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Embedding a micro-machined sensing element in a closed loop, force feedback system is a technique commonly used to realise high performance MEMS (micro-electro-mechanical systems) sensors due to the advantages of better linearity, increased dynamic range and reduced parameter sensitivity.Electro-mechanical Sigma Delta modulators (EMΣ∆) have been proposed for this reason and high order loops have been shown to enjoy a good signal to noise ratio (SNR) of more than 100dB. It is also well known that achieving stability in high order EMΣ∆s is a challenging task and in practice stability can be lost with large input signals or due to non-ideal effects in the circuits implemented. In this work we propose a novel differential frequency domain technique for closed loop control of micro-machined sensors. This method, called the electro-mechanical phase locked loop (EMPLL), uses a differential electro-mechanical phase locked loop to control and measure the deflection of micro-machined sensors. We believe that EMPLLs have the potential to have significant advantages over EMΣ∆s for high performance MEMS sensors. Preliminary research suggests that this novel approach will