Amplifier circuit, semiconductor device and electronic apparatus

This is a U.S. national stage of application No. PCT/JP2005/011171, filed on 17 Jun. 2005. Priority under 35 U.S.C. §119(a) and 35 U.S.C. §365(b) is claimed from Japanese Application No. 2004-215314, filed 23 Jul. 2004, the disclosure of which is also incorporated herein by reference.

This invention relates to an amplifier circuit which amplifies a voltage to be supplied to a targeted load, and a semiconductor device and an electronic apparatus utilizing the same.

Personal computers, car navigation equipment and audio equipment of recent years are often provided with a tray for allowing the entry and exit of a CD (Compact Disk) or a DVD (Digital Versatile Disk). The opening and closing of the tray are normally controlled by the drive of a load, such as a coil or motor including a rotor. There are proposals for various methods for load drive control; for example, Patent Document 1 discloses a technology in which a torque value to be supplied to a motor is controlled by detecting the speed and position of the motor and comparing the results of detection with target values.

[Patent Document 1]

Japanese Patent Application Laid-Open No. Hei05-328774.

Conventionally, there have been cases where an amplifier circuit for amplifying input voltage is used to supply drive voltage to a load, such as a motor. However, when a fault occurs in the amplifier circuit or in a circuit near it due to a certain factor, there have been cases where a sufficient drive voltage cannot be supplied to the load or, under certain circumstances, the function of the equipment is impaired. For example, when a short circuit occurs in the amplifier circuit or in a circuit near it, the drive voltage supplied to the load may become 0 V, and the tray may not be opened or closed. Therefore, it is preferable that even in an emergency, such as the occurrence of a fault, a certain voltage can be supplied as an act of necessity.

The present invention has been made in view of the problem as described above, and an object thereof is to provide an amplifier circuit capable of supplying a certain voltage in an emergency as an act of necessity, and a semiconductor apparatus and an electronic apparatus using it.

An embodiment of the present invention relates to an amplifier circuit. This amplifier circuit includes a clamp circuit which clamps a voltage corresponding to an input voltage, to a predetermined nonzero voltage. According to this embodiment, even if, for example, the voltage corresponding to the input voltage becomes a voltage value in the neighborhood of a ground potential, the voltage of a constant level can be secured. This amplifier circuit may further include a differential circuit which generates, as the voltage corresponding to the input voltage, an amplification voltage corresponding to a difference between the input voltage and a reference voltage, and when the difference between the input voltage and the reference voltage is zero, the clamp circuit may clamp a voltage corresponding to the amplification voltage, to a predetermined nonzero voltage. Thereby, even if the input voltage becomes equal to the reference voltage, the voltage corresponding to the amplification voltage obtained by the differential circuit is clamped to a predetermined nonzero voltage, so that the voltage of a constant level can be secured. This amplifier circuit may further include a compensation circuit which compensates for temperature characteristics of the clamp circuit. The clamp circuit may be a transistor of bipolar type.

Another embodiment of the present invention relates also to an amplifier circuit. This amplification circuit amplifier circuit comprises: a differential circuit which generates an amplification voltage corresponding to a difference between an input voltage and a reference voltage; a first output circuit which generates a first output signal upon receipt of input of the amplification voltage from the differential circuit; a second output circuit which generates a second output signal upon receipt of input of the amplification voltage from the differential circuit; and a selector circuit which selects either the first output circuit or the second output circuit, wherein when the first output circuit is selected by the selector circuit, the first output circuit outputs a voltage corresponding to the amplification voltage from the differential circuit and the second output circuit outputs a predetermined fixed voltage, wherein when the second output circuit is selected by the selector circuit, the second output circuit outputs a voltage corresponding to the amplification voltage from the differential circuit and the first output circuit outputs a predetermined fixed voltage, wherein the first output circuit includes a first clamp circuit which generates a clamp voltage so that the first output signal does not become a predetermined clamp voltage or below, irrespective of the amplification voltage from the differential circuit, and the first output circuit outputs the first output signal with a nonzero voltage in the event that the input voltage is equal to the reference voltage, and wherein the second output circuit includes a second clamp circuit which generates a clamp voltage so that the second output signal does not become a predetermined clamp voltage or below, irrespective of the amplification voltage from the differential circuit, and the second output circuit outputs the second output signal with a nonzero voltage in the event that the input voltage is equal to the reference voltage. This amplifier circuit may further comprise a compensation circuit which compensates for temperature characteristics of the first clamp circuit and the second clamp circuit. The first clamp circuit and the second clamp circuit may be transistors of bipolar type.

