Double balanced mixer in MMIC

摘要

The mixer comprises a set (1) of four cold transistors (2-5), which are of the Pseudomorphic High Electron Mobility Transistor (PHEMT) type, and the 180 deg. phase-shifted signals couplers for the radio-frequency signals (RF, RF'/2), the local oscillator signals (OL, OL') and the intermediate frequency signals (FI, FI') connected to the set by coplanar links of tape or waveguide type. The transistors (2-5) are in an in-line configuration with the midpoint input of the RF signal, and the end-points inputs of the RF'/2 signal, which is phase-shifted by 180 deg. with respect to the RF signal. The set of four transistors is constituted by two groups of transistors, (2,3) and (4,5), where the transistors in each group are connected by the drains (D), and the transistors of the two groups in the middle of line are connected by the sources (S), which is the common point receiving the radio-frequency signal. The RF coupler comprises three 180 deg. phase-shifted signals couplers of the drain-source type, including an input and two output couplers, for delivering the RF signal and two identically phase-shifted by 180 deg. RF'/2 signals to the set of four transistors. The signals are obtained by a selective summation of signals obtained at the outputs of two couplers, each receiving one of the phase-shifted signals delivered by the input coupler, via the drain and the source of a transistor, and deriving from the radio-frequency signal applied to the gate of the transistor. The two output couplers are connected so that the drain of first and the source of second are connected to the same potential but of opposite sign via resistors, whereas the source of first and the drain of second are connected to the ground via resistors. The radio-frequency signal appearing at the source of first coupler is combined by a capacitive link with the signal appearing at the drain of second coupler to constitute the RF signal, and the radio-frequency signals appearing at the drain of first coupler and the source of second coupler are distributed to the two outputs delivering the RF'/2 signals, which are electrically equilibrated. The set of four transistors and the couplers are implemented in the MMIC technology, or in hybrid technology.