Re: Ring Oscillator - for SRAM
in response to
by
posted on
Feb 17, 2015 09:23PM
I haven't been able to contribute to the discussion very often since I've become busy with work, but I thought I'd add to the oscillator discussion.
If you listen to the CIC presentation at around 30:20 (cued below) you'll hear SG mention that POET will begin working on SRAM structures once the VCSEL and the ring oscillator are completed.
http://youtu.be/ujw3l7uQRYQ?t=30m
It turns out that the ring oscillator is one of the basic building blocks of the SRAM
"A circular chain composed of an even number of inverters cannot be used as a ring oscillator; the last output in this case is the same as the input. However, this configuration of inverter feedback can be used as a storage element; it is the basic building block of static random access memory, or SRAM."
http://en.wikipedia.org/wiki/Ring_oscillator#Details
Interestingly, SRAM is described in both of the most recent US patents.
https://www.google.com/patents/CA2844987A1?cl=en&dq=ininventor:%22Geoff+W.+Taylor%22+sram&hl=en&sa=X&ei=gPPjVNfNIqqxsASR6oGADQ&ved=0CCQQ6AEwAQ
"[0093] Figure 26 shows the IV characteristic of a thyristor memory cell 100 according to the present invention. The thyristor has the non-conducting/OFF and the conducting/ON states to store a '0' and '1' respectively. With the thyristor operated this way it has the function of a flip flop. Therefore, it is an ideal static RAM (SRAM) cell. The cell has two devices (a thyristor and a load) compared to the flip flop (6T cell). Therefore smaller footprint and higher speed"
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It should be noted that SG did emphasize the utility of the Ring oscillator for comparing with CMOS and he didn't make any connection with the SRAM development to come. Also, I'm not 100% certain Taylor's universal memory uses an oscillator for the SRAM function (although it does describe a flip-flop which is often generated with an oscillator).
It think it plausible that if POET needed to produce a ring oscillator to showcase POET capabilities they may very well have chosen SRAM structures as the next target in a logical progression after the basic ring oscillator was complete.
I personally hope this is true because I've always had a fondness for the concept of POET universal memory above most of the other POET applications for the short term.