Still another embodiment of the present invention relates also to an amplifier circuit. This amplifier circuit comprises: a first transistor in which an input voltage or a voltage corresponding to the input voltage is inputted to a base thereof and a collector thereof is grounded; a constant-current source connected with an emitter of the first transistor; and a second transistor in which a supply voltage is connected with an emitter thereof and a collector thereof is connected with a load, wherein a path from a connection point of the first transistor and the constant-current source to a base of the second transistor is selectively configured to be either in a conductive state or in a nonconductive state, wherein the first transistor generates a clamp voltage in a manner such that a voltage obtained from the connection point does not become a predetermined clamp voltage or below, and wherein when the path is in a conductive state, the second transistor retrieves the clamp voltage generated by the first transistor.

Still another embodiment of the present invention relates to a semiconductor device. This semiconductor device includes any of the above-described amplifier circuits. Still another embodiment of the present invention relates also to a semiconductor device. This semiconductor device comprises: a differential circuit which generates an amplification voltage corresponding to a difference between an input voltage and a reference voltage; a first output circuit which generates a first output signal upon receipt of input of the amplification voltage from the differential circuit; a second output circuit which generates a second output signal upon receipt of input of the amplification voltage from the differential circuit; a selector circuit which selects either the first output circuit or the second output circuit; and a load connected between a first output terminal that outputs the first output signal and a second output terminal that outputs a second output terminal, wherein when the first output circuit is selected by the selector circuit, the first output circuit outputs a voltage corresponding to the amplification voltage from the differential circuit and the second output circuit outputs a predetermined fixed voltage, wherein when the first output circuit is selected by the selector circuit, the second output circuit outputs a voltage corresponding to the amplification voltage from the differential circuit and the first output circuit outputs a predetermined fixed voltage, wherein the first output circuit includes a first clamp circuit which generates a clamp voltage so that the first output signal does not become a predetermined clamp voltage or below, irrespective of the amplification voltage from the differential circuit, and the first output circuit outputs the first output signal with a nonzero voltage in the event that the input voltage is equal to the reference voltage, and wherein the second output circuit includes a second clamp circuit which generates a clamp voltage so that the second output signal does not become a predetermined clamp voltage or below, irrespective of the amplification voltage from the differential circuit, and the second output circuit outputs the second output signal with a nonzero voltage in the event that the input voltage is equal to the reference voltage.

Still another embodiment of the present invention relates to an electronic apparatus. This electronic apparatus includes the above-described semiconductor device.

According to the present invention, the voltage of a constant level can be secured.

FIG. 1 shows a structure of a semiconductor device according to an embodiment.

FIG. 2A shows a relationship between an input voltage and an output signal when an H-level signal is inputted to a FWD terminal and an L-level signal is inputted to a REV terminal; and FIG. 2B shows a relationship between an input voltage and an output signal when an L-level signal is inputted to the FWD terminal and an H-level signal is inputted to the REV terminal.

FIG. 3 shows a structure of an electronic equipment according to an embodiment.

