I discovered an interesting logic family not too long ago, called Integrated Injection Logic, or I2L. Signetics seems to have been a large-scale user of this technology. It boasts 1V supply rails using complimentary bipolar transistor circuits. For example, here's a typical inverter, expressed in the best ASCII art I can muster on work hours:



+Vbb is usually derived on-chip, and is typically 0.65V less than +Vcc, where +Vcc typically = 1.0V to 1.25V. The inverter works because Q1, a PNP transistor, is configured as a constant current source for Q2. If A is high-impedance (e.g., if A is high), then Q2 will be turned on by the current supplied by Q1. This brings Y low. Conversely, if A is low (tied to ground), then the voltage on Q2's base falls below 0.65V (typically 0.25V based on my measurements with 2N3904/2N3906 transistor pairs), thus turning it off, leaving Y in a high(-impedance) state.

Now, I know that I2L is ancient technology, but for its day it was earth-shaking, because it was very low power. A single NOR gate (the basic I2L gate) implemented with discrete transistors (let alone on-chip transistors!) could draw as little as 5 microwatts of power, if my math is right. So, in theory, a 6502 implemented in I2L could reasonably be expected to draw as little as 20mW of power, give or take some reasonable amount of tolerance for uncertainty. Let's call it 50mW to be conservative. Because it was current-mode, the logic was pretty fast too, being a bit faster than TTL of the day.

Could this logic make sense for use on a backplane bus, and if so, how would it be terminated? I ask because the PNP transistors seems, to me at least, to function in the same capacity as an active bus termination circuit. This would suggest plug-in cards would drive the bus with open-collector logic, and the backplane itself would implement the PNP current sources, to be shared by all the logic. This arrangement seems like it'd fundamentally alter how one should terminate the bus, if it's required at all.

What are your thoughts?

(only tangentially related: in the late 70's and early 80's Ferranti in the UK made gate arrays with capacities around 700 usable gates, which were used in Sinclair and Acorn machines. The arrays used Current Mode Logic, which has a load resistor so isn't quite the same thing. Chris Smith's excellent book says the gate consumption, at a 0.95V array supply, was 3uA for a 450ns gate delay in the low power versions, up to 210uA for an 8ns gate delay in the high speed versions. The chips were TTL compatible at the pins.)

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Hello,
for what i know the best way to absorbe reflection in bus terminatio is the array of shottky diodes (no dissipation, high speed)

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_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

I'm feeling deja vu all over again, as we had this discussion elsewhere. The article you reference is from 1998 and represents Dr. Johnson's thinking based upon the available Schottky diodes of the time. Schottky clamping arrays have gotten very fast compared to what was available 16 years ago. Individual diodes have reverse recovery times in the 4ns range, and clamping arrays, as one might use on an address or data bus, are typically in the 8ns range.

The static protection diodes in CMOS parts don't clamp at the five volt level, so I would have to question their effectiveness in suppressing bus reflections. That said, I don't see where reflections are going to be a problem in a system running at the speeds we usually use, unless the lines are significant in length.

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http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Hello everyone,

http://www.ti.com/lit/ds/sdfs093/sdfs093.pdf

this explain how work shottky diode barrier.

It raises a good point, about the capacitors in series with the resistors. The diodes only clamp voltages below ground, but the real termination is the 50-ohm resistors in series with the 47pF capacitors. The capacitors let the resistors do their terminating job without putting a DC load on the driver.

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The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?