Tunable Power Amplifier Using Thin-Film BST Capacitors

Thin-film barium strontium titanate (BST) capacitors were fabricated and applied to a power amplifier (PA). The PA using these capacitors in output matching network for PCS band was realized and the tunability of its output impedance was validated. The measured adjacent channel leakage power ratio (ACPR1) is -48.6dBc and consumption current (Icc) is 519mA, with a load impedance of 50ohm at output power of +28dBm and a center frequency of 1880MHz. The load performance was measured by ranging load impedance from 4:1 to 2:1 VSWR at output power of +28dBm. The measured maximum ACPR1 value is -40dBc in case of 0-V bias applied on BST capacitors, which corresponds to PA with fixed impedance (fixed-impedance PA). The ACPR1 performance deteriorated by 8.6dB to that with a load impedance of 50ohm. The maximum ACPR1 value was -44dBc when the voltage applied on BST capacitors are limited within 3.6V. The ACPR1 performance deteriorated by 4.6dB compared to that with a load impedance of 50ohm. The ACPR1´s load performance of tunable PA is improved by 4dB, compared to fixed-impedance PA