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enable button, shutting down the whole circuit

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Member level 3
Oct 24, 2010
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I am trying to create a "ON OFF" button for my circuit, so that i can shut it down and i don't consume any power.

The problem is that this part of the design for example, thx to shutting down the biasing, i get A at VDD, and C (due to no current in the small amplifier) also at VDD. But B remains like 20mV below VDD, and the top transistor, even though having Vgs=0, conducts approx half a uA!!! I tried adding a small transistor (pmos with drain on B) but still that small current remains. I tried an nmos (drain on D) But still i have that small current.

Is there any way i can shut it down completely? Or it's an order of magnitude of current that i have to survive with?

(tota budget of current 100uA, this branch 1uA in normal operation, 0.5uA in "OFF"!!)

thx edanow.jpg

Expected leakage will depend on technology, supply and size; it definitely seems too high: can you provide us with a more detailed schematic of this branch? e.g. where are the body terminals connected to?

This is the situation with my "OFF" state, all the details, gate currents zero (aA level).

Very surprising: to debug this I suggest
- check that your simulator accuracy is high (and that you are using a full analog simulator)
- run a simulation of this PMOS alone to characterize its subthreshold leakage (plot with log current scale and sweep Vgs at the circuit Vds)
- check your simulation temperature
- check that source and drain currents are (practically) the same

Let us know...

What's pmos and what process did you use?

ok i'll check all those on Monday......
What i remember is that
--i always check on transient the conservative simulation, so i guess this is pretty accurate
--this sim is for fast corner, 85 degrees, cause it's my worst case as fas as power consumption is concerned
--source and drain currents were the same that's why i didn't write them on the graph

--The process is quite old (0.6um)
--In this process the pmos is the Low Vthreshold model, pmos with body.

For all the rest, i will simulate on monday again, i cannot from home. Have a nice weekend :)

Some low vth mosfet will have a current leakage when Vgs=0.
Deplete MOSfet will have current always when Vgs=0.
What's the mosfet Vth?

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