JP2006180272A - Input/output switching circuit, and semiconductor integrated device mounted with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a terminal for both input and output while suppressing deterioration in the characteristic. <P>SOLUTION: An amplifier circuit AMP 2 amplifies a signal to be externally outputted at a prescribed amplification factor. A resistor R2 attenuates an output signal from the amplifier circuit AMP 2. An external terminal 12 outputs a signal attenuated by the resistor R2 externally. A switching element SW2 sets a potential of a connecting point N2 between the resistor R2 and the external terminal 12 to a ground potential. A path for leading the signal from the connecting point N2 to the input side is formed. When a signal is inputted from the external terminal 12, the output side of the amplifier circuit AMP 2 is set to a high impedance and the switching element SW2 is set to an ON state. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an input / output switching circuit applicable to an input / output interface of an AV device such as a television or a DVD recorder, and a semiconductor integrated device equipped with the input / output switching circuit.

  AV devices that reproduce and record video and audio, such as DVD players, DVD or HDD recorders, and game machines, have become widespread. Accordingly, the number of cables connected to viewing devices such as televisions is increasing. In many cases, a plurality of terminals for inserting cables for input from an external device and for output to the external device are provided on the front and rear surfaces of such a viewing device.

Patent Documents 1 and 2 disclose video input / output circuits that can share one video terminal for input and output. In FIGS. 1 and 2 of Patent Document 1, a switch 3 including a C-MOS analog switch IC is used to selectively switch between an input buffer 5 and an output buffer 6 so that one video terminal 1 is used for input and output. It is possible to switch to use. Also in FIGS. 1 and 2 of Patent Document 2, the path is switched by the switch 14.
JP 2002-262129 A JP 2004-104755 A

  In the circuits disclosed in Patent Documents 1 and 2, since one terminal is used for both input and output, the path is switched using a switch in the case of input and in the case of output. If a switch is used, it becomes a factor which reduces a signal characteristic. In particular, when an analog switch is used, the on-resistance increases.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an input / output switching circuit capable of providing an input / output terminal while suppressing deterioration in characteristics, and a semiconductor integrated device equipped with the input / output switching circuit. It is in.

  In order to solve the above problems, an input / output switching circuit according to an aspect of the present invention includes an amplifier circuit that amplifies a signal to be output to the outside with a predetermined gain, a resistor that attenuates an output signal of the amplifier circuit, and a resistor. From the external terminal that outputs the attenuated signal to the outside, the switching element for setting the potential at the connection point between the amplifier circuit and the resistor to a predetermined fixed potential, and the connection point between the resistor and the external terminal, A path for guiding a signal to the circuit, and a setting unit that sets the output side of the amplifier circuit to high impedance and sets the switching element to ON when the signal is input from the external terminal. “Gain” may be 1 ×. The “resistor” may function as a termination resistor when a signal is input from an external terminal. The “predetermined fixed potential” may be a ground potential. The “predetermined circuit element” may be a clamp circuit or an input terminal that receives a signal input from an external terminal.

  According to this aspect, by controlling the state of the amplifier circuit, the external terminal can be used for both input and output even if a member such as a switch that tends to deteriorate the characteristics is not used in the input path or the output path. Can do.

  Another embodiment of the present invention is also an input / output switching circuit. This input / output switching circuit outputs to the outside an amplifier circuit that amplifies a signal to be output to the outside with a predetermined gain, a first resistor that attenuates the output signal of the amplifier circuit, and a signal attenuated by the first resistor. A switching element for setting a potential at a connection point between the external terminal, the amplifier circuit, and the first resistor to a predetermined fixed potential; a second resistor inserted between the connection point and the switching element; The path that guides the signal to the specified circuit element from the connection point between the resistor and the external terminal, and when the signal is input from the external terminal, set the output side of the amplifier circuit to high impedance and set the switching element to ON And a setting unit.

  According to this aspect, by controlling the state of the amplifier circuit, the external terminal can be used for both input and output even if a member such as a switch that tends to deteriorate the characteristics is not used in the input path or the output path. Can do. In addition, the output characteristics of the amplifier circuit can be improved.

  When outputting a signal from the external terminal, the setting unit may set the amplifier circuit to a normal operation and set the switching element to OFF. Thereby, oscillation of the amplifier circuit can be suppressed. Further, the amplifier circuit and the setting unit may be configured by a semiconductor integrated circuit.

