A crystal oscillator start-up circuit (300,500) comprising: an H-bridge circuit comprising a plurality of switches (S1, S2, S3, S4, SR P, SR N) configured to be coupled to a crystal resonator; a comparator having a first comparator input configured to be switchably coupled to a terminal (314,316) of the crystal resonator, a second comparator input configured to be coupled to a supply node, a comparator clock input, and a comparator output configured to transition between a first state and a second state in response to a zero-crossing event of the motional current in the crystal resonator; a comparator clock generator having a first comparator clock generator input coupled to the comparator output, a second comparator clock generator input configured to receive a start signal, and a comparator clock generator output coupled to the comparator clock input; a switch control generator coupled to the comparator clock generator output and configured to generate a plurality of switch control signals (φ p, φ n, φ psub1, φ nsub1, φ psub2, φ nsub2) synchronous with respect to the comparator clock to control the plurality of switches, the plurality of switches being configured to apply a voltage between the crystal resonator terminals (314,316) in a first polarity during a first switch control phase (φ p) and in a second polarity during a second switch control phase (φ n), the second switch polarity being opposite to the first switch polarity, characterized in that during a respective first subphase (φ psub1, φ nsub1) of each respective switch control phase, the plurality of switches are configured in a first configuration to couple the supply node to a respective crystal resonator terminal (314, 316); and during a respective second subphase (φ psub2, φ nsub2) of each respective switch control phase, the plurality of switches are configured in a second configuration to couple the supply node to the respective crystal resonator terminal (314,316); wherein the resistance between the supply node and the respective crystal resonator terminal (314,316) is larger in the second configuration than the first configuration; and wherein the switch control generator is further configured to couple the first comparator input to the respective crystal resonator terminal (314,316) during each of the respective second sub-phases (φ psub2, φ nsub2). an H-bridge circuit comprising a plurality of switches (S1, S2, S3, S4, SR P, SR N) configured to be coupled to a crystal resonator; a comparator having a first comparator input configured to be switchably coupled to a terminal (314,316) of the crystal resonator, a second comparator input configured to be coupled to a supply node, a comparator clock input, and a comparator output configured to transition between a first state and a second state in response to a zero-crossing event of the motional current in the crystal resonator; a comparator clock generator having a first comparator clock generator input coupled to the comparator output, a second comparator clock generator input configured to receive a start signal, and a comparator clock generator output coupled to the comparator clock input; a switch control generator coupled to the comparator clock generator output and configured to generate a plurality of switch control signals (φ p, φ n, φ psub1, φ nsub1, φ psub2, φ nsub2) synchronous with respect to the comparator clock to control the plurality of switches, the plurality of switches being configured to apply a voltage between the crystal resonator terminals (314,316) in a first polarity during a first switch control phase (φ p) and in a second polarity during a second switch control phase (φ n), the second switch polarity being opposite to the first switch polarity, characterized in that during a respective first subphase (φ psub1, φ nsub1) of each respective switch control phase, the plurality of switches are configured in a first configuration to couple the supply node to a respective crystal resonator terminal (314, 316); and during a respective second subphase (φ psub2, φ nsub2) of each respective switch control phase, the plurality of switches are configured in a second configuration to couple the supply node to the respective crystal resonator terminal (314,316); wherein the resistance between the supply node and the respective crystal resonator terminal (314,316) is larger in the second configuration than the first configuration; and wherein the switch control generator is further configured to couple the first comparator input to the respective crystal resonator terminal (314,316) during each of the respective second sub-phases (φ psub2, φ nsub2).