A voltage controlled oscillator VCO, configured to provide an output signal of the VCO produced across output nodes, the VCO comprising: a transformer including a primary inductor and a secondary inductor, the secondary inductor inductively coupled to the primary inductor; a capacitor bank conductively coupled to the secondary inductor and a gain stage conductively coupled to the primary inductor and configured to receive a supply signal and to drive a differential current in the primary inductor, thereby inducing an output signal of the VCO across the secondary inductor having a frequency equal to a resonant frequency of the VCO; wherein the primary inductor includes first and second terminals (1024, 126), the secondary inductor includes third and fourth terminals (130, 132) and the gain stage includes a first transistor having a first drain and a first gate and a second transistor having a second drain and a second gate, wherein: the first drain is conductively coupled to the first terminal; the second drain is conductively coupled to the second terminal; the first gate is conductively coupled to the fourth terminal; the second gate is conductively coupled to the third terminal; and wherein the capacitor bank comprises a plurality of switched capacitors, the switched capacitors being selectively coupled between the third terminal and the fourth terminal when switched on,the VCO being characterised in that the capacitor bank provides a majority of a total capacitance of the VCO and in that the third and fourth terminals (130, 132) comprise the output nodes (114a, 114b). a transformer including a primary inductor and a secondary inductor, the secondary inductor inductively coupled to the primary inductor; a capacitor bank conductively coupled to the secondary inductor and a gain stage conductively coupled to the primary inductor and configured to receive a supply signal and to drive a differential current in the primary inductor, thereby inducing an output signal of the VCO across the secondary inductor having a frequency equal to a resonant frequency of the VCO; wherein the primary inductor includes first and second terminals (1024, 126), the secondary inductor includes third and fourth terminals (130, 132) and the gain stage includes a first transistor having a first drain and a first gate and a second transistor having a second drain and a second gate, wherein: the first drain is conductively coupled to the first terminal; the second drain is conductively coupled to the second terminal; the first gate is conductively coupled to the fourth terminal; the second gate is conductively coupled to the third terminal; and the first drain is conductively coupled to the first terminal; the second drain is conductively coupled to the second terminal; the first gate is conductively coupled to the fourth terminal; the second gate is conductively coupled to the third terminal; and wherein the capacitor bank comprises a plurality of switched capacitors, the switched capacitors being selectively coupled between the third terminal and the fourth terminal when switched on,the VCO being characterised in that the capacitor bank provides a majority of a total capacitance of the VCO and in that the third and fourth terminals (130, 132) comprise the output nodes (114a, 114b).