Tunable capacitors keep up 4G when signal strength suffers

16th July 2015

Barney Scott

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STMicroelectronics has launched the second generation of its electronically tunable capacitors for smartphones, introducing improvements including an increased tuning ratio that helps maximize mobile download speeds and call quality. ST’s STPTIC capacitors compensate for changing matching conditions to ensure optimal signal-power transfer between the smartphone’s antenna and power amplifier.

Even the way the user holds the handset can influence reception, and the improved 5:1 tuning ratio of the 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 high-quality Parascan dielectric and share a common package footprint and pin-out that allows using different nominal capacitances without changing the board design. STPTIC devices meet linearity specifications of 3G/4G modulation and have high quality factor up to 2.7GHz, which ensures low insertion losses and maximum power transfer, while their low leakage current saves power and helps extend handset battery life.

STPTIC capacitors are available in eight standard values from 1.5pF (STPTIC-15G2) to 8.2pF (STPTIC-82G2), and are controlled using a bias voltage from 1 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 antennas and connects to the smartphone host system via an industry-standard RF Front-End (RFFE) interface.

The STPTIC capacitors are in mass production now in 4-bump 0.4mm-pitch flip-chip packages, priced from $0.40 for orders of 1000 units.