JP2006319428A - Power amplifier integrated circuit and on-vehicle audio system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To output a signal having a voltage capable of being directly input from a signal output terminal of a power amplifier integrated circuit to another integrated circuit. <P>SOLUTION: A signal to be maintained at a predetermined level is input into a signal input terminal 43 of the power amplifier integrated circuit 3. A reference voltage generating circuit 46 is connected to the signal input terminal 43, and generates a reference voltage having a voltage lower than the voltage to be input into the signal input terminal 43. An analog operation amplification circuit 33 receives the input reference voltage, and outputs a signal having a voltage waveform varying using the reference voltage as a reference. A signal output terminal 38 outputs a signal generated by the amplification circuit 33. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power amplifier integrated circuit and an in-vehicle audio system.

  Patent Document 1 discloses an audio power amplifier IC (Integrated Circuit). The audio power amplifier IC includes a bias voltage generation circuit that controls generation of a bias voltage according to the voltage level of the standby signal. The audio power amplifier IC includes a reference voltage generation circuit, a comparator, a voltage detection circuit, and the like in addition to the bias voltage generation circuit. The internal circuits of these audio power amplifier ICs operate with the voltage (12V or the like) of the vehicle battery supplied to the VCC of the audio power amplifier IC.

Japanese Patent Laid-Open No. 11-88066 (abstract, detailed description of the invention, drawings)

  Some power amplifier integrated circuits output a waveform signal that changes in accordance with an audio signal or the like input thereto. Some power amplifier integrated circuits detect an abnormality such as a short circuit between output terminals and output an abnormality detection signal. These signals output from the power amplifier integrated circuit are input to, for example, a control integrated circuit that controls starting and stopping of the power amplifier integrated circuit. The control integrated circuit determines the operating state of the power amplifier integrated circuit based on these signals, and controls the start and stop of the power amplifier integrated circuit.

  However, as exemplified in Patent Document 1, the power amplifier integrated circuit operates with the voltage of the on-vehicle battery (12 V or the like), while a general integrated circuit such as a control integrated circuit has a voltage of 5 V or less, for example. Operate. A signal generated by an internal circuit of the power amplifier integrated circuit exceeds the input voltage range of a signal of a general integrated circuit such as a control integrated circuit.

  Therefore, when the signal output from the power amplifier integrated circuit is input to the control integrated circuit, the voltage level of the signal output from the power amplifier integrated circuit is set between the power amplifier integrated circuit and the control integrated circuit. It is necessary to provide a circuit that shifts the voltage level to a voltage level that can be input to the power supply, a circuit that converts the amplitude of the signal output from the power amplifier integrated circuit to a voltage range that can be input to the control integrated circuit, and the like.

  The power amplifier integrated circuit often adopts an open collector or an open drain as an output stage when outputting a digital value. However, in this case, if a pull-up resistor element is not provided between the power amplifier integrated circuit and the control integrated circuit in order to generate a voltage change corresponding to the on / off of the output stage, the control integrated circuit is significant. A signal having a different voltage level cannot be input.

  An object of the present invention is to obtain a power amplifier integrated circuit and an in-vehicle audio system that can output a signal having a voltage that can be directly input to another integrated circuit from a signal output terminal of the power amplifier integrated circuit.

  A power amplifier integrated circuit according to the present invention includes a signal input terminal to which a signal held at a predetermined level is input, and a reference voltage connected to the signal input terminal and having a voltage lower than the voltage input to the signal input terminal. A reference voltage generation circuit to generate, an analog operational amplifier circuit that outputs a signal having a voltage waveform that changes with reference voltage as a reference, and a signal output terminal that outputs a signal generated by the analog operational amplifier circuit And.

  In the power amplifier integrated circuit according to the present invention, in addition to the configuration of the above-described invention, the reference voltage generation circuit has an input stage NPN transistor whose base is connected to the signal input terminal, and the base is connected to the emitter of the input stage NPN transistor. , And a PNP transistor for limiter whose emitter is connected to the signal output terminal.

  The power amplifier integrated circuit according to the present invention includes a resistor element connected between the output of the analog operational amplifier circuit and the signal output terminal in addition to the above-described components of the invention.

  A power amplifier integrated circuit according to the present invention has a diagnostic switching element connected to a signal output terminal in addition to the components of the above-described invention, and an abnormality of the power amplifier integrated circuit or an input of the power amplifier integrated circuit. When the abnormality of the output signal is detected, the diagnostic switching element is controlled to be turned on.

  The power amplifier integrated circuit according to the present invention is connected to the signal input terminal in addition to the components of the above-described invention, and activates the power amplifier integrated circuit when the input voltage of the signal input terminal is equal to or higher than a predetermined voltage. It has a starting circuit.

  Another power amplifier integrated circuit according to the present invention includes a signal input terminal to which a signal held at a predetermined level is input, a signal output terminal, and a resistance element connected between the signal input terminal and the signal output terminal And a diagnostic switching element connected to the signal output terminal, and when the abnormality of the power amplifier integrated circuit or the abnormality of the input / output signal of the power amplifier integrated circuit is detected, the diagnostic switching element is controlled to be in an ON state. A diagnostic circuit.

  A third power amplifier integrated circuit according to the present invention includes a signal input terminal to which a signal held at a predetermined level is input, a signal output terminal, and a first input connected between the signal input terminal and the signal output terminal. One switching element, a second switching element connected between the signal output terminal and the ground, and a waveform signal inputted to and outputted from the power amplifier integrated circuit or a waveform signal inside the power amplifier integrated circuit, And a digital waveform output circuit that individually controls on / off of the one switching element and the second switching element.

  An in-vehicle audio system according to the present invention is connected to a power amplifier integrated circuit of each configuration according to the above-described invention connected to a vehicle battery, and a signal input terminal and a signal output terminal of the power amplifier integrated circuit are connected to the signal input terminal. And a control integrated circuit for inputting a signal held at a voltage lower than its own power supply voltage.

  Another in-vehicle audio system according to the present invention includes a power amplifier integrated circuit according to the above-described invention, which is connected to a vehicle battery and includes a resistance element connected between an output of an analog operational amplifier circuit and a signal output terminal; The signal input terminal and signal output terminal of the power amplifier integrated circuit are connected, and the control integrated circuit for inputting a signal held at a voltage lower than its own power supply voltage to the signal input terminal and the signal input terminal connected to the power An external reference voltage generation circuit that generates substantially the same voltage as the reference voltage generation circuit of the amplifier integrated circuit as an external reference voltage, one end connected to the signal output terminal of the power amplifier integrated circuit and the control integrated circuit, and the other end to the external reference And a capacitor connected to the output of the voltage generation circuit.

