This circuit can be used to build a clock to drive sequential logic circuits. However the frequency changes when the power supply voltage changes. A 555 astable is better and a quartz crystal oscillator is the best of the three.

Period = 2RC

Frequency = 1 / Period

Frequency = 1 / 2RC

The circuit is astable. That means it can not permanently settle in an on or off state. It has ZERO stable states. Whichever state it is in, the capacitor will charge or discharge eventually causing it to switch to the other state. Once in the other state, it is still unstable and the circuit oscillates.

• If A is high then B is low and C is high.
• Since B is low, the voltage at A will drop as the capacitor charges.
• When the voltage at A drops to half V_supply, B goes high and Q goes low. This forces A even lower.
• Now B is high so the capacitor charges in the opposite direction until A rises to half V_supply. When this happens, the circuit changes state again and we are back at step 1.

Here is a picoscope trace of the output of this circuit.
Note that the potential difference across C reverses so an electrolytic capacitor can not be used.