JP4519630B2 - Input/output switching circuit and semiconductor integrated device incorporating the same - Google Patents

Description

The present invention relates to an input/output switching circuit that can be applied to the input/output interfaces of AV devices such as televisions and DVD recorders, and to a semiconductor integrated device equipped with the circuit.

AV equipment that plays and records video and audio, such as DVD players, DVD or HDD recorders, and game consoles, is becoming more and more common. This is accompanied by an increase in the number of cables connected to viewing equipment such as televisions. Such viewing equipment often has multiple terminals on the front or back for plugging in cables for input from and output to external devices.

Patent Document 1 and Patent Document 2 disclose a video input/output circuit that can share one video terminal for input and output. In Figures 1 and 2 of Patent Document 1, a switch 3 made of a C-MOS analog switch IC selectively switches between an input buffer 5 and an output buffer 6, making it possible to switch one video terminal 1 for use as an input or an output. In Figures 1 and 2 of Patent Document 2, the path is also switched by a switch 14.
JP 2002-262129 A JP 2004-104755 A

In the circuits disclosed in Patent Documents 1 and 2, one terminal is used for both input and output, so a switch is used to switch the path between input and output. The use of a switch can cause degradation of signal characteristics. In particular, when an analog switch is used, the on-resistance becomes large.

The present invention was made in consideration of these circumstances, and its purpose is to provide an input/output switching circuit that can provide a terminal for both input and output while suppressing deterioration of characteristics, and a semiconductor integrated device equipped with the same.

In order to solve the above problem, an input/output switching circuit according to one embodiment of the present invention includes a selection circuit that selects a plurality of signals input from the outside, an amplifier circuit that amplifies the signal selected by the selection circuit at a predetermined amplification factor, an external terminal that outputs the output signal of the amplifier circuit to the outside, and a path that connects the external terminal and the input side of the selection circuit. When a signal is input from the external terminal, the output side of the amplifier circuit is set to high impedance. The "predetermined amplification factor" may be 1x.

According to this embodiment, by controlling the state of the amplifier circuit, the external terminal can be used for both input and output without using components that tend to deteriorate the characteristics, such as switches.

The amplifier circuit may include an operational amplifier and a resistor connected thereto for setting the gain. The resistor may function as a termination resistor when a signal is input from an external terminal. According to this embodiment, when the external terminal is used for output, a resistor for setting the gain of the amplifier circuit is used as a termination resistor when the external terminal is used for input, thereby reducing the number of components.

Another aspect of the present invention is also an input/output switching circuit. This input/output switching circuit includes a first external input terminal group that receives a plurality of signals input from the outside, a first selection circuit that selects a plurality of signals input from the first external input terminal group, a first amplifier circuit that amplifies the signal selected by the first selection circuit at a predetermined amplification factor, a first external output terminal that outputs an output signal of the first amplifier circuit to the outside, a second external input terminal group that receives a plurality of signals input from the outside, a second selection circuit that selects a plurality of signals input from the second external input terminal group, a second amplifier circuit that amplifies the signal selected by the second selection circuit at a predetermined amplification factor, a second external output terminal that outputs an output signal of the second amplifier circuit to the outside, and a path that connects the first external output terminal and the input side of the second selection circuit. When a signal is input from the first external output terminal, the output side of the first amplifier circuit is set to high impedance.

According to this embodiment, by controlling the state of the first amplifier circuit, the first external output terminal can also be used for input without using a component that is likely to deteriorate the characteristics, such as a switch.

The first amplifier circuit may include an operational amplifier and a resistor connected thereto for setting the gain. The resistor may function as a termination resistor when a signal is input from the first external output terminal. According to this aspect, when the first external output terminal is used for input, the resistor for setting the gain of the first amplifier circuit can be used as a termination resistor, thereby reducing the number of components.