  In the present invention, a signal having a voltage that can be directly input to another integrated circuit can be output from the signal output terminal of the power amplifier integrated circuit.

  Hereinafter, a power amplifier integrated circuit and an in-vehicle audio system according to embodiments of the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a system configuration diagram showing an in-vehicle audio system according to Embodiment 1 of the present invention. The in-vehicle audio system is an audio system mounted on a vehicle such as an automobile or a motorcycle. Vehicles such as automobiles and motorcycles have a battery 1 that outputs a voltage of 12 V (volts) or 24 V and a generator (not shown).

  A vehicle battery 1 and a generator (not shown) are connected to a power supply circuit 2 and a power amplifier integrated circuit 3 of the in-vehicle audio system. The power supply circuit 2 and the power amplifier integrated circuit 3 are directly connected to the positive terminal and the negative terminal of the battery 1 of the vehicle, and operate with the battery voltage. Note that the negative terminal of the battery 1 is generally connected to the vehicle ground 4.

  The power supply circuit 2 generates a predetermined stable voltage such as +5 V, for example, with the negative terminal of the battery 1 as a reference, and outputs it as a power supply voltage. The power supply voltage generated by the power supply circuit 2 is a circuit other than the power amplifier integrated circuit 3 of the in-vehicle audio system (hereinafter referred to as an internal circuit), for example, a radio receiver 5, a CD (Compact Disc) player 6, and a source selector 7. , The display device 8, the input device 9, the control integrated circuit 10, the external reference voltage generation circuit 11, and the like.

  The radio receiver 5 receives radio waves and outputs an audio signal to the source selector 7. The CD player 6 reads the data recorded on the CD and outputs an audio signal based on the read data to the source selector 7. The radio receiver 5 and the CD player 6 are sound source devices. The source selector 7 selects one of a plurality of sound source devices such as the radio receiver 5 and the CD player 6 and outputs an audio signal of the selected sound source device to the power amplifier integrated circuit 3.

  The display device 8 displays a list of a plurality of sound source devices. The input device 9 has a plurality of input keys operated by the user, and outputs an input signal corresponding to the operated input keys.

  The control integrated circuit 10 that operates with the voltage supplied from the power supply circuit 2 includes an AD (Analog to Digital) converter 12, an input / output port 13, and the like. The AD converter 12 samples the voltage level of the input signal and outputs a digital value corresponding to the voltage level. The input / output port 13 determines an input signal with a predetermined threshold, and outputs a value of 0 or 1 according to the determination result. Further, when a value of 0 or 1 is set, the input / output port 13 outputs a voltage level corresponding to the set value. The input / output port 13 outputs, for example, a voltage close to the ground potential based on a value of 0, and outputs a voltage close to the power supply voltage of the control integrated circuit 10 based on a value of 1, for example.

  The input / output port 13 of the control integrated circuit 10 is connected to a radio receiver 5, a CD player 6, a source selector 7, a display device 8, an input device 9, a power amplifier integrated circuit 3, and the like. A power amplifier integrated circuit 3 is connected to the AD converter 12.

  FIG. 2 is a circuit diagram showing the power amplifier integrated circuit 3 in FIG. The power amplifier integrated circuit 3 has audio signal output terminals 21 for four channels. The audio signal output terminal 21 of the power amplifier integrated circuit 3 may be for two channels or 5.1 channels.

  The audio signal output terminal 21 of each channel includes two audio signal output terminals 21. As shown in FIG. 1, a speaker 14 built in a vehicle door or the like is connected between the two audio signal output terminals 21. The power amplifier integrated circuit 3 amplifies the audio signal input thereto and outputs it from the audio signal output terminal 21 of each channel.

  Four resistance elements 22 are connected in series between the two audio signal output terminals 21 of each channel. The four resistance elements 22 are connected in parallel with the speaker 14. Each resistance element 22 generates a voltage having an amplitude that is about one quarter of the audio signal that the power amplifier integrated circuit 3 supplies to the speaker 14. The number of resistance elements 22 may be 1 to 3, or 5 or more.

  Both ends of one of the four resistance elements 22 are connected to a channel-specific circuit 23. The channel-specific circuit 23 has two input buffers 24 and 25. Both ends of the resistance element 22 are connected to two input buffers 24 and 25.

  One end of the input resistance element 26 is connected to the output of one input buffer 24. The other end of the input resistance element 26 is connected to the inverting input terminal of the operational amplifier 27. An output resistance element 28 is connected between the inverting input terminal and the output terminal of the operational amplifier 27.

  The output of the other input buffer 25 is connected to one end of the first voltage dividing resistor element 29 for each channel. One end of the channel-specific second voltage dividing resistor element 30 is connected to the other end of the channel-specific first voltage dividing resistor element 29. The other end of the channel-specific second voltage dividing resistor 30 is connected to the output of the reference voltage buffer 31. A reference voltage output from a reference voltage generation circuit 46 described later is input to the reference voltage buffer 31.

  A connection point between the channel-specific first voltage dividing resistor 29 and the channel-specific second voltage dividing resistor 30 is connected to the non-inverting input terminal of the operational amplifier 27.

  By adopting such a circuit configuration, the channel-specific circuit 23 uses the voltage of the resistance element 22 connected to the two input buffers 24 and 25 as a reference based on the reference voltage input to the reference voltage buffer 31. The level is shifted to a voltage level, amplified by a differential amplifier circuit composed of an input resistance element 26, an operational amplifier 27, and an output resistance element 28, and output.

  An adder circuit 32 is connected to the output terminal of the operational amplifier 27 of the circuit 23 for each channel. The adder circuit 32 includes an operational amplifier 33 as an analog operational amplifier circuit, the same number (here, four) of input resistance elements 34 and output resistance elements 35 as channels. Each input resistance element 34 is connected between the output of each channel-specific circuit 23 and the inverting input terminal of the operational amplifier 33. The output resistance element 35 is connected between the inverting input terminal and the output terminal of the operational amplifier 33. A reference voltage output from a reference voltage generation circuit 46 described later is input to the non-inverting input terminal of the adder circuit 32. The adder circuit 32 follows the voltage obtained by adding the plurality of voltages input to the plurality of input resistance elements 34 with the voltage input to the non-inverting input terminal as a reference, and outputs an output voltage that changes in the opposite phase to the output voltage. Output from 33 output terminals.

  One end of a low-pass filter resistance element 37 as a resistance element is connected to the output of the adder circuit 32. The other end of the low-pass filter resistance element 37 is connected to the signal output terminal 38.

