Looking first at attributes tied to this month's focus on line drivers, the
Nikon 4800 of Figure 1 provides one view of the video driver design required to get all your images to the big screen of your television.
Figure 1: The Nikon 4800 Digital Still Camera
The mid-tier point-and-shoot Nikon 4800 provides 4-Mpixel still images with a quite handy 8x optical zoom, but it is also capable of capturing QuickTime movie clips.
As with many DSC designs, the movie capture feature (up to VGA at 15 frames/second here) brings with it the need to see things on the home television as well as the small, 1.8-inch LCD.
Raw composite video signals are generated within the Sanyo-manufactured device responsible for all image processing, but provision of output levels suitable for direct interface to the host television requires additional care and components, Figure 2.
Figure 2: Circuit boards and components of the Nikon 4800 camera (Click to Enlarge Image)
The Nikon 4800 relies on a Toko TK15460L video amplifier and line driver to deliver composite signals to the output connector shared with the USB digital interface. While a description of composite video is outside the scope of this article, Maxim provides an excellent reference of the basics at http://pdfserv.maxim-ic.com/en/an/AN734.pdf. But in essence, the output video signal is a complex analog waveform that must be carefully controlled to make sure your movies look good on TV. Phase linearity, gain, impedance matching and signal filtering are all elements needed in the Toko video driver to keep things looking good.
Outside the Sanyo processor and its associated memory, parts upstream from the video driver output section service strictly analog needs. The MN39483 CCD image sensor from
Matsushita generates the analog signals for each pixel, which must be precisely clocked out and processed, a role taken by Analog Devices'
AD9948 CCD signal processor. ADI's device drives timing of the readout and provides the necessary double sampling to average away any noise. It then controls analog amplitude before conversion to a 10-bit digital signal for subsequent image processing.
Along with signal management, the 4800 illustrates the sizable job of creating numerous voltage rails from the 7.4-volt Li-ion power source to serve the CCD imager, logic components, signal processing and motor drives. The latter category pertains to both manipulation of lens train motors for zoom/focus and control of the iris/shutter mechanisms for exposure. A six-channel switching regulator from Fuji Electric (FA7709) handles most of the power-management needs while parts from Renesas (M50231) and
NEC (μPD168110) control motors and coils associated with system optics.
In the end, digital imaging remains a significantly analog exercise.
About the author
David Carey is president of Portelligent (www.teardown.com). The Austin, Texas, company produces teardown reports and related industry research on wireless, mobile and personal electronics.
