ACS32201 datasheet(21/65 Pages) IDT

21 / 65 page

IDT CONFIDENTIAL

V0.6 07/11

ACS32201

LOW-POWER, HIGH-FIDELITY, CLASS-D AMPLIFIER

Atten(in db) = (1 - ratio)(threshold-level);

•

For example,

• Ratio = 3:1

• Threshold = -40db

• Level = -44 db

The resulting attenuation required is 8db or a gain value of 0.1585.

The linear equation for calculating the gain is:

Gain =(level/threshold)ratio*(threshold/level)

•

State Transitions: In addition to calculating the new gain for the compressor, the gain calcu-

lation block will also select the filter coefficient for the attack/release filter. The rules for

selecting the coefficient are as follows:

In the compression region:

•

If the gain calculated is less than the last gain calculated (more compression is being

applied), then the filter coefficient is the compressor attack.

•

If the gain calculated is more than the last gain calculated (less compression), the filter coef-

ficient is the compressor release.

•

In the expansion region:

•

If the calculated gain is less than the last gain calculated (closing expander, the filter coeffi-

cient is the expander attack.

•

If the calculated gain is more than the last gain calculated, the filter coefficient is the

expander release.

In the linear region:

•

Modify gain until a gain of 1.0 is obtained.

•

If the last non-linear state was compression, use the compressor release.

•

If the last non-linear state was expansion, use the expander attack.

3. Attack/Release filter: In order to prevent objectionable artifacts, the gain is smoothly ramped

from the current value to the new value calculated by the gain calculation block. In the PC-based

comp/limiter, this is achieved using a simple tracking lowpass filter to smooth out the abrupt tran-

sitions. The calculation (using the coefficient (coeff) selected by the gain block) is:

Filtered_gain = coeff*last_filtered_gain + (1.0 - coeff)*target_gain;

This creates a exponential ramp from the current gain value to the new value.

ACS32201 Datasheet(PDF) 21 Page - Integrated Device Technology

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