  In addition to the audio signal output terminals 21 and signal output terminals 38 for the number of channels described above, the power amplifier integrated circuit 3 includes a power supply terminal 41, a ground terminal 42, a start / stop signal input terminal 43 as a signal input terminal, and a digital signal only. An output terminal 44 and the like are included. The number of terminals of the 4-channel power amplifier integrated circuit 3 is usually about 20 to 35. The power supply terminal 41 of the power amplifier integrated circuit 3 is connected to the plus terminal of the battery 1. The ground terminal 42 is connected to the negative terminal of the battery 1. The power amplifier integrated circuit 3 operates with the output voltage of the battery 1.

  The start / stop signal input terminal 43 is connected to the reference voltage generation circuit 46. The reference voltage generation circuit 46 includes an input stage NPN transistor 47. The start / stop signal input terminal 43 is connected to the base of the input stage NPN transistor 47. The collector of the input stage NPN transistor 47 is connected to the power supply terminal 41. One end of the first voltage dividing resistor 48 is connected to the emitter of the input stage NPN transistor 47. The other end of the first voltage dividing resistor element 48 is connected to one end of the second voltage dividing resistor element 49. The other end of the second voltage dividing resistor element 49 is connected to the anode of the diode 50. The cathode of the diode 50 is connected to the ground terminal 42.

  The voltage of the node to which the first voltage dividing resistor element 48 and the second voltage dividing resistor element 49 of the reference voltage generating circuit 46 are connected becomes a reference voltage. The voltage of this node is about half the voltage input to the start / stop signal input terminal 43. The node is connected to the reference voltage buffer 31 of the four channel-specific circuits 23 and the non-inverting input terminal of the operational amplifier 33 of the adder circuit 32.

  Note that a reference voltage buffer may be connected to the node, and the reference voltage generation circuit 46 may output the output voltage of the reference voltage buffer as a reference voltage. In this case, the reference voltage buffers 31 of the four channel-specific circuits 23 can be omitted.

  The base of the limiter PNP transistor 51 is also connected to the emitter of the input stage NPN transistor 47 of the reference voltage generation circuit 46. The emitter of the limiter PNP transistor 51 is connected to the signal output terminal 38. The collector of the limiter PNP transistor 51 is connected to the ground terminal 42 via the resistance element 52.

  In addition to the low-pass filter resistor element 37 and the limiter PNP transistor 51 described above, the signal output terminal 38 is connected to a short circuit detection circuit 56 as a diagnostic circuit and a window comparator 57.

  The short circuit detection circuit 56 has a diagnostic NPN transistor 59 as a diagnostic switching element. The collector of the diagnostic NPN transistor 59 is connected to the signal output terminal 38 via the protective resistance element 58. The emitter of the diagnostic NPN transistor 59 is connected to the ground terminal 42. The short circuit detection circuit 56 monitors the audio signal output terminals 21 for the four channels, and detects the short circuit of any of the audio signal output terminals 21 and controls the diagnostic NPN transistor 59 to be in an ON state. In other states, the short circuit detection circuit 56 controls the diagnostic NPN transistor 59 to be turned off.

  The short circuit detected by the short circuit detection circuit 56 includes, for example, a short circuit between the pair of audio signal output terminals 21 of each channel, a short circuit between the audio signal output terminal 21 and the power supply terminal 41, and the audio signal output terminal 21 and the ground terminal. 42 and the like.

  The window comparator 57 compares the potential at the other end of the low-pass filter resistance element 37 with a predetermined voltage range set in advance. The potential at the other end of the low-pass filter resistance element 37 is the voltage difference between the pair of signal output terminals 21 for each channel when the low-pass filter capacitor 15 is connected to the outside of the signal output terminal 38 as will be described later. The voltage is obtained by removing high-frequency components from the voltage waveform obtained by adding a plurality of channels. That is, the voltage corresponds to the sum of DC offset voltages output from a plurality of sets of channels. When the potential at the other end of the low-pass filter resistance element 37 is outside a predetermined voltage range set in advance, the window comparator 57 controls the digital signal dedicated output terminal 44 to a low level.

  In addition to the input stage NPN transistor 47 of the reference voltage generation circuit 46 described above, a start circuit 60 is connected to the start / stop signal input terminal 43. The start circuit 60 controls the start and stop of the internal circuit of the power amplifier integrated circuit 3. The internal circuit includes the above-described plurality of channel-specific circuits 23, the operational amplifier 27 of the channel-specific circuit 23, the operational amplifier 33 of the adder circuit 32, a short circuit detection circuit 56, a window comparator 57, and the like. The activation circuit 60 activates these internal circuits when the input voltage of the activation stop signal input terminal 43 becomes equal to or higher than a predetermined voltage such as 1.5V. The start circuit 60 stops the internal circuit of the power amplifier integrated circuit 3 when the input voltage of the start stop signal input terminal 43 becomes lower than a predetermined voltage. Note that the startup circuit 60 controls the start and stop of the internal circuits by controlling the connection of these internal circuits to the power supply terminal 41, for example.

  The start / stop signal input terminal 43, the signal output terminal 38, and the digital signal dedicated output terminal 44 of the power amplifier integrated circuit 3 having the above configuration are connected to the control integrated circuit 10 as shown in FIG. As described above, the control integrated circuit 10 includes the AD converter 12 and the input / output port 13.

  Specifically, the signal output terminal 38 of the power amplifier integrated circuit 3 is directly connected to the AD converter 12 of the control integrated circuit 10. The signal output terminal 38 is connected to one end of a low-pass filter capacitor 15 as a capacitor.

  Specifically, the start / stop signal input terminal 43 of the power amplifier integrated circuit 3 is connected to the input / output port 13 of the control integrated circuit 10 via the low-pass filter circuit (LPF) 16. A signal output from the input / output port 13 of the control integrated circuit 10 is input to the start / stop signal input terminal 43 via the low-pass filter circuit 16.

  The external reference voltage generation circuit 11 is connected to the start / stop signal input terminal 43 of the power amplifier integrated circuit 3. The external reference voltage generation circuit 11 has a circuit configuration similar to that of the reference voltage generation circuit 46 of the power amplifier integrated circuit 3. That is, the external reference voltage generation circuit 11 has an external NPN transistor 61 as shown in FIG. The start / stop signal input terminal 43 is connected to the base of the external NPN transistor 61. The collector of the external NPN transistor 61 is connected to the power supply circuit 2. One end of the external first voltage dividing resistor element 62 is connected to the emitter of the external NPN transistor 61. The other end of the external first voltage dividing resistor 62 is connected to one end of the external second voltage dividing resistor 63. The other end of the external second voltage dividing resistor 63 is connected to the anode of the external diode 64. The cathode of the external diode 64 is connected to the negative terminal of the battery 1.

