making a priority encoder with BJTs

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pgo1

Joined Nov 7, 2012
49
I am certain I found a schematic somewhere for a BJT based priority encoder (i.e. a cell where a high input turns low all the preceding stages) but now I can't find it. The circuit I am thinking of has two inputs and two BJTs. Can anyone confirm I didn't dream it? And also share a link :)
 

dl324

Joined Mar 30, 2015
15,112
I found a schematic somewhere for a BJT based priority encoder (i.e. a cell where a high input turns low all the preceding stages) but now I can't find it. The circuit I am thinking of has two inputs and two BJTs.
I've never seen such a circuit.

Did it look something like this (that I just threw together)?
1664384742920.png
Input B is the most significant bit (MSB), hence LED1 represents the MSB. D1 insures that Q2 will be off when Q1 is on.

This is the logic diagram:
1664387155271.png
EDIT: cleaned up logic diagram.

B represents MSB and the LED on the left is MSB. Don't obsess over the lack of resistors and loading the output of the AND gate. That's just how the simulator I use works...
 
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