A digitally controlled oscillator (DCO) may include a transformer, which may contain a secondary winding comprising a first port, a second port, and an array of capacitor units, wherein each capacitor unit includes a first NFET having a gate and a back gate connected to a control signal, and a drain connected to the first port; a second NFET having a gate connected to ground, a back gate connected to the control signal, and a drain connected to the source of the first NFET; and a third NFET having a gate and a back gate connected to the control signal, a drain connected to the source of the second NFET, and a source connected to the second port. The capacitor units may allow fine tuning of the DCO output frequency with a resolution of about 0.3 MHz and a range of about 80 MHz.