  The other end of the low-pass filter capacitor 15 is connected to a node to which the external first voltage dividing resistor element 62 and the external second voltage dividing resistor element 63 of the external reference voltage generating circuit 11 are connected. One end of the low-pass filter capacitor 15 is connected to the signal output terminal 38 as described above. The low-pass filter capacitor 15 and the low-pass filter resistor element 37 connected to the signal output terminal 38 in the power amplifier integrated circuit 3 constitute a low-pass filter circuit.

  Specifically, the digital signal dedicated output terminal 44 of the power amplifier integrated circuit 3 is connected to the input / output port 13 of the control integrated circuit 10. A signal output from the digital signal dedicated output terminal 44 of the power amplifier integrated circuit 3 is input to the input / output port 13 of the control integrated circuit 10.

  Next, the operation of the in-vehicle audio system according to Embodiment 1 having the above configuration will be described. First, the case where an in-vehicle audio system is started will be described.

  Before starting, the control integrated circuit 10 uses the input / output port 13 to control the start / stop signal input terminal 43 of the power amplifier integrated circuit 3 to a low level. When the start / stop signal input terminal 43 is at a low level, the start circuit 60 of the power amplifier integrated circuit 3 stops the internal circuit of the power amplifier integrated circuit 3.

  The control integrated circuit 10 outputs the sound source device list selection screen data from the input / output port 13 to the display device 8. The display device 8 displays a list of sound source devices such as radio and CD. Based on the display of the display device 8, the user performs an operation for causing the input device 9 to select a predetermined sound source device. The input device 9 outputs an input signal corresponding to the operation to the input / output port 13. The control integrated circuit 10 selects a predetermined sound source device based on the input signal from the input device 9.

  After selecting the sound source device, the control integrated circuit 10 outputs an activation signal from the input / output port 13 to the selected sound source device. The sound source device to which the activation signal is output starts operation and outputs an audio signal.

  Further, the control integrated circuit 10 outputs a selection signal for selecting the selected sound source device as a source from the input / output port 13 to the source selector 7. The source selector 7 selects a sound source device designated by the selection signal, and outputs an audio signal input from the selected sound source device to the power amplifier integrated circuit 3.

  Further, the control integrated circuit 10 uses the input / output port 13 to control the start / stop signal input terminal 43 of the power amplifier integrated circuit 3 to a high level. The voltage of the start / stop signal input terminal 43 is controlled to a voltage close to the power supply voltage of the control integrated circuit 10. The activation circuit 60 of the power amplifier integrated circuit 3 operates the internal circuit of the power amplifier integrated circuit 3 when the input voltage of the activation stop signal input terminal 43 becomes equal to or higher than a predetermined voltage. As a result, the plurality of channel-specific circuits 23 of the power amplifier integrated circuit 3, the operational amplifier 27 of the channel-specific circuit 23, the operational amplifier 33 of the adder circuit 32, the short-circuit detection circuit 56, the window comparator 57, and the like start operation.

  The power amplifier integrated circuit 3 in which the internal circuit is operating amplifies the audio signal input from the source selector 7 and outputs it from the audio signal output terminal 21 of each channel. The speaker 14 is driven by the power amplifier integrated circuit 3 and outputs sound.

  Through the series of controls by the control integrated circuit 10 described above, sound from the sound source device selected by the control integrated circuit 10 based on a user operation is output from the speaker 14.

  Thus, the power amplifier integrated circuit 3 outputs an audio signal from the audio signal output terminal 21 of each channel when the start / stop signal input terminal 43 is controlled to a high level by the control integrated circuit 10.

  On the other hand, each channel-specific circuit 23 of the power amplifier integrated circuit 3 level-shifts the voltage of the resistance element 22 connected between the two audio signal output terminals 21 of each channel to a voltage based on the reference voltage. Then, it is amplified by a differential amplifier circuit having an operational amplifier 27 and output. Each channel-specific circuit 23 outputs a waveform detection signal having a voltage that changes in accordance with an audio signal supplied from each channel to the speaker 14.

  The reference voltage generation circuit 46 outputs a voltage that is half of the voltage input to the start / stop signal input terminal 43 to the non-inverting input terminal as a reference voltage. Therefore, the circuit 23 for each channel levels the voltage of the resistance element 22 to a voltage having a waveform that changes around the voltage half of the voltage input to the start / stop signal input terminal 43 and changes according to the voltage of the resistance element 22. Shift and output.

  The waveform detection signal output from each channel circuit 23 is input to the adder circuit 32. The reference voltage generated by the reference voltage generation circuit 46 is input to the non-inverting input terminal of the operational amplifier of the adder circuit 32. The operational amplifier 33 adds the voltages of the waveform detection signals output from the plurality of channel-specific circuits 23 with the reference voltage as a reference, and outputs the result. The adder circuit 32 outputs a waveform detection signal obtained by adding waveforms for four channels that change with reference to the reference voltage.

  The added waveform detection signal output from the adder circuit 32 is output from the signal output terminal 38 to the outside of the power amplifier integrated circuit 3 via the low-pass filter resistance element 37. The signal output terminal 38 is connected to the low-pass filter capacitor 15 and the AD converter 12 of the control integrated circuit 10. The low-pass filter resistance element 37 and the low-pass filter capacitor 15 function as a low-pass filter circuit for the output signal of the adder circuit 32. Therefore, the AD converter 12 of the control integrated circuit 10 receives a signal obtained by removing the high frequency component from the added waveform detection signal output from the adder circuit 32. The AD converter 12 samples the input signal.

  By the way, the added waveform detection signal output from the adder circuit 32 has a voltage that changes with reference to the reference voltage generated in the power amplifier integrated circuit 3. This reference voltage is about half the voltage input to the start / stop signal input terminal 43. The start / stop signal input terminal 43 is controlled to a high level by the input / output port 13 of the control integrated circuit 10. The high level voltage output from the input / output port 13 by the control integrated circuit 10 is a voltage equal to or lower than the power supply voltage of the control integrated circuit 10. Therefore, the voltage output from the signal output terminal 38 of the power amplifier integrated circuit 3 basically changes within a range equal to or lower than the power supply voltage of the control integrated circuit 10.

  The base of the limiter PNP transistor 51 is connected to the emitter of the input stage NPN transistor 47. The base of the input stage NPN transistor 47 is connected to the start / stop signal input terminal 43. Therefore, if the voltage at the signal output terminal 38 of the power amplifier integrated circuit 3 exceeds the voltage input to the start / stop signal input terminal 43 for some reason, the limiter PNP transistor 51 is turned on. The voltage at the start / stop signal input terminal 43 is equal to or lower than the power supply voltage of the control integrated circuit 10. Therefore, the voltage of the signal output terminal 38 changes in a range equal to or lower than the power supply voltage of the control integrated circuit 10. The voltage at the signal output terminal 38 of the power amplifier integrated circuit 3 does not constantly exceed the power supply voltage of the control integrated circuit 10.

