We disclose frequency doublers for use in millimeter-wave devices. One such frequency doubler comprises at least one passive mixer comprising at least one of the following: at least one transistor configured to receive a back gate voltage; at least one first input driver circuit; and two second input driver circuits. We also disclose a method comprising determining a target output voltage of a frequency doubler comprising at least one passive mixer comprising at least one transistor configured to receive a back gate voltage; determining an output voltage of the frequency doubler; increasing a back gate voltage of the at least one transistor, in response to determining that the output voltage is below the target output voltage; and decreasing the back gate voltage of the at least one transistor, in response to determining that the output voltage is above the target output voltage.