From 1a94963fa108e2cd1ed2885ac9bb86ae6627c0b1 Mon Sep 17 00:00:00 2001 From: Bill Cox Date: Sun, 28 Sep 2014 06:49:11 -0400 Subject: [PATCH] update --- README.md | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) diff --git a/README.md b/README.md index 8c34686..5745f9d 100644 --- a/README.md +++ b/README.md @@ -152,6 +152,32 @@ same from N true random bits as M biased bits in this case. The program infnoise.c directly measures the entropy of INM output, and compares this to the estimated value. Simulations show that they correlate well. +There are two significant variations on the INM architecture so far. The first one, done +with CMOS transistors, which is suitable for an IC implementation, does a multiply by 2 by +stacking capacitors, and if the result is greather than Vref, it subtracts a value (using +a capacitor again) to reduce the value to below Vref. This is a literal implementation of +multiplication mod Vref. + +The board level versions were simplified using a couple of tricks. First, multiplication +by 2 modulo Vsup is accomplished by multiplying relative to either GND or Vsup. When +multiplying relative to GND, a 0.2V signal becomes 0.4V. When multiplying relative to a +3V Vsup, a 2.8V signal becomes 2.6V. The math comes out the same as if I'd multiplied +relative to GND, and simply subtracted Vsup if the result was > Vsup: + + Vsup - 2*(Vsup - A) = Vsup = 2*Vsup + 2*A = 2*A - Vsup + +So, we multiply by 2 either way, and only subtract out Vsup if needed. This is identical +to multiplication modulo Vsup. + +A second trick used to create the "small" version was to notice that the output of the +comparator could be used to combine both multiplier op-amps into 1. This abuse of the +comparator output needs to be carefully checked. In particular, the output is generally +treated as a digital signal, but in this case, it is used as an analog singal. Care +should be taken not to load the OUT signal significantly, and also to be sure the +comparator can drive the resistive load with no more droop than the buffer driving signal +B. However, don't be concerned about noise. Cross-talk is OK. It can only add to the +entropy. + ### Free As in Freedom I, Bill Cox, came up with the original CMOS based Infinite Noise Multiplier architecture