V

-dBV

IN

Increasing

Limiter

Level

Decreasing

Limiter

Level

LimiterLevel= 500mW

LimiterLevel= 630mW

= 400

LimiterLevel

mW

V

-dBV

IN

LargeFixedGain

Small

Fixed

Gain

Input signal initial amplitude - |Current input signal amplitude|

Output signal amplitude =

Compression ratio

(1)

0dBV

| 32 dBV|

8dBV =

4

-

-

-

(2)

TPA2016D2

Figure 23. Output Signal vs Input Signal State Diagram Showing Different Limiter Level Configurations

The limiter level and the fixed gain influence each other. If the fixed gain is set high, the AGC has a large limiter

range. The fixed gain is set low, the AGC has a short limiter range. Figure 24 illustrates the two examples:

Figure 24. Output Signal vs. Input Signal State Diagram Showing Same Limiter Level Configurations with

Different Fixed Gain Configurations

Compression Ratio: The compression ratio sets the relation between input and output signal outside the limiter

level region. The compression ratio compresses the dynamic range of the audio. For example if the audio source

has a dynamic range of 60dB and compression ratio of 2:1 is selected, then the output has a dynamic range of

30dB. Most small form factor speakers have small dynamic range. Compression ratio allows audio with large

dynamic range to fit into a speaker with small dynamic range.

The compression ratio also increases the loudness of the audio without increasing the peak voltage. The higher

the compression ratio, the louder the perceived audio.

For example:

• A compression ratio of 4:1 is selected (meaning that a 4dB change in the input signal results in a 1dB signal

change at the output)

• A fixed gain of 0dB is selected and the maximum audio level is at 0dBV.

When the input signal decreases to –32dBV, the amplifier increases the gain to 24dB in order to achieve an

output of –8dBV. The output signal amplitude equation is:

In this example:

14

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Product Folder Link(s): TPA2016D2