JP3717865B2 - Earphone detection circuit - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an earphone detection circuit. More particularly, the present invention relates to an earphone detection circuit that does not have a common ground terminal for left and right audio channels.
[0002]
[Prior art]
At present, the majority of audio signal output devices such as recording devices, camcorders, televisions, portable computers, etc. have two main audio output channels. These audio signal output devices include a socket for inserting an earphone plug so that the sound can be heard through the earphone in addition to the built-in speaker. Furthermore, these audio signal output devices incorporate an automatic detection device for automatically switching the audio providing mode. Thereby, when the earphone plug is inserted into the socket, an audio signal is sent to the earphone or other externally connected device. Conversely, if nothing is inserted into the socket, the audio signal is sent to a built-in device such as a pair of speakers.
[0003]
However, in order to realize the automatic switching function of the output path, an appropriate earphone drive circuit that can detect insertion of the earphone (or other output device) is necessary. FIG. 1 shows a conventional earphone driving circuit and a corresponding earphone detection circuit. In FIG. 1, the left and right audio channels are amplified through amplifiers 102 and 104, respectively. Thereafter, the direct current (DC) component of the amplified signal is removed by capacitors 106 and 108. Finally, the signal is fed to the earphone through contact points 118 and 120, respectively. When there is no earphone plug inside the socket, the contact point 124 and the audio signal transmission line 112 are in contact. Since the resistance value of the resistor 122 is significantly higher than the resistance value of the resistor 126, the detector 130 detects a zero voltage from the detection line 132. Thereby, the detector 130 correctly detects that the earphone plug is not inside the socket. Then, the transmission of the audio signal via the earphone drive circuit is stopped. Conversely, if the earphone plug is inserted into the socket, the contact point 124 is disconnected from the audio signal transmission line 112. As a result, a voltage of about V _CC is supplied to the detector 130. Thereby, the detector 130 correctly detects the presence of the earphone plug. Thus, the audio signal is transmitted through the earphone driving circuit.
[0004]
It may seem that there is no problem with this circuit arrangement. However, capacitors must have a large capacity and therefore tend to occupy a large volume. This is because a large capacitance is required for a good frequency response. Therefore, it is difficult to reduce the overall volume of the earphone drive circuit.
[0005]
In order to solve the problem of the large capacity of the capacitor, an earphone drive circuit having no capacitor has been developed as shown in FIG. 2A. As shown in FIG. 2A, since the potential at the center point serves as a common ground terminal, the earphone detection circuit 230 including the resistors 122 and 126 and the detection line 132 as shown in FIG. 1 cannot be used. Therefore, a special earphone detection circuit 230 suitable for the earphone drive circuit is required.
[0006]
[Problems to be solved by the invention]
In summary, conventional techniques for detecting the presence of an earphone include large volume circuits or are less efficient.
[0007]
An object of the present invention is to provide an earphone detection circuit having no capacitor. The earphone detection circuit detects the presence or absence of the earphone in cooperation with the earphone drive circuit, and sends an audio signal to the correct circuit according to the detection result.
[0008]
[Means for Solving the Problems]
In order to achieve these and other advantages, and in accordance with the problems of the present invention, as embodied and generally described herein, the present invention provides an earphone detection circuit that detects the insertion / extraction status of an earphone drive circuit. provide. The earphone drive circuit includes a left audio channel terminal, a right audio channel terminal, a virtual ground terminal, and a detection terminal. The earphone detection circuit includes a transistor, a plurality of resistors, a capacitor, and a detector. The transistor has four connection terminals. Both the first terminal and the fourth terminal are electrically connected, and an operating voltage is supplied to both. One terminal of the first resistor and the first terminal of the transistor are electrically connected. The other terminal of the first resistor and the second terminal of the transistor are electrically connected. One terminal of the second resistor and the third terminal of the transistor are both electrically connected. The other terminal of the second resistor is connected to the ground terminal. One terminal of the third resistor and the second terminal of the transistor are both electrically connected. The other terminal of the third resistor and the detection terminal of the earphone drive circuit are both electrically connected. One end of the capacitor is electrically connected to the second terminal of the transistor, and the other end of the capacitor is electrically connected to the ground terminal. The detector is electrically connected to the third terminal of the transistor.
