WM8181 查看數據表（PDF） - Wolfson Microelectronics plc

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WM8181

12-bit 2MSPS Serial Output CIS/CCD Digitiser

Wolfson Microelectronics plc 

Advanced Information

CCD SCANNER

WM8181

The differential nature of the WM8181 allows it to interface as easily to CCD sensors as to CIS. The

negative going video simply requires that the VINP and VINM pins are swapped over so that the

video signal is applied to VINM and the reference voltage is applied to VINP. The d.c. level of the

CCD output must lie within the input limits of the WM8181. A level shifter may be required to ensure

this. See Figure 8.

LEVEL SHIFT

DEPENDENT ON

VOUT DC LEVEL

BLACK

REFERENCE

LEVEL

VOUT

LEVEL

SHIFT

CCD

SENSOR

WM8181

VINP

MCLK

VSMP

DOUT

VINM

VREFIN

CLAMP

VRT VRB

SYSTEM

ASIC

SET VOLTAGE TO MATCH

VPP FROM SENSOR.

Figure 8 d.c. Coupled Negative Video

USING THE INTERNAL CLAMP

When using a CCD it is recommended that the designer use a.c. (capacitive) coupling between the

CCD output buffer and the input to the WM8181, shown in Figure 9. A CCD sensor has a negative

going video signal superimposed on a d.c. voltage of around 6V. The series capacitor between the

CCD buffer and the input to the WM8181 removes this large d.c. voltage while still allowing the video

signal through.

VOUT

CCD

SENSOR

4.7k

4.7k

220n

WM8181

VINP

MCLK

VSMP

DOUT

200p

VINM

CLAMP

VREFIN VRT VRB

SYSTEM

ASIC

SET VOLTAGE TO MATCH

VPP FROM SENSOR.

Figure 9 a.c. Coupled Negative Video

WOLFSON MICROELECTRONICS LTD

AI Rev 3.0 January 2000

11

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