The first amplifier circuit may further include a first resistor inserted in each path connecting the second external input terminal group and the input side of the second selection circuit, and a second resistor inserted between each connection point between the second selection circuit and the first resistor and a predetermined fixed potential. The first amplifier circuit may include an operational amplifier, a third resistor inserted in a feedback path from the output terminal to the input terminal, and a fourth resistor inserted between a connection point between the third resistor and the input terminal of the operational amplifier and the predetermined fixed potential. The first resistor and the third resistor, and the second resistor and the fourth resistor may correspond to each other. The resistance values of the "first resistor and the third resistor, and the second resistor and the fourth resistor" may be substantially the same. The "predetermined fixed potential" may be a ground potential.

According to this embodiment, signals can be input with the same characteristics whether they are input from the second external input terminal group or the first external output terminal.

Yet another aspect of the present invention is a semiconductor integrated device. This device includes an input/output switching circuit and a control unit that controls whether or not to set the high impedance.

In addition, any combination of the above components, and any conversion of the present invention between devices, methods, systems, etc., are also valid aspects of the present invention.

The present invention makes it possible to provide terminals that can be used for both input and output while suppressing deterioration of characteristics.

First, an overview of the present invention will be described. The present invention is an input/output switching circuit that selects signals input from multiple input terminals and outputs them from an output terminal. For example, an input/output switching circuit is used as follows: It is mounted on a display such as a television, and a cable connecting to a DVD player and a cable connecting to a game console are connected to its input terminals, and a cable connecting to an extension speaker is connected to its output terminal. The input/output switching circuit then selects an audio signal played by the DVD player and an audio signal played by the game console, and outputs them to the extension speaker. In this way, a desired signal can be selected from multiple input signals and output.

(Embodiment 1)
FIG. 1 is a diagram showing the configuration of an input/output switching circuit in the first embodiment. In this embodiment, an example in which the input/output switching circuit is configured as a semiconductor integrated circuit 100 will be described, but the present invention is not limited to the form of an integrated circuit. In FIG. 1, five input terminals 12, 14, 16, 22, and 24 are provided. The first input terminal 12, the second input terminal 14, and the third input terminal 16 are connected to the first selector 10 via the first resistor R12, the second resistor R14, and the third resistor R16, respectively. In addition, the fourth input terminal 22 and the fifth input terminal 24 are connected to the ninth resistor R42 and the tenth resistor R44, respectively.

The first resistor R12, the second resistor R14, the third resistor R16, the ninth resistor R42, and the tenth resistor R44 are resistors for protecting the first selector 10 and the second selector 20, and adjust the impedance seen from the corresponding input terminals 12, 14, 16, 22, and 24. The signals input to the input terminals 12, 14, 16, 22, and 24 (hereinafter, referred to as audio signals in this embodiment) are attenuated by a predetermined amount by these resistors.

The connection points between the first selector 10 and the first resistor R12, the second resistor R14, and the third resistor R16 are connected to ground potential via the fourth resistor R22, the fifth resistor R24, and the sixth resistor R26, respectively. In addition, the connection points between the second selector 20 and the ninth resistor R42 and the tenth resistor R44 are connected to ground potential via the eleventh resistor R52 and the twelfth resistor R54, respectively.

The fourth resistor R22, the fifth resistor R24, the sixth resistor R26, the eleventh resistor R52, and the twelfth resistor R54 function as termination resistors. These resistors prevent reflections at the ends of the cables connected to the input terminals 12, 14, 16, 22, and 24. The resistance values of these resistors are set according to the characteristic impedance of the cable used, but the general standard is 75 Ω.

The audio signal input from the first input terminal 12 is divided by the first resistor R12 and the fourth resistor R22 and input to the first selector 10. The same applies to the audio signals input to the second input terminal 14 and the third input terminal 16. The audio signals input from the fourth input terminal 22 and the fifth input terminal 24 are also divided and input to the second selector 20.

The first selector 10 and the second selector 20 are selectors with three input systems and one output system, and select and output one of three input signals. The first selector 10 and the second selector 20 may be switched by a microcomputer (described later) or may be switched manually. The output signal of the first selector 10 is input to the non-inverting input terminal of the first operational amplifier OP1. The output signal of the second selector 20 is input to the non-inverting input terminal of the second operational amplifier OP2.

