JP2001326539A - Input interface circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To substantially transmit only a signal component to a subsequent stage and to also reduce costs by suppressing a noise component. SOLUTION: In this input interface circuit 10, the voltage of an analog signal VSG with the ground level S-GND of a transmitting side device as reference is converted into current IC2 corresponding to the magnitude of the voltage through a V/I converting part 11, and the current IC2 is next converted into a voltage signal Vo with the ground level R-GND of a receiving side device as standard through an I/V converting part 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an input interface circuit for analog signals, and more particularly, to devices having a noise potential difference between a signal / ground connecting transmission / reception for transferring a video signal. The present invention relates to a technology of an input interface adapted to prevent the noise component from being transmitted to a subsequent stage when connected.

[0002]

2. Description of the Related Art As an example of connecting devices having a noise potential difference between the signal and ground described above, an example of a connection structure in a case of a vehicle-mounted device is shown in FIG. In FIG. 1, reference numeral 1 denotes an in-vehicle device (navigation unit) that supplies a video signal VSG, and 2 denotes an in-vehicle device (monitor) that receives the video signal VSG. The navigation unit 1 includes a control unit 1a for controlling arithmetic processing of data related to navigation and the like.
and a video output unit 1b that outputs a video signal VSG for display based on the control from a. On the other hand, monitor 2
Is an input interface unit 2a for receiving a video signal VSG supplied from the navigation unit 1, and a video signal VS output from the input interface unit 2a.
And a video processing unit 2b for processing G. In each of the in-vehicle devices 1 and 2, S-VB and R-VB indicate power supply lines, and S-GND and R-GND indicate ground lines.

Reference numeral 3 denotes an on-board battery, 4 denotes an AC generator (alternator) driven in conjunction with operation of an engine (not shown), and 5 denotes a diode for rectifying an AC voltage generated by the alternator 4. The voltage (DC voltage) rectified through the diode 5 is charged into the battery 3 (power supply voltage VB), and the on-vehicle devices 1 and 2 are charged.
Are supplied to the power lines S-VB and R-VB.

[0004] Each of the on-vehicle devices (navigation unit 1, monitor 2) and power supply (battery 3, alternator 4) are installed at different places in the vehicle body.
Also, lines such as cables for connecting between each other (power supply lines, ground lines, signal lines) are routed accordingly. Therefore, each line connecting between the power supply and each vehicle-mounted device and between each vehicle-mounted device has equivalent resistances r1 to r6 (portions surrounded by broken lines) as illustrated.

In such a connection configuration, the video signal VSG from the navigation unit 1 to the monitor 2 is 75
It is generally input as an unbalanced type of Ω system,
In the monitor 2, the video signal VSG is received by the input interface unit 2a and passed to the subsequent video processing unit 2b. FIG. 2 shows a configuration of a video signal input interface circuit according to an example of the prior art, and shows a circuit configuration of the input interface unit 2a corresponding to the configuration of FIG.

As shown in the figure, the input interface circuit has an amplifier circuit (input buffer) including an npn transistor TR connected in an emitter follower. In addition, an input resistor R1 and an emitter side of the transistor TR are provided. And the collector of the transistor TR.
It has resistors R3 and R4 for bias connected between the base and between the base and the emitter, respectively, and capacitors C1 and C2 for AC coupling between the input and output, respectively.

[0007] Note that r1 to r6 represent the equivalent resistance of each line connecting between the power supply and each of the in-vehicle devices 1 and 2 as described above.

[0008]

As described above, in the conventional connection configuration, each line connecting between the power supply and each of the on-vehicle devices 1 and 2 and between each of the on-vehicle devices 1 and 2 has a corresponding resistance value. (Equivalent resistances r1 to r6). For this reason, when a ripple current flows through each power supply / ground line (r1, r2, r5, r6) due to the operation of the alternator 4, the ground lines S-GND, R of the on-vehicle devices 1, 2
A potential difference between −GND occurs according to the magnitude of the equivalent resistance r3.

This potential difference is superimposed on the video signal VSG output from the navigation unit 1 and
Is input to the input interface unit 2a, and is sent to the subsequent video processing unit 2b as "noise". Noise caused by such a potential difference between the ground lines is also called “common mode noise”. In order to eliminate the potential difference between the in-vehicle devices 1 and 2 which is a cause of such common mode noise, it is sufficient if the resistance value of the line connecting the in-vehicle devices 1 and 2 can be made 0, but in practice it is not Near possible.