10 semiconductor device, 20 coil load, 50 electronic apparatus, 100 amplifier circuit, 110 differential circuit, 120 selector circuit, 150 a first output circuit, 150 b second output circuit, T 2 first output terminal, T 3 second output terminal, Tr 1 first transistor, Tr 2 a second transistor, Tr 2 b fifth transistor, Vin input voltage, Vb reference voltage, Vc amplification voltage, Vout 1 first output signal, Vout 2 second output signal

Firstly, an embodiment will be outlined. A semiconductor device according to the present embodiment is incorporated into an electronic equipment, such as a personal computer, a car navigation equipment, or an audio equipment, and carries out the opening and closing control of a CD tray or a DVD tray (hereinafter referred to as “loading control” as appropriate). An amplifier circuit in a semiconductor device is a so-called differential amplifier circuit and generates an amplification voltage corresponding to the difference between an input voltage from a variable voltage source and a reference voltage. The semiconductor device drives a rotor by supplying an output signal of a voltage corresponding to the amplification voltage (hereinafter sometimes referred to simply as “intermediate voltage” also) to one end of a coil load and an output signal of a predetermined fixed voltage, for instance, 0 V to the other end of the coil load and thereby having a current flow to the coil load by the voltage difference between those output signals. Hereinbelow, a rotor and a coil load are collectively referred to simply as a coil load.

This semiconductor device, excluding at least a variable voltage source and a coil load, is integrated in a package as a semiconductor circuit. It goes without saying that, depending on the semiconductor manufacturing process, the variable voltage source may also be integrated therewith. Although, as mentioned above, a semiconductor circuit including at least an amplifier circuit is used incorporated into an electronic equipment, such as a car navigation equipment or an audio equipment, there is the following agreement between a party that designs the semiconductor circuit, for example, an LSI (Large Scale Integration) maker, and a party that designs a set, such as a car navigation equipment or an audio equipment, by connecting a variable voltage source to a terminal of the LSI, for example, a set maker. That is, an LSI maker instructs a set maker to develop a packaging for application of a predetermined voltage to a terminal as LSI specifications. The set maker, following such instructions, develops the packaging for application of the predetermined voltage to the terminal.

After a semiconductor circuit is mounted on an electronic equipment by a set maker and the electronic equipment is shipped as a product, there may be a case where the variable voltage source breaks down due to a certain factor and the terminal is short-circuited to the ground. It is possible to cite an erroneous operation by a user, a physical shock having occurred during product transportation, etc., as above-mentioned factors. At this time, the input voltage may be 0 V and there will be zero difference between the input voltage and the reference voltage, so that the amplification voltage will take a voltage value in the neighborhood of ground potential, for instance, 0 V. At this time, if the amplification voltage, as it is, is supplied to the coil load, the voltage difference between the amplification voltage and the predetermined fixed voltage will be zero, and therefore the semiconductor device cannot drive the coil load and thus cannot perform the loading control of the tray. Accordingly, in a semiconductor device according to the present embodiment, a clamp circuit, which generates a voltage corresponding to the amplification voltage, namely, an intermediate voltage, is provided so as to clamp the intermediate voltage to a predetermined “non-zero” voltage when the terminal is short-circuited to the ground, that is, when the difference between the input voltage and the reference voltage is zero. In this manner, the semiconductor device can supply some fixed level of voltage to the coil load even in an emergency, thus realizing an emergency loading control of the tray.

FIG. 1 shows a structure of a semiconductor device 10 . FIG. 3 shows a structure of a personal computer 50 as an example of an electronic equipment carrying a semiconductor device 10 as shown in FIG. 1 . The personal computer 50 shown in FIG. 3 includes an input unit 54 , which receives inputted instructions from a user via an external device (not shown), such as a mouse or a keyboard; a DVD drive 60 , in which a DVD 64 is loaded; a storage unit 58 , such as a hard disk or memory for storage of files or data; a control unit 52 , such as a CPU (Central Processing Unit) that carries out exchange of data and signals with each component carried in the personal computer 50 and control of data input/output and operation of each component; and an output unit 56 , which outputs data stored in the DVD 64 or the storage unit 58 via an external display (not shown). The DVD drive 60 includes a DVD tray 62 for loading the DVD 64 and a semiconductor device 10 for the loading control of the DVD tray 62 . The control unit 52 according to the present embodiment carries out a loading control of the DVD tray 62 by outputting different signals to the semiconductor device 10 at a timing for drawing out the DVD tray 62 , at a timing for returning it, and at a timing without unloading or loading, respectively. While FIG. 3 shows a personal computer as an example of an electronic equipment, the electronic equipment may be a car navigation equipment or an audio equipment as other examples.

