JPH09275322A - Audio output circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an audio output circuit in which a radio wave noise is reduced without bringing a delivery side FET and a suction side FET (being components of a push-pull circuit whose sources and drains are connected both into a conductive state. SOLUTION: A steep rise of a gate waveform is suppressed by changing a resistance of input resistors 25, 28 provided to gates of delivery side FETs 9, 12 receiving a pulse width modulation signal and a resistance of input resistors 26, 27 provided to gates of suction side FETs 10, 11 receiving the pulse width modulation signal so as to reduce a radio wave noise without throughconduction of the FETs whose drains and sources are directly connected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio output circuit used in a vehicle audio device.

[0002]

2. Description of the Related Art In recent years, there has been a demand for high output and downsizing of audio output circuits in vehicle audio equipment.
It is realized by a combination of a push-pull circuit and a pulse width modulation circuit.

A conventional audio output circuit using pulse width modulation will be described below. FIG. 3 shows a circuit connection diagram of a conventional audio output circuit using pulse width modulation. In FIG. 3, reference numerals 1, 2, 3, and 4 are input terminals for pulse width modulation signals. 5,6,7,8 are input resistances, 9,10,1
Field-effect transistors (hereinafter referred to as FETs) 1 and 12 are output transistors. Reference numerals 13 and 14 are filter coils, and reference numerals 15, 16 and 17 are filter capacitors. Reference numeral 18 is a speaker for sound reproduction, and 19 is a power supply terminal.

The drains and sources of the FETs 9 and 10 are connected, the drains and sources of the FETs 11 and 12 are connected, and the sources of the FETs 10 and 11 are connected and grounded. I am configuring. The input terminals 1 to 4 are connected to the gates of the FETs 9 to 12 via the input resistors 5 to 8, respectively. The connection point between the drain and the source of the FET 9 and the FET 10 is grounded via the coil 13 and the capacitor 15, and the connection point between the drain and the source of the FET 11 and the FET 12 is grounded via the coil 14 and the capacitor 16. A speaker 18 is connected between a connection point between the coil 13 and the capacitor 15 and a connection point between the coil 14 and the capacitor 16, and a capacitor 17 is connected in parallel with the speaker 18,
A power supply terminal 19 is connected to each drain of the ETs 9 and 12.

Here, the pulse width modulation signals 20, 21, 22, and 23 shown in FIG. 4 are input to the input terminals 1, 2, 3, and 4. 24 and 30 are pulse width modulation signals 20 and 23
Is the voltage when the discharge side input signal rises, and 26 and 28 are the voltages when the suction side input signal as the pulse width modulation signals 21 and 22 rises. Two
5, 27, 29 and 31 are earth voltages.

The operation of the audio output circuit configured as described above will be described below. First, input signals 20, 21, 22, 23 are input terminals 1, 2,
When input to 3 and 4, the above FETs 9 and 12 are ON,
When the FETs 10 and 11 are off,
The state where 9 and 12 are OFF and the above FETs 10 and 11 are ON is alternately repeated with a slight interval. As a result, the current from the power supply terminal 19 is FET 9, coil 1
3, the flow of the speaker 18, the coil 14, and the FET 11, and the FET 12, the coil 14, the speaker 18, and the coil 1
3 and the flow of the FET 10 are alternately repeated. The coils 13, 14 and the capacitors 15, 16, 17 are filters for converting the pulse width modulation signal into the original signal. By inputting such a small signal, the above F
A large output is obtained by turning ET9 to 12 on and off.