[0010] The effect of common mode noise is monitored on monitor 2.
In this case, the video processing unit 2b cannot perform normal video signal processing, and therefore, there is a disadvantage that accurate information may not be displayed on a display controlled by the video processing unit 2b. If accurate information is not displayed on the display, a user (e.g., a driver) who selects and uses necessary information based on the navigation information displayed on the display when the vehicle is traveling should provide convenience. Is rather cumbersome and inconvenient.

Therefore, as a technique for removing such common mode noise, for example, a differential amplification input method using an operational amplifier (hereinafter referred to as an "operational amplifier") has been proposed. One example is shown in FIG. FIG.
The input interface circuit shown in FIG. 2 is different from the configuration of the input interface circuit shown in FIG.
And an operational amplifier O between the AC coupling capacitor C1
The difference is that a differential amplifier circuit using P is provided. The differential amplifier circuit further includes a capacitor C3 and a resistor R5 connected in series to a non-inverting (+) input terminal of the operational amplifier OP, and a capacitor connected in series to an inverting (-) input terminal of the operational amplifier OP. C4 and a resistor R6, a resistor R7 connected between the non-inverted (+) input terminal and the ground line R-GND, and a resistor connected between the output terminal of the operational amplifier OP and the inverted (-) input terminal. Device R8.

In an input interface circuit including a differential amplifier circuit using such an operational amplifier OP, even if noise is superimposed on an input signal (video signal VSG), its operation principle (differential amplification input system) requires that It is possible to prevent noise from being transmitted to the output side (video processing unit). However, in the current technology, the audio signal (20H
Operational amplifiers that process signals having a relatively narrow frequency band, such as about z to 20 kHz, are widely used because they are inexpensive.
An operational amplifier having an amplification characteristic that covers a wide frequency band as in z) has a disadvantage that the cost is extremely high.

In addition, at least R (red), G (green), B (blue) and SY
Since four NC (synchronous) circuits are required and at least four operational amplifiers are required accordingly, there is a problem that it is considerably difficult to apply to an input interface of a consumer device in terms of cost. SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems in the related art, and has an input interface circuit capable of suppressing a noise component, enabling transmission of substantially only a signal component to a subsequent stage, and reducing costs. The purpose is to provide.

[0014]

According to the present invention, there is provided an input interface circuit provided in a receiving device connected to a transmitting device for supplying an analog signal. A voltage / current (V / V) for converting the voltage of the analog signal based on the ground level of the transmitting device into a current corresponding to the magnitude of the voltage.
I) a conversion unit, and a current / current for converting the converted current into a voltage signal based on the ground level of the receiving device.
An input interface circuit comprising a voltage (I / V) conversion unit is provided.

According to the input interface circuit of the present invention, the input terminal of the receiving device converts the voltage of the analog signal with respect to the ground level of the transmitting device through the V / I converter to the magnitude of the voltage. After converting to a current according to
The converted current is converted into a voltage signal based on the ground level of the receiving device through the I / V converter. That is, the ground line of the first stage V / I converter and the ground line of the next stage I / V converter are separate systems.

Therefore, even if a potential difference due to noise or the like is induced between the ground line between the transmitting device and the receiving device, the influence of the noise potential difference does not spread to the circuit unit after the I / V conversion unit. . The reason is that the V / I converter performs V / I conversion based on the ground level of the transmitting device, and the I / V converter performs I / V conversion based on the ground level of the receiving device. This is because the noise potential difference between the ground lines is not involved in any of the conversion processes. As a result, only the signal components which are not affected by the noise potential difference can be transmitted to the circuit units subsequent to the I / V conversion unit.

Also, since the V / I conversion section and the circuit section subsequent to the I / V conversion section have separate ground lines, the differential amplification input using a comparatively expensive operational amplifier as in the prior art. A required input interface circuit can be constructed using relatively inexpensive transistor elements, resistance elements, and the like without employing a circuit configuration of the system. This contributes to cost reduction.

[0018]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 4 shows a configuration of a video signal input interface circuit according to an embodiment of the present invention. The video signal input interface circuit 10 according to the present embodiment is suitably used for in-vehicle equipment, and for example, as shown in FIG. 1, a video signal (analog signal) supplied from the navigation unit 1
Input interface unit 2a of monitor 2 for processing VSG
Used for

In the following description, the navigation unit 1 is a “transmitting device” in the sense of a device transmitting the video signal VSG, and the monitor 2 is a “reception device” in the sense of a device receiving the video signal VSG. Side device ”. In the input interface circuit 10 of the present embodiment, 11
Denotes a voltage / current (V / I) converter which is a feature of the present invention. The V / I converter 11 includes an npn transistor TR1 for inputting a video signal VSG to a base, an emitter of the transistor TR1 and a ground line S of a transmitting device.
-GND, a resistor R12 connected between the collector of the transistor TR1 and the power supply line R-VB, and a pnp transistor TR2 whose base is connected to the collector of the transistor TR1. ,
The emitter of the transistor TR2 and the power supply line R-V
B and a resistor R13 connected between the two.

