By Ray Fontaine

This is a three part blog series on full-frame (FF) format cameras. Part I reviews Nikon and Sony’s relationship, Part II will discuss Canon’s FF product strategy, and Part III will address new entrants to the sector and speculation on the future of FF format cameras.

Part I: Nikon vs. Sony and Nikon <3 (hearts) Sony

The recent high profile Apple vs. Samsung patent infringement case further emphasizes the incestuous nature of the supply chain for components in consumer electronics. Apple has traditionally sourced a great many components for its smartphones and tablets from its competitor Samsung. An analogous relationship exists in the DSLR world where Nikon both designs its own CMOS image sensors (CIS) to be fabricated by a foundry partner, and sometimes uses CIS components from its camera competitor Sony. That Nikon sources CIS components from Sony and Aptina is not news. What is somewhat interesting is that after a run of Nikon-designed CIS devices in Nikon FF and APS-C cameras, Sony has muscled its way back in for the FF format D800 [1].

Chipworks has monitored the pixel structures of CIS devices used in 10 Nikon DSLRs (APS-C and FF) since 2004. Six cameras using Nikon-designed, Renesas fabricated CIS are summarized in Table 1, while four cameras using Sony CIS are listed in Table 2. While these data points do not represent a comprehensive analysis of Nikon’s product portfolio, enough cameras have been analyzed to show Nikon’s preference of its own CIS components for prosumer and professional DSLRs (the D7000 and D800 being exceptions). Sony supplies the CIS for the D800, a camera with the resolution (36.3 Mp) and performance that approaches the performance of medium format cameras for some applications. Another interesting aspect of the D800 is its perhaps unintended use as a video camera featured in the filming of selected TV series [2, 3]. The D4 is Nikon’s flagship professional DSLR and uses a Nikon designed CIS, also featuring impressive low light and video performance [4].

Table 1: Nikon DSLRs with Nikon Designed, Renesas Fabbed CIS

Table 2: Nikon DSLRs with Sony CIS

Sony, as a product company, continues to pursue the APS-C and FF camera segments, so it is understandable that Nikon would want to differentiate itself by designing its own sensors. Then again, most consumers wouldn’t know the branding of a camera’s CIS components, so at some level, Nikon’s motives are open to speculation. Chipworks has analyzed the pixel structures of both devices, and while mostly of interest to process development engineers and pixel designers, these findings offer clues to Nikon’s strategy. Before the CIS pixels are reviewed, it is worth mentioning that camera performance is not attributed solely to CIS pixel performance, but also the low noise pixel array readout circuits, system level division of functionality, and ISP (image signal processor) chips which make major contributions toward the final specifications. For FF Nikon aficionados, the following pixel details should be interesting.

Sony IMX094 from the D800

The IMX094 is fabricated using 0.18 µm generation process technology to produce 4.75 µm pitch pixels. Of the 10 FF DSLRs analyzed by Chipworks (to be presented in Part II), the D800 represents the smallest FF pixels to date. Two pixels share common readout transistors using architecture familiar to those who have previously seen Sony’s recent APS-C CIS designs. The shared pixel layout and narrow metal lines afforded by a 0.18 µm process are critical to maintaining the fill factor needed to achieve a high performance 36 Mp FF pixel array.

Shared Pixels at Poly (L) and Pixel Cross Section (R) (click to enlarge)

Nikon NC81366W from the D4

The NC81366W is fabricated for Nikon by foundry partner Renesas using 0.25 µm design rules to produce the largish 7.3 µm pixels. While having largish pixels, a shared pixel architecture is still used to maximize individual pixel fill factor. The device features a pixel AR layer tuned for each of the three color channels (green and blue shown). For the first time in a Nikon FF DSLR, the shared pixel design includes a switch (T6) between the shared floating diffusion (FD) of in-column pairs to the adjacent in-column pixel pairs. Currently, Chipworks has not undertaken any design analysis of the row control circuitry, so the specific modes of still and video readout are not known. It is reasonable to assume that two or three like-color pixels can be summed together for high-speed, low noise video.

Shared Pixels at Poly (L) and Pixel Cross Section (R) (click to enlarge)

To speculate on Nikon’s choice of a Sony CIS for the D800, it may be related to Sony committing a 0.18 µm fab to FF wafer processing. Renesas has produced FF devices for Nikon using 0.35 µm (for the D3) and more recently 0.25 µm (for the D4) process generations. It seems likely that Sony’s advanced fab (0.18 µm) and maturity in the CIS sector positioned it to better meet the D800’s performance requirements.

While there are certainly those who groan at the prospect of cranking up the resolution of a FF sensor, the D800 appears to be a disruptive event in the FF camera segment – one that Canon is rumored to likely respond to [5]. In Part II, the Canon 1D X will be discussed, in addition to general observations of the FF camera market and the implications of a large resolution Canon FF sensor.

Part II: A Decade In, Canon Stays the Course (But Not in Pixel Design) 

Part III – New Entrants and a Look Forward

References

[1] http://www.dpreview.com/reviews/nikon-d800-d800e/

[2] http://www.prnewswire.com/news-releases/nikon-establishes-hollywood-video-credentials-as-the-d800-lands-leading-roles-168927306.html

[3] http://www.dpreview.com/articles/7228819844/photokina-2012-interview-dirk-jasper-of-nikon/print

[4] http://www.dpreview.com/products/nikon/slrs/nikon_d4

[5] http://www.canonrumors.com/2012/08/more-big-megapixel-talk/