JP2002208821A - Power amplifier start circuit device and method for controlling the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power amplifier starting circuit device which suppresses increase in the drive current and can also start a power amplifier output slowly in a small area. SOLUTION: This power amplifier start circuit device is provided with a 1st switch connected to the negative input of a power amplifier, a capacitor and a 1st resistor connected to the positive input node of the power amplifier, a 2nd switch connected in parallel with the capacitor, a 3rd switch connected between the 1st resistor and an analog reference voltage generation circuit, and a 4th switch connected between the output node of the power amplifier and a ground potential. Control is carried so that the 1st and 3rd switches are turned off in an initial state, the 2nd a 4th switches are also turned on, the power amplifier is turned on next, the 3rd switch is subsequently turned on, and the 2nd and 4th switched are turned off.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a power amplifier start-up circuit device mounted on audio equipment and the like, and a control method therefor.

[0002]

2. Description of the Related Art Heretofore, since the output potential of a power amplifier shows a steep step response at the same time when the power amplifier is started, there has been a problem that a loud glitch sound can be heard when a speaker is driven.

In order to avoid this problem, conventionally, FIG.
The following circuit devices have been proposed.

FIG. 6 is a circuit diagram of a conventional power amplifier start-up circuit device.

This power amplifier start-up circuit device has an analog reference potential generation circuit 14 connected to a power supply line VDD via a switch PSW, and the output of the analog reference potential generation circuit 14 constitutes the power amplifier 10. The input is connected to a positive input of the amplifier circuit 11 and a voltage follower amplifier 110 constituted by the amplifier circuit 111.

The power amplifier 10 includes an amplifier circuit 11 and a resistor 12, and the output of the amplifier circuit 11 is fed back to the negative input via the resistor 12. The switch SW1 is connected to the negative input of the power amplifier 10 via the resistor 13. Further, the output of the power amplifier 10 is connected to the output terminal 21. Similarly, the voltage follower amplifier 110 is connected to the output terminal 21 via the resistor R1.

Then, between the output terminal 21 and the ground,
A DC cut capacitor C1 and a resistor R2 are externally connected in series.

When the conventional power amplifier start-up circuit device starts up, the switch PSW is turned on, and the output potential V1 of the power amplifier 10 is gradually raised by the voltage follower amplifier 110, the resistor R1, and the DC cut capacitor C1. Like that.

[0009]

However, in the above-mentioned conventional circuit, when the DC cut capacitance C1 is increased in order to pass a low frequency, the rise becomes slow.
It is necessary to have the ability to make 1 smaller and allow a large drive current to flow through the voltage follower amplifier 10. As a result, there is a problem that the operating current of the voltage follower amplifier 10 increases and the area of the voltage follower amplifier 10 increases.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems. It is an object of the present invention to provide a power amplifier capable of suppressing an increase in drive current and having a small area and capable of gradually increasing the output of a power amplifier. An object of the present invention is to provide an amplifier start-up circuit device and a control method thereof.

[0011]

According to a first aspect of the present invention, there is provided a power amplifier start-up circuit device, comprising: a first switch connected to a negative input of a power amplifier; A capacitance and a first resistor connected to a positive input node of the amplifier, a second switch connected in parallel with the capacitance, and a second switch connected between the first resistor and an analog reference voltage generation circuit. 3 and a fourth switch connected between an output node of the power amplifier and a ground potential.

According to a second aspect of the present invention, in the power amplifier start-up circuit device according to the first aspect, the first and third power amplifiers are initialized in the initial state.
And turning on the second and fourth switches, and then turning on the power amplifier, then turning on the third switch, and turning on the second and fourth switches. It is characterized by comprising control means for controlling to turn off.

According to a third aspect of the present invention, there is provided a power amplifier start-up circuit device according to the second aspect, wherein a fifth terminal is provided between an output node of the power amplifier and the reference voltage generation circuit. And the control means controls to turn on the fifth switch when the power amplifier is powered down.

According to a fourth aspect of the present invention, in the power amplifier start-up circuit device according to any one of the first to third aspects, an input amplifier is connected to a stage preceding the first switch. A positive input of the power amplifier is connected to a positive input of the input amplifier.