The V / I converter 11 comprises a two-stage V / I converter as will be described later. The first stage V / I converter comprises a transistor TR1 and resistors R11 and R12. The V / I converter of the stage includes a transistor T
R2 and a resistor R13. Also,
Reference numeral 12 denotes a current / voltage (I / V) converter, which includes a collector of the transistor TR2 and a ground line R-
It is constituted by a resistor R14 connected between the ground and GND. The voltage signal Vo subjected to the I / V conversion through the resistor R14 is sent to a subsequent video processing unit as a signal that faithfully reproduces the original video signal VSG as described later.

Reference numeral 13 denotes a filter, and a resistor R15 and a capacitor C1 connected in series between the power supply line R-VB and the ground line S-GND of the transmitting device.
0. The filter 13 (resistor R15, capacitor C10) converts the ripple voltage superimposed on the power supply line R-VB as noise into the V / I converter 11
This is to prevent the operation from being affected.

Also, a resistor R15 and a capacitor C10
Is connected between the connection node N of the transistor TR1 and the base of the transistor TR1, a bias resistor R16 is connected between the base of the transistor TR1 and the ground line S-GN of the transmission-side device.
A resistor R17 for bias is also connected to D. Further, an input resistor R18 is provided between the input end of the video signal VSG and the ground line S-GND of the transmitting device.
Is connected.

C11 is a capacitor for connecting the input terminal of the video signal VSG to the base of the transistor TR1 in an AC manner, and C12 is an AC terminal for connecting the output terminal of the I / V-converted voltage signal Vo and the subsequent video processing unit. 3 shows a capacitor for coupling. As can be seen from the configuration shown, V /
The ground (GND) line of the I conversion unit 11 is connected to the ground (GND) of the circuit unit subsequent to the I / V conversion unit 12.
Line, that is, the ground line R-GN of the receiving device
D is electrically disconnected and electrically connected to the ground line S-GND of the transmitting device.

As described above, in the video signal input interface circuit 10 of the present embodiment, the V / I conversion unit 11 and the subsequent circuit units (including the I / V conversion unit 12) separate each ground line. It is characterized by a system. Further, a further feature of the present embodiment resides in that the characteristics of the first-stage transistor TR1 in the V / I converter 11 are actively used.

FIG. 5 shows the output current-voltage characteristics of the transistor TR1 when the emitter is grounded. The input current (base current I _B ) is 3 μA, 6 μA,.
.., 27 μA, the change of the output current (collector current Ic) with respect to the change of the output voltage (collector-emitter voltage V _CE ). It should be noted that the characteristics shown are measured under the condition that the ambient temperature is 25 ° C.

As can be seen from the characteristic diagram of FIG. 5, in the normal operating region (the region where V _CE is approximately 4-5 V or more), even if the output voltage V _CE changes by about 1-2 V, the output current Ic is not so large. It has not changed and has an almost constant value. In other words, the power supply voltage (R-VB) that determines the collector-emitter voltage V _CE and the ground potential (S-GND) of the transmitting device are slightly (1) due to superposition of noise or the like.
This means that even if it fluctuates, the collector current Ic having a substantially constant value can be obtained without the influence of the noise potential difference being exerted on the collector current Ic. The interface circuit 10 of the present embodiment positively utilizes this characteristic.

Hereinafter, the operation of the video signal input interface circuit 10 according to the present embodiment will be described with reference to FIGS. First, the video signal VSG from the transmitting device is transmitted to the V / I converter 11 via the capacitor C11.
Is input to the base of the transistor TR1 in the first stage of
The transistor TR1 is connected to a resistor R1 on the emitter side.
1 acts as an emitter follower amplifier, and allows a current (alternating current) proportional to the video signal VSG applied to both ends of the input resistor R18 to flow.

Further, a transistor TR1 having a common emitter is provided.
_Has a sufficiently large current amplification factor (h _FE ), the current flowing through the resistor R12 on the collector side (collector current IC
1) is the same current as this (except that the collector operates as a common-emitter amplifier, so the output to the next stage is inverted). At this time, from the characteristics of the transistor TR1 (see FIG. 5), the collector current IC1 is
It is not significantly affected by the fluctuation of the emitter-to-emitter voltage V _CE and depends only on the base input. That is, the collector current IC1
Is substantially unaffected by the fluctuation of the ground potential (S-GND) or the fluctuation of the power supply voltage (R-VB) of the transmitting device, and is substantially constant. And the resistor R on the collector side
A potential difference proportional to the collector current IC1 appears at both ends of the reference numeral 12.