[0009]
In the second embodiment of the present invention, the capacitor inside the earphone detection circuit is removed. The electrical connection portions of the second terminal of the transistor and the third resistor, the first resistor, and the second terminal of the transistor are all connected to the ground terminal. A circuit module having this rearrangement is inferior in terms of the resistor-capacitor effect, but omitting the capacitor reduces the overall occupied volume of the circuit.
[0010]
In summary, the main advantages are: In the present invention, in order to easily attach the earphone detection circuit to the earphone drive circuit that cannot initially detect the insertion / extraction state, the conduction state when a potential difference exists between the gate terminal and the source / drain terminal of the transistor. Use the difference. As a result, the overall size of the earphone drive circuit can be reduced, and the audio signal output device can have an automatic audio signal switching capability.
[0011]
Both the foregoing general description and the following detailed description are exemplary and are intended to provide a detailed description of the claimed invention.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The presently preferred embodiment of the invention will now be described in detail. An example of this is shown in the accompanying drawings. The same reference numerals are used for the same or similar parts.
[0013]
In order to explain the innovative features of the present invention, an earphone driving circuit according to the prior art will be briefly described with reference to FIG. 2A. In FIG. 2A, the earphone drive circuit does not have a ground terminal as a substance. The earphone drive circuit is connected to a virtual ground line 214 having a virtual ground voltage of about V _CC / 2. The portion including the resistors 122 and 126 and the detection line 132 shown in FIG. 1 is used as the earphone detection circuit 230. The entire circuit is shown in FIG. 2B. The same elements as those shown in FIGS. 1 and 2A are denoted by the same reference numerals in FIG. 2B.
[0014]
As shown in FIG. 2B, the audio signal transmission line 212 is at a voltage of V _CC / 2 due to a DC voltage bias when there is no earphone. Accordingly, the detector 240 detects a voltage of about V _CC / 2 on the detection line 132. However, the digital electronic circuit detects its state according to the criteria of high voltage or low voltage. For example, in the earphone drive circuit, a voltage V _CC between 2.3V and 3V is considered a high digital level, while a voltage V _CC between 0V and 0.8V is considered a low digital level. Thus, the voltage V _CC / 2 (about 1.5V) detected by detector 240 is approximately halfway between the high and low digital levels. This is an ambiguous situation that makes it difficult to determine the earphone insertion / extraction conditions by the earphone drive circuit.
[0015]
Therefore, it is difficult to use a small earphone driving circuit including the conventional earphone detection circuit as shown in FIG. 2A. Therefore, in order to facilitate the use of such a small earphone drive circuit, an earphone detection circuit is introduced in the present invention. Obviously, the present invention can be applied to circuits other than small earphone driving circuits.
[0016]
FIG. 3 is a diagram showing a circuit combining an earphone detection circuit and an earphone drive circuit according to one preferred embodiment of the present invention. An earphone detection circuit 300 having a transistor 300, a plurality of resistors 340, 342 and 344, a capacitor 346, and a detector 360 is shown in FIG. The detection terminal 322 is electrically connected to the audio signal transmission line 312. The transistor 300 has four terminals including a first terminal 330, a second terminal 332, a third terminal 334, and a fourth terminal 336. The first terminal 330 is electrically connected to the fourth terminal 336. The operating voltage (V _CC ) is supplied to both the first terminal 330 and the fourth terminal 336. One end of resistor 340 is electrically connected to the first terminal of transistor 300 and the other terminal is electrically connected to second terminal 332 of transistor 300. One end of the resistor 342 is electrically connected to the third terminal 334 of the transistor 300, and the other terminal is connected to the ground terminal. One end of the resistor 344 is electrically connected to the second terminal 332 of the transistor 300, and the other terminal is electrically connected to the detection terminal 322. One end of the capacitor 346 is electrically connected to the second terminal 332 of the transistor 300, and the other terminal is connected to the ground terminal. The detector 360 is electrically connected to the third terminal 334 of the transistor 300.
