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diode connected and current source loads

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deepa

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diode connected load

isnt a diode connected transistor a better constant current source than a current course one,,since in the diode connected one Vgd =0 => the transistor is always in saturation ,but in current source transistor Vb given at the gate must be such that for all the output swings the transistor is in saturation,which limits the output swing???
 

diode connected gm source

well ,if we are able to assure tht Vb is such that the transistor is always in saturation ,then it a better load than the diode connected load,since a diode connected load has an output res of 1/Gm
 

diode connected load inverter

1. firstly for a current souce you want a very high output impedance, which is not possible with a diode connected device as luckypearl25 has mentioned.
2. Voltage swing is better for a regular transistor (say NMOS) because the drain can go Vtn below the gate and still be in sat. whereas, with the diode connected guy your drain can go low only until your gate.
3. How are you going to generate a current from a diode connected transistor?
 

diode connected transistor

No, the output resistance is quite low
 

what is diode connected load

The output resistance is low (1/gm) but It may be prefer to use the diode connected load since the gain is very linear and doesnt depends on the gm or the currents : Av=-gm1/gm2 which is ratio of the tr. dimensions
 
connecting diodes as load

diode connected load is a better choice for preamplifier at high speed comparator
or amplifier.

depend on your application
 

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