Joerg said:
I know, I know. The topper was a design (no, not by me) where a whole uC
plus periphery was supplied via one (!) port pin substrate diode. Guess
they needed to save that one cent for a rectifier diode. Now that was a
real white knuckle design.
I 'designed by acident' a sync amp. The scenario: monitor wants
composite sync at TTL level, computer delivers sync at video signal
level. Monitor input is at 0 volts, no pull up resistor.
Thus, I built a little amp with a CMOS inverter. This worked but the
extra power supply bothered me. Then, I switch off the power, but the
thing keeps working. Hmm, there was no voltage on teh input and teh sync
output is insufficient as well.
I decide to use just a decoupling cap, no power connection. Doesn't work.
I take the decoupling cap off and bing the thing works.
Must be the most ugly analog CMOS amp in existence. I suppose the
monitor outputs some pull-up voltage whenever it detects a signal on the
sync input. Never tried to figure it out; it worked and it was a one-off.
Thomas