HdrChopper
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Hello,
Typically when a circuit is said to work under sub-threshold both types of devices are under that condition: for instance a differential nmos pair biased with a tiny current will be under sub-threshold, and if a pmos acitve load is used then they most probably will be under sub-threshold. At Vdd=1.2v, in order not to have those pmos in subthreshold you would need a very small W/L ratio which might cause some headroom problems in this example. Although such circuit can be considered to work under sub-threshold, that does not mean all its transistor are in such condition. Eventually you might have a combination of some of the working under subthershold and others that do not.
Hope this helps. Tosei
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