WM8903 datasheet(46/178 Pages) WOLFSON

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WM8903

Production Data

PD, Rev 4.5, June 2012

ADC OVERSAMPLING RATIO (OSR)

The ADC oversampling rate is programmable to allow power consumption versus audio performance

trade-offs. The default oversampling rate is high for best performance; using the lower OSR setting

reduces ADC power consumption.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R10 (0Ah)

Analogue ADC

ADC_OSR128

ADC Oversampling Ratio

0 = Low Power (64 x fs)

1 = High Performance (128 x fs)

Note that the Low Power options is

not supported when

CLK_SYS_MODE=10

Table 15 ADC Oversampling Ratio

Note that the Low Power (64 x fs) oversampling option is not supported when CLK_SYS_MODE=10

(see “Clocking and Sample Rates”, Table 62).

DYNAMIC RANGE CONTROL (DRC)

The dynamic range controller (DRC) is a circuit which can be enabled in the digital data path of the

ADC. Its function is to adjust the signal gain in conditions where the input amplitude is unknown or

varies over a wide range, e.g. when recording from microphones built into a handheld system. The

DRC can apply Compression and Automatic Level Control to the signal path. It incorporates ‘anti-clip’

and ‘quick release’ features for handling transients in order to improve intelligibility in the presence of

loud impulsive noises.

The DRC is enabled as shown in Table 16.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R40 (28h)

DRC 0

DRC_ENA

DRC enable

1 = enabled

0 = disabled

Table 16 DRC Enable

COMPRESSION/LIMITING CAPABILITIES

The DRC supports two different compression regions, specified by R0 and R1, separated by a “knee”

at input amplitude T. For signals above the knee, the compression slope R0 applies; for signals below

the knee, the compression slope R1 applies.

The overall DRC compression characteristic in “steady state” (i.e. where the input amplitude is near-

constant) is illustrated in Figure 30.

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