[0017]
For ease of explanation, in this embodiment, transistor 300 is a P-type metal oxide semiconductor field effect transistor (p-channel MOSFET ). Accordingly, the four terminals are a source terminal 330, a gate terminal 332, a drain terminal 334, and a substrate terminal 336, respectively. However, elements other than the P-channel MOSFET may be used. A type of transistor having similar voltage conduction characteristics can be used with minor modifications.
[0018]
The operation of the earphone driving circuit will be briefly described below. FIG. 4A is a graph showing voltage fluctuations detected at the transistor gate (point P) when the earphone is inserted or pulled out in the circuit shown in FIG. FIG. 4B is a graph showing voltage fluctuation detected by the detector 360 when the earphone is inserted or pulled out in the circuit shown in FIG. Before the earphone plug is inserted into the earphone drive circuit, the detection terminal 322 is electrically connected to the audio signal transmission line 312. When there is no audio signal output, the audio signal transmission line 312 is at a voltage level of about V _CC / 2. Thus, the voltage at the detection terminal 322 is also at about V _CC / 2. Since the resistance of resistor 340 is significantly higher than the resistance of resistor 344, the voltage level at point P is slightly higher than V _CC / 2 (as shown in FIG. 4A). Therefore, the potential difference between the source terminal 330 and the gate terminal 332 is slightly lower than V _CC / 2, but is high enough to make the transistor 300 conductive. Thus, detector 360 detects a voltage close to V _CC (as shown in FIG. 4B).
[0019]
When the earphone plug is inserted into the earphone driving circuit, the detection terminal 322 is disconnected from (at time T ₁ of the FIGS. 4A and 4B) audio signal transmission line 312. Since the path connected to the detection terminal 322 suddenly becomes a high impedance circuit, the potential at the point P changes. At point P, charging of capacitor 346 is started, and the potential rises until point P reaches a potential close to voltage V _CC (time T _{2 in} FIG. 4A). As point P approaches voltage V _CC , transistor 300 gradually stops. Accordingly, the voltage detected by the detector 360 (that is, the potential at the drain terminal 334) gradually decreases to zero (time T ₂ ′ in FIG. 4B). Thereby, the detector 360 detects the presence of the earphone. When the detector 360 detects the presence of the earphone, the audio signal is immediately transmitted to the user's earphone through the earphone drive circuit.
[0020]
In the period between T ₂ and T ₃ , the earphone is inserted in the earphone drive circuit, and the voltage V _{CC at the} point P is maintained. At time T _3, the earphone plug is pulled out from the earphone drive circuit. Accordingly, the detection terminal 322 is electrically connected to the audio signal transmission line 312 again. Since the voltage at the detection terminal 322 is substantially equal to the sum of V _CC / 2 and the voltage of the audio signal, the potential at the point P begins to decrease (period between T ₃ and T _{5 in} FIG. 4A). Due to the resistor-capacitor effect of the earphone detection circuit, there is a transient voltage fluctuation at point P (the period between T ₄ and T _{5 in} FIG. 4A) until it settles to a stable value. Further, as the potential at the point P decreases, the potential difference between the gate terminal 332 and the source terminal 330 gradually increases until the transistor 300 becomes conductive. Eventually, the voltage detected by detector 360 (potential at drain terminal 334) rises to a level close to V _CC . Accordingly, the detector 360 detects that there is no earphone plug in the earphone driving circuit, and sends the signal to a circuit different from the earphone driving circuit.
[0021]
In another embodiment, capacitor 346 can also be omitted. FIG. 5 is a diagram showing an earphone detection circuit according to a second preferred embodiment of the present invention. 5, the same elements as those shown in FIG. 3 are denoted by the same reference numerals. Since the earphone detection circuit of FIG. 5 operates in the same mode as that of FIG. 3, detailed description thereof is omitted. In this embodiment, the resistor-capacitor effect is slightly increased, but the size of the earphone detection circuit is reduced.
[0022]
In conclusion, in the present invention, the voltage conduction characteristics of the transistor are used in order to make it easy to attach the earphone detection circuit to the earphone drive circuit that cannot originally detect the insertion / extraction state. Furthermore, the overall size of the earphone detection circuit can be reduced.
[0023]
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. Therefore, changes and modifications included in the scope of claims appended hereto and their equivalents are intended to be included in the present invention.
