An amplitude regulating circuit for an oscillator with an input for a supply signal having an electrical quantity depending on an amplitude of an oscillation of the oscillator has a supply circuit with a control input for a first control signal and a supply output for the supply signal based on the first control signal, a reference circuit with an input for a reference supply signal having a reference quantity, a reference supply circuit with a reference control input for a second control signal and a reference supply output for the reference supply signal based on the second control signal and a comparator circuit with a first control signal output for the first control signal based on the electrical quantity and the electrical reference quantity and a second control signal output for the second control signal based on the electrical quantity and the electrical reference quantity.