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WiMAX (worldwide interoperability for microwave access) is a standards-based wireless technology that provides broadband connections over long and short distances. WiMAX is becoming popular as it can be used for a number of applications, including last-mile broadband connections, hotspots, cellular backhaul, and high-speed enterprise connectivity for business.

The 2.5 GHz to 2.7 GHz band is available for mobile and fixed wireless services in the United States. This band is also underused and potentially available in many countries throughout South America and Europe as well as some countries in the Asia-Pacific region. The 3.3 GHz and 3.5 GHz bands are allocated for fixed wireless services in many countries worldwide and are well-suited to WiMAX solutions for both fixed and mobile services^[1].

The company's model SIM-U432H+ is an upconverter mixer designed for WiMAX applications and is based on a combination of low-temperature co-fired ceramic (LTCC) technology, semiconductor technology, and a highly manufacturable circuit layout. This combination^[2] results in small size, high insensitivity to electrostatic discharge (ESD), excellent stability with temperature and high IP3.

The SIM-U432H+ mixer (Figure 1) is built on an LTCC substrate, suited for designs with multilayer circuits. In contrast to conventional planar circuit designs, in which all circuit elements are placed on one side of a single-layer printed circuit board, LTCC circuits can be designed and fabricated in three dimensions, even with embedded components between layers to save space. The approach results in a mixer that measures just 0.2 in. × 0.18 in. × 0.08 in. (5.1 mm × 4.6 mm × 2.1 mm), which is smaller than some commercial semiconductor-based mixers. Although the SIM-U432H+ mixer incorporates semiconductors to accomplish its non-linear frequency-translation function, it is a passive design that operates without dc bias (compared to a standard semiconductor or integrated-circuit mixer that requires the application of a constant dc bias voltage).

The SIM-U432H+ is a double-balanced mixer (Figure 2) built around a reliable diode quad. Except for the diodes, the entire structure is implemented in multiple layers of LTCC and is, therefore, inherently hermetic. By integrating components in LTCC, the mass of the mixer is minimized, making it extremely rugged in terms of withstanding shock and vibration. In fact, the entire mixer structure can withstand the environmental extremes usually experienced only by military components, in terms of temperature, humidity, vibration and mechanical shock.

The mixer is RoHS compliant, constructed without lead-based solder or other hazardous materials. It is built to withstand severe ESD scenarios under conditions normally hazardous to monolithic semiconductor mixers. The SIM-U432H+, like other members of the company's SIM mixer line, meets Class 1C ESD requirements, a level of 1000 V when tested under the human body model (HBM) conditions (compared to standard semiconductor mixers that are rated as Class 1A, 250 V for HBM testing). The SIM-U432H+ mixer also meets Class M2 ESD requirements (testing at 100 V according to the ESD machine model).

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