Slide 48 of 64
So here we see the main result for the Hitachi transistor, peaking at just a shade above 100 microamps at around 45 GHz. Of course one can always operate with lower currents than at the peak, but then the speed drops. We do this anyway in slower parts of the circuit to conserve power. The Hitachi paper points out that at only 30 microamps the device still has a transition frequency or fT of 30 GHz. To achieve best performance the CML differential pair must sweep the oncoming transistor to the peak and stop there.