An impedance matching circuit disposed on one of input and output sides of an element to be evaluated matches I/O impedances of the element. The impedance matching circuit includes a matching substrate having a surface, a main line on the surface, passive circuits having stubs and FETs alternatingly connected in series and electrically connected to the main line to change impedance of the main line, and a plurality of switching FETs connected in series between the main line and the respective passive circuits switched on and off in accordance with characteristics of the element. The impedances of the matching substrate can be changed as required by electrically connecting the passive circuit to the main line by switching of the FETs. Even when a considerable change occurs in the I/O impedances of the element due to fabrication variations and in large signal (non-linear) operation of a power FET, I/O impedances of an evaluating object can be matched easily and promptly by appropriate switching of the FETs.
The present invention provides a millimeter-wave passive FET switch by using impedance transformation network to transfer the effective capacitance seen from the drain to source of an FET at off-state to low impedance, while transfer low impedance seen at on-state to high impedance. Since both on-state and off-state are transferred to high impedance, and low impedance respectively, a high-performance switch can be achieved. Since the size of the transformation network is small, the performance of the switch can be promoted with low cost.
The present invention provides a semiconductor switching circuit and a semiconductor device using the switching circuit that can maintain sufficient isolation characteristics even when dealing with high frequency signals. The semiconductor switching circuit includes a first semiconductor switching element connected between a first terminal and a second terminal, a second semiconductor switching element, one end of the second switching element being connected to one of the first and second terminals, and an open stub connected to the other end of the second switching element.
An impedance matching device is provided, for which the electric characteristics at an output terminal are accurately analyzed. The matching device is provided with an input detector for detecting RF voltage and current at the input terminal, and an output detector for detecting RF voltage outputted from the output terminal. The matching device also includes a controller for achieving impedance matching between a high frequency power source connected to the input terminal and a load connected to the output terminal. The impedance matching is performed by adjusting variable capacitors based on the detection data supplied from the input detector. When the impedance of the power source is matched to that of the load, the controller calculates the output impedance, RF voltage and RF current at the output terminal, based on the adjusted capacitances of the capacitors, a pre-obtained reactance-impedance data and the detection data supplied from the output detector.
Three or more MESFETs are fabricated side by side on a semiconductor chip. A transmission line substantially identical in width with an area within which the MESFETS are fabricated is formed in parallel with the row of MESFETs. The MESFETs are connected to the transmission line at a side, constituting one edge of the transmission line. Further, regulation circuits are connected in shunt with the transmission line, and outputs of the MESFESTS are merged while being matched by the transmission line and the regulation circuits.