This potential difference is input to the next stage V / I converter (transistor TR2, resistor R13), and the first stage V / I converter
/ I converter (transistor TR1, resistors R11, R1
V / I conversion is performed in the same manner as in 2), and the power supply voltage (R-VB)
Is converted to an almost constant value current (collector current IC2) which is not so much affected by the fluctuation of. This collector current IC2 is connected to a resistor R14 that constitutes the I / V converter 12.
Through the ground line R-GND. As a result, the collector current IC2 is connected across the resistor R14.
, A potential difference (voltage signal Vo) appears.

As described above, in the circuit configuration according to the present embodiment, the V / I conversion unit 11 performs the current (collector current) proportional to the voltage of the video signal VSG with reference to the ground level (S-GND) of the transmitting device. IC2) and functions as a kind of current source. Therefore, the I / V conversion unit 12
Since the impedance when looking at the / I conversion unit 11 is very large, the I / V conversion unit 12 uses the ground potential (S-GND) of the transmitting device as viewed from the ground potential (R-GND) of the receiving device. Fluctuation or power supply voltage (R-VB)
Of the V / I converter 11 (collector current IC2) without receiving the fluctuation of the potential (i.e., even if these fluctuations of the potential occur).
Can be converted to This voltage signal Vo is a signal based on the ground level (R-GND) of the receiving device.

In this way, a signal (voltage signal Vo) that faithfully reproduces the original video signal VSG can be obtained.
Moreover, a video signal (voltage signal) in which a noise component caused by a potential fluctuation or a power supply voltage (R-VB) fluctuation between the ground line S-GND of the transmitting device and the ground line R-GND of the receiving device is suppressed. Vo) can be obtained.

FIGS. 6A and 6B illustrate the degree of the noise removing effect. FIG. 6A shows the input / output voltage-frequency characteristics of the noise component according to the circuit configuration of this embodiment (FIG. 4).
(B) shows the input / output voltage-frequency characteristics of the noise component according to the circuit configuration of the conventional example (FIG. 2). Here, the “noise input” means that a noise voltage due to a potential fluctuation is induced between the ground line S-GND of the transmitting device and the ground line R-GND of the receiving device as shown in FIG. Means that a virtual signal source corresponding to the noise voltage is inserted.
In the circuit configuration shown in FIG. 4, the noise signal sources are the ground side of the input resistor R18 (the ground line S-GND of the transmitting device) and the ground line of the monitor (R-GND).
In the meantime, in the circuit configuration of FIG. 2, both ends of r3 (S
(Between −GND and R-GND), and this is referred to as “noise input”. The “noise output” refers to the noise level that appears at the point of the C12 output in FIG. 4 and the C2 output in FIG.

The values, voltage values, etc. of the respective elements employed in calculating the characteristics shown in FIG. 6 are as follows. This embodiment (FIG. 4) R11: 820Ω, R12: 470Ω, R13: 470
Ω, R14: 1.2 kΩ, R15: 10 kΩ, R16:
10kΩ, R17: 22kΩ, R18: 75Ω, C1
0: 47 μF, C11: 47 μF, C12: 47 μF,
VSG: 0V, R-VB: DC7V.

Conventional example (FIG. 2) R1: 75Ω, R2: 1 kΩ, R3: 10 kΩ, R4:
10 kΩ, C1: 47 μF, C2: 3.3 μF, VS
G: 0 V, R-VB: DC 5.3 V. As is clear from the characteristic diagram of FIG. 6, the signal frequency is 10H
When the frequency changes from z to 10 MHz over a wide band, a noise output of a level that is not so different from the level of the noise input appears in the conventional example (see FIG. 6B). The level is almost equal to 0 (see FIG. 6A).

In other words, while the noise component is transmitted to the subsequent video processing unit in the conventional example, it is possible to prevent the noise component from being transmitted to the video processing unit in the present embodiment. Means Moreover, in this embodiment, a wide frequency band (10 Hz to 10 M
Hz), the relatively inexpensive transistors and resistors can be used without using expensive operational amplifiers for processing video signals as in the prior art (FIG. 3). A required input interface circuit can be constructed by using such a method. That is, an expensive operational amplifier is not required, and the cost can be reduced.

