The invention relates to a respiratory gas supply circuit (1) for an aircraft carrying passengers and crewmembers (30), comprising a source of breathable gas (R1, R2), at least one supply line (2) connected to said pressurized source, a regulating device (12) provided on said supply line for controlling the supply of breathable gas, a mixing device (9) provided on said supply line, said mixing device further comprising an ambient air inlet (10) for mixing said ambient air with said breathable gas to provide to at least one passenger or crewmember a respiratory gas corresponding to a mixture of said breathable gas and ambient air, wherein said regulating device is driven by a control signal (FIO2 )