According to a fifth aspect of the present invention, in the power amplifier start-up circuit device according to the third or fourth aspect, between the reference voltage generating circuit and the fifth switch. And a second resistor connected thereto.

According to a sixth aspect of the present invention, in the power amplifier start-up circuit device according to the first to fifth aspects, the output node of the power amplifier and the fourth switch are connected to each other. A third resistor is connected therebetween.

According to a seventh aspect of the present invention, in the control method of the power amplifier start-up circuit device, the first switch connected to the negative input of the power amplifier, the capacitance connected to the positive input node of the power amplifier, and A resistor, a second switch connected in parallel with the capacitance, a third switch connected between the resistor and an analog reference voltage generation circuit, and an output node of the power amplifier and a ground potential. In a power amplifier start-up circuit device having a fourth switch connected to the power amplifier start-up circuit device, the first and third switches are turned off in the initial state, and the second and fourth switches are turned on. After the power amplifier is turned on, the third switch is turned on, and the second and fourth switches are turned off.

According to a control method of a power amplifier start-up circuit device according to an eighth aspect of the present invention, in the control method of the power amplifier start-up circuit device of the seventh aspect, the output node of the power amplifier and the reference voltage generating circuit are provided. A fifth switch is provided between the power amplifier and the power amplifier, and the fifth switch is turned on when the power amplifier is powered down.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] FIG. 1 is a circuit diagram showing a power amplifier start-up circuit device according to a first embodiment of the present invention.

This power amplifier start-up circuit device has a power amplifier 10 similar to the conventional one. That is,
The output of the analog reference potential generating circuit 14 connected to the power supply line VDD via the switch PSW is connected to the positive input of the amplifier 11 constituting the power amplifier 10.

The power amplifier 10 includes an amplifier circuit 11 whose ON / OFF is controlled by a control signal APD1 and a resistor 12, and the output of the amplifier circuit 11 is fed back to the negative input via the resistor 12. A resistor 1 is connected to the negative input of the power amplifier 10.
3 is connected to the switch SW1. further,
A resistor R3 is connected to a positive input node of the power amplifier 10, and a capacitor C2 is externally connected via a terminal 22.

The switch S is connected in parallel with the capacitor C2.
W2 is connected, and a switch SW3 is connected between the resistor R3 and the analog reference voltage generation circuit 14. The output side of the power amplifier 10 is connected to the ground GND via the switch SW4, and is connected to the output side of the analog reference potential generation circuit 14 via the switch SW5.

Then, between the output terminal 21 and the ground,
A DC cut capacitor C1 and a resistor R2 are externally connected in series.

Next, the operation of the power amplifier start-up circuit device configured as described above will be described with reference to the timing chart of FIG.

In the initial state before time t1, that is, before the power amplifier 10 rises, the switches SW2 and SW4
Is turned on. That is, if the V1 node and the V2 node are set to an undefined state before the power amplifier 10 rises, the rise time changes each time the rise is started. In this case, it is set to GND).

Power amplifier 1 whose switch PSW is turned on
When 0 rises (time t1), the APD1 signal goes to “H” level and the amplifier circuit 11 is turned on.
At the same time, the switch SW3 is turned on, and the switch SW2 is turned on.
And the switch SW4 is turned off. As a result, the node V2 slowly rises to the analog reference potential Vef due to the time constant of the capacitor C2 and the resistor R3.

The V1 node, which is the output of the power amplifier 10, slowly rises from 0V to the analog reference potential Vef together with the V2 node due to an imaginary short. As a result, click noise of the power amplifier output can be reduced.

Thereafter, once the power amplifier 10 is started up, when the APD1 signal is set to the "L" level and the power amplifier 10 is powered down (time t2), the switch SW5 is turned on to set the V1 node to the reference potential. Ve
Fix to f. This is because when the power amplifier 10 is powered down, the potential of the V1 node decreases, and when the power amplifier 10 is restarted, click noise occurs. To avoid this, the switch SW5 is turned on at the same time when the power amplifier 10 is powered down, and the V1 node is raised to about the output voltage of the analog reference voltage generation circuit 14.
As a result, even if the power amplifier 10 is turned on / off, V
Since one node does not change, no click noise occurs. Further, when the power amplifier 10 is not used, the power consumption can be reduced by keeping the power down.

