STV-676-E01 STMicroelectronics, STV-676-E01 Datasheet - Page 6

• Manufacturer Part Number: STV-676-E01
• Description: KIT EVAL FOR STV0676 DSP
• Manufacturer: STMicroelectronics

Specifications of STV-676-E01

• Sensor Type: CMOS Imaging, Color (RGB)
• Sensing Range: VGA
• Interface: I²C, Digiport
• Sensitivity: 30 fps
• Embedded: Yes, MCU, 8-Bit
• Utilized Ic / Part: STV0676, VV6411, VV6501
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Voltage - Supply: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 497-3888; STV-676-E01

Overview
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Auto exposure and gain control
The STV0676 automatically controls the sensor exposure, which is evaluated (and, where
necessary modified) once per frame, where a frame consists of 2 video fields. The video
fields are identical in length, that is, they do not contain any of the half line detail of the
analogue video standards like CCIR or NTSC. Two fields per frame are required by the
internal sensor video timing model. Integration time, sensor analogue gain and STV0676
digital gain are all used to control the overall exposure. The STV0676 exposure algorithm
uses an asymptotic approach in calculating the change required in the present exposure
value to approach the requested exposure target.
Defect correction
STV0676 automatically detects and corrects pixel defects without the need for any
additional components or sensor calibration procedures. This greatly simplifies camera
assembly and test when compared with previous EEPROM-based defect correction
schemes. The pixel defect correction scheme ensures that the STV0676 + ST CMOS
sensor appears as a ‘defect free’ chipset.
Video compression (VC) engine
The video compression engine performs 3 main functions:
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The data stream from the VP can be up to VGA size. The scaler in VC can downsize this
image. Once scaled the video stream is then converted into M-JPEG format. M-JPEG
simply treats video as a series of JPEG still images. The conversion is realised via a
sequential DCT (discrete cosine transform) with Huffman encoding. After transfer over USB,
the M-JPEG stream is decoded in the device driver running on the host.
The VC module is capable of compression ratios of up to 100:1 although this is scene-
dependent. Image framerate produced by the STV0676 chipset is fixed and furthermore the
available USB bandwidth is also fixed (within the software driver). The VC module varies the
compression ratio to match the fluctuating input video data rates to the available USB
bandwidth and required framerate.
The final stage of the VC block manages the data transfer from the local VC FIFO store to
the USB core. STV0676 performs this management automatically by employing long-term
(frame-level) and short-term (block-level) compression management.
up scaling of input YCbCr 4:2:2 video stream from the VP (typically to scale from QVGA
to CIF image formats),
compression and encoding of YCbCr stream into Motion-JPEG (M-JPEG) format,
USB bandwidth monitoring.
STV0676