  We consider a high-frequency response of electrons in a single miniband of
superlattice subject to dc and ac electric fields. Action of ac electric field
causes oscillations of electron's effective mass in miniband, which result in a
parametric resonance. We have established a theoretical feasibility of
phase-sensitive parametric amplification at the resonance. The parametric
amplification does not require operation in conditions of negative differential
conductance. Therefore a formation of destructive domains of high electric
field inside the superlattice can be prevented. Here we concentrate on the
parametric up- and down-conversion of electromagnetic radiation from available
frequencies to desirable THz frequency range.
