It takes a -300mV P2P sine wave with a 2V supply and turns it into a squared-up pulse train. The quiescent voltage at the base of switching transistor Q2 seems to be pretty stable with temperature variation, only a couple of mV change over 0-70 degrees C.
Also seems to work out to a couple MHz, so there's that.
Unfortunately, it does use five transistors other than the switch. :-( But it was fun to use PNP current mirrors...
Why? Wouldn't a comparator chip work better?
Or are you just having fun with circuit design today?
-- Tim Wescott Control systems, embedded software and circuit design I'm looking for work! See my website if you're interested http://www.wescottdesign.com
I'm on vacation, and sadly these days I've mostly been writing code for real work and haven't had much opportunity to sit down with a pencil and graph paper and think about circuits.
There could be a slight cost savings over a single comparator. IIRC jellybean SMT BJTs are about two pennies in quantities of a hundred, while single comparators are around 25 cents for the same.
Also most cheap comparator ICs that I've seen like the 339 family either don't have guaranteed specs at ~2 volts, or don't like you taking the inputs too negative wrt ground, or would require one input to be grounded so as not to exceed the common mode voltage, or some combination etc. so making it work right _might_ not be as simple as just tossing a single 25 cent IC comparator section and 4 resistors at the problem.
I think discretes can still make sense sometimes at very low and very high voltages.
Perhaps a RS485 differential receiver could work also.
-- Dipl.-Inform(FH) Peter Heitzer, peter.heitzer@rz.uni-regensburg.de
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