WM8778 datasheet(35/50 Pages) WOLFSON

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WM8778

PP Rev 1.7 June 2004

MAXIMUM GAIN (ALC ONLY) AND MAXIMUM ATTENUATION

To prevent low level signals being amplified too much by the ALC, the MAXGAIN register sets the

upper limit for the gain. This prevents low level noise being over-amplified. The MAXGAIN register

has no effect on the limiter operation.

The

attenuation below the static (user programmed) gain. For the ALC, it defines the lower limit for the

gain.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R16 (10h)

0010000

ALC Control 1

6:4

MAXGAIN

111

(+24dB)

Set Maximum Gain for the PGA (ALC

only):

111 : +24dB

110 : +20dB

…..(-4dB steps)

010 : +4dB

001 : 0dB

000 : 0dB

Maximum Attenuation of PGA

R20 (14h)

0010100

Limiter Control

3:0

MAXATTEN

0110

Limiter

(attenuation

below static)

0011 or lower

: -3dB

0100: -4dB

…. (-1dB steps)

1100 or higher

: -12dB

ALC (lower PGA

gain limit)

1010 or lower

: -1dB

1011 : -5dB

….. (-4dB steps)

1110 : -17dB

1111 : -21dB

HOLD TIME (ALC ONLY)

The ALC also has a hold time, which is the time delay between the peak level detected being below

target and the PGA gain beginning to ramp up. It can be programmed in power-of-two (2

n) steps, e.g.

2.67ms, 5.33ms, 10.67ms etc. up to 43.7ms. Alternatively, the hold time can also be set to zero. The

hold time only applies to gain ramp-up, there is no delay before ramping the gain down when the

signal level is above target.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R17 (11h)

0010001

ALC Control 2

3:0

HLD[3:0]

0000

ALC Hold Time Before Gain is

Increased:

0000: 0ms

0001: 2.67ms

0010: 5.33ms

… (time doubles with every step)

1111: 43.691s

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