The Ai4100 has a high speed black level cancellation

function, which by means of a register setting enhances the

setting speed within a fixed period from access to the serial

interface, It increases the gain of the setting DAC within a

f i x e d a fixed p e riod a n d in turn increases th e

charge/discharge current to the OBCAP capacitor.

The Mode 3 register D3 to D0 data controls the black level

boost function. The default setting is always low gain

High-speed Black Level Cancellation

(D3~D0-5’b0). By setting the register D2~D0, the gain

becomes high by 1 to 7 times that of the OBP pulse period

after any access to the serial interface. After that period, the

gain returns to low. When setting D3 to 1’b1, the gain is

always high. The CSN signal becomes the starting point of

the OBP pulse count.

The following figure shows the black loop setting gain boost

timing chart when the boost controls is on (D3=“0”) and the

boost period is set to 3.

The total gain for a CCD input signal covers from -1.94dB to

36dB. The CDS range is 0/6/12/-1.94 dB. The PGA rough is

0/6/12/18 dB and ADC fine is 0 to 6dB, 0.047dB/step. The

CDS gain is controlled by a 2-bit register and the PGA gain is

controlled by a 9-bit register

Gain Control Circuit

ㆍThe signal from the CCDIN input through a CDS and PGA

ㆍThe signal from the ADIN input through an PGA at the

ADIN mode.

ㆍThe signal from the ADIN input at the ADIN mode.

The Ai4100 includes one 20MHz 10-bits AD converter. The

ADC converters the following signals.

A/D Converter Circuit

The analog input range of the ADC is determined by the

internal reference voltage. The full scale of the ADC is 1.0

A/D Conversion Range

Symbol

Parameter

Condition

Min.

Typ.

Max.

Unit

CSN Setup Time

-

10

-

-

ns

CSN Hold Time

-

10

-

-

ns

7

A

High gain

CSN

OBP

Counter

Black loop

gain

1

2

3

0

31

2

01

2

0

High gain

Low gain

Black Loop Setting Gain Boost Timing

Black Level Calibration Timing

Blanking

CCD

ADCLK

OBP

OBCAP

Effective Pixel

Signal

Blanking

Optical Black Period

Effective Pixel

Signal

Resulting Black

Calibration Level

(Hold)

Previous Black

Level