CK and Impedance Matching

When the nearby environment changes, the radio inside the handset is susceptible to external interference and impedance mismatch. For example, putting the phone next to your head or covering it with your hand changes the antenna performance and can result in poor call quality. Because the impedance of the environment cannot be controlled, the phone needs to respond to changing conditions in order to maintain acceptable performance – as opposed to irritating conversations where one or both parties is forced to repeat, “Can you hear me now?”

The technique called Impedance Matching alters the impedance the antenna presents to the rest of the RF circuitry to keep the loads “matched” and maintain the performance over differing conditions. In terms of RF design, this is Smith-chart load tuning to keep the VSWR closer to ideal (1.0).

Various circuits are used for impedance matching: the CLC pi-network, where the two shunt capacitors are tunable and the inductor is fixed; the double Pi CLCLC, where the three shunt capacitors are tunable; and the “L-shaped” CC circuit, where a series and shunt capacitor are both tunable.

CK devices are ideally suited to impedance matching applications because they offer:

• High Quality (Q) factor. CK’s tunable capacitors have the highest usable Q factor in the industry – meaning the Q quoted in the specifications is delivered to the circuit on the board in practice, not just in theory.
• Wide tuning range. CK’s tuning range of 5:1 for shunt capacitors means the user can have from 1pF to 5pF or any value in between for the matching circuit.
• Small volume. The small volume of CK devices leads to easy integration into tuning modules. At 2 mm² and 0.4mm thick, CK devices allow for the building of small, streamlined tuning modules.