A crystal oscillator circuit (40; 44; 47) comprising: • a crystal (X 1); • oscillator circuitry (11; 21; 31; 41) connected to said crystal (X 1) and configured to generate a crystal oscillation signal at an oscillation frequency; and • a kick-start circuit (12; 42; 45; 48) configured to inject a number of pulses into said crystal during a start-up period of the crystal oscillator circuit, wherein said oscillator circuitry (11; 21; 31; 41) comprises a first differential pair of transistors (M 1, M 2), wherein • the first differential pair of transistors, in the oscillating mode, are cross-coupled so that a gate terminal of a first transistor (M 1) of the first differential pair is coupled to a drain terminal of a second transistor (M 2) of the first differential pair, and a gate terminal of the second transistor (M 2) of the first differential pair is coupled to a drain terminal of the first transistor (M 1) of the first differential pair, each one of said drain terminals of the first and second transistors of the first differential pair further being coupled to a terminal of said crystal (X 1) to generate said crystal oscillation signal at said oscillation frequency; characterized in that said oscillator circuitry (11; 21; 31; 41) is configured to operate in a selectable one of at least an oscillating mode and a start-up mode, wherein • said kick-start circuit (12; 42; 45; 48), in the start-up mode, is configured to drive the gate terminals of said first and second transistors (M 1, M 2) of the first differential pair with said number of pulses during said start-up period of the crystal oscillator circuit; and • the crystal oscillator circuit is further configured to disconnect, in the start-up mode, the gate terminal of the first transistor (M 1) of the first differential pair from the drain terminal of the second transistor (M 2) of the first differential pair, and the gate terminal of the second transistor (M 2) of the first differential pair from the drain terminal of the first transistor (M 1) of the first differential pair. • a crystal (X 1); • oscillator circuitry (11; 21; 31; 41) connected to said crystal (X 1) and configured to generate a crystal oscillation signal at an oscillation frequency; and • a kick-start circuit (12; 42; 45; 48) configured to inject a number of pulses into said crystal during a start-up period of the crystal oscillator circuit, wherein said oscillator circuitry (11; 21; 31; 41) comprises a first differential pair of transistors (M 1, M 2), wherein • the first differential pair of transistors, in the oscillating mode, are cross-coupled so that a gate terminal of a first transistor (M 1) of the first differential pair is coupled to a drain terminal of a second transistor (M 2) of the first differential pair, and a gate terminal of the second transistor (M 2) of the first differential pair is coupled to a drain terminal of the first transistor (M 1) of the first differential pair, each one of said drain terminals of the first and second transistors of the first differential pair further being coupled to a terminal of said crystal (X 1) to generate said crystal oscillation signal at said oscillation frequency; characterized in that said oscillator circuitry (11; 21; 31; 41) is configured to operate in a selectable one of at least an oscillating mode and a start-up mode, wherein • said kick-start circuit (12; 42; 45; 48), in the start-up mode, is configured to drive the gate terminals of said first and second transistors (M 1, M 2) of the first differential pair with said number of pulses during said start-up period of the crystal oscillator circuit; and • the crystal oscillator circuit is further configured to disconnect, in the start-up mode, the gate terminal of the first transistor (M 1) of the first differential pair from the drain terminal of the second transistor (M 2) of the first differential pair, and the gate terminal of the second transistor (M 2) of the first differential pair from the drain terminal of the first transistor (M 1) of the first differential pair.