The disclosure relates to technology for shifting a frequency range of a signal. In one aspect, a circuit comprises a frequency mixer, a frequency synthesizer configured to generate an oscillator signal, a programmable driver, and a controller. The programmable driver is configured to receive the oscillator signal from the frequency synthesizer and to provide the oscillator signal to the oscillator input of the frequency mixer. The programmable driver is configured to have a variable drive strength. The controller is configured to control the drive strength of the programmable driver based on a frequency of the oscillator signal to adjust a rise time and a fall time of the oscillator signal at the oscillator input of the frequency mixer.