2 ms·

Nice work! Any article that features results from a test PCB is a winner in my book! > Let me know if you find similar devices. The Rohm high-frequency BJTs l

Nice work! Any article that features results from a test PCB is a winner in my book! > Let me know if you find similar devices. The Rohm high-frequency BJTs look promising: 2SC3838K is the fastest (fT wise), but there are several others (see page C28 of Rohm's 2019 catalog). I only checked the datasheet for the one, but it's got a very nice Figure 10, showing that it'll probably switch fastest around 20mA collector current, and should be about 3x faster there than the MMBTH10L at 4mA.

blattimwind 7y ago
The thing is that if you want logic to go fast proper you don't use saturation logic (DTL/RTL/TTL), but current steering logic (ECL). That way your usable clocks gets much closer to the fT of the transistors involved, instead of being limited to a tiny fraction of it. That's how Cray built supercomputers after the CDC6600/7600.
- TheOtherHobbes 7y ago
  At the cost of insane power/heat budgets - although one of the nice things about ECL is the power draw is relatively constant because the transistors don't saturate, and you don't get the spikes and PSU hash you get with TTL etc. ECL was amazing for its time, but I'm honestly more impressed by modern PC/phone electronics. PCBs and chip designs are mass-produced commodity products clocked at microwave frequencies - sometimes with battery power. This is incredibly impressive compared to the state of the art in the 60s and 70s. And it's taken for granted as an everyday thing.
  - thedance 7y ago
    It seems like the power consumption of this computer must have been pretty spectacular anyway. 60mW per gate is no joke.
  - fanf2 7y ago
    I recently found a 1980s Cray installation guide which has a lot more detail on the power, cooling, and other physical requirements. https://news.ycombinator.com/item?id=22284518 https://news.ycombinator.com/item?id=22284518
    - dfox 7y ago
      One notable thing about the constant power draw of ECL and Cray-1 in particular is that power draw is constant enough that the logic supply is unregulated, just rectified and filtered output of 400Hz transformers (placed physically in the "bench part" of the chasis). What is regulated is the 208V/400Hz supply for the thing (produced by the motor generator shown in the article), but regulation of that IIRC involves manual turning of physical knobs during installation/maintenance and is more about compensating for unstable mains on the input side.

blattimwind 7y ago

The thing is that if you want logic to go fast proper you don't use saturation logic (DTL/RTL/TTL), but current steering logic (ECL). That way your usable clocks gets much closer to the fT of the transistors involved, instead of being limited to a tiny fraction of it. That's how Cray built supercomputers after the CDC6600/7600.

TheOtherHobbes 7y ago
At the cost of insane power/heat budgets - although one of the nice things about ECL is the power draw is relatively constant because the transistors don't saturate, and you don't get the spikes and PSU hash you get with TTL etc. ECL was amazing for its time, but I'm honestly more impressed by modern PC/phone electronics. PCBs and chip designs are mass-produced commodity products clocked at microwave frequencies - sometimes with battery power. This is incredibly impressive compared to the state of the art in the 60s and 70s. And it's taken for granted as an everyday thing.
- thedance 7y ago
  It seems like the power consumption of this computer must have been pretty spectacular anyway. 60mW per gate is no joke.
- fanf2 7y ago
  I recently found a 1980s Cray installation guide which has a lot more detail on the power, cooling, and other physical requirements. https://news.ycombinator.com/item?id=22284518 https://news.ycombinator.com/item?id=22284518
  - dfox 7y ago
    One notable thing about the constant power draw of ECL and Cray-1 in particular is that power draw is constant enough that the logic supply is unregulated, just rectified and filtered output of 400Hz transformers (placed physically in the "bench part" of the chasis). What is regulated is the 208V/400Hz supply for the thing (produced by the motor generator shown in the article), but regulation of that IIRC involves manual turning of physical knobs during installation/maintenance and is more about compensating for unstable mains on the input side.