An electronic device may include wireless circuitry having a radio-frequency mixer. The mixer may include a first pair of mixer transistors configured to receive an oscillating signal, a second pair of mixer transistors configured to receive the oscillating signal, and a bias circuit configured to receive the oscillating signal and to generate a corresponding output voltage for controlling an amount of current flowing through the first and second pairs of mixer transistors. The bias circuit can be configured as a replica envelope detection circuit. The bias circuit can include a pair of bias transistors coupled to a tail transistor that receives the output voltage of the replica envelope detection circuit.