  In addition, the short circuit detection circuit 56 of the power amplifier integrated circuit 3 includes a short circuit between the pair of audio signal output terminals 21 of each channel, a short circuit between the audio signal output terminal 21 and the power supply terminal 41, and the audio signal output terminal 21 and the ground terminal 42. When a short circuit is detected, the diagnostic NPN transistor 59 is controlled to be on. When the diagnostic NPN transistor 59 is turned on, the low-pass filter resistance element 37 is grounded. The voltage at the signal output terminal 38 is a low level voltage close to the ground voltage regardless of the output voltage of the adder circuit 32.

  As a result, the AD converter 12 of the control integrated circuit 10 directly connected to the signal output terminal 38 of the power amplifier integrated circuit 3 can sample the voltage output from the signal output terminal 38 of the power amplifier integrated circuit 3. it can. The AD converter 12 has a voltage based on the output of the adder circuit 32 that changes in its input voltage range, a low-level voltage generated by the short-circuit detection circuit 56, and a limiter PNP transistor 51 that is on. A high level voltage can be sampled.

  The window comparator 57 of the power amplifier integrated circuit 3 compares the voltage at the other end of the low-pass filter resistance element 37 with a predetermined voltage range set in advance. When the voltage at the other end of the low-pass filter resistance element 37 falls outside a predetermined voltage range set in advance, the window comparator 57 controls the digital signal dedicated output terminal 44 to a low level. The digital signal dedicated output terminal 44 is connected to the input / output port 13 of the control integrated circuit 10. The input / output port 13 generates a digital value of 1 or 0 based on the voltage input from the digital signal dedicated output terminal 44.

  The control integrated circuit 10 determines the operating state of the power amplifier integrated circuit 3 based on the voltage value sampled by the AD converter 12 and the digital value generated by the input / output port 13 based on the input voltage.

  For example, if the voltage value sampled by the AD converter 12 is a value close to the ground potential, the control integrated circuit 10 determines that the output of the power amplifier integrated circuit 3 is short-circuited. Then, the control integrated circuit 10 uses the input / output port 13 to control the start / stop signal input terminal 43 of the power amplifier integrated circuit 3 to a low level.

  The activation circuit 60 of the power amplifier integrated circuit 3 stops the internal circuit of the power amplifier integrated circuit 3 when the input voltage of the activation stop signal input terminal 43 becomes lower than a predetermined voltage. As a result, the plurality of channel-specific circuits 23 of the power amplifier integrated circuit 3, the operational amplifier 27 of the channel-specific circuit 23, the operational amplifier 33 of the adder circuit 32, the short-circuit detection circuit 56, the window comparator 57, etc. stop their operations. Further, the power amplifier integrated circuit 3 does not output audio signals from the plurality of audio signal output terminals 21 to the speaker 14. The speaker 14 does not output sound.

  In addition, for example, when the voltage value sampled by the AD converter 12 is shifted by a predetermined value from the half value of the power supply voltage of the control integrated circuit 10, the control integrated circuit 10 causes the DC voltage to be applied to the speaker 14. Judge that it is supplied. Then, the control integrated circuit 10 executes control for suppressing the DC voltage.

  In addition, for example, when the control integrated circuit 10 determines that an abnormal DC voltage is supplied to the speaker 14 based on the digital value generated by the input / output port 13, the start / stop signal of the power amplifier integrated circuit 3 is The input terminal 43 is controlled to a low level. Thereby, the internal circuit of the power amplifier integrated circuit 3 is stopped. The speaker 14 does not output sound.

  As described above, according to the first embodiment, the control integrated circuit 10 has a high-level signal held at the start / stop signal input terminal 43 of the power amplifier integrated circuit 3 at a voltage lower than its own power supply voltage. Enter. The waveform signal output from the adder circuit 32 of the power amplifier integrated circuit 3 changes based on a reference voltage that is approximately half of the voltage input to the start / stop signal input terminal 43.

  Therefore, the signal output terminal 38 of the power amplifier integrated circuit 3 and the AD converter 12 of the control integrated circuit 10 are directly connected, and the waveform signal is directly input from the power amplifier integrated circuit 3 to the control integrated circuit 10. Can do.

  Further, for example, when the control integrated circuit 10 fails and the failed control integrated circuit 10 is replaced with a new control integrated circuit 10, the power supply voltages of these control integrated circuits 10 are, for example, 5V and 3.3V. Even when they are different, the detection signal interface is maintained. The replaced control integrated circuit 10 can control the power amplifier integrated circuit 3 and the like based on the detection signal from the power amplifier integrated circuit 3.

  In the power amplifier integrated circuit 3 of the first embodiment, the input stage NPN transistor 47 and the limiter PNP transistor 51 of the reference voltage generation circuit 46 are connected between the signal output terminal 38 and the start / stop signal input terminal 43. Is connected. Therefore, when the voltage at the signal output terminal 38 is about to exceed the voltage at the start / stop signal input terminal 43, the limiter PNP transistor 51 is turned on, and the voltage at the signal output terminal 38 is input to the start / stop signal input terminal 43. And the power supply voltage of the control integrated circuit 10 are difficult to exceed. The power amplifier integrated circuit 3 does not output an excessive voltage exceeding the power supply voltage of the control integrated circuit 10 to the control integrated circuit 10.

  In the power amplifier integrated circuit 3 of the first embodiment, a low-pass filter resistor element 37 is connected between the output of the adder circuit 32 and the signal output terminal 38. Therefore, a low-pass filter circuit that removes a high-frequency component from the output signal of the adder circuit 32 can be configured simply by connecting the low-pass filter capacitor 15 to the outside of the signal output terminal 38.

  The power amplifier integrated circuit 3 of the first embodiment has a short circuit detection circuit 56. The short-circuit detection circuit 56 includes a diagnostic NPN transistor 59 whose collector is connected to the signal output terminal 38. When a short circuit of the power amplifier integrated circuit 3 is detected, the short-circuit detection circuit 56 controls the diagnostic NPN transistor 59 to be on. Therefore, the waveform signal output from the adder circuit 32 and the digital detection signal from the short circuit detection circuit 56 can be output from one signal output terminal 38.

  Moreover, the diagnostic NPN transistor 59 of the short circuit detection circuit 56 is connected between the signal output terminal 38 and the low-pass filter resistance element 37. Therefore, even when the low-pass filter capacitor 15 is connected to the outside of the signal output terminal 38 to constitute a low-pass filter circuit, the voltage level of the signal output terminal 38 is not affected by this, and the diagnostic NPN By the on / off control of the transistor 59, the voltage level quickly changes to 0 or 1.

