The following is a circuit I got from a research paper and I am trying to analyze it. The inverter is a high speed inverting buffer whose output is always one. The circuit starts functioning when the inverter sends an output of zero. I will quote the sentences in the paper about the idle conditions (When inverter output is one)
"The output of inverter biases Q1 Such that its emitter Voltage is higher than the base voltage of Q3, thus cutting off the collector current of Q3. Capacitor C6 will have been charged to 5 volts through R17 with a time constant of about 5 us"
When the inverter ouput is zero,
"The inverter generates a fast falling edge and quickly turns off Q1 thus turning on Q2.The collector of Q2 draws a constant 23 ma from C1, thus discharging it at the uniform rate of 0.1 volts per nanoSecond"
My doubts :
1) How turning off Q1 can turn on Q2?
2) When Q2 is turned on, how the collector become constant taking 23 mA from C1?