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GARTHWILSON
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PostPosted: Sat Nov 05, 2011 12:06 am 
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The input capacitance for the latch is 3.5pF, BC109C collector capacitance is 6pF, for the BFR90 is nearly 0.5pF.

So there's 10pF, and even if there were no additional capacitance in the PC board and IC sockets and anything else there, 10pF with a 4.7K resistor makes for 47ns time constant. That's a very, very slow rise time for a gate output, and it's only part of the full prop delay of the gate.
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Dajgoro
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PostPosted: Sat Nov 05, 2011 12:10 am 
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GARTHWILSON wrote:
Quote:
The input capacitance for the latch is 3.5pF, BC109C collector capacitance is 6pF, for the BFR90 is nearly 0.5pF.

So there's 10pF, and even if there were no additional capacitance in the PC board and IC sockets and anything else there, 10pF with a 4.7K resistor makes for 47ns time constant. That's a very, very slow rise time for a gate output, and it's only part of the full prop delay of the gate.


I used 1k as a base resistor and 500 ohm for the collector resistor. I think that when the gate is switching it would create lots of interference...

Any clue for the mystery problem on page 3?
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Dajgoro
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PostPosted: Wed Nov 09, 2011 12:50 pm 
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I've found this: http://www.paleotechnologist.net/?p=530
Now my question is: How fast is this gate?
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GARTHWILSON
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PostPosted: Wed Nov 09, 2011 6:08 pm 
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Dajgoro wrote:
Now my question is: How fast is this gate?

According to TI's data sheet, the propagation time is over 100ns. Just the output rise and fall time is 100ns typical, 300ns max.
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Dajgoro
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PostPosted: Thu Nov 10, 2011 12:19 am 
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Hmm, could the 555 be useful?
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