How can you generate this waveform?
yes, micro.
You could conceivably do it with a single 600Hz clock (could well be 555) and a counter(74xx or 4060) to count out pulses for the initial 100%-on-phase. You could use one or more 74xx flip flops for gating, maybe an inverter or nor gate to stop the counter after the initial phase is over and reset it at the start. Needless to say this doing it the hard way.
The final output level would involve an opamp and probably a transistor if you're actually using this to drive something.
PS- is this a solenoid drive circuit with a startup boost? they have single chips that do all this, like DRV101 etc