Efficient RF voltage transformer with bandpass filter characteristics

A microwave bandpass filter with a large ratio between the output and the input impedance has been designed and fabricated. Consequently, it functions both as a voltage transformer and a bandpass filter, or transfilter for brevity. It represents a two-port micro-acoustic resonator employing Lamb waves in a thin piezoelectric AlN film grown onto a Si carrier substrate with a centre frequency of around 887 MHz. The transfilter has a transformer ratio of 10 and a voltage efficiency of over 80%. The component has a small size ( <; 0.5 mm²) and is shown to sustain power levels of 250 mW. It can be used in a variety of cases where both voltage amplification and frequency filtering are required. Examples include: charge pumps in RFID tags, energy scavenging, remotely triggered switches, wake-up radios in wireless networks, stand-by units in home electronics etc.