Why CML divider with sensitivity window can't work at very low frequency?

CML divider has a sensitivity window. When the operating frequency is high enough or low enough it can not work. It's easy to understand that it can't work at high frequency. But why it can't work at very low frequency?

Added after 55 minutes:

Maybe I got the answer.

The CML divider has a self-oscillation frequency. The self-oscillation frequency is quite low compared with the operating frequency. If the input signal is low frequency and low level the self-oscillation will dominate so it can't divide the input signal.

Any comments are welcome.

There is another explanation of this thing
" .... The ostensible loss in sensitivity below 18 GHz
is caused by the low slew rate of the input signal and will
disappear for square pulses....." on p. 3.

By the way, what is the easy way to simulate sensetivity of a divider vs freq?

Could anyone clarify that point plz. why CML divider can't work at lower frequencies ?!
Thx in advance

Hi khalifas ,

The CML divider CAN work at low frequency if the slope of the input signal is large enough, if not, parasitic oscillation will occur at the zero crossing point of the input signal.

Rds
Buckaroo