  Yet another embodiment of the present invention is a semiconductor integrated device. This apparatus may include the input / output switching circuit of the above-described aspect, and the setting unit may be configured by a control circuit. The “control circuit” may be a microcomputer. According to this aspect, the system including the above-described input / output switching circuit can be simplified.

  It should be noted that any combination of the above-described constituent elements and a representation obtained by converting the expression of the present invention between apparatuses, methods, systems, and the like are also effective as an aspect of the present invention.

  According to the present invention, it is possible to provide an input / output terminal while suppressing deterioration of characteristics.

  First, the outline of the present invention will be described. The present invention is an input / output switching circuit applicable to an output portion such as a selector circuit that selects signals input from a plurality of input terminals and outputs the signals from an output terminal. For example, the input / output switching circuit performs input / output switching of a front terminal of a display such as a television. The user can connect a cable to the terminal to record a television program on a recording device such as a DVD recorder or an HDD recorder, or to output video and audio from a game device from the display. Thus, the present invention provides a technique for providing a terminal that can be used for both input and output.

(Embodiment 1)
FIG. 1 is a diagram illustrating a configuration of an input / output switching circuit according to the first embodiment. In FIG. 1, an amplifier circuit AMP2 amplifies a signal to be output to the outside (hereinafter described as an example of a video signal) with a predetermined gain. The amplifier circuit AMP2 includes an operational amplifier and a resistor inserted in a feedback path connecting the output terminal and the input terminal. A desired gain can be obtained by adjusting a resistance value such as the resistance. For example, the gain is set to 6 dB, 9 dB, and 12 dB. The amplifier circuit AMP2 may be provided in the semiconductor integrated circuit. A selector (not shown) may be provided in the previous stage of the amplifier circuit AMP2, and a system of signals selected from a plurality of input signals by the selector in the semiconductor integrated circuit may be input to the amplifier circuit AMP2. .

  The amplifier circuit AMP2 has a function of transitioning to a high impedance mode in which the output impedance is set to infinity. 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 manually. In order to enter the high impedance mode, for example, the power supply of the operational amplifier may be turned off. As described above, by switching on / off the power supply of the operational amplifier, the transition to the high impedance mode or the return to the normal operation mode can be controlled.

  A resistor R2 is inserted in the path between the amplifier circuit AMP2 and the external terminal 12. In a certain standard, the resistance value of the resistor R2 is set to 75Ω. In that case, the amplifier circuit AMP2 functions as a 75Ω driver. The external terminal 12 is a terminal provided in the set device, and is connected to a cable for connecting to an external device such as a recording device. The amplifier circuit AMP2 may be provided in the semiconductor integrated circuit, and the circuit elements after the resistor R2 may be provided outside the semiconductor integrated circuit.

  A connection point between the amplifier circuit AMP2 and the resistor R2 is connected to the ground potential via the switching element SW2. For the switching element SW2, a FET (Field Effect Transistor) such as a MOS (Metal Oxide Semiconductor) type or a bipolar transistor can be used. The switching element SW2 is not limited to these, and any element that exhibits a switching action may be used. The on / off control of the switching element SW2 may be controlled by a microcomputer, which will be described later, or may be controlled manually.

  A path for guiding a signal input from the external terminal 12 to the input side from a connection point N2 between the resistor R2 and the external terminal 12 is provided. Here, the input side may be an input terminal of the semiconductor integrated circuit or another circuit, for example, an input terminal of another semiconductor integrated circuit.

  Next, the operation of the input / output switching circuit shown in FIG. 1 will be described. First, the case where the external terminal 12 is used for output will be described. The amplifier circuit AMP2 is set to the normal operation mode, and the switching element SW2 is set to OFF. The amplifier circuit AMP2 amplifies the input video signal with a set gain and outputs the amplified video signal. The output signal of the amplifier circuit AMP2 is attenuated by a predetermined amount by the resistor R2 and output from the external terminal 12. The output impedance of the input / output switching circuit is a combination of the output impedance of the amplifier circuit AMP2 and the impedance of the resistor R2.

  Next, the case where the external terminal 12 is used for input will be described. The amplifier circuit AMP2 is set to the high impedance mode, and the switching element SW2 is set to ON. In this case, the amplifier circuit AMP2 becomes invisible from the connection point N2, and the resistor R2 is short-circuited to the ground potential. The resistor R2 functions as a termination resistor, and the resistance value becomes visible as input impedance.