[0024]
【The invention's effect】
In the present invention, the overall size of the earphone drive circuit can be reduced, and the audio signal output device can have an automatic audio signal switching capability.
[Brief description of the drawings]
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this invention. The drawings illustrate embodiments of the present invention and together with the description of the text, serve to explain the principles of the invention.
FIG. 1 shows a conventional earphone driving circuit and an earphone detection circuit corresponding to the earphone driving circuit.
FIG. 2A is a diagram showing a conventional earphone drive circuit.
2B is a diagram showing a circuit combining the earphone drive circuit of FIG. 2A and the earphone detection circuit of FIG. 1;
FIG. 3 is a diagram showing a circuit combining an earphone detection circuit and an earphone drive circuit according to one preferred embodiment of the present invention.
4A is a graph showing voltage fluctuation detected by a transistor gate when an earphone is inserted or pulled out in the circuit shown in FIG. 3; FIG. (B) is a graph showing the voltage fluctuation detected by the detector when the earphone is inserted or pulled out in the circuit shown in FIG.
FIG. 5 is a diagram showing an earphone detection circuit according to a second preferred embodiment of the present invention.

Claims (3)

An earphone detection device suitable for detecting an insertion / extraction state of an earphone from an earphone drive circuit having a detection terminal, the earphone detection device having a first terminal, a second terminal, a third terminal, and a fourth terminal A transistor, wherein the first terminal and the fourth terminal are electrically connected to each other, both of which are electrically connected to the operating voltage;
A first resistor having a first terminal and a second terminal, wherein the first terminal is electrically connected to the first terminal of the transistor and the second terminal is electrically connected to the second terminal of the transistor The first resistor
A second resistor having a first terminal and a second terminal, wherein the first terminal is electrically connected to the third terminal of the transistor, and the second terminal is electrically connected to the ground terminal. Two resistors,
A capacitor having a first terminal electrically connected to the second terminal of the transistor and a second terminal electrically connected to the ground terminal;
A third resistor having a first terminal and a second terminal, wherein the first terminal is electrically connected to the second terminal of the transistor and the second terminal is electrically connected to the detection terminal The third resistor;
A detector electrically connected to the third terminal of the transistor;
The earphone detection device comprising: An earphone detection device suitable for detecting a connection state of an earphone to a drive circuit, wherein the earphone detection device is
A transistor having a first terminal, a second terminal, a third terminal and a fourth terminal, wherein the first terminal and the fourth terminal are both electrically connected to an operating voltage;
A first resistor having a first terminal and a second terminal, wherein the first terminal is electrically connected to the first terminal of the transistor and the second terminal is electrically connected to the second terminal of the transistor The first resistor being
A second resistor having a first terminal and a second terminal, wherein the first terminal is electrically connected to the third terminal of the transistor and the second terminal is electrically connected to the ground terminal. The second resistor;
A third resistor having a first terminal and a second terminal, wherein the first terminal is electrically connected to the second terminal of the transistor and the second terminal is electrically connected to the detection terminal of the drive circuit The third resistor being,
A detector electrically connected to the third terminal of the transistor;
The earphone detection device comprising: A connection detection device including a detection circuit that detects a connection state of an earphone to an earphone drive circuit, wherein the earphone drive circuit includes a detection terminal, and the connection detection device includes:
A transistor having a first terminal, a second terminal, a third terminal and a fourth terminal, wherein the first terminal and the fourth terminal are both electrically connected to an operating voltage;
A first resistor having a first terminal and a second terminal, wherein the first terminal is electrically connected to the first terminal of the transistor and the second terminal is electrically connected to the second terminal of the transistor The first resistor being
A second resistor having a first terminal and a second terminal, wherein the first terminal is electrically connected to the third terminal of the transistor and the second terminal is electrically connected to the ground terminal. The second resistor;
A third resistor having a first terminal and a second terminal, wherein the first terminal is electrically connected to the second terminal of the transistor and the second terminal is electrically connected to the detection terminal The third resistor;
A detector electrically connected to the third terminal of the transistor;
With
The connection detection device according to claim 1, wherein the first resistor has a resistance value significantly higher than that of the third resistor .

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