The FET is turned on when the gate voltage is higher than the source voltage to some extent, the resistance value between the drain and the source is reduced, and a current flows between the drain and the source. Pulse width modulated signal 20, 2
Nos. 1, 22 and 23 are F on the discharge side, as shown in FIG.
FET1 on the suction side directly connected to ET9, 12
When 0 and 11 are turned on at the same time, the time lag t is set so that the current of FETs 9 and 10 or 12 and 11 does not penetrate.
Have one. The rise and fall of the gate voltage are performed with a time constant determined by the size of the input resistors 5 to 8 and the gate capacitance of each of the FETs 9 to 12. Therefore, the discharge side FET 9,
12 and the suction side FETs 10 and 11 are not penetrated, when the time lag t1 is determined, the input resistance 5
6, 7, 8 are adjusted. Here, when the value of the input resistance is made small, the rising and the falling are sharp as shown in FIG. 5A and the penetration is lost, but the ringing of the voltage becomes large and it causes radio noise. Also,
When the value of the input resistors 5 to 8 is increased, the rising and falling become gentle, but the FET 9, 10 or 1
1, 12 penetrate.

[0008]

However, in the audio output circuit having the above-mentioned conventional configuration, the input resistors 5, 6, 7, 8 are used.
Is FET9 to FET10 or FET12 to FE
In order to eliminate the penetration due to the flow of current with T11, the values of the input resistors 5 to 8 are set small, and the input resistors of the same size are used to improve the distortion factor of the circuit. There is a problem in that the rising edge of ~ 12 becomes steep and causes generation of radio noise.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide an audio output circuit in which the FET does not penetrate and the radio noise is small.

[0010]

In order to achieve this object, the audio output circuit of the present invention is connected to the value of the input resistance connected to the gate of the discharge side field effect transistor and the gate of the suction side field effect transistor. It is possible to realize an audio output circuit using a push-pull circuit with a small radio noise without the field effect transistor penetrating.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention is
The source of the first field-effect transistor on the discharge side and the drain of the second field-effect transistor on the suction side are connected to each other, and the connection point is grounded via the coil and the first series body of the capacitor. The source of the second field effect transistor is connected to the drain of the first field effect transistor on the suction side, and the connection point is grounded via the coil and the second series body of the capacitor, and Two
Of each of the field effect transistors is connected to a power supply terminal and the sources of the first and second field effect transistors on the suction side are grounded, and the coils and capacitors of the first and second series bodies are connected. An audio output circuit in which a speaker is connected between connection points, each gate of the first field effect transistor on the ejection side, the first field effect transistor on the suction side, and the second field effect transistor on the ejection side. And a pulse width modulation signal having a reversed polarity via the input resistance to each gate of the second field effect transistor on the suction side, and the first and second field effect transistors on the ejection side. Is a voice output circuit characterized in that the input resistance values of the first and second field-effect transistors on the suction side are different from the input resistance value of Prevents penetration effect transistor and the suction-side field effect transistor, it is possible to realize a small audio output circuit radio wave noise.

A second aspect of the present invention is the audio output circuit according to the first aspect, wherein the resistance value of the input resistance is set to about 2: 1 on the suction side with respect to the discharge side. It is possible to reduce the radio noise without optimizing the distortion rate.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a circuit diagram of an audio output circuit according to an embodiment of the present invention. In FIG.
Is a signal input terminal on the discharge side, 2 and 3 are signal input terminals on the suction side, and 25 and 28 are input terminals 1 and 4 and a FET on the discharge side.
Input resistors inserted between the gates 9 and 12, 26 and 27 are input resistors inserted between the input terminals 2 and 3 and the gates of the FETs 10 and 11 on the suction side, and 9 and 12 are FETs on the discharge side.
Reference numerals 0 and 11 are FETs on the suction side, 13 is a filter coil provided at the connection point between the source of the FET 9 on the discharge side and the drain of the FET 10 on the suction side to restore the original waveform, and 14 is the FET 12 on the discharge side. FE and suction side FE
A coil of a filter provided at the connection point with the drain of T11 for returning the pulse width modulation signal to the original signal, and 15 is a coil 13
And a ground, a filter capacitor for returning the pulse width modulation signal to the original waveform, 16 is a capacitor for a pulse width modulation signal provided between the coil 14 and the ground, and 17 is a coil 13 and a capacitor. A capacitor of a filter provided between the connection point of 15 and the connection point of the coil 14 and the capacitor 16 for returning the pulse width modulation signal to the original waveform, 18 is a speaker for acoustic reproduction provided in parallel with the capacitor 17, and 19 is a discharge It is a power supply terminal connected to the drains of the FETs 9 and 12 on the side.

