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NAND outputs tied to ground
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JuanGg:
Attached is the schematic for the square wave generator from a Hameg HM604 scope. I was just taking a look when I noticed there are three NAND gates with their outputs tied to ground. Seems that their inputs are held always high, so the output should be low anyways. Is this a way to "terminate" gates, as one would do with an unused op-amp? But one would not care about the outputs then.

It also seems that amplitude is controlled by changing the supply of the output gates, it seems to be a sort of voltage regulator in there, although I don't see how it regulates without feedback.

Any ideas?
    Juan
Zero999:
No, the output of unused or any gates shouldn't be directly tied to either supply rail, but left unconnected. It's only the inputs which need to be connected to +V or 0V, to prevent them floating.
wraper:

--- Quote from: JuanGg on June 10, 2019, 01:05:24 pm ---Is this a way to "terminate" gates, as one would do with an unused op-amp?

--- End quote ---
Nope, it's when someone designs a circuit without an idea what he/she is doing. Shouldn't cause failure but it's really dumb.
Andy Watson:
I would hope that Hameg do know what they are doing!  The chip is question is driving the output with fast edges - my guess would be that it's an attempt to lower the ground impedance to the substrate of the chip.
wraper:

--- Quote from: Andy Watson on June 10, 2019, 03:54:39 pm ---my guess would be that it's an attempt to lower the ground impedance to the substrate of the chip.

--- End quote ---
If they cared about impedance, they would connect multiple logic gates in parallel. Not attach 600  ohm load to the output of single gate.
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