A seventh resistor R32 that functions as a feedback resistor is connected between the output terminal and the inverting input terminal of the first operational amplifier OP1, and an eighth resistor 34 is connected between the connection point between the inverting input terminal and the seventh resistor 32 and ground potential. The first operational amplifier OP1, the seventh resistor R32, and the eighth resistor R34 form a non-inverting amplifier.

In this non-inverting amplifier, the inverting input terminal voltage is (resistance value of the eighth resistor R34) / {(resistance value of the seventh resistor R32) + (resistance value of the eighth resistor R34)} * output terminal voltage Vo. Since the non-inverting input terminal voltage and the inverting input terminal voltage of the operational amplifier OP1 are virtually short-circuited, the relationship in the following formula 1 holds between the non-inverting input terminal voltage Vi and the output terminal voltage Vo.

Vi=R34/(R32+R34)*Vo
Vo=(1+R32/R34)Vi...(Formula 1)
Therefore, the gain of the non-inverting amplifier is (1+R32/R34), and a desired gain can be obtained by adjusting at least one of the seventh resistor R32 and the eighth resistor R34.

In addition, at least one of the seventh resistor R32 and the eighth resistor R34 may be configured as a variable resistor, and the gain of the non-inverting amplifier may be dynamically changed by adjusting the variable resistor. For example, a microcontroller (described later) may adaptively change the gain depending on the signal selected by the first selector 10.

Similarly, a thirteenth resistor R62 functioning as a feedback resistor is connected between the output terminal and the inverting input terminal of the second operational amplifier OP2, and a fourteenth resistor R64 is connected between the connection point between the inverting input terminal and the thirteenth resistor 62 and ground potential. The second operational amplifier OP2, the thirteenth resistor 62, and the fourteenth resistor R64 constitute a non-inverting amplifier. The operating principle of this non-inverting amplifier is as described above.

The first operational amplifier OP1 has a mode (hereinafter referred to as high impedance mode) in which the impedance of its output terminal is infinite. The transition to this mode and the return from this mode to the normal operation mode may be controlled by a microcomputer, which will be described later, or may be controlled manually. To enter the high impedance mode, for example, the power supply to the first operational amplifier OP1 may be turned off. In this way, the transition to the high impedance mode or the return to the normal operation mode can be controlled by controlling the power supply to the first operational amplifier OP1 on and off.

The output terminal of the first operational amplifier OP1 is connected to the first output terminal 32 of this input/output switching circuit. Therefore, the first selector 10 selects, and the amplified signal of the non-inverting amplifier including the first operational amplifier OP1 is output to the outside from the first output terminal 32. In this case, the first operational amplifier OP1 operates in the normal operation mode. Similarly, the output terminal of the second operational amplifier OP2 is connected to the second output terminal 34 of this input/output switching circuit.

In this embodiment, the first output terminal 32 is a terminal for both input and output. That is, the first output terminal 32 and an external device can be connected with a cable, and a signal from the device can be input to this input/output switching circuit. At that time, the first operational amplifier OP1 is set to a high impedance mode. This prevents a signal from being output from the first operational amplifier OP1 to the first output terminal 32. In contrast, a signal input from the outside to the first output terminal 32 is input to the second selector 20 via the seventh resistor R32. The connection point between the seventh resistor R32 and the second selector 20 is connected to the ground potential via the eighth resistor R34.

When a signal is input from the first output terminal 32, the seventh resistor R32 and the eighth resistor R34 perform the functions corresponding to the ninth resistor R42 and the twelfth resistor R52. That is, the eighth resistor R34 functions as a termination resistor, the seventh resistor R32 adjusts the impedance, and the signal divided by the seventh resistor R32 and the eighth resistor R34 is input to the second selector 20. For example, if the resistance values and characteristics of the seventh resistor R32 and the ninth resistor R42, and the eighth resistor R34 and the twelfth resistor R52 are matched, the input system will be the same regardless of whether the cable from the external device is connected to the fourth input terminal 22 or the first output terminal 32, and the characteristics will also be consistent.

In addition, at least one of the seventh resistor R32 and the eighth resistor R34 is configured as a variable resistor, and when a signal is input from the first output terminal 32, the resistance value is set to match that of the ninth resistor R42 and the twelfth resistor R52, and when a signal is output from the first output terminal 32 to the outside, the resistance value is set to a different value, thereby making it possible to set the gain of the non-inverting amplifier including the first operational amplifier OP1 to a desired value.

