IC Biasing with Current Sources

[howiehoward]

I understand current sources are used to bias IC circuits, but how does the Ro (Dynamic Output Resistance) of the current source (Either simple, Widlar, or Wilson) effect the amplifier? Why is a higher Ro better than a lower Ro?

 

[berkeman]

Two advantages come to mind: -1- The higher output impedance of a current source let's you set higher gains in diffamp configurations (where the current sources are in the collectors). -2- You can usually have more accurate current sources via mirroring, as compared to the accuracy of on-chip resistors.