When the pulse width modulation signals 20, 21, 22, and 23 having the opposite phases are input to the input terminals 1, 4 and 2, 3 configured as described above, the FETs 9 to 12 are input.
Turns on when the gate potential becomes Hi, and current flows from the drain to the source. FET9,10,11,
When the signals 20, 21, 22, and 23 are input to 12, respectively, the FETs 9 and 12 are turned off and the FETs 10 and 11 are turned off.
N state, FET9,12 is ON, FET10,11
Is alternately turned off, and the current is the power supply terminal 1
9 to FET 12, coil 14, speaker 18, coil 13, FET 10, ground, and power supply terminal 19
To FET 9, coil 13, speaker 18, coil 1
4, the FET 11, and the flow of ground are alternately repeated. The FET is turned on when the gate voltage becomes higher than the source voltage to some extent, the resistance value between the drain and the source becomes small, and the current flows from one side to the other side. Therefore, the pulse width modulation signal 20,
21, 22 and 23 are FETs on the discharge side and their FETs.
There is a time lag so that the FETs on the suction side that are directly connected to are turned on at the same time and the currents of both FETs do not penetrate.

By the way, when the time lag is determined so that the discharge side FET and the suction side FET are not penetrated, when the value of the input resistance is reduced, the rise and fall become steep and the penetration is eliminated, but the voltage ringing is large. May cause radio noise. Further, when the value of the input resistance is increased, the rising and falling become gentle, but the FET penetrates. Therefore, in the present embodiment, the values of the input resistances 25 and 28 of the discharge side FETs 9 and 12 and the input resistances 26 and 27 of the suction side FETs 10 and 11 are changed to reduce the input resistance of one FET and to reduce the other F
By increasing the input resistance of ET, the penetration of the FET can be suppressed and the generation of radio noise can be reduced. Specifically, discharge side FET
The input resistance of the suction side FET is about 2 to 1 with respect to the input resistance of
It can be optimized by setting the ratio to.

[0016]

As described above, in the audio output circuit according to the present invention, the resistance value of the input resistance of the FET is made different between the discharge side and the suction side to be amplified, so that the radio noise is circuited without passing through the FET. The effect of being able to reduce it is obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an audio output circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing a pulse width modulation input waveform according to the same embodiment.

FIG. 3 is a circuit diagram showing a conventional audio output circuit.

FIG. 4 is a diagram showing a pulse width modulation input waveform of the circuit.

5A is a diagram showing a change in gate voltage due to a gate resistance, and FIG. 5B is a diagram showing ON / OFF timing of the gate voltage.

[Explanation of symbols]

 1-4 Input terminal 5-8, 25-28 Input resistance 9-12 FET 13,14 Coil 15, 16, 17 Capacitor 18 Speaker

Claims (2)

[Claims] 1. A source of a first field effect transistor on the discharge side and a drain of a second field effect transistor on the suction side are connected and the connection point is grounded via a first series body of a coil and a capacitor. , The source of the second field effect transistor on the discharge side and the drain of the first field effect transistor on the suction side are connected, and the connection point is grounded via the second series body of the coil and the capacitor, Drains of the first and second field effect transistors of the first and second field effect transistors are connected to the power supply terminal, and the first and second of the suction side are connected.
Is a sound output circuit in which the source of each of the field effect transistors is grounded, and a speaker is connected between the connection points of the coils of the first and second series bodies and the capacitor, the first field effect on the discharge side. A transistor and gates of the first field effect transistor on the suction side and a second gate on the discharge side
Of the field-effect transistor and the gate of the second field-effect transistor on the suction side are supplied with pulse width modulation signals having polarities inverted via input resistors, respectively, and the first and second circuits on the ejection side are supplied. The voice output circuit is characterized in that the input resistance values of the first and second field effect transistors on the suction side are different from the input resistance value of the field effect transistor. 2. The audio output circuit according to claim 1, wherein the input resistance has a resistance value of about 2: 1 on the suction side with respect to the discharge side.