To lower the potential of the output node V1 of the power amplifier 10, the switch PSW is turned off, and the APD1 is turned off.
The signal is set to the “L” level, the switches SW1 and SW3 are turned off, the off state of the switch SW5 is maintained, and the switches SW2 and SW4 are turned on.
Thereby, the V2 node is connected to the capacitor C2 and the resistor R3.
And the V1 node, which is the output of the power amplifier 10, can slowly fall by the ON resistance of the switch SW4 and the time constant of the capacitor C1.

As described above, in the present embodiment, the rising of the output of the power amplifier 10 is made smooth by inputting the potential raised by the time constant of the capacitor C2 and the resistor R3 to the positive input of the power amplifier 10. Therefore, click noise at the time of rising can be suppressed.

[Second Embodiment] FIG. 3 is a circuit diagram showing a power amplifier start-up circuit device according to a second embodiment of the present invention.

In the power amplifier start-up circuit device of the present embodiment, an input amplifier 30 having an amplifier circuit 31 that is turned on / off by an APD2 signal is connected to a switch SW1 in the circuit of FIG. The V2 node is connected to the positive input. Further, the output of the amplifier circuit 31 is fed back to the negative input via the resistor 32. And
The V3 node connected to the negative input of the amplifier circuit 31 has 3
Resistors R4 are connected in parallel, and a capacitor C3 is connected to each resistor R4 in series.

The operation of the power amplifier start-up circuit device of this embodiment will be described with reference to the timing chart of FIG.

In the initial state before time t1, the switch S
W1 is on in the initial state (the switch SW1 is always on). Before power amplifier 10 rises (initial state)
If the V1, V2, and V3 nodes are in an indefinite state, the rise time changes each time the rise occurs. Therefore, the switches SW2 and SW4 are turned on to set a predetermined fixed voltage (in this case, ground GND). Keep it.

When the power amplifier 10 starts up (at time t)
In 1), the switch SW3 is turned on, the APD1 signal and the APD2 signal are both set to “H” level, and the switch SW2 is turned on.
And switch SW4 is turned off. As a result, the V2 node slowly rises to the analog reference potential due to the time constant of the capacitor C2 and the resistor R3.

The V4 node between the switch SW1 and the resistor 103 slowly rises together with the V2 node and the V3 node. As a result, the V1 node, which is the output of the power amplifier 10, slowly rises together with the V2 node and the V4 node. As a result, click noise of the power amplifier output can be reduced.

Thereafter, once the power amplifier 10 is started up, when the APD1 signal is set to the "L" level and the power amplifier 10 is powered down (time t2), the switch SW5 is turned on to bring the V1 node to the reference potential. Ve
f. Therefore, even if the power amplifier 10 is turned on / off, the V1 node does not change, so that no click noise occurs at this time. Further, when the power amplifier 10 is not used, power consumption can be reduced by keeping the power down.

To lower the output node V1 of the power amplifier 10, the switch PSW is turned off, the APD1 signal and the APD2 signal are set to "L" level, and the switch SSW is turned off.
W3 is turned off, the switch SW5 is kept off, and the switches SW2 and SW4 are turned on. As a result, the V2 node falls with the time constant of the capacitor C2 and the resistor R3, the V4 node slowly falls with the V2 node, and the V1 node slowly falls with the on-resistance of the switch SW4 and the time constant of the capacitor C1. it can.

As described above, even in the configuration in which the input amplifier is provided in the stage preceding the power amplifier, the same effect as that of the first embodiment can be obtained.

[Third Embodiment] FIG. 5 is a circuit diagram showing a power amplifier start-up circuit device according to a third embodiment of the present invention.

In the power amplifier start-up circuit device of the present embodiment, a resistor 41 is connected between the analog reference voltage generating circuit 14 and the switch SW5 in the circuit of FIG. A resistor 42 is connected between the switch 42 and the switch SW4.

