V

-dBV

IN

V

-dBV

IN

Increasing

FixedGain

Decreasing

FixedGain

TPA2016D2

Figure 21. Input Signal Voltage vs Gain

Thus the AGC performs a mapping of the input signal vs. the output signal amplitude. This mapping can be

modified according to the variables from Table 1.

The following graphs and explanations show the effect of each variable to the AGC independently and which

considerations should be taken when choosing values.

Fixed Gain: The fixed gain determines the initial gain of the AGC. Set the gain using the following variables:

• Set the fixed gain to be equal to the gain when the AGC is disabled.

• Set the fixed gain to maximize SNR.

• Set the fixed gain such that it will not overdrive the speaker.

Figure 22 shows how the fixed gain influences the input signal amplitude vs. the output signal amplitude state

diagram. The dotted 1:1 line is displayed for reference. The 1:1 line means that for a 1dB increase in the input

signal, the output increases by 1dB.

Figure 22. Output Signal vs Input Signal State Diagram Showing Different Fixed Gain Configurations

If the Compression function is enabled, the Fixed Gain is adjustable from –28dB to 30dB. If the Compression

function is disabled, the Fixed gain is adjustable from 0dB to 30dB.

Limiter Level: The Limiter level sets the maximum amplitude allowed at the output of the amplifier. The limiter

should be set with the following constraints in mind:

• Below or at the maximum power rating of the speaker

• Below the minimum supply voltage in order to avoid clipping

Figure 23 shows how the limiter level influences the input signal amplitude vs. the output signal amplitude state

diagram.

Copyright © 2008, Texas Instruments Incorporated

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