Datasheet

APPLICATION INFORMATION
AUTOMATIC GAIN CONTROL
ReleaseTime
E
Limiterthreshold
GAIN
A
C
B
D
AttackTime
Limiterthreshold
Limiterthreshold
HoldTime
INPUTSIGNAL
OUTPUTSIGNAL
Limiterthreshold
TPA2017D2
SLOS584 – APRIL 2009 ..................................................................................................................................................................................................... www.ti.com
The Automatic Gain Control (AGC) feature provides continuous automatic gain adjustment to the amplifier
through an internal PGA. This feature enhances the perceived audio loudness and at the same time prevents
speaker damage from occurring (Limiter function).
The AGC works by detecting the audio input envelope. The gain changes depending on the amplitude, the limiter
level, the compression ratio, and the attack and release time. The gain changes constantly as the audio signal
increases and/or decreases to create the compression effect. The gain step size for the AGC is 0.5 dB. If the
audio signal has near-constant amplitude, the gain does not change. Figure 19 shows how the AGC works.
A. Gain decreases with no delay; attack time is reset. Release time and hold time are reset.
B. Signal amplitude above limiter level, but gain cannot change because attack time is not over.
C. Attack time ends; gain is allowed to decrease from this point forward by one step. Gain decreases because the
amplitude remains above limiter threshold. All times are reset
D. Gain increases after release time finishes and signal amplitude remains below desired level. All times are reset after
the gain increase.
E. Gain increases after release time is finished again because signal amplitude remains below desired level. All times
are reset after the gain increase.
Figure 19. Input and Output Audio Signal vs Time
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