  In the power amplifier integrated circuit 3 according to the first embodiment, the start circuit 60 that controls the start / stop of the internal circuit has the internal circuit when the input voltage of the start / stop signal input terminal 43 is equal to or higher than a predetermined voltage. When the input voltage is lower than the predetermined voltage, the internal circuit is stopped. Therefore, even if the high level voltage supplied to the start / stop signal input terminal 43 by the control integrated circuit 10 is the power supply voltage of the control integrated circuit 10 or a voltage lower than that, the start circuit 60 is not connected to the internal circuit. Start and stop can be controlled. The start / stop signal input terminal 43 can also be used as a terminal for inputting a voltage for generating a reference voltage. The voltage output from the signal output terminal 38 can be limited without increasing the number of pins of the power amplifier integrated circuit 3.

  In the first embodiment, the external reference voltage generation circuit 11 is connected to the start / stop signal input terminal 43 of the power amplifier integrated circuit 3, and the external reference voltage generation circuit 11 is connected to the reference of the power amplifier integrated circuit 3. A reference voltage substantially the same as that of the voltage generation circuit 46 is generated, and the other end of the low-pass filter capacitor 15 is connected to the external reference voltage generation circuit 11.

  Therefore, when the power amplifier integrated circuit 3 is stopped, a voltage substantially equal to the reference voltage is input to the AD converter 12 of the control integrated circuit 10. When the power amplifier integrated circuit 3 is activated, the voltage of the signal input to the control integrated circuit 10 starts changing from a voltage substantially equal to the reference voltage. Therefore, the voltage obtained by removing the high frequency component from the signal output from the adder circuit 32 is input to the control integrated circuit 10 immediately after the power amplifier integrated circuit 3 is started.

  On the other hand, when the other end of the low-pass filter capacitor 15 is connected to, for example, the negative terminal of the battery 1, the AD converter of the control integrated circuit 10 when the power amplifier integrated circuit 3 is stopped. A voltage at the minus terminal is input to 12. For example, the low-pass filter capacitor 15 is charged to the reference voltage after the power amplifier integrated circuit 3 is started, and then follows the signal output from the adder circuit 32. Therefore, the voltage of the signal input to the control integrated circuit 10 is not after the charging time corresponding to the time constant of the low-pass filter capacitor 15 has elapsed since the power amplifier integrated circuit 3 is activated. The voltage does not follow the voltage output from the signal output terminal 38 by the amplifier integrated circuit 3. The control integrated circuit 10 cannot use the output of the AD converter 12 at least during the charging time. Even if a short circuit occurs in the output of the power amplifier integrated circuit 3, the control integrated circuit 10 cannot be controlled to stop the power amplifier integrated circuit 3 at least during the charging time.

Embodiment 2. FIG.
FIG. 3 is a system configuration diagram showing an in-vehicle audio system according to Embodiment 2 of the present invention. The in-vehicle audio system includes a power amplifier integrated circuit 3, a power supply circuit 2, a radio receiver 5, a CD player 6, a source selector 7, a display device 8, an input device 9, and a control integrated circuit 10. The radio receiver 5, the CD player 6, the source selector 7, the display device 8, and the input device 9 have the same functions as the components having the same names in the first embodiment, and have the same reference numerals as those in the first embodiment. The illustration and description are omitted.

  The power amplifier integrated circuit 3 and the power supply circuit 2 are connected to a battery 1 of the vehicle. The power supply circuit 2 supplies a predetermined voltage to the radio receiver 5, CD player 6, source selector 7, display device 8, input device 9, and control integrated circuit 10.

  The power amplifier integrated circuit 3 has a start / stop signal input terminal 43. The start / stop signal input terminal 43 is connected to the start circuit 60 and one end of a built-in pull-up resistor element 71 as a resistor element. The signal output terminal 38 and one end of the protective resistance element 58 are connected to the other end of the built-in pull-up resistance element 71. The collector of the diagnostic NPN transistor 59 of the short circuit detection circuit 56 is connected to the other end of the protective resistance element 58. The protective resistance element 58 prevents damage to the diagnostic NPN transistor 59 due to overcurrent.

  The signal output terminal 38 of the power amplifier integrated circuit 3 is connected to the input / output port 13 of the control integrated circuit 10.

  The constituent elements other than those described above of the power amplifier integrated circuit 3 have the same functions as the constituent elements having the same names as those of the first embodiment, and the description thereof is omitted.

  Next, the operation of the in-vehicle audio system according to Embodiment 2 having the above configuration will be described.

  When the start / stop signal input terminal 43 is controlled to a high level by the control integrated circuit 10, the start circuit 60 operates an internal circuit such as the short circuit detection circuit 56. As a result, the power amplifier integrated circuit 3 starts operation, amplifies the audio signal input from the source selector 7, and outputs the amplified audio signal from the audio signal output terminal 21 to the speaker 14.

  The short circuit detection circuit 56 detects a short circuit between the pair of audio signal output terminals 21 of each channel, a short circuit between the audio signal output terminal 21 and the power supply terminal 41, a short circuit between the audio signal output terminal 21 and the ground terminal 42, and the like. The diagnostic NPN transistor 59 is controlled to be on.

  When the diagnostic NPN transistor 59 is turned on, a current flows through the built-in pull-up resistor element 71. The voltage at the signal output terminal 38 is a low level voltage close to the ground voltage.

  When the diagnostic NPN transistor 59 is off, no current flows through the built-in pull-up resistor element 71. The voltage at the signal output terminal 38 becomes the voltage at the start / stop signal input terminal.

  The control integrated circuit 10 directly connected to the signal output terminal 38 monitors the voltage input from the signal output terminal 38 to the input / output port 13. When the digital value corresponding to the low level is output from the input / output port 13, it is determined that the output of the power amplifier integrated circuit 3 is short-circuited. Then, the control integrated circuit 10 uses the input / output port 13 to control the start / stop signal input terminal 43 of the power amplifier integrated circuit 3 to a low level.

  The activation circuit 60 of the power amplifier integrated circuit 3 stops the internal circuit of the power amplifier integrated circuit 3 when the input voltage of the activation stop signal input terminal 43 becomes lower than a predetermined voltage. As a result, the internal circuit of the power amplifier integrated circuit 3 stops operating. Further, the power amplifier integrated circuit 3 does not output audio signals from the plurality of audio signal output terminals 21 to the speaker 14. The speaker 14 does not output sound.

  Operations other than those described above of the in-vehicle audio system according to the second embodiment are the same as those of the first embodiment, and a description thereof will be omitted.

