V

- dBV

IN

Large Limiter

Range

Small

Compression

Region

Large

Compression

Region

Small Limiter

Range

Rotation

Point @

lower gain

Rotation

Point @

higher gain

time

time

NoiseGateThreshold

No

Audio

Gaindoesnotchange

inthisregion

TPA2016D2

Figure 26. Output Signal vs Input Signal State Diagram Showing the Effects of the Limiter Range to the

Compression Region

Noise Gate Threshold: The noise gate threshold prevents the AGC from changing the gain when there is no

audio at the input of the amplifier. The noise gate threshold stops gain changes until the input signal is above the

noise gate threshold. Select the noise gate threshold to be above the noise but below the minimum audio at the

input of the amplifier signal. A filter is needed between delta-sigma CODEC/DAC and TPA2016D2 for

effectiveness of the noise gate function. The filter eliminates the out-of-band noise from delta-sigma modulation

and keeps the CODEC/DAC output noise lower than the noise gate threshold.

Figure 27. Time Diagram Showing the Relationship Between Input Signal Amplitude, Noise Gate

Threshold and Gain Versus Time

Maximum Gain: This variable limits the number of gain steps in the AGC. This feature is useful in order to

accomplish a more advanced output signal vs. input signal transfer characteristic.

For example, to prevent the gain from going above a certain value, reduce the maximum gain.

However, this variable will affect the limiter range and the compression region. If the maximum gain is

decreased, the limiter range and/or compression region is reduced. Figure 28 illustrates the effects.

16

Copyright © 2008, Texas Instruments Incorporated

Product Folder Link(s): TPA2016D2