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The key element determining the dynamic performance of such a PLL is the
phase detector between the beam oscillation and the internal oscillation.
Most circuits use a quadrature phase detector, for which the high
frequency carrier at twice the excitation frequency is attenuated by a
low-pass circuit. The remaining ripple of this component contributes to
the bandwidth/noise performance of the PLL.
In this paper we propose an alternative solution for the filter, notably
an adaptive notch filter. We explain in detail design considerations and
the resulting improvements in PLL bandwidth and/or noise figure.
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