WM8181

Advanced Information

WOLFSON MICROELECTRONICS LTD

AI Rev 3.0 January 2000

10

SYSTEM

ASIC

CIS

SENSOR

V

OUT

WM8181

VSMP

DOUT

MCLK

VINP

VINM

CLAMP

VREFIN

V R T

V R B

EXACT CIRCUITRY

MAY VARY

DEPENDING ON

SENSOR USED

BLACK

REFERENCE

LEVEL

SET VOLTAGE TO MATCH V

SENSOR OR TIE TO AVDD TO SET

FULL-SCALE INPUT TO 1.5V

Figure 6 d.c. Coupled Positive Video

Some of the newer CIS devices have a reference voltage that corresponds closely to the black level.

In most cases this reference voltage cannot be applied directly to the VINM pin because the black

video output can go below this value and will be outside the range of the ADC. To overcome this,

VINM should be driven from a voltage that is slightly more negative than the CIS reference voltage.

This is shown in Figure 7. The input current to VINM is small but care should be taken to ensure that

R2 and R3 do not load the CIS reference circuit.

SYSTEM

ASIC

CIS

SENSOR

V

OUT

WM8181

VSMP

DOUT

MCLK

VINP

VINM

CLAMP

V

REF

VREFIN

V R T

V R B

EXACT CIRCUITRY

MAY VARY

DEPENDING ON

SENSOR USED

SET VOLTAGE TO MATCH V

SENSOR OR TIE TO AVDD TO SET

FULL-SCALE INPUT TO 1.5V

Figure 7 CIS with Reference Voltage