JP2000032339A - Signal switching circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a signal switching circuit, with which an audio video signal composed of a video signals and left and right audio signals and left and right headphone signals can be outputted while being switched to output both the signals from one jack, with simple configuration. SOLUTION: When a microcomputer 2 detects a plug is connected to a jack 1, the microcomputer 2 switches 1st-3rd switches to the side of an input terminal B. When a four-pole mini plug for outputting the audio video signal is connected, a transistor Q2 is not turned into a connected state but when a stereo mini plug for outputting the headphone signals is connected, the transistor Q2 is turned into the connected state. By detecting the presence/absence of signals at an AHDET terminal, the microcomputer 2 changes over the 1st-3rd switches.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a camera-integrated VT.
R and the like, provided in a relatively small video and audio equipment such as an audio / video signal (hereinafter, A
The present invention relates to a signal switching circuit that can switch and output both signals so that both signals can be output from one jack.

[0002]

2. Description of the Related Art In the field of a camera-integrated VTR, devices employing a DV system for recording a compressed signal compressed by using digital information compression technology on a smaller video cassette are increasing. The transformation is more advanced than ever.

Under such circumstances, for example, in a camera-integrated VTR adopting a DV system, a DC adapter for power supply is provided in addition to an output terminal for video and audio signals, despite its small size. It is necessary to provide various input / output terminals such as a terminal, a DV terminal for inputting / outputting a DV system compressed signal, and a microphone connection terminal for connecting an external microphone.

[0004] Therefore, unless one connection terminal is shared for input and output of a plurality of signals, the number of connection terminals on the camera-integrated VTR body becomes too large, and the layout of these connection terminals and the camera There have been problems such as limitations in determining the design of the body VTR itself.

[0005] FIG. 2 is mounted on a small-sized audiovisual device in which a signal input / output terminal cannot be provided much as described above.
A conventional signal switching circuit that can automatically switch and output an AV signal and a headphone signal in accordance with a connected device. FIG.
It is a figure which shows a polar mini plug and a stereo mini plug attached to the headphone signal cable.

[0006] In the signal switching circuit shown in FIG.
A jack to which either one of the pole mini plug or the stereo mini plug is selectively connected, 3 detects that the plug is connected to the jack 1, and the connected plug is a four pole for AV signal. Whether the plug is a mini plug or a stereo mini plug for headphone signals is determined, and a first switch (SW1), a fourth switch (SW4), and a fifth switch (SW5) are determined according to the determination result. The microcomputer that switches between Also, V
cc1 is a first voltage source connected to the 1F section of the jack 1 via a resistor R1, and Vcc4 is a fourth voltage source connected to a selected terminal Z of a fifth switch (SW5) via a resistor R5. It is.

On the other hand, as shown in FIG. 3, a four-pole mini-plug attached to an AV signal cable and a stereo mini-plug attached to a headphone signal cable are used to transmit a plurality of different signals. It is divided into a signal transmission unit. Then, as shown in the figure, in the 4-pole mini plug for AV signals, in order from the tip, portion A is a left channel audio signal, portion B is a video signal, portion C is GND, and portion D is a right channel audio signal. In the stereo mini-plug for headphone signals, part A is assigned to the left channel headphone signal, part B is assigned to the right channel headphone signal, and parts C and D are assigned to GND in order from the tip. Have been.

[0008] When the plugs are connected to the jack 1 of the signal switching circuit shown in FIG.
, A first signal terminal 1A, a second signal terminal 1B, a ground terminal 1C, and a third signal terminal 1D.

As described above, a four-pole mini plug or a stereo mini plug is connected to the jack 1. In the signal switching circuit shown in FIG. 2, as described below, the plug is changed according to the potential at the PDET terminal of the microcomputer 3. Are connected, and the potential at the AHDET terminal is detected in order to determine which plug is connected. Hereinafter, the operation of the conventional signal switching circuit shown in FIG. 2 will be described.

When the plug is connected to the jack 1, the 1E portion provided on the jack 1 is pushed away by the non-signal transmitting portion of the connected plug, and the 1E portion and the 1F portion come into contact. Accordingly, the 1E and 1F portions of the jack 1 are both grounded, and the voltage from the first voltage source Vcc1 is not applied to the microcomputer 3 side, and the PDET
The potential at the terminal has a value close to zero.

As described above, when the microcomputer 3 detects that the plug is connected to the jack 1, the microcomputer 3 switches the fifth switch (SW5) to the selected terminal Z side. In addition,
Also when the power is turned on to the signal switching circuit including the microcomputer 3 after the plug is connected to the jack 1, the microcomputer 3 can detect that the plug is connected, and the fifth switch (S
W5) can be switched to the selected terminal Z side.

