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Start up for the bias circuit

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raj_shekar

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The attached bias circuit requires startup or not ?
 

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  • biasckt.jpg
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Don't think so: starting your ibias will start up the circuit.
 

This circuit seems so complex. It might be simpled.
 

When you switch on the current, There can be a possibility that vbiasp reduced to zero and vcasp node(uncertain or may be at vdd), then no current will be mirrored. In that case i have to add a start up, to pull down the "vcasp" node and pullup "vcasn" node. if it is ok how can i add start up here
 

Pls copy the bias needed to be started anc compare it with the original current bias to generate start-up signal.
 

When you switch on the current, There can be a possibility that vbiasp reduced to zero and vcasp node(uncertain or may be at vdd), then no current will be mirrored. In that case i have to add a start up, to pull down the "vcasp" node and pullup "vcasn" node.

Don't think so: I've simulated your circuit with initial conditions = vdd for vbiasp & vcasp , as well as 0V for vcasn & vbiasn, see the foll. figure:


300 MC simulations vs. PVT didn't show a single startUp failure.
 

while doing transient with the supply ramp for few nano seconds,
i am getting zero value for vbiasp
 

while doing transient with the supply ramp for few nano seconds,
i am getting zero value for vbiasp

You are right: there exists another stable operating point, possibly depending on the topology of your original current source. So to be on the safe side, you better add a start-up circuit (which pulls up vbiasp until vdd is settled).
 

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