  We present an experimental method to perform dual-channel lock-in
magnetometry of time-dependent magnetic fields using a single spin associated
with a nitrogen-vacancy (NV) color center in diamond. We incorporate
multi-pulse quantum sensing sequences with phase estimation algorithms to
achieve linearized field readout and constant, nearly decoherence-limited
sensitivity over a wide dynamic range. Furthermore, we demonstrate unambiguous
reconstruction of the amplitude and phase of the magnetic field. We show that
our technique can be applied to measure random phase jumps in the magnetic
field, as well as phase-sensitive readout of the frequency.
