Design of Cascode Current source

[rahbi]

how should we start to design a Cascode current source for an 8-bit current steering DAC?
what are the main points that we should consider, or the important design step??

 

[prestonee]

in an 8 bit current steering dac, you first determine what your lsb voltage is, you then decide what current you want to be responsible for that voltage. This will determine the resistor you use.
you then design stamps of current mirrors across increasing the width of the device by a factor of 2(usually done by adding devices in parallel). also it is common to maintain constant current and so you have dummy currents flowing when not being used, this decreases the switching time (increasing speed).
-Pb