Production Data

WM2331

WOLFSON MICROELECTRONICS LTD

PD Rev 1.4 April 2001

15

INTERNAL

REFERENCE

BUFFER

1µF

tantalum

0.1µF

V

REFSENSE

AGND

VBG

–

–

+

+

R

B

R

A

MODE =

AVDD/2

Figure 15 ORG Operating with External Divider (for Intermediate Reference Voltages)

DC CLAMP

AIN

CLAMPIN

CLAMP

SW1

CONTROL

REGISTER

S/H

R

IN

C

IN

+

-

10-bit

DAC

Vclamp

Vin

Figure 16 Schematic of Clamp Circuitry

The WM2331 provides a clamp function for restoring the DC reference level of AC coupled input

signals. Figure 17 shows an example of using the clamp to restore the black level of a composite

video input AC coupled to AIN. While the clamp pin is held high, the clamp amplifier forces the

voltage at AIN to equal the clamp reference voltage, setting the DC voltage at AIN for the video black

level.

VIDEO AT AIN

CLAMP

Line sync

Black

level

Figure 17 Example Waveforms for Line-Clamping to a Video Input Black Level