In the Miller sweep circuit:

1. Constant charging current is maintained by keeping the voltage across the charging resistor and hence the current through it
2. A step input is converted into a linear ramp by using an operational integrator
3. The timing capacitor is charged linearily from a constant current source
4. The timing capacitor is charged from a constant voltage source

In the miller sweep circuit A step input is converted into a linear ramp by using an operational integrator.