The so called Synchronous Electric Charge Extraction (SECE) interface is an electrical circuit to extract energy from a piezoelectric transducer and to put it onto a storage device like a large capacitor. The advantage of the SECE interface is the load independent power transfer. But the maximum efficiency the SECE interface in combination with the piezoelectric transducer can achieve greatly depends on the electromechanical coupling of the transducer. The SECE interface works very well with weak to mid-range electromechanically coupled piezoelectric transducers. But with strong coupled transducer the power extracted by SECE interface decreases. This paper shows how the SECE interface can be tuned to deliver the maximum power almost independent of the electromechanical coupling factor.

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A compensated charge pump for use in phase-locked loops (PLLs) is presented, which reaches several of the desired design goals for this type of circuit. The measured mismatch between the source and sink currents is below 2.1% for a large output voltage headroom of 83.3% of the supply, while still having a high output resistance of 140 kΩ. This behaviour is reached with a novel dual compensation method. The circuit was implemented in a 180 nm CMOS technology using a 3 V supply.

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