  We study dynamics of antiferromagnets induced by simultaneous application of
dc spin current and ac charge current, motivated by the requirement of
all-electrically controlled devices in THz gap (0.1-30 THz). We show that ac
electric current, via N\'eel spin orbit torques, can lock the phase of a steady
rotating N\'eel vector whose precession is controlled by a dc spin current. In
the phase-locking regime the frequency of the incoming ac signal coincides with
the frequency of autooscillations which for typical antiferromagnets fall into
the THz range. The frequency of autooscillations is proportional to the
precession-induced tilting of the magnetic sublattices related to the so-called
dynamical magnetization. We show how the incoming ac signal can be detected
from the measurement of the dc-current dependencies of the constant dynamical
magnetization. We formulate the conditions of phase-locking based on relations
between parameters of an antiferromagnet and the characteristics of the
incoming signal (frequency, amplitude, bandwidth, duration). We also show that
the rotating N\'eel vector can generate ac electrical current via inverse
N\'eel spin-orbit torque. Hence, antiferromagnets driven by dc spin current can
be used as tunable detectors and emitters of narrow-band signals operating in
the THz range.
