WM8737 datasheet(18/40 Pages) CIRRUS

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WM8737L

Production Data

PD, Rev 4.4, January 2012

PGA CONTROL

The Left and Right PGAs match the input signal levels to the ADC input ranges. The PGA gain is

logarithmically adjustable from –97dB to +30dB in 0.5dB steps. Each PGA can be controlled either by

the user or by the ALC function (see “Automatic Level Control” section). When ALC is enabled for one

or both channels then writing to the corresponding PGA gain control register has no effect. The gain

is independently adjustable on both Right and Left Line Inputs. By setting the LVU or RVU bits whilst

programming the PGA gain, both channels can be simultaneously updated. The inputs can also be

muted under software control. The PGA control register maps are shown in Table 7.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R0 (00h)

Left Channel

PGA

7:0

LINVOL[7:0]

C3h

( 0dB )

Left Channel Input Volume Control

00000000: MUTE

00000001: -97dB

00000010: -96.5dB

…

11000011: 0dB

…

11111111: +30dB

LVU

Left PGA volume update

0: Store LINVOL in left intermediate

latch but do not update left gain.

1: Update both PGA gains

simultaneously (left gain = LINVOL,

right gain = right intermediate latch).

R1 (01h)

Right Channel

PGA

7:0

RINVOL[7:0]

C3h

( 0dB )

Right Channel Input Volume Control.

Same as LINVOL.

RVU

Right PGA volume update

0: Store RINVOL in right

intermediate latch but do not update

right gain.

1: Update both PGA gains

simultaneously (right gain =

RINVOL, left gain = left intermediate

latch).

Table 7 PGA Software Control

ZERO-CROSS DETECTION

To avoid zipper or click noises, it is preferable to change the microphone preamplifier and PGA gains

only when the input signal is at zero. The WM8737L has built-in zero-cross detectors to achieve this.

This function is enabled by setting the LMZC, LPZC, RMZC and RPZC bits. The zero-cross detection

feature includes a programmable time-out, selected by writing to LZCTO[1:0] and RZCTO[1:0]. If no

zero crossing occurs within the time-out period then the WM8737L changes the PGA or microphone

preamplifier gains when the time-out elapses.

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