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TM-6760 Series Progressive Scan Shutter Cameras
3.3 Progressive Scanning
Standard TV-system scanning is 525 lines interlace scanning as specified in the RS-170 protocol. Every other horizontal line (odd lines and even lines) is scanned at a 60Hz rate per field, and the scanning is completed with two fields (one frame) at 30Hz rate. Because of the interlace scanning, the vertical resolution of CCD cameras is limited at 350 TV lines, regardless of the horizontal resolution. When electronic shutter is applied, the CCD can hold only one field of charge at each exposure. Therefore, the vertical resolution of the electronic-shutter camera is only 244 TV lines. The situation is the same for an HDTV-format camera, since it has interlaced scanning and the vertical resolution of the shuttered image is 500 lines.
The TM-6760 uses a state-of-the-art progressive scanning interline transfer CCD which scans all lines sequentially from top to bottom at one frame rate (60Hz). Like a non-interlace computer screen, it generates a stable, crisp image without alternating lines and provides full vertical TV resolution of 484 lines (a normal TV monitor display may not be able to show images due to monitor scanning).
The interline transfer architecture is also important to generate simultaneous shuttering. This is different from full frame transfer architecture which requires a mechanical shutter or strobe light in order to freeze the object motion.
The TM-6760 outputs the progressive scan image with an electronic shutter in two different formats:
•Progressive scanning digital and analog output
The CCD signal goes through A/D and D/A converters and through 10-bit in, 8-bit out look-up table (LUT). The digital output is available from 31-pin connector with RS-644 format (25MHz clock rate).
•Partial scan output
Partial scan: centered 200 lines at 120 frames per second.
The analog output is the same as 75 ohms, 1Vp-p format at 60/30Hz rate available from BNC and 12-pin connector.
•Two-row binning
Two-row binning combines two horizontal rows into one. This reduces the vertical resolution by half (242 lines) and doubles the frame rate to 120 Hz. See “Scan Modes” on page 22 for more information.
3.4Electronic Shutter
The TM-6760 has a substrate drain-type shutter mechanism which provides a superb picture at various speeds without smearing. A built-in manual shutter speed control selects the electronic shutter rate of 1/125 (non-async mode only), 1/250, 1/500, 1/1,000, 1/2,000, 1/4,000, 1/8,000, 1/16,000, or 1/32,000 second.
With VINIT high (5V), the CCD keeps discharging. With a negative pulse to VINIT, the camera resets and purges the charge momentarily. Then it starts integrating for the period of shutter control set by either an external pulse width or internal shutter control. Progressive scanning permits a full 484 lines of vertical resolution, as compared to a conventional CCD camera which captures only half the vertical lines per shutter.
