Today's designs call for increased miniaturization and integration. They also must be robust so that they achieve good yields while providing the lowest possible bill-of-material (BOM) cost. In addition to the number and types of parts and their associated costs, the price depends on the size of the printed-circuit board (PCB) and the enclosure. In an application note titled "Anaren 0404 (BD2425N100ATI) Balun Optimized for Texas Instruments CC2530 Transceiver," Anaren shows how 100% RF tested components can be integrated to increase yield while decreasing size and time to market. These objectives are met in a small, simple balun-based solution, which is optimized for use with Texas Instruments' CC2530 transceiver.
The 11-page note begins by comparing different baluns. The CC2530's receiver low-noise amplifier (LNA) and transmitter power amplifier (PA) are attached to the same set of balanced package pins. As a result, only an impedance-matched, balanced-to-single-ended transformation is needed for connection to external circuitry. Compared to a lumped-element implementation, Anaren's approach takes up less PCB area with fewer external matching components. Two Anaren baluns are recommended for use with the CC2530 transceiver. Either 1-mm2 multilayer balun requires only two additional matching components: a direct-current (DC) blocking capacitor and an inductor for impedance matching.
The note cautions readers about using alternate vendorsespecially for inductorsas vendors of inductors and capacitors have their own ways of realizing parts with associated differences in parasitic values. Even from a single vendor, component series are made differently with corresponding ranges in parasitic circuit elements. In addition, parasitic differences can arise from one value to the next in the same component series.
The document emphasizes that changes in the placement or value of the components and the dimensions of the PCB traces can impact performance. The DC blocking capacitor and inductor for impedance matching should therefore be positioned as close as possible to the balun. Also, designers are reminded that the values of the inductor and capacitor depend on the length of the transmission line used between the CC2530 chip and the balun. If that length is increased, the inductor and capacitor values should be decreased (with the opposite being true if the length of the line is decreased).