WM8181
Advanced Information
VOUT
VINP
MCLK
VSMP
CIS
SENSOR
SYSTEM
ASIC
WM8181
DOUT
BLACK
REFERENCE
LEVEL
VINM
CLAMP
VRT VRB
VREFIN
EXACT CIRCUITRY
MAY VARY
DEPENDING ON
SENSOR USED
SET VOLTAGE TO MATCH VPP FROM
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.
VOUT
VINP
MCLK
CIS
SENSOR
VSMP
SYSTEM
ASIC
WM8181
VREF
DOUT
VINM
CLAMP
VRT VRB
VREFIN
EXACT CIRCUITRY
MAY VARY
DEPENDING ON
SENSOR USED
SET VOLTAGE TO MATCH VPP FROM
SENSOR OR TIE TO AVDD TO SET
FULL-SCALE INPUT TO 1.5V
Figure 7 CIS with Reference Voltage
AI Rev 3.0 January 2000
10
WOLFSON MICROELECTRONICS LTD
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
