Why should the output impedance of a current source be much greater than the input impedance of the load?
The output impedance shunts the source in a current source:







simulate this circuit &ndash; Schematic created using CircuitLab

If the source impedance were in series, it would have no effect on the source's behavior, because the current source would simply compensate for its presence to produce the required output current.

Since the source impedance is shunting the source, it must have a high value to avoid drawing away source current and reducing the current delivered to the load.