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 mm 2 ) 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.Introduction: Passive CMOS-based RFID tags attain energy from the interrogation signal which is rectified and subsequently accumulated over a period of time. Practical reading distances require voltage amplification which is achieved by various variants of the Dickson multistage rectifier [1], also referred to as charge pump, representing a network of rectifying devices (transistors or Schottky diodes) and capacitors. Their voltage efficiency, however, is low and declines rapidly with the degree of amplification.In a different context, remotely triggered switches (RTSs) are needed in remotely controlled devices such as wake-up radios in wireless sensor networks, home electronics etc. The basic circuit of an RTS was proposed by Gu and Stankovic [2] and is illustrated in Fig. 1.
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