Accelerate the Response of Tpa2028d1 to Sudden Sound Signal (short Prompt Sound)

abstract

Tpa2028d1 is a low-power class D amplifier with AGC / DRC function launched by Ti for portable devices. Because of its outstanding performance, it has been widely used in the industry. It can be configured through I2C, so that designers can optimize chip settings according to different applications and obtain better results.

This paper discusses how to optimize the tpa2028d1 setting so that it can better and quickly respond to sudden sounds in smart phones and other devices, such as keyboard sound, prompt sound and so on.

1. Introduction

Tpa2028d1 is a high efficiency class D amplifier launched by Ti for mobile devices. The integrated DRC and AGC functions can automatically adjust the gain of the amplifier according to the size of the input signal, so as to prevent the clipping distortion of the power amplifier, and effectively improve the average output power, so as to improve the playback effect of music.

Tpa2028d1 has flexible configurability. Designers can access its registers through I2C to configure multiple parameters such as amplifier enable, gain and response speed, so that it can be optimized for different application scenarios.

Since DRC and AGC will adjust the gain according to the signal size, certain attack time and release time need to be set for continuous music signals to ensure excellent playback effect. However, for the sudden sound signal, the maintenance time is too short, and due to the need of power saving, it is necessary to enable tpa2028d1 before playing and turn it off after playing. Therefore, in some designs, when playing, for example, keyboard sound or photo sound, the sound is too small, or the sound changes gradually.

By analyzing the causes of this phenomenon, this paper discusses how to solve similar problems by optimizing the setting of chip parameters.

2. Two closing / enabling modes of tpa2028

Tpa2028 can be turned off and enabled by hardware and software.

L enable and close the hardware through the chip EN pin;

L enable and close mode of software through chip register 0x01 bit6 en and bit5 SWS

two point one

two point two

2.1 hardware off / enable

close:

L when the EN pin is set low, the chip enters the off state and all registers are cleared

Enable:

L when the EN pin is set high, the chip enters the enable state, and all registers enter the initial state, such as table 1. Since the power amplifier is enabled in the initial status register 0x01 en = 1 SWS = 0, it can be played directly;

Table 1. Initial value of tpa2028d1 register

The design of tpa2028d1 is that the initial gain of the amplifier is determined by the fixed gain after the chip is enabled. The initial value of tpa2028d1 fixed gain register reg5 / bit5:0 is 00110, that is, 6dB. Therefore, the initial value of the gain of the amplifier in this state is fixed at 6dB. Since the initial value of Max gain register reg7 / bit7:4 is 30dB, the played signal slowly increases from 6dB to 30dB at the speed of 1.81s/6db of the initial value of release time register reg3 / bit5:0. As shown in Figure 1. Therefore, it will cause obvious fading effect, and the signal with too short time will cause too small phenomenon.

Figure 1. Hardware enable tpa2028d1 gain increment

2.2 software shutdown / enable

close:

L en = 0 (reg1 / bit6) or SWS = 1 (reg1 / bit5)

Enable:

L en = 1 (reg1 / bit6) or SWS = 0 (reg1 / bit5)

EN and SWS will not clear the setting state of the register, and all register values maintain the original settings. Therefore, tpa2028d1 can change according to the set fixed gain, Max gain and release time after the software is enabled. As shown in Figure 2. Therefore, you only need to set the appropriate fixed gain, Max gain and release time to control this change, so as to eliminate the fade in and fade out problems caused by AGC and DRC.

Figure 2. Hardware enable tpa2028d1 gain increment

It should be noted that since the establishment of the internal state of the chip takes time, there will be a certain output delay. The delay of tpa2028 is about 6ms. Because this time is relatively short compared with the time of ramp up, and there is a certain delay when the processor plays sudden sounds, the output delay can be ignored in general design. However, if the processor plays without delay in the actual application, it can be solved by adding a 6ms delay before the processor plays the pop-up file.

Figure 3. Output delay

Accelerate the Response of Tpa2028d1 to Sudden Sound Signal (short Prompt Sound) 1

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