JP2006180128A - Input/output switching circuit, and semiconductor integrated circuit device mounted with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an input/output switching circuit with a terminal for both input and output while suppressing deterioration in the characteristic of the circuit. <P>SOLUTION: A first selector 10 selects any of a plurality of signals externally inputted. A first operational amplifier OP 1 amplifies the signal selected by the first selector 10 at a prescribed amplification factor. An output signal from the first operational amplifier OP 1 is externally outputted from a first output terminal 32. A path is provided between the first output terminal 32 and a second selector 20. When a signal is inputted from the first output terminal 32, the first operational amplifier OP 1 is set to a high impedance state. A eighth resistor 34 functions as a termination resistor when the signal is inputted from the first output terminal 32. <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 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 a selection circuit that selects a plurality of externally input signals, and an amplification that amplifies the signals selected by the selection circuit at a predetermined amplification factor. A circuit, an external terminal for outputting an output signal of the amplifier circuit to the outside, and a path connecting the external terminal and the input side of the selection circuit. When a signal is input from an external terminal, the output side of the amplifier circuit is set to high impedance. The “predetermined amplification factor” may be 1.

  According to this aspect, by controlling the state of the amplifier circuit, the external terminal can be used for both input and output without using a member such as a switch that easily deteriorates characteristics.

  The amplifier circuit may include an operational amplifier and a resistor connected to the operational amplifier for setting a gain. The resistor may function as a termination resistor when a signal is input from an external terminal. According to this aspect, when the external terminal is used for output, the resistance for setting the gain of the amplifier circuit is used, and when the external terminal is used for input, the number of parts is reduced by diverting it as a termination resistor. Can do.

  Another embodiment of the present invention is also an input / output switching circuit. The input / output switching circuit includes a first external input terminal group that receives a plurality of externally input signals, a first selection circuit that selects a plurality of signals input from the first external input terminal group, and a first selection A first amplification circuit for amplifying a signal selected by the circuit at a predetermined amplification factor; a first external output terminal for outputting an output signal of the first amplification circuit to the outside; and a second for receiving a plurality of signals inputted from the outside An external input terminal group; a second selection circuit that selects a plurality of signals input from the second external input terminal group; a second amplification circuit that amplifies the signal selected by the second selection circuit at a predetermined amplification rate; A second external output terminal that outputs the 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 aspect, by controlling the state of the first amplifier circuit, the first external output terminal can be used for input without using a member that easily deteriorates characteristics, such as a switch.

  The first amplifier circuit may include an operational amplifier and a resistor connected to the operational amplifier for setting a 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 number of components can be suppressed by diverting the resistor for setting the gain of the first amplifier circuit as the termination resistor.

  A first resistor inserted in each path connecting the second external input terminal group and the input side of the second selection circuit, each connection point between the first external input terminal group and the first resistor, and a predetermined And a second resistor inserted between the first and second fixed potentials. The first amplifier circuit includes an operational amplifier, a third resistor inserted in a feedback path from its output terminal to its input terminal, a connection point between the third resistor and the input terminal of the operational amplifier, a predetermined fixed potential, A fourth resistor inserted between the first and second resistors. The first resistor and the third resistor, and the second resistor and the fourth resistor may be associated with 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 value. The “predetermined fixed potential” may be a ground potential.

  According to this aspect, even if a signal is input from the second external input terminal group or a signal is input from the first external output terminal, it can be input with the same characteristics.

  Yet another embodiment 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 impedance to high impedance.

  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 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 is used as follows. It is mounted on a display such as a television, and its input terminal is connected to a cable connecting to a DVD player and a cable connecting to a game machine, and its output terminal is connected to a cable connecting to an expansion speaker. The input / output switching circuit selects an audio signal reproduced by the DVD player and an audio signal reproduced by the game machine, and outputs the selected audio signal to the extension speaker. In this way, a desired signal can be selected and output from a plurality of input signals.

(Embodiment 1)
FIG. 1 is a diagram illustrating a configuration of an input / output switching circuit according to the first embodiment. In the present embodiment, an example in which the input / output switching circuit is configured by the semiconductor integrated circuit 100 will be described, but the present invention is not limited to 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. 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 the corresponding input terminals 12, The impedance seen from 14, 16, 22, and 24 is adjusted. Signals input to the input terminals 12, 14, 16, 22, 24 (hereinafter referred to as audio signals in the present embodiment) are attenuated by a predetermined amount by these resistors.

