A GaAs passive mixer with an ultra-wide IF bandwidth

This paper presents a GaAs double-balanced mixer (DBM) applying an improved Marchand balun. This structure is achieved by adding a frequency-tuning tail capacitor to the end of the imbalanced coil. By using this tail capacitor, the size of balun is greatly reduced and the IF bandwidth is largely extended. The equivalent circuit modeling and working principle of this structure are described in this paper. The RF bandwidth of the proposed mixer is from 6GHz to 18GHz. The measurement result shows that the mixer’s IF bandwidth ranges from DC to 8GHz with the conversion loss less than 10dB. Because of the good amplitude and phase performance of the proposed balun, the LO to IF isolation is also improved. The total chip area is 950 × 600µm2.