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Volume 24 (Sep 14, 2004)
The 8-bit microcontroller-A hit product that supports digital still cameras (DSCs) from behind the scenes (2/2)
8-bit microcontrollers and the important role they play inside digital cameras
There are cases in which digital cameras realize all of their functions through the main chip and do not employ a subchip.
Ordinarily, digital cameras comprise a main chip that primarily controls the image processing of still and moving images and major functions, and a subchip that deals with system controls such as key input and power supply control (Figure 2). NEC Electronics' 8-bit microcontroller is employed as a subchip that sends control signals to each respective unit while at the same time supplying power at the optimum supply timing.
For example, pressing the shutter button sends a control signal to the main chip indicating that the shutter button has been pressed. The main chip issues commands that set the correct light sensitivity for the CCD, the appropriate shutter speed for the shutter motor driver and the proper lens aperture adjustment. In other words, the 8-bit microcontroller is the starting point from which each of the units commences operation at the optimum timing. The 8-bit microcontroller therefore makes it possible to take advantage of the split second you have to capture a great shot.
Digital cameras have complex inner structures that use numerous power supply voltages; digital analog systems require a power supply of 5V, image processors require 3V and LCD panels require 12V and 15V. The 8-bit microcontroller that controls these power supplies initiates and continues operations without stopping until they have been completed. For this reason, the 8-bit microcontroller requires both a wider range of voltages than any other LSI chip and a reduced consumption current. In addition, the 8-bit microcontroller carries out strobe control.
Currently, the most commonly used microcontroller for digital cameras is the µPD78003x (Photo 1). The industry's top-level, low-voltage (1.8V) A/D converter is built into this compact 64-pin QFP package with an edge measuring a mere 10 x 10 mm.
At NEC Electronics, we are currently developing a product enclosed in a 6 6 mm BGA package that effectively uses the features of the µPD78003x, improves the operation speed to 16 MHz and converts the program memory space into flash memory. Also, adding a low-voltage detection function strengthens the reset function and reduces the number of external parts. In this way, we are contributing to the evolution of ultrathin, compact digital cameras with multiple functions and high performance.
The evolution of the digital camera appears to be branching out in a variety of directions. NEC Electronics' 8-bit microcontroller is not only supporting the evolution of the digital camera, but also evolving right along side it.
