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Design >> Analog Design >> Current Sense amplifier design
https://designers-guide.org/forum/YaBB.pl?num=1337616603

Message started by Larry_80 on May 21^st, 2012, 9:10am

Title: Current Sense amplifier design
Post by Larry_80 on May 21^st, 2012, 9:10am

Hello Guys,
Please i need help in designing a current sense amplifier. Pls find attached is the schematic. During a read, the read current is lets say Iread=10uA.
So the differential current Idl-Idlb should be 10uA. I am operating at low voltages and transistors M2 and M4 are always in Linear region since ysel="vdd" during sense amp operation.
My problem is this: I cannot get the differential voltage Vdl-Vdlb to be more than about 5mV during a read operation (Iread=10uA). I tried increasing the DC current in both branches and i always still get only the 5mV differential voltage (Vdl-Vdlb). Please note during read, i attach a current source of 10uA from Vbl to ground (in that direction) in my simulation.

Does anyone know what region of operation the transistors should be in during reset phase (No read current) and during the read phase? I am not sure if there is such a requirement.

Ps: I am desperately seeking a methodical approach to design this ckt, and haven't been successful in finding any literature that highlights a method.

Title: Re: Current Sense amplifier design
Post by aaron_do on May 21^st, 2012, 6:06pm

disclaimer: I've never designed a current sense amplifier before :D

When you pump in the 10uA current, what are the DC voltages Vdl and Vdlb? If they are both low, then probably your circuit it too big.

BTW, are the cross coupled PMOS devices a latch? If so, and if both Vdl and Vdlb are high, then maybe your latch just isn't strong enough.

Actually its a little tough to debug without some actual voltages in the circuit.

Aaron

Title: Re: Current Sense amplifier design
Post by pixel on May 23^rd, 2012, 12:10am

I think you should try different architecture. Diode connected NMOS at the bottom do not allow voltage difference.

Title: Re: Current Sense amplifier design
Post by Larry_80 on May 23^rd, 2012, 8:26am

They are actually N MOSFETS, i just used jfet symbol for illustration sorry :). Apparently all the xstors must remain in saturation for the amplifier to work like it should.

Title: Re: Current Sense amplifier design
Post by loose-electron on May 24^th, 2012, 1:27pm

tell us what you are trying to do.

Not the circuits you are thinking of using.