Returning to FIG. 1 , the semiconductor device 10 according to the present embodiment includes a variable voltage source 12 , a coil load 20 , and an amplifier circuit 100 . Note that the rotor is now shown. The amplifier circuit 100 amplifies an input voltage Vin inputted from the variable voltage source 12 via a loading control terminal T 1 and supplies it to the coil load 20 . The positive electrode side of the variable voltage source 12 is connected to the loading control terminal T 1 of the amplifier circuit 100 , whereas the negative electrode side of the variable voltage source 12 is grounded. According to the present embodiment, the input voltage Vin to the amplifier circuit 100 is variable, but it may, or course, be fixed. If the input voltage Vin is variable, it is possible to control the revolution speed of the coil load 20 according to the voltage value of the input voltage Vin, and consequently, it is possible to control the speed of unloading/loading of the tray.

The coil load 20 is connected between a first output terminal T 2 and a second output terminal T 3 of the amplifier circuit 100 . A first output signal Sig 1 is supplied via the first output terminal T 2 , and a second output signal Sig 2 is supplied via the second output terminal T 3 . Although the detail will be described later, when the first output signal Sig 1 is active and at the same time the second output signal Sig 2 is a predetermined fixed voltage, the coil load 20 rotates in positive direction and the tray is inserted into the equipment. On the other hand, in a reverse situation, the coil load rotates in reverse direction and the tray is drawn out of the equipment. The switching of these output signals is done by a selector circuit 120 to be described later. The predetermined fixed voltage in the present embodiment is a voltage value in the neighborhood of ground potential, which is 0 V for instance.

The amplifier circuit 100 includes a differential circuit 110 for generating an amplification voltage Vc corresponding to the difference between an input voltage Vin and a reference voltage Vb; a first output circuit 150 a for outputting a first output signal Sig 1 upon receipt of the input of an amplification voltage Vc from the differential circuit 110 ; a second output circuit 150 b for outputting a second output signal Sig 2 upon receipt of the input of an amplification voltage Vc from the differential circuit 110 ; and a selector circuit 120 for selecting either one of the first output circuit 150 a and the second output circuit 150 b . The first output circuit 150 a and the second output circuit 150 b are referred to as the output circuit 150 as appropriate.

The differential circuit 110 includes a first constant-current source 102 , a first transistor Tr 1 of PNP type, a first differential amplifier 106 , a first voltage-dividing resistor R 1 , and a second voltage-dividing resistor R 2 . Here, note also that the resistance values of the first voltage-dividing resistor R 1 and the second voltage-dividing resistor R 2 are denoted by R 1 and R 2 , respectively.

An input voltage Vin from the variable voltage source 12 is inputted to a noninverting input terminal of the first differential amplifier 106 via a loading control terminal T 1 . The emitter of the first transistor Tr 1 is connected to one end of the first constant-current source 102 , the collector is connected to the output side of the first differential amplifier 106 , and furthermore the base is connected to the collector. The other end of the first constant-current source 102 is connected to a supply voltage source Vcc. Here, a threshold voltage between the base and emitter of the first transistor Tr 1 is denoted by Vbe. This threshold voltage Vbe is a voltage at which an on-off switching of the transistor takes place, for instance, 0.7 V. Note that 0.7 V is a constant level of voltage value where the coil load 20 can be driven. Also, as will be described later, the first transistor Tr 1 is provided to compensate for the temperature characteristics of a second transistor Tr 2 a and a fifth transistor Tr 2 b.