When the fifth switch (SW5) is switched to the selected terminal Z side, the current from the fourth voltage source Vcc4 is applied to the selected terminal Z of the fifth switch (SW5) and the first signal terminal 1A. Is supplied to the portion A of the plug connected via the. At this time, as shown in FIG. 3, the impedance of the connection destination of the portion A differs between the case where the 4-pole mini plug for the AV cable is connected and the case where the stereo mini plug for the headphone cable is connected. I have.

At this time, the voltage from the fourth voltage source Vcc4 is
The voltage is divided by the resistance value of the resistor R5 and the impedance before the plug connected thereto. For example, when a 4-pole mini-plug for an AV cable is connected, the impedance before the portion A is several tens KΩ. Since the above is relatively high, the potential detected at the AHDET terminal of the microcomputer 3 becomes relatively high. On the other hand, when the stereo mini-plug for the headphone cable is connected, the impedance detected at the AHDET terminal of the microcomputer 3 is relatively low because the impedance ahead of the portion A is relatively low at several hundreds Ω or less. .

In this manner, the potential at the AHDET terminal of the microcomputer 3 depends on whether the plug connected to the jack 1 is a four-pole mini plug for an AV cable or a stereo mini plug for a headphone cable. Therefore, the microcomputer 3 can determine which plug is connected based on this, and when it is determined that the four-pole mini-plug is connected, the first
Switch (SW1), the fourth switch (SW4) and the fifth switch (SW5) are switched to the selected terminal X side, and when it is determined that the stereo mini plug is connected, the first switch (SW1), the fourth switch (SW4) and the fifth switch (SW5) are switched to the selected terminal Y side.

[0015]

However, in the conventional signal switching circuit described above, the fifth switch (SW)
5) is a terminal X to be selected when outputting the AV signal.
And a selected terminal Z for supplying a current from the fourth voltage source Vcc4 to a connected plug, in addition to a selected terminal Y selected when outputting a headphone signal,
The configuration of the three-input changeover switch increases the circuit scale and is disadvantageous in cost.

In order to switch the first switch (SW1), the fourth switch (SW4) and the fifth switch (SW5), the microcomputer 3 outputs two types of switching signals indicated by switching 1 and switching 2. Therefore, there is a problem that the limited number of pins of the microcomputer 3 is pressed down.

Further, in the conventional signal switching circuit, A of the microcomputer 3
If the potential at the HDET terminal is higher than a predetermined threshold level, it is determined that a four-pole mini plug for an AV cable is connected. It is necessary to set the threshold level to about 1/2 of the operating voltage of the microcomputer 3.

Here, the voltage from the fourth voltage source Vcc4 is
Since the voltage is applied to the AHDET terminal of the microcomputer 3 and also to the plug connected via the jack 1 at the same time, the connection is made at the moment when the fifth switch (SW5) is switched to the selected terminal Z side. There is a case where noise is emitted from the device, and if it is too large, there is a problem that the quality is not good.

[0019]

SUMMARY OF THE INVENTION In order to solve the above problems, a signal switching circuit according to the present invention is for outputting an audio video signal comprising a video signal and left and right audio signals to an externally connected device. And a jack to which a four-pole plug and a headphone plug for outputting left and right headphone signals are selectively connected, and outputs a test signal to determine the type of plug connected to the jack, A discriminating means for outputting a discrimination signal according to the impedance of a plug connection destination; a first state in which the video signal and the left and right audio signals are selected and output to the jack; Switching means for selecting a headphone signal and an inspection signal from the discriminating means and outputting the selected signal to the jack; and a discriminating signal output from the discriminating means. A microcomputer for switching the switching means to the first state or the second state, and the jack is capable of transmitting a signal to each pole of the four-pole plug separately. And the switching means is constituted by first to third changeover switches, wherein the first changeover switch outputs the video signal in the first state and the second changeover switch has the second connection terminal. In the state, the right headphone signal is output to the second connection terminal, and the second switch outputs the left audio signal in the first state and the left headphone signal in the second state. A headphone signal is output to the first connection terminal, and the third switch outputs the right audio signal in the first state and the identification signal in the second state. The identification signal from the means is output to the fourth connection terminal, the third connection terminal is grounded, and the signal level of the test signal output by the determination means is equal to the right audio signal. It is characterized in that the signal level is set lower than the signal level of the signal.

[0020]

FIG. 1 shows a signal switching circuit according to an embodiment of the present invention. Hereinafter, a signal switching circuit according to an embodiment of the present invention will be described with reference to the drawings. The same components as those of the conventional signal processing circuit are denoted by the same reference numerals, and the description thereof will be partially omitted.

