W6662CF 데이터 시트보기 (PDF) - Winbond

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W6662CF

SCANNER ANALOG FRONT END

Winbond 

Preliminary W6662CF

6. FUNCTIONAL DESCRIPTIONS

Figure 4 is the block diagram of W6662, it consists of three channel clamp circuit for CDS mode, a

multiplexer to mux 3-channel inputs and outputs to a correlated double sampling (CDS), a

programmable gain control and offset adjustment amplifier, a 12-bit analog-to-digital converter.

Bandgap reference circuit generate voltage reference signals for input signals clampping and

correlated sampling use (in CDS mode), for offset D/A converter and output A/D converter use. The

select signals SEL1 and SEL0 are used to select the offset registers and gain registers, the input

channels may be selected simultaneously.

6.1 Clamp Circuit

The capacitor between the output of CCD/CIS device and W6662 is used to block the DC voltage

(even as high voltage). The clamp circuit is used to remove unwanted common-mode voltage in the

input pixel data and to get a maximum input signal span when the input is driven by CCD device as

shown in Figure 6-1. The input pins of W6662 are clampped to a internal offset voltage while valid

pixel signal is input. The clamp switches at three channels of figure 6-1 are turn on whenever

CDSCK1 goes high. Figure 6-2 shows the waveform between output of CCD device and input of

W6662, the voltage change on the capacitor will be clampped.

The value of input capacitor is calculated as follows:

tCLP

CMAX =

(RON + RCCDS) × ln (VC/VCLPTolerance)

CMIN =

IBIAS × tC2I

dV

where

CMAX is the maximum capacitor value.

CMIN is the minimum capacitor value.

tCLP is the high pulse width of the CDSCK1 clock input.

RON is switch resistance during clampping and is equivalent to 5K.

RCCDS is the source resistance of CCD device.

VC is the voltage change on the input capacitor must be clampped.

VCLPTolerance is the tolerance voltage error at the end of clampping.

IBIAS is the input leakage current on the input of the W6662 device.

dV is the maximum voltage drift on the input of the W6662 device.

tC2I is the time stamp from the end of clampping point to the acture input data sampling point, equal

to tC2S + tSPD + tACD or may be approximated as conversion time tCVR.

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