Embodiments of communications devices and methods for operating a communications device are described. In an embodiment, a communications device includes a complex multiplier configured to multiply a first input complex signal with a second input complex signal to generate an output complex signal, an amplifier configured to amplify an imaginary part of the output complex signal to generate an amplification result, a delay element configured to delay a rotation angle signal that is related to the second input complex signal, and a subtractor configured to subtract the amplification result from the delayed rotation angle signal to generate the rotation angle signal. Other embodiments are also described.

Embodiments of communications devices and methods for operating a communications device are described. In an embodiment, a communications device includes a complex multiplier configured to multiply a first input complex signal with a second input complex signal to generate an output complex signal, an amplifier configured to amplify an imaginary part of the output complex signal to generate an amplification result, a delay element configured to delay a rotation angle signal that is related to the second input complex signal, and a subtractor configured to subtract the amplification result from the delayed rotation angle signal to generate the rotation angle signal. Other embodiments are also described.

A universal nonlinear variable delay filter includes a first mixer configured to convert an input signal to an up-converted signal including a frequency corresponding to a selected time delay. The input signal includes an original frequency. The variable delay filter also includes a nonlinear filter that filters the up-converted signal and generates a delayed signal that is delayed by the selected time delay. The variable delay filter further includes a second mixer configured to convert the delayed signal to a down-converted signal including a frequency substantially equal to the original frequency.

A signal frequency conversion circuit is configured to reduce power consumption and resource costs of the signal frequency conversion circuit. Embodiments of the present disclosure include a primary-stage frequency conversion module and at least one subsequent-stage frequency conversion module that is in series connection, where the primary-stage frequency conversion module includes a first filter and a numerically controlled oscillator NCO, and an output of the first filter is connected to an input of the NCO; each subsequent-stage frequency conversion module includes a second filter and a subsequent-stage frequency conversion unit, and an output of the second filter is connected to an input of the subsequent-stage frequency conversion unit; and an output of the NCO is connected to an input of a second filter in a first subsequent-stage frequency conversion module in the at least one subsequent-stage frequency conversion module in series connection.

A signal frequency conversion circuit is configured to reduce power consumption and resource costs of the signal frequency conversion circuit. Embodiments of the present disclosure include a primary-stage frequency conversion module and at least one subsequent-stage frequency conversion module that is in series connection, where the primary-stage frequency conversion module includes a first filter and a numerically controlled oscillator NCO, and an output of the first filter is connected to an input of the NCO; each subsequent-stage frequency conversion module includes a second filter and a subsequent-stage frequency conversion unit, and an output of the second filter is connected to an input of the subsequent-stage frequency conversion unit; and an output of the NCO is connected to an input of a second filter in a first subsequent-stage frequency conversion module in the at least one subsequent-stage frequency conversion module in series connection.