hi,
You can use a comparator to detect the difference in the voltage levels.
The comparator can be configured to give a TTL output level whenever the signal is greater than say, 50mVolt.
A fast comparator will give TTL pulses each time it senses greater than 50mV,
so you could use a simple resistor/capacitor filter to remove the comparator output 'spikes' or allow the high output edges to re-trigger a monstable to give a clearer pulse.
Do you know how to do that?