The voltage occurring between the emitter of the first transistor Tr 1 and the first constant-current source 102 is voltage-divided into a reference voltage Vb by the first voltage-dividing resistor R 1 and the second voltage-dividing resistor R 2 and inputted to the inverting input terminal of the first differential amplifier 106 . The first constant-current source 102 controls the current to be sent to the first transistor Tr 1 , the first voltage-dividing resistor R 1 , and the second voltage-dividing resistor R 2 .

Here, the amplification voltage Vc outputted by the first differential amplifier 106 is expressed, using the input voltage Vin, as:

Vc=V in×( R 1 +R 2)/ R 2 −Vbe   (1)

As is indicated by the above equation (1), the larger the input voltage Vin, the larger the amplification voltage Vc will be. When a voltage value Vin in the neighborhood of ground potential is inputted, the amplification voltage Vc may be a negative voltage value or a voltage value near 0 V.

The selector circuit 120 controls the first output signal Sig 1 and the second output signal Sig 2 by controlling the ons and offs of various switches within the first output circuit 150 a and second output circuit 150 b to be described later, and thereby controls the coil load 20 . More specifically, the selector circuit 120 selects either one of the first output signal Sig 1 and the second output signal Sig 2 as a voltage signal corresponding to the amplification voltage Vc and the other thereof as a predetermined fixed voltage.

The selector circuit 120 includes an XOR gate S 1 , a first AND gate S 2 , and a second AND gate S 3 . A FWD signal A is inputted to a first input terminal I 1 of the XOR gate S 1 and a third input terminal I 3 of the first AND gate S 2 via a FWD terminal T 4 . A REV signal B is inputted to a second input terminal I 2 of the XOR gate S 1 and a sixth input terminal I 6 of the second AND gate S 3 via a REV terminal T 5 . The XOR gate S 1 performs an exclusive-OR operation on the two input signals and outputs the result of the operation to a fourth input terminal I 4 of the first AND gate S 2 and a fifth input terminal I 5 of the second AND gate S 3 . The first AND gate S 2 and the second AND gate S 3 perform AND operations on the inputted signals and control the various switches within the first output circuit 150 a and the second output circuit 150 b , respectively, using the results of the AND operations as a first control signal C and a second control signal D, respectively.

The selector circuit 120 controls the ons and offs of the various switches within the first output circuit 150 a and the second output circuit 150 b according to the H level and L level of the FWD signal A and the REV signal B given by a control unit 52 as shown in FIG. 3 . In this manner, the selector circuit 120 selectively turns the path to be described later of either one of the first output circuit 150 a and the second output circuit 150 b into a conductive state or a nonconductive state. When the coil load 20 is run in positive rotation, that is, when the tray is inserted into the equipment, a FWD signal A of H level and at the same time a REV signal B of L level are inputted to the selector circuit 120 . At this time, the selector circuit 120 outputs a first control signal C of H level and a second control signal D of L level. As a result, the first output circuit 150 a is selected, and the amplifier circuit 100 outputs a voltage corresponding to the amplification voltage Vc from the differential circuit 110 as the first output signal Sig 1 and a predetermined fixed voltage as the second output signal Sig 2 . In the present embodiment, it is to be noted that a signal of L level turns on a switch and a signal of H level turns off a switch.

When the coil load 20 is run in reverse rotation, that is, when the tray is drawn out of the equipment, a FWD signal A of L level and at the same time a REV signal B of H level are inputted. At this time, the selector circuit 120 outputs a first control signal C of L level and a second control signal D of H level. As a result, the second output circuit 150 b is selected, and the amplifier circuit 100 outputs a voltage corresponding to the amplification voltage Vc from the differential circuit 110 as the second output signal Sig 2 and a predetermined fixed voltage as the first output signal Sig 1 .