The second selector 20 selects one of the audio signals input from the fourth input terminal 22, the fifth input terminal 24, and the first output terminal 32, and outputs it to the second operational amplifier OP2. In this embodiment, since the second output terminal 34 is not used as an input/output terminal, the second operational amplifier OP2 does not need a high impedance mode like the first operational amplifier OP1. Of course, it may have that mode and be in standby to save power when no signal is output from the second selector 20.

As described above, according to this embodiment, by providing the first operational amplifier OP1 with the function of transitioning to a high impedance mode, the terminal connected to the output terminal can be used as an input/output terminal. In other words, it is possible to avoid collisions between input and output signals without using a switching element such as an analog switch. Furthermore, because no such switch is used, it is possible to prevent the deterioration of characteristics that would otherwise occur.

In addition, by reusing the resistors for setting the gain inserted between the feedback system of the first operational amplifier OP1 and the ground potential as attenuation resistors and termination resistors for the input signal, it is possible to perform termination processing without using switch elements or the like. This can also prevent the deterioration of characteristics. It is also possible to reduce the number of parts. Since no switch is required on the output side of the first operational amplifier OP1, the output impedance can be reduced. Furthermore, since the input system from the first output terminal 32 is arranged inside the semiconductor integrated circuit 100, there is no need to increase wiring outside the semiconductor integrated circuit 100, and the entire system can be simplified.

In the circuit shown in FIG. 1, six input systems can be realized with five input terminals 12, 14, 16, 22, and 24, and the number of terminals can be reduced. In addition, when a terminal for both input and output is provided, flexible wiring becomes possible for the user who uses the device equipped with it. For example, when this input/output switching circuit is applied to a television or a DVD deck, the first output terminal 32 for both input and output can be arranged on the front. In general, it may be difficult to arrange all terminals on the front in terms of area or design, and terminals are often provided on the back or side of the device. In such cases, when a terminal for both input and output is provided on the front, the user can easily realize the desired wiring without having to reach to the back or side. In other words, whether it is necessary to input a signal to the device or to output a signal from it to the outside, it can be realized just by changing the cable connection at the terminal.

(Embodiment 2)
2 is a diagram showing the configuration of an input/output switching circuit in the second embodiment. Description of common parts with the first embodiment will be omitted. In the second embodiment, in order to use the terminal of the device for both input and output, a path is provided from a node N2 in a path connecting the first output terminal 32 of the semiconductor integrated circuit 100 and a terminal of a set device (not shown) on which the semiconductor integrated circuit 100 is mounted to the sixth input terminal 26. This path may be provided outside the semiconductor integrated circuit 100, for example, on an application board of the set device. The sixth input terminal 26 is connected to the second selector 20 via a fifteenth resistor R46. The connection point between the fifteenth resistor R46 and the second selector 20 is connected to the ground potential via a sixteenth resistor R56.

A first switch SW2 is inserted between the node N2 and the first output terminal 32, and a second switch SW4 is inserted between the node N2 and the sixth input terminal 26. The on/off of these switches SW2 and SW4 is controlled by a predetermined signal. This signal may be generated by a microcomputer (described later) or may be generated manually. When controlled by a digital signal, the second switch SW4 is provided with an inverted signal of the signal provided to the first switch SW2. Therefore, either an input system or an output system is formed between the node N2 and the semiconductor integrated circuit 100.

As described above, according to the second embodiment, by providing a path outside the semiconductor integrated circuit 100 to use the terminals of the device for both input and output, it is possible to provide a terminal for both input and output using an existing semiconductor integrated circuit 100.

(Embodiment 3)
3 is a diagram showing the configuration of an input/output switching circuit in the third embodiment. The third embodiment is an example in which the input/output switching circuit described in the first embodiment and a control unit 50 such as a microcomputer are integrated into one chip. Descriptions of parts common to the first embodiment will be omitted. The semiconductor integrated circuit 100 in the third embodiment includes a control unit 50, which controls the transition of the first operational amplifier OP1 to a high impedance mode or the return to a normal operation mode. The control unit 50 also controls the selection of input signals in the first selector 10 and the second selector 20. The control unit 50 may perform these controls in response to an instruction from a user interface (not shown), or may perform the controls based on a detection signal from a sensor (not shown).

