Abstract: The peak level of a high frequency analog signal in an RF receiver is detected by a system which samples the signal and compares it against a static threshold, generating an above/below status. The system is implemented with a sampler of sufficient aperture bandwidth to capture the signal in question, operated at a clock frequency, dynamically chosen as a function of fLO (local oscillator frequency) and the desired fIF (intermediate frequency), to minimize in-band intermodulation products. The sampler produces kickback intermodulation products that are positioned out-of-band, or are of low enough power in-band so as to be inconsequential. Samples are taken for a statistically significant period of time, and the status is used to adapt the threshold to systematically determine the peak amplitude of the signal being observed.

Abstract: Apparatus and methods calibrate and control detector gain in a Mueller-Muller timing detector. A Mueller-Muller circuit obtains timing information for a received signal in which the receiving device samples the signal once per baud period.

Abstract: Methods and apparatus for reducing sensitivity to nonlinearities in the receiver of a digital communications system are disclosed. One aspect can be referred to as a Post-Distortion Decision Feedback Equalizer (PDFE). A gain stage is often implemented as a variable gain amplifier (VGA), and can introduce significant nonlinearities, a problem exacerbated by signals with a large peak-to-average ratio (PAR). One embodiment provides feed forward information from the VGA regarding its status to a DFE, and the DFE adjusts its filtering based on the provided information. The advantages are also applicable to fixed-gain amplifiers and to transversal filters.

Abstract: A method of background calibration of aperture center errors in a data communication system is provided. In an implementation, in response to detection of a low sampler output (“0”) in between two high sampler outputs (“1”), the method includes: determining a direction of an ADC output signal at the time of the detected low output; and adjusting timing at a selected sampler based on the determined signal direction. In an example implementation, the method includes watching for bubbles in the thermometer code output, and estimating the first derivative of the signal at the time of the bubble, then estimating the sign of the errors. In an example implementation, the errors are used in a control loop to reduce the aperture center error.

Abstract: Apparatus and methods reduce channel-dependent phase detector offset and/or gain errors. A conventional Mueller-Muller phase detector places a main cursor at the midpoint of a pre-cursor and a post-cursor. However, for example, when the impulse response of an associated transmission line is not symmetric, the main cursor can be misaligned by conventional Mueller-Muller techniques. By providing a replica clock and data recovery path, trial and error experiments on the phase detector offset and/or gain can be performed, and relatively good values found for the phase detector offset and/or gain without disturbing the reception of data by the phase detector that is being used to receive data. These settings can then be used by the phase detector that is being used to receive data, which can improve the bit error rate of the phase detector.

Abstract: A method and apparatus for controlling the effective gain of an ADC when the ADC is occasionally or continuously calibrated using the statistics of the input signal and when the statistics are not stationary.

Abstract: A method of background calibration of aperture center errors in a data communication system is provided. In an implementation, in response to detection of a low sampler output (“0”) in between two high sampler outputs (“1”), the method includes: calculating a signal derivative of an ADC output signal at the time of the detected low output; and adjusting timing at a selected sampler based on the calculated signal derivative. In an example implementation, the method includes watching for bubbles in the thermometer code output, and estimating the first derivative of the signal at the time of the bubble, then estimating the sign of the errors. In an example implementation, the errors are used in a control loop to reduce the aperture center error.

Abstract: A method of background calibration of threshold errors in a data communication system is provided. In an implementation, the method uses sampler statistics just after foreground calibration as the reference signal in a control loop method to remove individual sampler offsets. In an implementation in which an analog to digital converter (ADC) includes a plurality of sub-ADCs, gain, offset, and individual threshold errors across parallel, time-interleaved sub-ADCs are minimized by establishing individual comparator statistics for the average sub-ADC after an initial foreground calibration, then forcing each individual comparator to maintain its statistics over time, in the background, by continuously adjusting its threshold.

Abstract: Apparatus and methods calibrate and control detector gain in a Mueller-Muller timing detector. A main signal path includes a Mueller-Muller based timing error detector (MM TED). The main signal path generates a main error signal for clock recovery. A secondary signal path that includes a secondary MM TED. Each signal path samples soft symbols from a received signal. The sampling of the secondary MM TED is deliberately offset in time. A scale factor applied to the main error signal and to a secondary error signal is adaptively adjusted based on a comparison between the main error signal and the secondary error signal.

Abstract: The adverse effects of RF and baseband circuits are mitigated using a post-compensation method wherein a transfer function that would un-distort or complement a distorted waveform is parameterized to a relatively small number of degrees of freedom; and the parameters are estimated in a feedback loop. The error function of the feedback loop is generated by comparing some relatively low-order statistics that are known a priori or can be computed with relative certainty from the decided output waveform—to the statistics of the corrected signal.

