The electrical signals generated by photodiodes are very weak and require amplification. The key challenge is how to reduce the noise generated by amplification. The D3 incorporates three stages of amplification circuitry within the image sensor to minimize the accumulation of noise that can occur when low-level signals are transmitted to a single-stage output amplifier. By amplifying electrical signals at the earliest point, the signal is strengthened and the influence of circuit noise reduced. For the signal output amplifier, the D3 employs a differential signal amplifier that enables cancellation of incidental noise during signal transmission from the image sensor pre-amplifier to the output stage. Working together, these cascaded amplifiers achieve a high signal to noise ratio that far surpasses the performance of all other professional digital SLRs.
The D300, on the other hand, employs Nikon’s first-ever column-parallel A/D converters within an imaging sensor. The low-voltage differential signal output (LVDS) enables high-speed processing and lower noise. The Nikon D300’s image sensor has photodiodes laid out vertically in approximately 4,000 lines, each of which has an A/D converter. Compared with structures that do not adopt parallel processing, the speed of each line’s A/D conversion can be slower, thereby minimizing wideband noise. This simplifies the A/D converter’s structure, keeping noise generation to a minimum, and power consumption low. Noise cancellation is conducted before and after conversion in a dual-stage process, contributing to a high signal-to-noise ratio.
The D3 employs a comprehensive range of measures to minimize noise, raising performance throughout the wide ISO sensitivity range to unprecedented levels. Early stage pre-amplification of electrical charges from the imaging sensor, noise cancellation using differential signal output and output-stage amplifier structure all dramatically improve the image quality of analog signals before A/D conversion. After conversion, the noise is further reduced using digital signal processing. Moreover, a user-selectable setting in the menu allows the high ISO noise reduction function to be automatically activated for ISO 2000 and above. Thorough noise reduction measures and optimized algorithms in both analog and digital processing provide professional photographers with natural-looking images of a quality, resolution and accuracy that has never before been possible.