  The connection point between the first resistor R12, the second resistor R14, the third resistor R16, and the first selector 10 is connected to the ground potential via the fourth resistor R22, the fifth resistor R24, and the sixth resistor R26, respectively. Is in contact with The connection points of the ninth resistor R42 and the tenth resistor R44 and the second selector 20 are in contact with the ground potential through 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 reflection at the end of the cable connected to each input terminal 12, 14, 16, 22, 24. The resistance values of these resistors are set according to the characteristic impedance of the cable to be used, but are 75Ω in a general standard.

  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 audio signals input to the second input terminal 14 and the third input terminal 16. In addition, the audio signals input from the fourth input terminal 22 and the fifth input terminal 24 are also respectively divided and input to the second selector 20.

  The first selector 10 and the second selector 20 are selectors with three inputs and one output, and select one of the three input signals for output. The first selector 10 and the second selector 20 may be switched by a microcomputer, which will be 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 functioning as a feedback resistor is connected between the output terminal and the inverting input terminal of the first operational amplifier OP1, and between the connection point of the inverting input terminal and the seventh resistor 32 and the ground potential. The eighth resistor 34 is connected. The first operational amplifier OP1, the seventh resistor R32, and the eighth resistor R34 constitute 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. Become. Since the non-inverting input terminal voltage and the inverting input terminal voltage of the operational amplifier OP1 are virtually short-circuited, the relationship of the following formula 1 is established between the non-inverting input terminal voltage Vi and the output terminal voltage Vo.

Vi = R34 / (R32 + R34) * Vo
Vo = (1 + R32 / R34) Vi (Expression 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.

  Further, at least one of the seventh resistor R32 and the eighth resistor R34 may be a variable resistor, and the gain of the non-inverting amplifier may be dynamically changed by adjusting the variable resistor. For example, a microcomputer described later may adaptively change the gain according to a 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 connection point between the inverting input terminal and the thirteenth resistor 62; A fourteenth resistor R64 is connected between the 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 for making the impedance of its output terminal infinite (hereinafter referred to as a high impedance mode). 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 first operational amplifier OP1 may be turned off. In this way, by switching on / off the power supply of the first operational amplifier OP1, the transition to the high impedance mode or the return to the normal operation mode can be controlled.

  The output terminal of the first operational amplifier OP1 is connected to the first output terminal 32 of the 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 from the first output terminal 32 to the outside. 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 the input / output switching circuit.

  In the present embodiment, the first output terminal 32 is an input / output terminal. That is, the first output terminal 32 and an external device can be connected by a cable, and a signal from the device can be input to the input / output switching circuit. At this time, the first operational amplifier OP1 is set to the high impedance mode. As a result, no signal is output from the first operational amplifier OP1 to the first output terminal 32. On the other hand, 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 in contact with the ground potential via the eighth resistor R34.

  The seventh resistor R32 and the eighth resistor R34 exhibit functions corresponding to the ninth resistor R42 and the twelfth resistor R52 when a signal is input from the first output terminal 32. That is, the eighth resistor R34 functions as a termination resistor, the seventh resistor R32 adjusts the impedance, and a 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 combined, a cable from an external device is connected to the fourth input terminal 22 or the first output terminal 32. Regardless of which one is connected, the input system is the same, and the characteristics are also the same.

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

  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 the present embodiment, since the second output terminal 34 is not used as an input / output terminal, the second operational amplifier OP2 does not need the high impedance mode unlike the first operational amplifier OP1. Of course, when the mode is provided and a signal is not output from the second selector 20, it may stand by for power saving.

  As described above, according to the present embodiment, by providing the first operational amplifier OP1 with a function of shifting to the high impedance mode, a terminal connected to the output terminal can be used as an input / output terminal. That is, the collision between the input signal and the output signal can be avoided without using a switch element such as an analog switch. In addition, since such a switch is not used, it is possible to prevent deterioration of characteristics due to the switch.

  In addition, a resistor for setting a gain inserted between the feedback system of the first operational amplifier OP1 and the ground potential is diverted as an attenuation resistance and a termination resistance of the input signal, so that a switch element or the like is not used. Termination can be performed. Moreover, the characteristic deterioration by it can be prevented. In addition, the number of parts can be reduced. Further, since no switch is required on the output side of the first operational amplifier OP1, the output impedance can be lowered. Further, since the input system from the first output terminal 32 is arranged in the semiconductor integrated circuit 100, it is not necessary to increase the 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 by five input terminals 12, 14, 16, 22, and 24, and the number of terminals 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 first output terminal 32 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. 2 is a diagram illustrating a configuration of an input / output switching circuit according to the second embodiment. Description of common parts with the first embodiment is omitted. In the second embodiment, since the terminal of the device is used for both input and output, the sixth node starts from the node N2 in the path connecting the first output terminal 32 of the semiconductor integrated circuit 100 and the terminal of the set device (not shown) on which the device is mounted. A path leading to the input terminal 26 is provided. This path is provided outside the semiconductor integrated circuit 100, and may be provided, for example, on an application board of a set device. The sixth input terminal 26 is connected to the second selector 20 via the fifteenth resistor R46. The connection point between the fifteenth resistor R46 and the second selector 20 is in contact with the ground potential via the 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. On / off of these switches SW2, 4 is controlled by a predetermined signal. This signal may be generated by a microcomputer, which will be described later, or may be generated manually. When controlled by a digital signal, the inverted signal of the signal given to the first switch SW2 is given to the second switch SW4. Therefore, either the input system or the output system is formed between the node N2 and the semiconductor integrated circuit 100.