Further, since the input interface circuit 10 of the present embodiment is provided with the filter 13 (the resistor R15 and the capacitor C10), even when the ripple voltage is superimposed on the power supply line R-VB, the ripple voltage becomes V as noise. It is possible to prevent the operation of the / I conversion unit 11 from being affected. In the embodiment shown in FIG.
As a transistor constituting the I conversion section 11, np
n transistor TR1 and pnp transistor TR at the next stage
Although the case of using 2 has been described, it goes without saying that the number, type, combination of conductivity types, etc. of the transistors used are not limited to this. In short, the V / I converter 11
However, as described above, it is sufficient if the configuration is such that the V / I conversion operation can be performed in two stages.

For example, when the combination of the conductivity types of the transistors TR1 and TR2 is reversed from that of the embodiment of FIG.
A pnp transistor in the first stage of the / I conversion unit 11 and n in the next stage
A pn transistor may be used. Further, a MOS transistor (n-channel type, p-channel type) can be used instead of the bipolar transistor used in the embodiment of FIG.

The selection of such elements (conductivity type, type, installation number, etc.), including other elements such as resistors and capacitors, can be appropriately changed in accordance with the required circuit design conditions. Will be apparent to those skilled in the art.

[0039]

As described above, according to the input interface circuit of the present invention, the first-stage circuit section (V / I conversion section) and the subsequent circuit sections (including the I / V conversion section) include: By using a separate system for each ground line, it is possible to suppress noise components and transmit substantially only signal components to the subsequent stage, and to reduce costs.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a problem that occurs when on-vehicle devices having a noise potential difference are connected to each other.

FIG. 2 is a circuit diagram showing a configuration of a video signal input interface circuit according to an example of the related art.

FIG. 3 is a circuit diagram showing a configuration of a video signal input interface circuit according to another example of the related art.

FIG. 4 is a circuit diagram showing a configuration of a video signal input interface circuit according to an embodiment of the present invention.

FIG. 5 shows output current of a transistor in the circuit of FIG.
FIG. 3 is a diagram illustrating voltage characteristics.

6 is a diagram showing input / output voltage-frequency characteristics of a noise component of the circuit of FIG. 4 in comparison with the case of a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Navigation unit (transmission side apparatus) 2 ... Monitor (reception side apparatus) 10 ... Video signal input interface circuit 11 ... Voltage / current (V / I) conversion part 12 ... Current / voltage (I / V) conversion part 13 Filters C10 to C12 Capacitors IC1 and IC2 Collector currents R11 to R18 Resistors R-VB Power line of receiving device (monitor) R-GND Ground line of receiving device (monitor) S-GND Transmitter (Navigation unit)
TR1, TR2: Transistor VSG: Video signal (analog signal) Vo: Voltage signal after I / V conversion (analog signal)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5J090 AA01 AA45 CA04 CA41 CA47 CA87 CN04 HA02 HA10 HA19 HA25 HA29 KA00 KA01 KA03 KA27 KA41 KA51 MA01 MA21 SA07 SA08 TA01 TA02 TA03 5J092 AA01 AA45 CA04 CA41 CA47 CA87 HA25 HA19 HA KA00 KA01 KA03 KA27 KA41 KA51 MA01 MA21 SA07 SA08 TA01 TA02 TA03 UR07 5K046 AA01 BA01 BA05 BB03 CC04 CC26 ZZ09 5K052 AA01 AA11 BB29 BB35 DD08 DD12 DD13 DD20 FF11 GG12

Claims (4)

[Claims] An input interface circuit provided in a receiving device connected to a transmitting device that supplies an analog signal, wherein the voltage of the analog signal with respect to a ground level of the transmitting device is set to the voltage. And a current / voltage converter for converting the converted current into a voltage signal based on the ground level of the receiving device. An input interface circuit characterized by the following. 2. The voltage / current conversion section includes: a first transistor that inputs the analog signal to a base;
A first resistor connected between the emitter of the first transistor and the ground line of the transmitting device; a second resistor connected between the collector of the first transistor and a power supply line; A second transistor having a base connected to a collector of the first transistor, and a third resistor connected between an emitter of the second transistor and the power supply line; 2. The input interface circuit according to claim 1, wherein a collector of the transistor is connected to an input terminal of the current / voltage converter. 3. The current / voltage converter includes a fourth resistor connected between a collector of the second transistor and a ground line of the receiving device, wherein the fourth resistor is connected to the second resistor. 3. The input interface circuit according to claim 2, wherein a voltage signal obtained by current / voltage conversion is transmitted to a subsequent stage. And a fifth resistor and a capacitor connected in series between the power supply line and a ground line of the transmitting device, wherein a connection node of the fifth resistor and the capacitor is provided. The input interface circuit according to claim 2, wherein the input interface circuit is connected to a base of the first transistor via a sixth resistor.