The difference in readout techniques has significant implications for the sensor architecture, features and limitations.

Power consumation:

Since the signal processing and amplification has to be performed on separate chips and that the readout can only be done once the light is shut out, the energy (and voltage) requirment is higher in CCD sensors.

A typical CCD will consume 2 to 5W of power and CMOS chip about 20mW to 50mW.

Sensor/ System Complexity:

All the circuity can be integrated in the chip on a CMOS sensor, leading to very complex chips. Manufacturing cost of a CMOS chip is lower than for a CCD, but the fabrication processes arr more complex and more expensive. In conclusion, the costs are equivalent. If an upgrade of the system is required, a sensor and DSP upgrade can be done at the same and is relatively easy. The CMOS technology has permitted Kodak to offer an affordable upgrade of the Kodak DCS Pro 14 to the Kodak Pro dslr with the new Filfactory CMOS sensor. Since all the conversion and processing can not be performed on the sensor itself, a CCD camera needs several chips to convert and amplify the light collected.

Signal to noise:

The circuitry integrated to the CMOS sensor (i.e. the amplifier) result in a higher background noise as compared to a CCD sensor with the circuitry being on separate chips. Canon apply a post-processing circuit to compensate for the high background noise: the backound noise is measured just before the exposure and deducted to the final signal. This is a processor intensive task. For scientific purpose, the CCD sensors can be cooled down to -70 resulting in a higher dynamic range that a CMOS sensor could ever achieve.

Since each photosite has an output amplifier, variation in the gain amplification resulted in lower uniformity in CMOS sensor. Feedback-base amplifiers and parallel processing have made the CCD and CMOS sensors comparable, althoug the CCDs still have an edge in the darkness.

CCD or CMOS

The CMOS and CCD are two different technologies with different pro and cons. CCDs are the choice for digital cameras (i.e. Minolta Xt, Sony Cybershot, Canon Powershots, Olympus Camedia) and most of the 6MPs DSLR (i.e, Nikon D70 and D100, Fuji S Pro 2). Since CMOS sensors don't suffer from the decrease in the signal-to-noise ratio as resolution increases, CMOS sensors are superior to CCD sensor for sensors larger or equal to the APS format.

New technologies are currently in development, including the interesting Foveon X3 technology and the HIT (Hybrid indirect technology (see next page)