Abstract: Second order distortion products in a digital receiver front end are converted into broadband noise. An illustrative embodiment includes a noise generator, first and second combiners, and a non-linear device (e.g., an analog-to-digital converter). An input signal is combined with the noise signal by the first combiner, and the combined signal is applied to the non-linear device. The output signal from this device is applied to the second combiner. The second combiner is also driven with a time-delayed version of the noise signal, and performs a reconstructive multiplication, synchronously recovering the desired output signal. Even-order distortion products introduced by the non-linear device persist only as a low level of wideband noise in the final output signal.

Abstract: A dithered analog-to-digital converter includes a correlator to detect dither residue in the output signal. The correlator output is accumulated and used in a feedback loop to control the gain of the dither signal so as to null the residue. Problems associated with the low bandwidth of the feedback loop, and corruption of the accumulator value due to overload, are addressed by provision of a preload register from which the accumulator is initialized on power-up and on detection of an overload. This approach provides quick settling time and avoids statistical anomalies associated with decimation approaches to overload.

Abstract: A technique for correcting settling, feedthru, and higher order error mechanisms in a dithered analog-to-digital conversion circuit is disclosed. For each conversion cycle of an ADC, a dither signal is generated by converting a current dither value from a sequence of dither values and is then added to an analog input signal. The analog input signal and dither signal are converted by the ADC, and the current dither value subtracted, to form a digital output signal. Correction signals proportional to dither values which precede or follow the current dither value in the sequence are also generated each conversion cycle and subtracted from the analog input signal. The proportions used to produce the correction signals are adjusted dynamically according to the amount of correlation between the digital output signal and the dither values used to form the correction signals. The correction signals are thereby made to equal the amount of error contributed by a corresponding one of the error mechanisms.

Abstract: Local oscillator feedthrough in a superheterodyne receiver is eliminated by a servo loop-controlled compensation circuit that dynamically tracks the feedthrough signal and adjusts both the phase and amplitude of a compensating signal as needed to maintain the level of the feedthrough signal below a threshold value.