  As described above, according to the second embodiment, the control integrated circuit 10 inputs a signal held at a voltage lower than its own power supply voltage to the start / stop signal input terminal 43 of the power amplifier integrated circuit 3. .

  When the diagnostic NPN transistor 59 of the short circuit detection circuit 56 is in the OFF state, the signal output terminal 38 is connected to the start / stop signal input terminal 43 via the built-in pull-up resistor element 71. The voltage of the signal output terminal 38 is substantially the same as the high level voltage of the control integrated circuit 10.

  When the diagnostic NPN transistor 59 of the short circuit detection circuit 56 is turned on, the voltage of the signal output terminal 38 becomes a low level voltage close to the potential of the ground terminal 42. This voltage is substantially the same as the low level voltage of the control integrated circuit 10.

  Therefore, the signal output terminal 38 of the power amplifier integrated circuit 3 is directly connected to the input / output port 13 of the control integrated circuit 10, and the high level voltage and the low level voltage of the signal output terminal 38 of the power amplifier integrated circuit 3 are connected. Direct input to the control integrated circuit 10 is possible.

  In the second embodiment, a built-in pull-up resistor element 71 is connected between the diagnostic NPN transistor 59 of the short circuit detection circuit 56 and the start / stop signal input terminal 43. In addition, for example, the output stage transistor of the short-circuit detection circuit 56 is a PNP type, a built-in pull-down resistor element is connected between the collector of the PNP transistor and the ground terminal, and the emitter of the PNP transistor is connected to the start / stop signal. You may make it connect to the input terminal 43. FIG.

Embodiment 3 FIG.
FIG. 4 is a system configuration diagram showing an in-vehicle audio system according to Embodiment 3 of the present invention. The in-vehicle audio system includes a power amplifier integrated circuit 3, a power supply circuit 2, a radio receiver 5, a CD player 6, a source selector 7, a display device 8, an input device 9, and a control integrated circuit 10. The radio receiver 5, the CD player 6, the source selector 7, the display device 8, and the input device 9 have the same functions as the components having the same names in the first embodiment, and have the same reference numerals as those in the first embodiment. The illustration and description are omitted.

  The power amplifier integrated circuit 3 and the power supply circuit 2 are connected to a battery 1 of the vehicle. The power supply circuit 2 supplies a predetermined voltage to the radio receiver 5, CD player 6, source selector 7, display device 8, input device 9, and control integrated circuit 10.

  The power amplifier integrated circuit 3 has a start / stop signal input terminal 43. The start circuit 60 and one end of the first switching element 81 are connected to the start / stop signal input terminal 43. One end of the protective resistance element 83 and one end of the second switching element 82 are connected to the other end of the first switching element 81. The other end of the second switching element 82 is connected to the ground terminal.

  The other end of the protective resistance element 83 is connected to the signal output terminal 38. The signal output terminal 38 of the power amplifier integrated circuit 3 is connected to the AD converter 12 of the control integrated circuit 10.

  The power amplifier integrated circuit 3 has a window comparator 84 as a digital waveform output circuit. Window comparator 84 compares the sum of the voltages output from the plurality of sets of channels with a predetermined voltage range set in advance. When the sum of the voltages output from the plurality of sets of channels is on the plus side with respect to a predetermined voltage range set in advance, the window comparator 84 closes the first switching element 81. The window comparator 84 closes the second switching element 82 when the sum of the voltages output from the multiple sets of channels is on the minus side of a predetermined voltage range set in advance.

  The constituent elements other than those described above of the power amplifier integrated circuit 3 have the same functions as the constituent elements having the same names as those of the first embodiment, and the description thereof is omitted.

  Next, the operation of the in-vehicle audio system according to Embodiment 2 having the above configuration will be described.

  When the start / stop signal input terminal 43 is controlled to a high level by the control integrated circuit 10, the start circuit 60 operates an internal circuit such as the short circuit detection circuit 56. As a result, the power amplifier integrated circuit 3 starts operation, amplifies the audio signal input from the source selector 7, and outputs the amplified audio signal from the audio signal output terminal 21 to the speaker 14.

  Window comparator 84 compares the sum of the voltages output from the plurality of sets of channels with a predetermined voltage range set in advance. When the sum of the voltages output from the plurality of sets of channels is on the plus side with respect to a predetermined voltage range set in advance, the window comparator 84 closes the first switching element 81.

  When the first switching element 81 is closed, one end of the protective resistance element 83 is connected to the start / stop signal input terminal 43. The potential of the signal output terminal 38 changes to a voltage close to the voltage of the start / stop signal input terminal 43 according to a time constant determined by the resistance value of the protective resistance element 83 and the wiring capacitance connected to the signal output terminal 38. In a steady state, a voltage slightly lower than the voltage at the start / stop signal input terminal 43 is input to the AD converter 12 of the control integrated circuit 10.

  Further, when the sum of the voltages output from the plural sets of channels is on the minus side of a predetermined voltage range set in advance, the window comparator 847 closes the second switching element 82.

  When the second switching element 82 is closed, one end of the protective resistance element 83 is connected to the ground terminal 42. The potential of the signal output terminal 38 changes to a voltage close to the ground terminal 42 according to a time constant determined by the resistance value of the protective resistance element 83 and the wiring capacitance connected to the signal output terminal 38. During steady operation, a voltage slightly higher than the voltage at the ground terminal 42 is input to the AD converter 12 of the control integrated circuit 10.

  The AD converter 12 of the control integrated circuit 10 directly connected to the signal output terminal 38 samples the voltage at the signal output terminal 38 and outputs the voltage value. The control integrated circuit 10 controls the operation of the power amplifier integrated circuit 3 and the like based on this voltage value.

  Operations other than those described above of the in-vehicle audio system according to the third embodiment are the same as those in the first embodiment, and a description thereof is omitted.

  As described above, according to the third embodiment, the control integrated circuit 10 inputs a signal held at a voltage lower than its own power supply voltage to the start / stop signal input terminal 43 of the power amplifier integrated circuit 3. . The window comparator 84 of the power amplifier integrated circuit 3 closes the first switching element 81 to the negative side when the sum of the voltages output from the plurality of sets of channels becomes positive from a predetermined voltage range set in advance. Then, the second switching element 82 is closed. The voltage of the signal output terminal 38 changes in a range from a voltage slightly lower than the input voltage of the start / stop signal input terminal 43 to a voltage slightly higher than the voltage of the ground terminal 42.

  Therefore, the signal output terminal 38 of the power amplifier integrated circuit 3 is directly connected to the AD converter 12 of the control integrated circuit 10, and the high level voltage and the low level voltage of the signal output terminal 38 of the power amplifier integrated circuit 3 are controlled. Can be directly input to the integrated circuit 10.

