-mentioned first method.
However, in the case of this example, the analog switches an1 to ann reach a constant wavelength width by the signal input, and are not in the grounded state as in the first embodiment, but in the open state. become.

[0045]

As described above, according to the present invention,
The empty line that is not the signal line in the interface cable is used as the noise detection line to detect the noise level superimposed on the interface cable and cancel the input level of the signal line corresponding to this detection level. Therefore, it is possible to provide an interface circuit that is relatively low in cost and highly resistant to external noise.

Further, according to the present invention, it is possible to realize with relatively inexpensive components such as a resistor, a capacitor, an amplifier and an analog switch without using a balanced type electric wire, and the unbalanced line configuration is maintained. Since the noise resistance can be improved, there is an effect that the cost of the transmission cable can be reduced especially in the case of long distance transmission.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration example of a conventional unbalanced interface circuit.

FIG. 2 is a circuit diagram showing an example of a reception line of the printer of FIG.

3 is a waveform diagram showing an example when a noise input having a time constant or less is superimposed on a signal line of normal Hi in the receiving line of FIG. 2, and (2) is an input of an input element due to the external noise. A waveform diagram showing the action of the potential and the time constant of the receiving unit, (3) is a waveform diagram showing an example when noise input to the signal line having a width exceeding the time constant is superimposed on the signal line of normal Hi, (4) [Fig. 4] is a waveform diagram showing changes in the input point of the receiving element and the output when noise having a width exceeding the time constant is input.

FIG. 4 is a circuit diagram showing a configuration example of a conventional balanced type interface circuit.

FIG. 5 is a circuit diagram showing a configuration of an unbalanced interface circuit according to the first embodiment of the present invention.

6 is a circuit diagram in FIG. 5, where (1) is noise [T1]
And a waveform diagram showing the state of the input potential of the signal [T2] exceeding the specified width Ts for signal separation, (2) is the receiving element rec
It is a waveform diagram which shows the electric potential change of the input point a (a1-an) of 1-recn, and the electric potential change of the detection part b point.

FIG. 7 is a circuit diagram showing a configuration of an unbalanced interface circuit according to a second embodiment of the present invention.

8 is a waveform diagram showing a state of a change in an input potential of an input point b of the inverting amplifier of FIG. 7 and a state of a potential change of an inverting output bout of the inverting amplifier at that time.

[Explanation of symbols]

 11 host computer 12 transmission line (cable) 13 printer 14 wavelength measurement circuit (counter) 15 analog switch dr1-drn signal output driver L1-Ln signal line Ld noise detection line GND grounding line a1-an input point r1-rn low pass Filter resistor rec1-recn Receiver element g1-gn Ground terminal Rd Noise detection resistor cd Noise detection capacitor op Operational amplifier (including inverting amplifier) an1-ann Analog switch Lbr1-Lbrn Signal potential adjustment resistor

Claims (11)

[Claims] 1. In a transmission line for communicating digital data using an unbalanced signal line, a noise detection signal line provided in a transmission cable together with other signal lines, and reception of the digital data. A noise detecting means for detecting noise superimposed on the signal line by connecting to the noise detecting signal line in a section, and all the other elements in the transmission cable corresponding to the noise level detected by the noise detecting means. And a signal line noise correction means for canceling the input noise level superimposed on the signal line of FIG. 2. The control means for causing the signal line noise correction means to execute a correction for canceling the input noise level for a certain period of time according to the wavelength of the noise detected by the noise detection means. The interface circuit described in. 3. The interface circuit according to claim 1, wherein the noise detecting means is a filter circuit having the same characteristics as a low-pass filter of the other signal line including a resistor and a capacitor. 4. The signal line noise correction means includes an operational amplifier that generates an in-phase correction output from the output of the noise detection means, and the correction output of the operational amplifier for each reception element of all the other signal lines. 4. The interface circuit according to claim 1, further comprising an analog switch connected to the ground terminal. 5. The switching means for measuring the wavelength of the noise detected by the noise detecting means, and switching the analog switch from the ground side to the operational amplifier side for a certain period of time in accordance with the measured wavelength. The interface circuit according to claim 4, further comprising a wavelength measuring circuit that outputs a signal. 6. The signal line noise correction means includes an inverting amplifier that generates an inverted output of an opposite phase from the output of the noise detection means as a correction output, and an input line of each of the reception elements of all the other signal lines. A plurality of signal level correcting resistors each having one end thereof connected, and a plurality of analog switches respectively connecting the correction output of the inverting amplifier to the plurality of signal level correcting resistors. The interface circuit according to any one of Items 1 to 3. 7. The control means measures the wavelength of the noise detected by the noise detection means, and switches the plurality of analog switches from the open side to the close side for a certain period of time according to the measured wavelength. The interface circuit according to claim 4, further comprising a wavelength measuring circuit that outputs a switching signal. 8. The interface circuit according to claim 1, wherein the signal line for noise detection uses an empty signal line of the transmission cable. 9. The interface circuit according to claim 5, wherein the wavelength measuring circuit includes a counter for measuring the wavelength. 10. A reception section of a transmission line for communicating digital data using an unbalanced signal line, wherein noise superimposed on a signal line for noise detection provided on a transmission cable together with other signal lines A noise detection step of detecting, and a signal line noise correction step of canceling an input noise level superimposed on all the other signal lines in the transmission cable corresponding to the noise level detected in the noise detection step. A noise correction method for an interface circuit. 11. A wavelength measuring step for measuring a wavelength of noise detected in the noise detecting step, and a correction for canceling the input noise level in the signal line noise correcting step according to the wavelength measured in the wavelength measuring step. 11. The noise correction method for an interface circuit according to claim 10, further comprising a control step of performing control for executing the above for a certain period of time.