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For analog Design you would want to use High VT devices, as they are the ones with good rds. From my experience, even if you use devices with different VTs your yield should not be impacted. You can confirm this by performing Monte Carlo Simulations.
Processes allow multi VT devices, e.g Standard VT, High VT and Low VT devices in addition to zero VT devices and designers can combine devices, dilligently decide where to use.
A good example is if you have headroom problems, you can make the input pair devices of opamp, a standard VT device, with load devices and tail current devices still at HVT.
Try not to use other than HVT for current sources, as everything other than HVT devices have poor RDS, which is important for constant current source.
ic_engr.
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