STV6404E-001 datasheet(8/54 Pages) STMICROELECTRONICS

8 / 54 page

VV5404 & VV6404

CD5404-6404F-A

8/54

Exposure Control

The exposure time for a pixel and the gain of the input amplifier to the 8-bit ADC are programmable via the serial

interface. The explanation below assumes that the gain and exposure values are updated together as part of a 5 byte

serial interface auto-increment sequence.

The exposure is divided into 2 components - coarse and fine. The coarse exposure value sets the number of lines a

pixel exposes for, while the fine exposure sets the number of additional pixel clock cycles a pixel integrates for. The

sum of the two gives the overall exposure time for the pixel array.

30 fps mode: Exposure Time = (Clock Divisor) x (Coarse x 393 + Fine) x (CKI clock period)/

25 fps mode: Exposure Time = (Clock Divisor) x (Coarse x 471 + Fine) x (CKI clock period)

If an exposure value is loaded outwith the valid ranges listed in the above table the value is clipped to lie within the

above ranges.

Exposure and gain values are re-timed within the sensor to ensure that a new set of values is only applied to the

sensor array at the start of each frame. Bit 0 of the Status Register is set high when a new exposure value is written

via the serial interface but has not yet been applied to the sensor array.

There is a 1 frame latency between a new exposure value being applied to the sensor array and the results of the

new exposure value being read-out. The same latency does not exist for the gain value. To ensure that the new

exposure and gain values are aligned up correctly the sensor delays the application of the new gain value by one

frame relative to the application of the new exposure value.

To eliminate the possibility of the sensor array seeing only part of the new exposure and gain setting, if the serial

interface communications extends over a frame boundary, the internal re-timing of exposure and gain data is disabled

while writing data to any location in the Exposure page of the serial interface register map. Thus if the 5 bytes of

exposure and gain data is sent as an auto-increment sequence, it is not possible for the sensor to consume only part

of the new exposure and gain data.

Value

Units

30 fps mode

25 fps mode

Min.

Max.

Min.

Max.

Coarse

Video Lines

302

Fine

Pixel Clocks

356

434

Table 3 : Coarse and Fine Exposure Ranges.

Gain Code, G[2:0]

Amplifier Gain

Table 4 : Main Gain Steps.

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