  FIG. 2 is a diagram illustrating a case where the input / output switching circuit according to the first embodiment is configured by the semiconductor integrated circuit 100. FIG. 2 shows an example in which the entire input / output switching circuit shown in FIG. In FIG. 2, the resistor R <b> 2 and the switching element SW <b> 2 are also configured in the semiconductor integrated circuit 100. The external terminal 14 in FIG. 2 indicates a terminal of the semiconductor integrated circuit 100, not a terminal of the set device. When a video signal is input from the external terminal 14 via the connection point N2, the clamp circuit 20 fixes a reference potential such as a black level included in the video signal waveform to be constant.

  The control unit 50 is configured by a microcomputer or the like, and controls the transition of the amplifier circuit AMP2 to the high impedance mode or the return to the normal operation mode. Further, on / off control of the switching element SW2 is performed. The control unit 50 may perform these controls according to an instruction from a user interface (not shown), or may perform it based on a detection signal from a sensor (not shown). In addition, when the semiconductor integrated circuit 100 is mounted on a set device, the control unit 50 can also control the entire set device. In this case, the amplifier circuit AMP2 simply outputs an output signal to the outside. Instead, it may be taken into the set device.

  As described above, according to the present embodiment, since the amplifier circuit AMP2 has a function of transitioning to the high impedance mode, a terminal from which an output signal is output to the outside can be used as an input / output terminal. At this time, the collision between the input signal and the output signal can be avoided without using a switch element such as an analog switch for the input path and the output path. In addition, since such a switch is not used, it is possible to prevent deterioration of characteristics due to the switch.

  In addition, the circuit configuration when used for signal output and the circuit configuration when used for signal input can be configured by one circuit, that is, this input / output switching circuit, by switching the switching element SW2. Input impedance and output impedance can also be set in one circuit configuration. In addition, when a signal for attenuating the output signal of the amplifier circuit AMP2 is input from an external terminal, the number of components can be reduced by diverting it as a termination resistor. Furthermore, when the amplifier circuit AMP2, the resistor R2, and the switching element SW2 are built in the semiconductor integrated circuit 100, the system can be simplified.

  Further, by providing the external terminals 12 and 14 that are also used as input / output, the number of terminals of the set device or the semiconductor integrated circuit 100 can be reduced. In addition, when an input / output terminal is provided, flexible wiring is possible for a user who uses a device equipped with the terminal. For example, when this input / output switching circuit is applied to a television, a DVD deck, or the like, the input / output terminal may be disposed on the front. In general, it may be difficult in terms of area or design to arrange all the terminals on the front, and the terminals are often provided on the back and side surfaces of the device. In such a case, when the input / output terminal is provided on the front surface, the user can easily realize a desired wiring without reaching the back surface or the side surface. That is, in either case of inputting a signal to the device or outputting a signal to the outside from the device, it can be realized only by changing the cable at the terminal.

(Embodiment 2)
FIG. 3 is a diagram illustrating a configuration of the input / output switching circuit according to the second embodiment. In FIG. 3, a first resistor R4 is inserted in a path between the amplifier circuit AMP2 and the external terminal 12. A connection point between the first resistor R4 and the external terminal 12 is in contact with the ground potential via the second resistor R6 and the switching element SW2. In one standard, the resistance values of the first resistor R4 and the second resistor R6 are set to 75Ω. Since other configurations are the same as those of the first embodiment, description thereof is omitted.

  Next, the operation of the input / output switching circuit shown in FIG. 3 will be described. First, the case where the external terminal 12 is used for output will be described. The amplifier circuit AMP2 is set to the normal operation mode, and the switching element SW2 is set to OFF. The amplifier circuit AMP2 amplifies the input video signal with a set gain and outputs the amplified video signal. The output signal of the amplifier circuit AMP2 is attenuated by a predetermined amount by the first resistor R4 and output from the external terminal 12. The output impedance of the input / output switching circuit is a combination of the output impedance of the amplifier circuit AMP2 and the resistance value of the first resistor R4. Further, when the switching element SW2 is set to ON while the amplifier circuit AMP2 is set in the normal operation mode, the output signal of the amplifier circuit AMP2 is divided by the resistor voltage dividing circuit including the first resistor R4 and the second resistor R6. And output from the external terminal 12.

  Next, the case where the external terminal 12 is used for input will be described. The amplifier circuit AMP2 is set to the high impedance mode, and the switching element SW2 is set to ON. In this case, the first resistor R4 becomes invisible from the connection point N2, and the second resistor R6 is short-circuited to the ground potential. The second resistor R4 functions as a termination resistor, and its resistance value becomes visible as input impedance.

