Datasheet

time
Gain-dB
InputSignal
Amplitude-Vrms
time
NoiseGateThreshold
No
Audio
Gaindoesnotchange
inthisregion
V
OUT
-dBV
V - dBV
IN
1:1
Large Limiter
Range
Small
Compression
Region
Large
Compression
Region
Small Limiter
Range
Rotation
Point @
lower gain
Rotation
Point @
higher gain
TPA2028D1
SLOS660B –JANUARY 2010–REVISED SEPTEMBER 2012 www.ti.com
Figure 35. 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 TPA2028D1 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 36. 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 37 illustrates the effects.
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