In FIG. 1, reference numeral 1 denotes a jack to which either one of a 4-pole mini plug attached to an AV signal cable and a stereo mini plug attached to a headphone signal cable is selectively connected, and 2 denotes a jack. The PDET terminal detects that a plug has been connected to the jack 1, and determines whether the connected plug is a 4-pole mini-plug for AV signals or a stereo mini-plug for headphone signals by the AHDET terminal. The microcomputer outputs a switching signal to the first switch (SW1) to the third switch (SW3) according to the result of the determination.

The jack 1 includes a first connection terminal 1A, a second connection terminal 1B, a ground terminal 1C, and a third connection terminal 1.
D, and 1 to detect that the plug is connected
The first connection terminal 1A, which is constituted by an E section and a 1F section,
Second connection terminal 1B, ground terminal 1C, third connection terminal 1
D is provided to be connected to each of the parts A to D of the plug shown in FIG. 3 when the plug is connected.

The SW 1 receives a video signal at the selected terminal X and a right channel headphone signal at the selected terminal Y, and switches one of the signals of the jack 1 based on a switching signal from the microcomputer 2. Second connection terminal 1
A first switch SW2 that selectively outputs to B, a left channel audio signal is input to a selected terminal X and a left channel headphone signal is input to a selected terminal Y, based on a switching signal from the microcomputer 2 A second switch SW3 for selectively outputting one of the signals to the first connection terminal 1A of the jack 1 has a right channel audio signal input to the selected terminal X and a transistor Q1 connected to the selected terminal Y. A fourth signal for receiving a signal from the emitter side and selectively outputting one of the signals to the third connection terminal 1D of the jack 1 based on a switching signal from the microcomputer 2;
Switch.

Vcc1 is connected to jack 1 via resistor R1.
The first voltage source Vcc2 connected to the 1F section of
Vcc3 is a second voltage source connected to the base side of the transistor Q1 via the second transistor 2 and the third voltage source connected to the emitter side of the transistor Q2. The collector side of the transistor Q1 is connected to the base side of the transistor Q2 via a resistor R3, and the emitter side and the base side of the transistor Q2 are connected via a resistor R4.

At this time, the second voltage source Vcc2 is set to about 1V, the third voltage source Vcc3 is set to about 3V, and the added resistance value of the resistance value of the resistor R3 and the resistance value of the resistor R4 is A.
The impedance is set to several tens KΩ or less, which is the impedance at the portion D of the 4-pole mini plug for the V signal.

In the signal switching circuit according to the embodiment of the present invention, when a four-pole mini plug or a stereo mini plug is connected to the jack 1 in the above-described configuration, the potential at the PDET terminal of the microcomputer 2 is changed. The potential at the AHDET terminal is detected to detect that the plug is connected and to determine which plug is connected. Hereinafter, the operation of the signal switching circuit according to the embodiment of the present invention will be described.

First, when no plug is connected to the jack 1, the 1F portion of the jack 1 is in the released state.
The voltage obtained by dividing the voltage from the first voltage source Vcc1 by the resistor R1 and the internal resistance of the microcomputer 2 is applied to the PD of the microcomputer 2
Applied to the ET terminal. Therefore, the PD in the microcomputer 2
At the ET terminal, the potential divided at this time is detected.

On the other hand, when the plug is connected to the jack 1, the 1E portion provided on the jack 1 is pushed away by the non-signal transmitting portion of the connected plug, and the 1E portion and the 1F portion come into contact. Therefore, the 1E section and the 1F section of the jack 1 are both grounded, and the voltage from the first voltage source Vcc1 is
PD is not applied to the microcomputer 2 side,
The potential at the ET terminal has a value close to zero.

In this manner, the microcomputer 2 can detect that the plug is connected to the jack 1.
When detecting that the plug is connected, the microcomputer 2 switches the first to third switches (SW1 to SW1).
3) is switched to the selected terminal Y side. Jack 1
When the power is turned on to the signal switching circuit including the microcomputer 2 after the plug is connected to the microcomputer 2, the microcomputer 2 can detect that the plug is connected, and the first to third switches (SW
1 to SW3) can be switched to the selected terminal Y side.

When the third switch (SW3) is switched to the selected terminal Y side, the emitter side of the transistor Q1 and the portion D of the plug connected to the jack 1 are in a connected state, and a four-pole miniature AV cable is used. Since the impedance of the connection destination of the portion A is different between the case where the plug is connected and the case where the stereo mini plug for the headphone cable is connected, the operating state of the transistor Q2 is accordingly changed.

At this time, the current flowing through the transistor Q1 is a current inversely proportional to the magnitude of the emitter resistance of the transistor Q1 if the second voltage source Vcc2 and the resistance R2 are constant, but the transistor Q2 flows through the transistor Q1. The connection state is established only when the current is large.