The resistor 41 works so as to prevent noise generated when the switch SW5 is turned on and off from flowing to the node V5, and the resistor 42 works as a power amplifier 10
Control the fall time of the output node V1 of
Can fall slowly.

[0044]

As described above in detail, according to the power amplifier start-up circuit device of the first and second aspects and the control method of the power amplifier start-up circuit device of the seventh aspect, the power amplifier output is smoothed. Therefore, glitch noise can be reduced. Further, since the amplifier required in the conventional circuit can be omitted, low power and small area can be realized. Further, since a low-noise potential can be input to the positive input node of the power amplifier by the capacitance and the first resistor, floor noise can be reduced.

According to the power amplifier start-up circuit device of the third aspect and the control method of the power amplifier start-up circuit device of the eighth aspect, the fifth switch is turned on at the time of power-down after the power amplifier is started. As a result, the output potential can be fixed to a predetermined potential, so that power can be reduced without generating glitch noise.

According to the power amplifier start-up circuit device of the fourth aspect, the rise of the input amplifier can be made smooth and the floor noise of the input amplifier can be reduced.

In the power amplifier start-up circuit device according to the fifth aspect of the present invention, it is possible to avoid generation of noise when the fifth switch is turned on.

In the power amplifier start-up circuit device according to the present invention, the potential of the output node of the power amplifier can be quickly lowered.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a power amplifier start-up circuit device according to a first embodiment of the present invention.

FIG. 2 is a timing chart showing the operation of the first embodiment.

FIG. 3 is a circuit diagram showing a power amplifier start-up circuit device according to a second embodiment of the present invention.

FIG. 4 is a timing chart showing the operation of the second embodiment.

FIG. 5 is a circuit diagram showing a power amplifier start-up circuit device according to a third embodiment of the present invention.

FIG. 6 is a circuit diagram of a conventional power amplifier start-up circuit device.

[Explanation of symbols]

 Reference Signs List 10 power amplifier 14 analog reference potential generating circuit PSW overall power switch SW1 first switch SW2 second switch SW3 third switch SW4 fourth switch SW5 fifth switch R3 first resistor 41 second resistor 42 3 resistor C2 capacitor APD1, APD2 control signal

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference)

Claims (8)

[Claims] 1. A first amplifier connected to a negative input of a power amplifier.
A capacitor connected to a positive input node of the power amplifier, a first resistor, a second switch connected in parallel with the capacitance, and a first resistor and an analog reference voltage generating circuit. A power amplifier start-up circuit device comprising: a third switch connected therebetween; and a fourth switch connected between an output node of the power amplifier and a ground potential. 2. In an initial state, the first and third switches are turned off, the second and fourth switches are turned on, and then the power amplifier is turned on. 2. The power amplifier start-up circuit device according to claim 1, further comprising control means for controlling a switch to be turned on and the second and fourth switches to be turned off. 3. A fifth switch is connected between an output node of the power amplifier and the reference voltage generation circuit, and the control unit turns on the fifth switch when powering down the power amplifier. 3. The power amplifier start-up circuit device according to claim 2, wherein the control is performed as follows. 4. The power amplifier according to claim 1, wherein an input amplifier is connected in front of said first switch, and a positive input of said power amplifier is connected to a positive input of said input amplifier. Start-up circuit device. 5. The power amplifier start-up circuit device according to claim 3, wherein a second resistor is connected between the reference voltage generation circuit and the fifth switch. 6. The power amplifier start-up circuit device according to claim 1, wherein a third resistor is connected between an output node of said power amplifier and said fourth switch. 7. A first amplifier connected to a negative input of a power amplifier.
A switch connected to a positive input node of the power amplifier, a second switch connected in parallel with the capacitance, and a second switch connected between the resistor and an analog reference voltage generating circuit. 3 and a fourth switch connected between the output node of the power amplifier and the ground potential. And turning on the second and fourth switches and then turning on the power amplifier, then turning on the third switch and turning off the second and fourth switches. A method for controlling a power amplifier start-up circuit device, comprising: 8. A fifth switch is provided between an output node of the power amplifier and the reference voltage generating circuit, and the fifth switch is turned on when the power amplifier is powered down. The control method for a power amplifier start-up circuit device according to claim 7.