  FIG. 4 is a diagram illustrating a case where the input / output switching circuit according to the second embodiment is configured by the semiconductor integrated circuit 100. FIG. 4 shows an example in which the entire input / output switching circuit shown in FIG. In FIG. 4, the first resistor R4, the second resistor R6, and the switching element SW2 are also configured in the semiconductor integrated circuit 100. The external terminal 14 in FIG. 4 indicates a terminal of the semiconductor integrated circuit 100, not a terminal of the set device. Since the clamp circuit 20 and the control unit 50 are the same as those in the first embodiment, description thereof is omitted.

  As described above, according to the present embodiment, as in the first embodiment, the amplifier circuit AMP2 has a function of transitioning to the high impedance mode, so that the terminal from which the output signal is output is used as an input / output terminal. can do. At this time, the collision between the input signal and the output signal can be avoided without using a switch element such as an analog switch for the input path and the output path. In addition, since such a switch is not used, it is possible to prevent deterioration of characteristics due to the switch.

  Further, by providing a resistance voltage dividing circuit including the first resistor R4 and the second resistor R4 on the output side of the amplifier circuit AMP2, the output load capacity of the amplifier circuit AMP2 can be reduced. Therefore, it is possible to prevent oscillation of the amplifier circuit AMP2 and suppress characteristic deterioration. Therefore, the circuit configuration of the first embodiment and the circuit configuration of the second embodiment can be appropriately used depending on the characteristics of the amplifier circuit AMP2, such as using the circuit configuration of the second embodiment when the amplifier circuit AMP2 easily oscillates.

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

  In the embodiment, the video signal has been described as an example, but the present invention can be applied to other signals as long as the output signal of the amplifier circuit is attenuated using a resistor. Further, even when the amplifier circuit AMP2 is provided in the semiconductor integrated circuit and other circuit elements are provided externally, the switching element SW2 is controlled to be turned on / off by a signal line passing through the terminal of the semiconductor integrated circuit from the microcomputer in the semiconductor integrated circuit. May be.

2 is a diagram illustrating a configuration of an input / output switching circuit according to Embodiment 1. FIG. It is a figure which shows the case where the input-output switching circuit in Embodiment 1 is comprised with the semiconductor integrated circuit. FIG. 6 is a diagram illustrating a configuration of an input / output switching circuit according to a second embodiment. It is a figure which shows the case where the input-output switching circuit in Embodiment 2 is comprised with the semiconductor integrated circuit.

Explanation of symbols

  AMP2 amplifier circuit, SW2 switching element, N2 connection point, R2 resistor, R4 first resistor, R6 second resistor, 12 external terminal, 14 external terminal, 20 clamp circuit, 50 control unit, 100 semiconductor integrated circuit.

Claims (5)

An amplification circuit for amplifying a signal to be output to the outside with a predetermined gain;
A resistor for attenuating the output signal of the amplifier circuit;
An external terminal for outputting a signal attenuated by the resistor to the outside;
A switching element for setting a potential at a connection point between the amplifier circuit and the resistor to a predetermined fixed potential;
A path for guiding a signal to a predetermined circuit element from a connection point between the resistor and the external terminal;
When a signal is input from the external terminal, a setting unit that sets the output side of the amplifier circuit to high impedance and sets the switching element to ON,
An input / output switching circuit comprising: An amplification circuit for amplifying a signal to be output to the outside with a predetermined gain;
A first resistor for attenuating the output signal of the amplifier circuit;
An external terminal for outputting a signal attenuated by the first resistor to the outside;
A switching element for setting a potential at a connection point between the amplifier circuit and the first resistor to a predetermined fixed potential;
A second resistor inserted between the connection point and the switching element;
A path for guiding a signal to a predetermined circuit element from a connection point between the first resistor and the external terminal;
When a signal is input from the external terminal, a setting unit that sets the output side of the amplifier circuit to high impedance and sets the switching element to ON,
An input / output switching circuit comprising:   3. The input / output switching circuit according to claim 2, wherein when the signal is output from the external terminal, the setting unit sets the amplifier circuit to a normal operation and turns on the switching element. 4.   4. The input / output switching circuit according to claim 1, wherein the amplifier circuit and the setting unit are configured by a semiconductor integrated circuit. An input / output switching circuit according to any one of claims 1 to 3,
The semiconductor integrated device according to claim 1, wherein the setting unit includes a control circuit.

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