The control unit 50 can control the entire set device in which the semiconductor integrated circuit 100 is mounted. Although not shown, the output signals of the first operational amplifier OP1 and the second operational amplifier OP2 can be taken into the set device in addition to being output to the outside.

As described above, according to the third embodiment, it is possible to realize a semiconductor integrated circuit 100 for a specific device that has an input/output switching function built in.

The present invention has been described above based on an embodiment. This embodiment is merely an example, and it will be understood by those skilled in the art that various modifications are possible in the combination of each component and each processing process, and that such modifications are also within the scope of the present invention.

In the embodiment, an audio signal is used as an example, but the invention can also be applied to other signals, such as video signals. Also, in the embodiment, an example in which two selectors 10 and 20 are provided is described, but one or three or more selectors are also possible. Furthermore, in the embodiment, an example in which one terminal is provided for both input and output is described, but it is of course possible to provide multiple terminals. Furthermore, the number of terminals can be reduced, and flexible wiring is possible.

FIG. 2 is a diagram illustrating a configuration of an input/output switching circuit according to the first embodiment. FIG. 11 is a diagram illustrating a configuration of an input/output switching circuit according to a second embodiment. FIG. 11 is a diagram illustrating a configuration of an input/output switching circuit according to a third embodiment.

Explanation of symbols

10 first selector, 12 first input terminal, 14 second input terminal, 16 third input terminal, 20 second selector, 22 fourth input terminal, 24 fifth input terminal, first output terminal, second output terminal, OP1 first operational amplifier, OP2 second operational amplifier, R32 seventh resistor, R34 eighth resistor.

Claims (6)

a first external input terminal group for receiving a plurality of signals input from an external source;
a first selection circuit that selects a plurality of signals input from the first external input terminal group;
a first amplifier circuit that amplifies the signal selected by the first selection circuit at a predetermined amplification factor;
a first external output terminal that outputs an output signal of the first amplifier circuit to an external device;
a second external input terminal group for receiving a plurality of signals input from the outside;
a second selection circuit that selects a plurality of signals input from the second external input terminal group;
a second amplifier circuit that amplifies the signal selected by the second selection circuit at a predetermined amplification factor;
a second external output terminal that outputs an output signal of the second amplifier circuit to the outside;
a path connecting a first external output terminal and an input side of the second selection circuit;
13. An input/output switching circuit, comprising: a first amplifier circuit configured to set an output side of the first amplifier circuit to a high impedance when a signal is input from the first external output terminal. The first amplifier circuit is
An operational amplifier,
a resistor connected thereto for setting a gain;
2. The input/output switching circuit according to claim 1 , wherein the resistor functions as a termination resistor when a signal is input from the first external output terminal. a first resistor inserted in each path connecting the second external input terminal group and an input side of the second selection circuit;
a second resistor inserted between each connection point between the second selection circuit and the first resistor and a predetermined fixed potential;
The first amplifier circuit is
An operational amplifier,
a third resistor inserted in a feedback path from the output terminal to the input terminal;
a fourth resistor inserted between a connection point between the third resistor and the input terminal of the operational amplifier and a predetermined fixed potential;
2. The input/output switching circuit according to claim 1 , wherein the first resistor corresponds to the third resistor, and the second resistor corresponds to the fourth resistor. a fifth resistor inserted in each path connecting the first external input terminal group and an input side of the first selection circuit;
4. The input/output switching circuit according to claim 3, further comprising a sixth resistor inserted between each connection point between said first selection circuit and said fifth resistor and a predetermined fixed potential. An input/output switching circuit according to any one of claims 1 to 4 ;
A control unit that controls whether to set the impedance to high impedance;
A semiconductor integrated device comprising: 6. The semiconductor integrated device according to claim 5, wherein the control section controls the selection operation of the input signal in the first selection section and the second selection section.

Images