WM8940CGEFLSLASHRV datasheet(32/91 Pages) WOLFSON

32 / 91 page

WM8940

Production Data

PD, Rev 4.3, November 2011

LIMITER MODE

In limiter mode, the ALC will reduce peaks that go above the threshold level, but will not increase the

PGA gain beyond the starting level. The starting level is the PGA gain setting when the ALC is

enabled in limiter mode. If the ALC is started in limiter mode, this is the gain setting of the PGA at

start-up. If the ALC is switched into limiter mode after running in ALC mode, the starting gain will be

the gain at switchover. The diagram below shows an example of limiter mode.

Figure 13 ALC Limiter Mode Operation

ATTACK AND DECAY TIMES

The attack and decay times set the update times for the PGA gain. The attack time is the time

constant used when the gain is reducing. The decay time is the time constant used when the gain is

increasing. In limiter mode, the time constants are faster than in ALC mode. The time constants are

shown below in terms of a single gain step, a change of 6dB and a change of 90% of the PGAs gain

range.

Note that, these times will vary slightly depending on the sample rate used (specified by the SR

WM8940CGEFL/RV 数据表(PDF) 32 Page - Wolfson Microelectronics plc