a mixer stage is provided that mixes a differential input signal with a differential square - wave signal of an oscillator , having a first amplifier element and a second amplifier element , each of which amplifier elements has a first current connection , a second current connection , and a connection for the differential input signal , having four control elements and also a first output and a second output , wherein the four control elements are modulated in pairs by the differential square - wave signal , thereby connecting each second current connection alternately , and in each case individually , to one of the two outputs . the mixer stage has field - effect transistors as amplifier elements whose first current connections are connected to a constant reference voltage . in addition , a method for mixing frequencies that uses this mixer stage is also disclosed .