Further, when the coil load 20 is not driven, that is, when the tray is not opened or closed because the CD or DVD is being used by the equipment, a FWD signal A and a REV signal B, which are both H level or L level, are inputted. At this time, the selector circuit 120 outputs a first control signal C and a second control signal D, which are both of L level. At this time, neither of the first output circuit 150 a and the second output circuit 150 b is selected. As a result, a predetermined fixed voltage is applied to both ends of the coil load 20 , so that the coil load 20 is not driven.

The output circuit 150 generates an output signal of a voltage corresponding to the amplification voltage Vc supplied by the differential circuit 110 , and supplies the output signal to one end of the coil load 20 via the first output terminal T 2 or the second output terminal T 3 . A predetermined fixed voltage is applied to the other end of the coil load 20 . As mentioned above, the switching control of the output signal is done by the selector circuit 120 . The first output circuit 150 a and the second output circuit 150 b are connected in parallel between the differential circuit 110 and the coil load 20 . Since the second output circuit 150 b has a structure identical to that of the first output circuit 150 a , a description will be given hereinbelow of the first output circuit 150 a and the description of the second output circuit 150 b will be omitted as appropriate.

The first output circuit 150 a is provided therewithin with a second transistor Tr 2 a of bipolar PNP type which generates a clamp voltage to prevent the first output signal Sig 1 from going below a predetermined clamp voltage, without depending on the value of the amplification voltage Vc from the differential circuit 110 . Although the detail will be described later, because of this second transistor Tr 2 a , a first output signal Sig 1 can be outputted at a nonzero voltage even when the input voltage Vin is equal to the reference voltage Vb.

The first output circuit 150 a includes a second constant-current source 152 a , a second transistor Tr 2 a , a second operational amplifier 156 a , a third transistor Tr 3 a of NPN type, a fourth transistor Tr 4 a of NPN type, a first switch SW 1 a , a second switch SW 2 a , and an inverting circuit 166 a.

The collector of the second transistor Tr 2 a is grounded, and the emitter is connected to one end of the second constant-current source 152 a . The other end of the second constant-current source 152 a is connected to a supply voltage source Vcc. The intermediate voltage Vda between the emitter of the second transistor Tr 2 a and the second constant-current source 152 a is inputted to the noninverting input terminal of the second operational amplifier 156 a which constitutes a so-called voltage follower. The output side of the second operational amplifier 156 a is connected to the base of the third transistor Tr 3 a via the first switch SW 1 a . The collector of the third transistor Tr 3 a is connected to the supply voltage source Vcc and further connected to the inverting input terminal of the second operational amplifier 156 a , and the emitter is connected to the collector of the fourth transistor Tr 4 a . The emitter of the fourth transistor Tr 4 a is grounded, and the base is connected to the supply voltage source Vcc via the second switch SW 2 a . A first output signal Sig 1 of a first output voltage Vout 1 occurring between the emitter of the third transistor Tr 3 a and the collector of the fourth transistor Tr 4 a is supplied to one end of the coil load 20 via the first output terminal T 2 .

When the first output circuit 150 a is selected by the selector circuit 120 , the first switch SW 1 a is turned on, the second switch SW 2 a off, the third switch SW 1 b off, and the fourth switch SW 2 b on. At this time, the path leading from the connection point between the emitter of the second transistor Tr 2 a and the second constant-current source 152 a to the third transistor Tr 3 a goes into a conductive state, and a voltage corresponding to the amplification voltage Vc is outputted via the second operational amplifier 156 a in the first output circuit 150 a and the first output circuit 150 a . Also, the output from a third operational amplifier 156 b in the second output circuit 150 b is cut off by the third switch SW 1 b in the off state, a seventh transistor Tr 4 b is turned on, and a predetermined fixed voltage is outputted. On the other hand, when the second output circuit 150 b is selected by the selector circuit 120 , the first switch SW 1 a is turned off, the second switch SW 2 a on, the third switch SW 1 b off, and the fourth switch SW 2 b on.

