Quartz oscillator circuit of the self-polarised type, comprising, in an active branch of the oscillator circuit, an amplifier with an output which is connected to a first electrode of the quartz (Xtal) and an input which is connected to a second electrode of the quartz (Xtal), an output capacitor (Cout) being connected to the first electrode of the quartz (Xtal) and an input capacitor (Cin) being connected to the second electrode of the quartz (Xtal), the amplifier being polarised by a current which is generated in an amplitude regulation assembly, the amplitude regulation assembly comprising an amplitude regulation stage having a current source and the amplitude regulation assembly further comprising a polarisation transistor of current which is controlled by a gate of the transistor via the amplitude regulation stage and connected to the amplifier, in order to polarise it, the second electrode of the quartz (Xtal), which is connected to the amplifier input, being connected to the gate of the polarisation transistor and to the amplitude regulation stage so as to vary the polarisation current through the polarisation transistor and to regulate the oscillation amplitude of the quartz (Xtal), characterised in that the amplitude regulation stage comprises a first current mirror of a MOS type which comprises a diode-connected transistor of a second type of conductivity, one source of which is connected to a first terminal (Vdd) of a supply voltage source, a gate of the diode-connected transistor is connected to the gate of the polarisation transistor which is also of the second type of conductivity and to the second electrode of the quartz (Xtal), in that the gate of the diode-connected transistor is connected to one side of a filter resistor (Rf) whilst another side of the filter resistor (Rf) is connected to a gate of another transistor of the second type of conductivity of the first current mirror and to a first electrode of a filter capacitor (Cf), a second electrode of which is connected to the first terminal (Vdd) of the supply voltage source, in that a source of the other transistor of the second type of conductivity is connected to the first terminal (Vdd) of the supply voltage source via a base resistor (Rb) in order to determine a regulation current of the current source, in that the amplitude regulation stage further comprises a second current mirror, which comprises a first diode-connected transistor of a first type of conductivity, a source of which is connected to the second terminal of the supply voltage source and which corresponds to the current source, in that a drain of this diode-connected transistor and which is also of the first type of conductivity is connected to a drain of the other transistor of the second type of conductivity of the first current mirror, in that a gate of the diode-connected transistor of the first type of conductivity is connected to a gate of a second transistor of the first type of conductivity of the second current mirror, in that a source of this second transistor of the first type of conductivity is connected to the second terminal of the supply voltage source, and in that a drain of this second transistor of the first type of conductivity is connected to the diode-connected transistor of the first current mirror, to the second electrode of the quartz (Xtal) and to the gate of the polarisation transistor of the second type of conductivity for control of the current in the polarisation transistor.