Tunable capacitors provide increased range for antenna matching

July 16, 2015 // By Graham Prophet
STMicroelectronics has introduced the second generation of its electronically tunable capacitors for smartphones, introducing improvements including an increased tuning ratio that helps maximise mobile download speeds and call quality.

STPTIC capacitors compensate for changing matching conditions to ensure optimal signal-power transfer between the smartphone’s antenna and power amplifier. An improved 5:1 tuning ratio of the new STPTIC G2 series allows the system to apply extra correction when needed. Other improvements include lower parasitic resistance and inductance, which boost efficiency and reduce heat dissipation, and a higher ESD rating for greater robustness.

All devices in ST’s STPTIC family feature ST’s Parascan dielectric and share a common package footprint and pin-out that allows use of different nominal capacitances without changing the board design. STPTIC devices meet linearity specifications of 3G/4G modulation and have high quality factor (Q) up to 2.7 GHz, which ensures low insertion losses and maximum power transfer, while their low leakage current saves power and helps extend handset battery life.

These capacitors are available in eight standard values from 1.5 pF (STPTIC-15G2) to 8.2 pF (STPTIC-82G2), and are controlled using a bias voltage from 1V to 24V. This can be provided by ST’s STHVDAC-253M controller, which is designed specifically to deliver the wide-tuning bias-voltage required. The controller provides three outputs to control STPTICs for multiple antennae and connects to the smartphone host system via an industry-standard RF Front-End (RFFE) interface.

In 4-bump 0.4 mm-pitch flip-chip packages, they are priced from $0.40 (1000).

STMicroelectronics; www.st.com/rf-tunable-capacitors-nb