AD9925BBCZRL datasheet(36/96 Pages) AD

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AD9925

Rev. A | Page 36 of 96

ONTROL

can ac-

t configurations to further suppress

me-

erates in the normal shutter

ield. The SUBCKPOL,

alues section.

FF)

eration

precision shutter operations are used when

D and HD outputs may be suppressed during the

this bit is set high, at the next VD edge,

re operation. If a value greater

SHUTTER TIMING C

The CCD image exposure time is controlled by the substrate

clock signal (SUBCK), which pulses the CCD substrate to clear

out accumulated charge. The AD9925 supports three types of

electronic shuttering: normal, high precision, and low speed.

Along with the SUBCK pulse placement, the AD9925

commodate different readou

the SUBCK pulses during multiple field readouts. The AD9925

also provides programmable outputs to control an external

chanical shutter (MSHUT), a strobe/flash (STROBE), and the

CCD bias select signal (VSUB).

Normal Shutter Operation

By default, the AD9925 always op

configuration, in which the SUBCK signal pulses in every VD

field (see Figure 45). The SUBCK pulse occurs once per line,

and the total number of repetitions within the field will deter-

mine the length of the exposure time. The SUBCK pulse polar-

ity and toggle positions within a line are programmable using

the SUBCKPOL and SUBCK1TOG registers (see Table 19). The

number of SUBCK pulses per field is programmed in the

SUBCKNUM register (Addr 0x63).

As shown in Figure 45, the SUBCK pulses will always begin

in the line following the SG active line, which is specified

in the SGACTLINE registers for each f

SUBCK1TOG, SUBCK2TOG, SUBCKNUM, and SUBCKSUP-

PRESS registers are updated at the start of the line after the sensor

gate line, as described in the Updating New Register V

High Precision Shutter Operation

High precision shuttering is used in the same manner as norma

shuttering, but it uses an additional register to control the last

SUBCK pulse. In this mode, the SUBCK still pulses once per

line, but the last SUBCK in the field will have an additional

SUBCK pulse, the location of which is determined by the

SUBCK2TOG register, as shown in Figure 46. Finer resolution

of the exposure time is possible using this mode. Leaving the

SUBCK2TOG register set to its maximum value (0xFF FF

will disable the last SUBCK pulse (default setting).

Low Speed Shutter Op

Normal and high

the exposure time is less than one field long. For exposure time

longer than one field interval, low speed shutter operation is

used. The AD9925 uses a separate exposure counter to achieve

long exposure times. The number of fields for the low speed

shutter operation is specified in the EXPOSURE register

(Addr 0x62). As shown in Figure 47, this shutter mode will

suppress the SUBCK and VSG outputs for up to 4095 fields (VD

periods). The V

exposure period by programming the VDHDOFF register to 1.

To generate a low speed shutter operation, it is necessary to

trigger the start of the long exposure by writing to the TRIGGE

the AD9925 will begin an exposu

than 0 is specified in the EXPOSURE register, AD9925 will

suppress the SUBCK output on subsequent fields.

If the exposure is generated using the TRIGGER register and

the EXPOSURE register is set to 0, then the behavior of the

SUBCK will not be any different than that of normal shutter o

high precision shutter operations, in which the TRIGGER regis-

ter is not used.

SUBCK

SUBCK PROGRAMMABLE SETTINGS:

1. PULSE POLARITY USING THE SUBCKPOL REGISTER.

2. NUMBER OF PULSES WITHIN THE FIELD USING THE SUBCKNUM REGISTER (SUBNUM = 3 IN THE ABOVE EXAMPLE).

tEXP

XSG

3. PIXEL LOCATION OF PULSE WITHIN THE LINE AND PULSE WIDTH PROGRAMMED USING SUBCK1 TOGGLE POSITION REGISTER.

tEXP

Figure 45. Normal Shutter Mode

AD9925BBCZRL 数据表(PDF) 36 Page - Analog Devices

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