According to the present embodiment, the threshold voltage between the base and emitter of the second transistor Tr 2 a is the same as the threshold voltage Vbe between the base and emitter of the first transistor Tr 1 . The intermediate voltage Vda, which takes a value of the threshold voltage Vbe added to the amplification voltage Vc, is expressed as:

When the coil load 20 is driven in positive rotation, the first output voltage Vout 1 is equal to Vda and thus can be expressed, using the input voltage Vin, as follows:

V out1 =V in×( R 1 +R 2)/ R 2

The threshold voltage Vbe between the base and emitter of the second transistor Tr 2 a goes down gradually due to the heating resulting from use. At this time, if the first transistor Tr 1 is not provided in the amplifier circuit 100 , then there will be no factor of the threshold voltage Vbe on account of the first transistor Tr 1 in the above equation (1). Consequently, the parameter of threshold voltage Vbe remains in the above equation (2), and the intermediate voltage Vda may change along with the change in the threshold voltage Vbe between the base and emitter of the second transistor Tr 2 a . As a result, even under the same conditions, for example, even if the same input voltage Vin and resistance values R 1 and R 2 are given, the gain will change with the passage of time.

In the present embodiment, a first transistor Tr 1 is provided to compensate for the temperature characteristics of a second transistor Tr 2 a . When the threshold voltage Vbe between the base and emitter of the second transistor Tr 2 a drops, the threshold voltage Vbe between the base and emitter of the first transistor Tr 1 drops the same way. At this time, according to the above equations (1) and (2), they are in such directions as to cancel out each other, and as a result, the change in the threshold voltage Vbe between the base and emitter of the second transistor Tr 2 a can be absorbed. As such, the change in the gain under the same conditions can be reduced. The fifth transistor Tr 2 b can obtain an effect similar to that of the second transistor Tr 2 a.

Hereinbelow, a description will be give of an operation of the semiconductor device 10 according to the present embodiment. According to the above equation (1), as the input voltage Vin increases, the amplification voltage Vc increases. However, as a result of the provision of a second transistor Tr 2 a , the following operation will be further performed. When the amplification voltage Vc increases, the degree of on of the second transistor Tr 2 a weakens and the collector current gets smaller. When the amplification voltage Vc further increases, the second transistor Tr 2 a is turned off, and as a result, an intermediate voltage Vda clamped to the voltage when it is turned off is inputted to the noninverting input terminal of the second operational amplifier 156 a and is outputted as a first output voltage Vout 1 .

When a short-circuiting of a loading control terminal T 1 to the ground takes place, an input voltage Vin which is in the neighborhood of ground potential, for instance, 0 V, is inputted to the noninverting input terminal of the first differential amplifier 106 . At this time, the input voltage Vin becomes equal to the reference voltage Vb, and the amplification voltage Vc takes a voltage value in the neighborhood of ground potential, for instance 0 V. At this time, the second transistor Tr 2 a is turned on, a collector current which is rather large flows, and the intermediate voltage Vda is clamped to the threshold voltage Vbe between the base and emitter of the second transistor Tr 2 a and outputted as a first output voltage Vout 1 . Accordingly, even in an emergency, the intermediate voltage Vda is clamped to a nonzero predetermined voltage, which is the threshold voltage Vbe between the base and emitter of the second transistor Tr 2 a , so that a nonzero output signal can be supplied to the coil load 20 . The second output circuit 150 b also performs an operation similar to that of the first output circuit 150 a.

Hereinbelow, a description will be given of how the output signal at an amplifier circuit 100 changes, using drawings. FIG. 2A shows a relationship between the input voltage Vin applied to a loading control terminal T 1 and the output signal of the amplifier circuit 100 when an H-level signal is inputted to the FWD terminal T 4 and an L-level signal to the REV terminal T 5 , and FIG. 2B shows a relationship between the input voltage Vin applied to a loading control terminal T 1 and the output signal of the amplifier circuit 100 when an L-level signal is inputted to the FWD terminal T 4 and an H-level signal is inputted to the REV terminal T 5 . The horizontal axis represents the input voltage Vin applied to the loading control terminal T 1 , and the vertical axis represents the output signal of the amplifier circuit 100 .

