Adaptive Two-Point Modulation of Wireless Phase Locked Loops

Two-point modulation, a form of two-degrees-of-freedom control, extends the modulation bandwidth of a phase-locked loop beyond its closed-loop bandwidth. However, its acceptable performance depends critically on the relative gain of two modulation paths, one of which includes the plant-a voltage controlled oscillator (VCO). This gain-balance problem is troublesome, especially in wireless communication applications, where the VCO gain is generally unknown and subject to drift. The proposed solution is via a canonical problem in model reference adaptive control.