  As described above, according to the second embodiment, a path for sharing input / output terminals of a device is provided outside the semiconductor integrated circuit 100, so that the existing semiconductor integrated circuit 100 can be used. A terminal also serving as an output can be provided.

(Embodiment 3)
FIG. 3 is a diagram illustrating a configuration of an input / output switching circuit according to the third embodiment. The third embodiment is an example in which the input / output switching circuit described in the first embodiment and the control unit 50 such as a microcomputer are integrated into one chip. A description of portions common to the first embodiment will be omitted. The semiconductor integrated circuit 100 according to the third embodiment includes a control unit 50, which controls the transition of the first operational amplifier OP1 to the high impedance mode or the return to the normal operation mode. Further, the selection operation of the input signal in the first selector 10 and the second selector 20 is controlled. 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).

  The control unit 50 can control the entire set device on which the semiconductor integrated circuit 100 is mounted. Further, although not shown, not only the output signals of the first operational amplifier OP1 and the second operational amplifier OP2 may be output to the outside, but may be taken into the set device.

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

  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 audio signal has been described as an example, but the present invention can also be applied to other signals such as a video signal. In the embodiment, the example in which the two selectors 10 and 20 are provided has been described. However, one or more than three selectors may be provided. Furthermore, in the embodiment, an example in which one input / output terminal is provided has been described, but it is of course possible to provide a plurality of terminals. Furthermore, the number of terminals can be reduced and flexible wiring is possible.

2 is a diagram illustrating a configuration of an input / output switching circuit according to Embodiment 1. FIG. FIG. 6 is a diagram illustrating a configuration of an input / output switching circuit according to a second embodiment. FIG. 10 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 1st operational amplifier, OP2 2nd operational amplifier, R32 7th resistor, R34 8th resistor.

Claims (6)

A selection circuit for selecting a plurality of externally input signals;
An amplification circuit that amplifies the signal selected by the selection circuit at a predetermined amplification rate;
An external terminal for outputting the output signal of the amplifier circuit to the outside;
A path connecting the external terminal and the input side of the selection circuit,
An input / output switching circuit, wherein, when a signal is input from the external terminal, the output side of the amplifier circuit is set to high impedance. The amplifier circuit is
An operational amplifier,
A resistor for setting a gain connected thereto, and
The input / output switching circuit according to claim 1, wherein the resistor functions as a terminating resistor when a signal is input from the external terminal. A first external input terminal group for receiving a plurality of externally input signals;
A first selection circuit for selecting a plurality of signals input from the first external input terminal group;
A first amplifier circuit for amplifying a signal selected by the first selection circuit at a predetermined amplification rate;
A first external output terminal for outputting an output signal of the first amplifier circuit to the outside;
A second external input terminal group for receiving a plurality of externally input signals;
A second selection circuit for selecting a plurality of signals input from the second external input terminal group;
A second amplifying circuit for amplifying the signal selected by the second selecting circuit at a predetermined gain;
A second external output terminal for outputting an output signal of the second amplifier circuit to the outside;
A path connecting the first external output terminal and the input side of the second selection circuit,
An input / output switching circuit, wherein when a signal is input from the first external output terminal, the output side of the first amplifier circuit is set to high impedance. The first amplifier circuit includes:
An operational amplifier,
A resistor for setting a gain connected thereto, and
The input / output switching circuit according to claim 3, wherein the resistor functions as a terminating 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 the input side of the second selection circuit;
A second resistor inserted between each connection point between the first external input terminal group and the first resistor and a predetermined fixed potential; and
The first amplifier circuit includes:
An operational amplifier,
A third resistor inserted in a feedback path from the output terminal to the input terminal;
A connection point between the third resistor and the input terminal of the operational amplifier, and a fourth resistor inserted between a predetermined fixed potential,
4. The input / output switching circuit according to claim 3, wherein the first resistor and the third resistor, and the second resistor and the fourth resistor are associated with each other. An input / output switching circuit according to any one of claims 1 to 5;
A control unit for controlling whether to set the high impedance;
A semiconductor integrated device comprising:

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