Datasheet

V -dBV
OUT
V -dBV
IN
Increasing
FixedGain
Decreasing
1 :1
2
:
1
4
:
1
8
:
1
1 :1
2
:
1
4
:
1
8
:
1
Rotation
Point@
lowergain
Rotation
Point@
highergain
1
24 dB = 1 × 32
4
æ ö
-
ç ÷
è ø
1
Gain change = 1 × Input signal change
Compression ratio
æ ö
-
ç ÷
è ø
TPA2028D1
www.ti.com SLOS660B –JANUARY 2010–REVISED SEPTEMBER 2012
The gain change equation is:
(3)
(4)
Consider the following when setting the compression ratio:
• Dynamic range of the speaker
• Fixed gain level
• Limiter Level
• Audio Loudness vs Output Dynamic Range.
Figure 34 shows different settings for dynamic range and different fixed gain selected but no limiter level.
Figure 34. Output Signal vs Input Signal State Diagram Showing Different Compression Ratio
Configurations with Different Fixed Gain Configurations
The rotation point is always at Vin = 10dBV. The rotation point is not located at the intersection of the limiter
region and the compression region. By changing the fixed gain the rotation point will move in the y-axis direction
only, as shown in the previous graph.
Interaction between compression ratio and limiter range: The compression ratio can be limited by the limiter
range. Note that the limiter range is selected by the limiter level and the fixed gain.
For a setting with large limiter range, the amount of gain steps in the AGC remaining to perform compression are
limited. Figure 35 shows two examples, where the fixed gain was changed.
1. Small limiter range yielding a large compression region (small fixed gain).
2. Large limiter range yielding a small compression region (large fixed gain).
Copyright © 2010–2012, Texas Instruments Incorporated 17
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