ST claims first USB video compliant tri-mode camera processor

A new low-cost CMOS image sensor and digital camera processor chipset from STMicroelectronics is said to be the first to provide both tri-mode operation and compatibility with the year-old USB Video Class Compliance standard, according to its maker. Tri-mode operation facilitates use as a webcam, a digital still camera and as a video camcorder.

The VC6700 CMOS image sensor has 2 megapixels, can support up to 20fps at UXGA (1,600 x 1,200) resolution (or 40 fps at SVGA 800 x 600 resolution) and uses significantly less power than image sensors based on CCD technology. (Operating on a single 3.3v supply, power consumption is 70mA at maximum resolution and frame rate.) It is also compatible with 1/2-inch format lenses (corresponding with an approximately 8mm diagonal image), and comes in a standard 48CLCC package (approximately 15 mm x 13 mm).

STMicro's companion STV0684 Digital Camera Processor provides USB 2.0 compatibility, enabling webcam operation with no need to install any drivers on the host PC. It incorporates STMicro patented video processor algorithms for noise reduction and anti-vignetting. It also has PAL and NTSC encoding, with on-chip digital to analog converter for TV display, and audio digital to analog converter for audio playback.

It has a flexible TFT-TFD display interface with direct support for camera displays from Casio, Epson, and AU Optronics. It is USB audio and video class compliant and USB mass storage class compliant. The camera processor's ST20 32bit core allows OEMs to design their own advanced user interfaces, utilizing its OS-20 operating system. The STV0684 comes in a small BGA package (12 mm x 12 mm).

Both the image sensor and camera processor are manufactured in STMicro's plant in Crolles, France.

CCD image sensors established technical superiority over CMOS back in the early days of video, according to ST, but now lower-cost CMOS image sensors are making a comeback. CMOS uses less power, costs less and also has the advantage of allowing designers to build signal processing onto the same chip — something that's prohibitively expensive with CCD image sensors. The VC6700 image sensor preprocesses the image with dark calibration and defect correction, for example, and also incorporates an on-chip audio preamplifier.

STMicro said the ultimate goal is to put an entire system — including image sensor, memory and processing — on a single chip.

According to STMicro, an early problem with CMOS image sensors — the appearance of fixed-pattern noise resulting from slight variations between amplifiers located next to each pixel — has been solved. STMicro said the CMOS image sensor delivers "approximate CCD image quality, with superb performance in low light and bright light environments." Nevertheless, the spec sheet lists the VC6700's S/N ratio at 41 dB; while CCD image sensors commonly exceed 50dB.

The USB Video Device Class Specification (Revision 1.0) was released in September 2003. It supports codecs based both on individual frames (DV, MJPEG), and based on motion compression (MPEG-2 and -4).

Likely applications for the STMicro chip set include digital still cameras, solid state video camera recorders and embedded cameras. In large quantities, the chip set will cost about $10 — making it viable for use with one or two of its three output modes. But someday, cameras offering all three-modes (live webcam, stills, recorded video) may become common. For developers of digital cameras, STMicro is offering a complete reference design, including the sensor and coprocessor, firmware and software drivers.

- Cliff Roth

EE Times