Abstract: A digital transmitter includes a digital-to-digital sigma-delta modulator (SDM) receiving digital baseband data (fBB) which sigma-delta modulates the baseband signal to generate a digital SDM signal. The digital SDM signal is digitally mixed with an oscillation signal (fLO) to frequency shift the baseband data to fLO+/?fBB. The frequency shifted signal is filtered to remove either the upper or lower frequency band and the remaining signal is converted to an RF analog signal for eventual RF transmission. In another embodiment, the digital-to-digital SDM is a multi-level SDM that generates N parallel binary (digital) waveform signals which are each individually mixed with the oscillation signal. The resulting N frequency shifted SDM signals are summed and filtered, or in the alternative are each filtered and summed, to generate the RF analog signal.

Abstract: A low noise oscillator includes a resonator 102 that is excited with a pulsed signal (i.e., an impulse of energy) to replace energy lost to parasitic resistive losses once every Nth period (where N=1, 2, 3 . . . ). The resonating signal is monitored by a level detector and when the signal falls below a predetermined threshold, the pulse generator outputs a pulse or adjusts pulse width, pulse amplitude (or both) of a pulsed signal to create the necessary impulse for application to the resonator to recoup losses resulting from resonator operation. A phase shifting circuit may be provided to ensure the pulses are time aligned with the resonating signal to reduce noise.

Abstract: Narrowband interference in a wideband RF signal is reduced by a notch filter operating at IF between down- and up-converters supplied by a local oscillator (LO) at a frequency controlled by a control circuit. The control circuit detects interference by determining power in each of a plurality of narrowband channels, also at IF via another down-converter with a controlled LO frequency, relative to power of the wideband RF signal and scaled in accordance with the wideband and narrowband bandwidths. The control circuit controls the LOs for scanning the narrowband channels to determine a channel with greatest interference and to filter out this narrowband channel with the notch filter. In the absence of interference, the notch is tuned outside the signal bandwidth.

Abstract: The present invention provides a serrodyne architecture that is capable of operating at high frequencies. The architecture generally includes a coupler, a delay line, and a switching system. The delay line is coupled to a reflective port of the coupler. The switching system is coupled to the delay line at different points and is configured to selectively shunt those points on the delay line to change the effective electrical length of the delay line. The effective electrical length is changed throughout the period, corresponding to the amount the frequency of the input signal is shifted. In operation, an input signal is provided to an input port of the coupler, and an output signal is provided at the output port, wherein the input signal and the output signal vary by a translation frequency, which is controlled based on how the effective electrical length of the delay line is changed.

Abstract: Narrowband interference in a wideband RF signal is reduced by a notch filter operating at IF between down- and up-converters supplied by a local oscillator (LO) at a frequency controlled by a control circuit. The control circuit detects interference by determining power in each of a plurality of narrowband channels, also at IF via another down-converter with a controlled LO frequency, relative to power of the wideband RF signal and scaled in accordance with the wideband and narrowband bandwidths. The control circuit controls the LOs for scanning the narrowband channels to determine a channel with greatest interference and to filter out this narrowband channel with the notch filter. In the absence of interference, the notch is tuned outside the signal bandwidth.

Abstract: A method and system for reducing local oscillator leakage from radio frequency mixers is disclosed. Compensating circuits are used to reduce or eliminate unwanted leakage from the mixer output signal by controlling the current in individual branches of a balanced input circuit of the mixer. The current is directly controlled by adjusting the voltage on the bases of the differential type amplifier input transistors, or by injecting current directly into the individual branches, or by extracting current directly from the individual branches. The current is also indirectly controlled by increasing the temperature of the mixer components with power dissipation elements that are not connected to the mixer. The compensating circuits are made of different combinations of resistor, transistor and current sink components.