hi keith,
thanks for your response. To clarify, the only function is the function of the chip. I'm actually not interested in the accuracy of the mirror, i'm more interested in the range of current i can create.
For example, if i were able to change the biasing resistor on my mirror, i would ideally like to exploit the full range of Vgs (ie: 0-Vdd), which in turn would allow me to get my maximium range of currents. However, MOSFETs are limited by their threshold voltage making it impossible to keep the MOSFET is saturation and having Vgs less then Vt.
not sure how much that cleared things up haha. I'm not very good at explaining things.
As a side note, i also wouldnt mind learning the benefits in general of FETs vs BJTs as current mirrors in general.