MMICs for Broadband Receiver Applications

This paper details the design, realisation and measured performance of a set of MMICs for broadband receiver applications. Five different MMICs are described: A 0.5 to 20GHz dual channel limiter, a 2 to 18GHz dual channel Low Noise Amplifier (LNA), a DC to 20GHz dual channel Single Pole Double Throw (SPDT) switch, a 2 to 18GHz upconverter and a companion downconverter. The MMICs can be used to implement a compact, dual channel 2-18GHz receiver and an example of this is also described. Dual Channel Limiter Introduction (Limiter) Limiters are used at the front-end of a system to protect more sensitive circuitry that follows. A limiter should attenuate any high power input signals to a level that the following receive circuitry can withstand without damage. This dual channel limiter MMIC was designed to provide receiver protection for a broadband monopulse system [1]. PIN diodes are a popular technology choice for limiter realisations because they are able to handle relatively large amounts of power using a comparatively small device. An integrated realisation allows accurate amplitude and phase matching of the two channels, which is important for a monopulse system, and results in low parasitics which facilitates the very large operating bandwidth of the design. Triquint Semiconductor Texas’ Vertical PIN diode (VPIN) process was selected for the realisation of the Monolithic Microwave IC (MMIC). A PIN diode takes its name from its structure; it comprises a region of high resistivity intrinsic material sandwiched between a region of Ptype semiconductor and N-type semiconductor. When the PIN diode is forward biased, charge carriers are injected into the I region lowering its resistance. Thus at RF and microwave frequencies a PIN diode behaves as a current controlled resistor. Figure 1 shows an equivalent electrical circuit model for a PIN diode at RF/microwave frequencies. A model for a discrete, packaged diode would also need to incorporate appropriate packaging parasitics.