Broadband high-frequency hybrids

Analog integrated circuit designs are often differential and require differential-to-single-ended hybrids for spectral measurements. This paper describes a broadband, high-frequency hybrid, whose output signal is proportional to the difference of two input ports, i.e. proportional to the differential signal. The main novelty of this hybrid is its high bandwidth (two to three decades). Such high bandwidth is obtained through combining broadband structures: a pair of broadband impedances are used to scale the two incoming signals; a symmetric structure of two identical broadband directional couplers and a power combiner are used afterwards to obtain the differential signal. The high bandwidths of both the impedances, the directional couplers and the power combiner make it possible to obtain a differential coupling factor and a common-mode rejection ratio which is frequency insensitive over several decades in frequency. Measurements support the statement that bandwidths of more than three decades can be obtained using the proposed hybrid.