  By the way, when the output stage to the signal output terminal 38 has an open collector or open drain configuration and a pull-up resistor element is connected to the signal output terminal 38 as in the prior art, the voltage of the signal output terminal 38 is changed from a low level to a high level. The time for changing to the level and the time for changing from the high level to the low level are different from each other. In general, the time for changing from the low level to the high level is longer than the time for changing from the high level to the low level due to a time constant determined by the relationship between the pull-up resistance element and the wiring capacitance. For this reason, when the output stage to the signal output terminal 38 has an open collector or open drain configuration, information cannot be output by the signal density wave determined by the ratio of the high level period and the low level period of the signal. .

  On the other hand, by disposing the protective resistance element 83 between the connection point between the first switching element 81 and the second switching element 82 and the signal output terminal 38 as in the third embodiment, The time for the potential of the signal output terminal 38 to change from the low level to the high level is substantially equal to the time for the change from the high level to the low level. Therefore, the power amplifier integrated circuit 3 is directly connected to the control integrated circuit 10 without providing a circuit for shaping the waveform between the control integrated circuit 10 and the control integrated circuit 10. On the other hand, it is possible to output information by the signal density wave determined by the ratio between the high level period and the low level period of the signal.

  Each of the above embodiments is an example of a preferred embodiment of the present invention, but the present invention is not limited to this, and various modifications and changes can be made without departing from the scope of the invention. It is.

  In each of the above embodiments, a case where a waveform signal and various detection signals are output from the power amplifier integrated circuit 3 directly connected to the vehicle battery 1 to the control integrated circuit 10 operating at a voltage lower than the battery voltage. It is described as an example. In addition, for example, when the power supply circuit 2 directly connected to the battery 1 of the vehicle detects an abnormality of the battery 1 or an abnormality of its own output voltage and outputs this detection signal to the control integrated circuit 10. By applying the configuration of the present invention, the power supply circuit 2 and the control integrated circuit 10 can be directly connected.

  Each of the above embodiments has been described by taking an in-vehicle audio system as an example. In addition to this, for example, in a vehicle navigation system having a function of an in-vehicle audio system or an audio system used at home, the power amplifier integrated circuit and the control integrated circuit may be directly connected. Good.

  The present invention can be used for an in-vehicle audio system connected to a battery of a vehicle.

FIG. 1 is a system configuration diagram showing an in-vehicle audio system according to Embodiment 1 of the present invention. FIG. 2 is a circuit diagram showing the power amplifier integrated circuit in FIG. FIG. 3 is a system configuration diagram showing an in-vehicle audio system according to Embodiment 2 of the present invention. FIG. 4 is a system configuration diagram showing an in-vehicle audio system according to Embodiment 3 of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Battery 3 Power amplifier integrated circuit 10 Control integrated circuit 11 External reference voltage generation circuit 15 Low pass filter capacitor (capacitor)
33 Operational Amplifier (Analog Operational Amplifier Circuit)
37 Low-pass filter resistance elements (resistance elements)
38 Signal output terminal 43 Start / stop signal input terminal (signal input terminal)
46 reference voltage generation circuit 47 input stage NPN transistor 51 limiter PNP transistor 56 short circuit detection circuit (diagnostic circuit)
59 NPN transistor for diagnosis (switching element for diagnosis)
60 Start-up circuit 71 Built-in pull-up resistance element (resistance element)
81 First switching element 82 Second switching element 84 Window comparator (digital waveform output circuit)

Claims (9)

A signal input terminal to which a signal held at a predetermined level is input;
A reference voltage generating circuit that is connected to the signal input terminal and generates a reference voltage having a voltage lower than a voltage input to the signal input terminal;
An analog operational amplifier circuit that receives the reference voltage and outputs a signal having a voltage waveform that changes with the reference voltage as a reference;
A signal output terminal for outputting a signal generated by the analog operational amplifier circuit;
A power amplifier integrated circuit comprising: The reference voltage generation circuit includes an input stage NPN transistor having a base connected to the signal input terminal,
A limiter PNP transistor having a base connected to an emitter of the input stage NPN transistor and an emitter connected to the signal output terminal;
The power amplifier integrated circuit according to claim 1.   2. The power amplifier integrated circuit according to claim 1, further comprising a resistance element connected between an output of the analog operational amplifier circuit and the signal output terminal.   A diagnostic switching element connected to the signal output terminal, and when the abnormality of the power amplifier integrated circuit or the abnormality of the input / output signal of the power amplifier integrated circuit is detected, the diagnostic switching element is controlled to be in an ON state; 4. The power amplifier integrated circuit according to claim 3, further comprising a diagnostic circuit.   5. A start circuit connected to the signal input terminal and starting the power amplifier integrated circuit when an input voltage of the signal input terminal is equal to or higher than a predetermined voltage. A power amplifier integrated circuit according to claim 1. A signal input terminal to which a signal held at a predetermined level is input;
A signal output terminal;
A resistance element connected between the signal input terminal and the signal output terminal;
A diagnostic switching element connected to the signal output terminal, and when the abnormality of the power amplifier integrated circuit or the abnormality of the input / output signal of the power amplifier integrated circuit is detected, the diagnostic switching element is controlled to be turned on; A diagnostic circuit;
A power amplifier integrated circuit comprising: A signal input terminal to which a signal held at a predetermined level is input;
A signal output terminal;
A first switching element connected between the signal input terminal and the signal output terminal;
A second switching element connected between the signal output terminal and the ground;
A digital waveform output circuit that individually controls on / off of the first switching element and the second switching element based on a waveform signal input to and output from the power amplifier integrated circuit or a waveform signal inside the power amplifier integrated circuit;
A power amplifier integrated circuit comprising: A power amplifier integrated circuit according to any one of claims 1 to 7, connected to a battery of a vehicle,
An integrated circuit for control in which the signal input terminal and the signal output terminal of the power amplifier integrated circuit are connected, and a signal held at a voltage equal to or lower than its own power supply voltage is input to the signal input terminal;
An in-vehicle audio system comprising: The power amplifier integrated circuit according to claim 3 connected to a battery of a vehicle;
An integrated circuit for control in which the signal input terminal and the signal output terminal of the power amplifier integrated circuit are connected, and a signal held at a voltage equal to or lower than its own power supply voltage is input to the signal input terminal;
An external reference voltage generation circuit that is connected to the signal input terminal and generates a voltage substantially the same as the reference voltage generation circuit of the power amplifier integrated circuit as an external reference voltage;
A capacitor having one end connected to the signal output terminal of the power amplifier integrated circuit and the control integrated circuit, and the other end connected to the output of the external reference voltage generation circuit;
An in-vehicle audio system comprising:

Images