As shown in FIG. 2A , when an H-level signal is inputted to the FWD terminal T 4 and an L-level signal to the REV terminal T 5 , the first output signal Sig 1 becomes active while the second output signal Sig 2 becomes 0 v. As already described, the amplifier circuit 100 drives the coil load 20 , using the voltage difference between the first output signal Sig 1 and the second output signal Sig 2 . The greater the difference, the higher the revolution speed of the coil load 20 will be.

As shown in FIG. 2B , the first output signal Sig 1 becomes 0 V while the second output signal Sig 2 becomes active. The polarity of the second output signal Sig 2 in FIG. 2B is opposite to the polarity of the first output signal Sig 1 in FIG. 2A . This is the same as the case of FIG. 2A in that the coil load 20 is driven, using the voltage difference between the first output signal Sig 1 and the second output signal Sig 2 , but it differs in that the coil load 20 is driven in reverse rotation.

As shown in FIG. 2A , the second transistor Tr 2 a generates a clamp voltage to prevent the first output signal Sig 1 from dropping below a predetermined clamp voltage. Accordingly, even when a short-circuiting of the loading control terminal T 1 to the ground has taken place, that is, even when the voltage applied to the loading control terminal T 1 has taken a voltage value in the neighborhood of ground potential, for instance, 0 V, the amplifier circuit 100 can supply a nonzero and constant level of voltage to the coil load 20 , thus realizing an emergency loading control of the tray.

The correspondence in structure between the present invention and the embodiments are exemplified here. “Clamp circuit” corresponds to the second transistor Tr 2 a and the fifth transistor Tr 2 b ; a “first clamp circuit” corresponds to the second transistor Tr 2 a ; a “second clamp circuit” corresponds to the fifth transistor Tr 2 b . A “compensation circuit” corresponds to the first transistor Tr 1 . “First transistor” corresponds to the second transistor Tr 2 a and the fifth transistor Tr 2 b , whereas a “second transistor” corresponds to the third transistor Tr 3 a.

The present invention has been described based on the embodiments. The embodiments are merely exemplary, and it is understood by those skilled in the art that various modifications to the combination of each component and process thereof are possible and such modifications are also within the scope of the present invention. Such modification will be described as follow.

An element to be driven by the amplifier circuit 100 in the embodiments was the coil load 20 , but this should not be considered as limiting. Any equipment that operates by using the amplifier circuit 100 as a means for supplying the power will serve the purpose. For example, it may be a motor, an LED element, an organic EL (Electro-Luminescence) element, a heater, a fan or a communication unit. According to this modification, in an emergency such as the occurrence of a fault, nonzero clamp voltage is delivered as a drive voltage in order that no voltage less than or equal to a predetermined voltage should occur, so that a certain drive can be achieved as an act of necessity in an emergency.

Although the amplifier circuit 100 according to the present embodiment is provided with the differential circuit 110 , the amplifier circuit 100 excluding the difference circuit 110 is proposed here. Then, the input voltage Vin, from the variable voltage source 12 , which has been inputted via the loading control terminal T 1 is directly (that is, as a 1×amplification voltage Vc) inputted to the base of the second transistor Tr 2 a . At this time, when the input voltage Vin becomes 0 V due to a reason such as occurrence of abnormality, the amplification voltage Vc becomes 0 V. However, since the amplification voltage Vc is clamped to a nonzero voltage, a constant voltage can be secured as an output of the amplifier circuit 100 the same way as in the embodiment. Thereby, this modification can obtain the same effect as in the embodiment.

The present invention can be used for electronic equipment and the like which control the opening and closing of a tray.