That is, when a four-pole mini plug for an AV cable is connected, the impedance ahead of the portion A,
That is, since the emitter resistance of the transistor Q1 is several tens KΩ or more, only a small current flows through the transistor Q1. Therefore, the transistor Q2 is not in the connected state, and the potential on the collector side of the transistor Q2 detected at the AHDET terminal of the microcomputer 2 has a value close to zero.

On the other hand, when the stereo mini plug for the headphone cable is connected, the emitter side of the transistor Q1 is grounded and the emitter resistance becomes 0, so that only the transistor Q2 is connected to the transistor Q1. Sufficient current flows. Therefore, the AH of the microcomputer 2
The potential on the collector side of the transistor Q2 at this time is detected by the DET terminal.

As described above, the predetermined potential is detected at the AHDET terminal of the microcomputer 2 only when the plug connected to the jack 1 is a stereo mini plug for a headphone cable. It is possible to determine whether or not the plug is connected.

When the microcomputer 2 determines that the four-pole mini-plug is connected, it switches the first to third switches (SW1 to SW3) to the selected terminal X side,
When it is determined that the stereo mini plug is connected, the first to third switches (SW1 to SW3) are switched to the selected terminal Y side.

As described above, in the signal switching circuit according to the embodiment of the present invention, the plug connected to the jack 1 is a 4-pole mini plug for an AV cable, or a stereo mini plug for a headphone cable. Are determined by the first switch (SW1) to the third switch (S1).
W3) is switched to the selected terminal Y side, and the transistor Q2
Is detected by detecting the collector-side potential of the resistor R2.
, The voltage applied to the plug can be reduced. Therefore, the third switch (SW3) is connected to the selected terminal Y.
The noise generated from the connected device at the moment of switching to the side is negligible.

When the first switch (SW1) to the third switch (SW3) are switched to the selected terminal Y while the 4-pole mini plug for the AV cable is connected, the left switch A channel headphone signal and a right channel headphone signal are output from the first signal terminal 1A and the second signal terminal 1B. However, since these output signals are generally output after cutting the DC component, noises due to the fluctuation of the DC component as described above are not output from these outputs.

As a matter of course, whether the plug connected to the jack 1 is a 4-pole mini plug for an AV cable,
Alternatively, when determining whether the stereo mini plug is for a headphone cable, the left channel headphone signal and the right channel headphone signal are first switched (S
If the mute is performed before the W1) and the second switch (SW2), the device connected to the jack 1 will not be affected.

[0039]

According to the signal switching circuit of the present invention, the first to third switching switches can be two-input signal switching switches, so that not only the switching means can be easily configured but also the microcomputer can be used. Since the first to third changeover switches can be switched by only one changeover signal, there is an effect that the limited number of pins of the microcomputer is not pressed.

Also, since the signal level of the test signal output from the discriminating means is set lower than the signal level of the right audio signal, the signal emitted from the connected device when discriminating the connected plug is determined. Noise can be minimized.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a signal switching circuit according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining a conventional signal switching circuit.

FIG. 3 is a diagram showing each part and impedance of a 4-pole mini plug and a stereo mini plug.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Jack 1A ... 1st signal terminal 1B ... 2nd signal terminal 1C ... Ground terminal 1D ... 3rd signal terminal 2, 3 ... Microcomputer Vcc1-Vcc4 ... 1st-4th voltage source SW1-SW5 ... First to fifth switches Q1, Q2: transistors R1 to R5: resistors

Claims (3)

[Claims] 1. A four-pole plug for outputting an audio / video signal comprising a video signal and left and right audio signals to an externally connected device and a headphone plug for outputting left and right headphone signals are selectively connected. A determination unit that outputs an inspection signal to determine a type of a plug connected to the jack, and outputs a determination signal according to an impedance of a connection destination of the plug; Switching means for selecting the video signal and the left and right audio signals and outputting them to the jack, while in the second state, selecting the left and right headphone signals and the inspection signal from the discriminating means and outputting them to the jack A microcomputer for switching the switching means to a first state or a second state in accordance with a determination signal output from the determination means And a signal switching circuit. 2. The jack comprises first to fourth connection terminals capable of separately transmitting signals to respective poles of the four-pole plug, and the switching means includes first to third switching switches. The first changeover switch outputs the video signal in the first state and outputs the right headphone signal to the second connection terminal in the second state, the second changeover switch Outputting the left audio signal in the first state and outputting the left headphone signal to the first connection terminal in the second state, wherein the third switch is connected to the first switch. In the state, the right audio signal is output, and in the second state, the identification signal from the identification means is output to the fourth connection terminal, and the third connection terminal is grounded. Signal switching circuit according to claim 1. 3. The signal switch according to claim 1, wherein a signal level of the test signal output by the determination unit is set to a lower level than a signal level of the right audio signal. circuit.