A 4.2-ps ECL ring-oscillator in a 285-GHz fmax SiGe technology

This letter reports on the room temperature operation of a conventional SiGe bipolar ECL ring oscillator with a minimum stage delay of 4.2 ps for /spl sim/250 mV single ended voltage swing. To our knowledge, this is the lowest reported delay for a gate fabricated using transistor devices. The circuit uses 0.12 × 2 μm
²
emitter size SiGe n-p-n transistors with a room temperature f
_T
of 207 GHz and f
_max
(unilateral gain extrapolation) of 285 GHz. The ring oscillator was studied as a function of various device and circuit parameters and it was found that minimum delay is more dependent on the parasitic resistance and capacitance in the n-p-n device than on pure transit time across the device.