Abstract: Methods and apparatus for reducing sensitivity to nonlinearities in the receiver of a digital communications system are disclosed. One aspect can be referred to as a Post-Distortion Decision Feedback Equalizer (PDFE). A gain stage is often implemented as a variable gain amplifier (VGA), and can introduce significant nonlinearities, a problem exacerbated by signals with a large peak-to-average ratio (PAR). One embodiment provides feed forward information from the VGA regarding its status to a DFE, and the DFE adjusts its filtering based on the provided information. The advantages are also applicable to fixed-gain amplifiers and to transversal filters.

Abstract: Large interfering signals (interferers) with spectra near a desired signal can cause distortion in a wireless receiver due to a non-linear signal path. It is typically a performance advantage to attenuate these interferers earlier in the signal path, rather than later in the signal path, because these interferers can cause saturation of amplifying stages. In certain situations, the frequency offset of an interfering signal, with respect to the desired signal, can be on the order of 10 megahertz (MHz), whereas the center frequencies can be on the order of several gigahertz (GHz). Thus, a filter with “baseband” precision would be needed at radio frequency to notch out the interferer, which is relatively difficult to do. Disclosed is a technique to estimate the relative strength and center frequency of the interferer and to place the center frequency of a notch filter adaptively and precisely at the interferer location.

Abstract: The adverse effects of RF and baseband circuits are mitigated using a post-compensation method wherein a transfer function that would un-distort or complement a distorted waveform is parameterized to a relatively small number of degrees of freedom; and the parameters are estimated in a feedback loop. The error function of the feedback loop is generated by comparing some relatively low-order statistics that are known a priori or can be computed with relative certainty from the decided output waveform—to the statistics of the corrected signal.

Abstract: Methods and apparatus for reducing sensitivity to nonlinearities in the receiver of a digital communications system are disclosed. One aspect can be referred to as a Post-Distortion Decision Feedback Equalizer (PDFE). A gain stage is often implemented as a variable gain amplifier (VGA), and can introduce significant nonlinearities, a problem exacerbated by signals with a large peak-to-average ratio (PAR). One embodiment provides feed forward information from the VGA regarding its status to a DFE, and the DFE adjusts its filtering based on the provided information. The advantages are also applicable to fixed-gain amplifiers and to transversal filters.

Abstract: Transceivers with multiple gain stages that include open loop and closed loop amplifiers are subject to differential non-linearity (DNL) errors in their total gain versus gain index curve due to the gain step variability of the open loop amplifiers. The initial and time varying DNL can be reduced by a control loop that uses the relative gain step precision of the closed loop amplifiers and of passive attenuators to establish a control loop to reduce the DNL of the total gain.

Abstract: Apparatus and methods determine a frequency associated with a relatively strong interfering signal (interferer) using relatively simple run-length counting techniques. Counts of run-lengths can be analyzed to estimate a frequency of the interferer. For example, a peak run-length can be associated with a frequency. In one embodiment, counts of run-lengths are used to construct a theoretical peak run-length, which is then associated with a frequency for the interferer. A theoretical count associated with the theoretical peak run-length can also be used as an indication of a signal strength of the interferer.

Abstract: An analog-to-digital converter (ADC) of a radio receiver can consume a relatively large amount of power. It is typically desirable to minimize power consumption, particularly with battery-powered devices, such as in wireless receivers. In certain conditions, the effective number of bits (ENOB) required from an ADC of a receiver can vary. The power consumption of certain ADC topologies, such as pipelined converter topologies, can vary with the number of bits. One embodiment dynamically varies the ENOB of an ADC to more optimally consume power. This can extend battery life.

Abstract: The signal strength of an out-of-channel interferer is estimated by measuring the transition density of the sign of the down-converted signal. RF interferers at a higher or lower frequency than the desired RF signal appear as high frequency content in the down-converted signal, thus increasing the likelihood of zero-crossings.

Abstract: The adverse effects of RF and baseband circuits are mitigated using a post-compensation method wherein a transfer function that would un-distort or complement a distorted waveform is parameterized to a relatively small number of degrees of freedom; and the parameters are estimated in a feedback loop. The error function of the feedback loop is generated by comparing some relatively low-order statistics that are known a priori or can be computed with relative certainty from the decided output waveform—to the statistics of the corrected signal.

Abstract: In a Frequency Duplex Division (FDD) radio, the transmit and receive signals are separated by frequency. In a wireless application, the power of the transmitted signal is typically much larger than the power of the received signal. A duplexer is used to separate the transmit and receive signals. Despite the operation of the duplexer, a residual transmit signal, or echo, can be present at the receiver input as a result of finite attenuation in the duplexer and other sources of transmit to receive crosstalk. With a relatively linear low-noise amplifier (LNA) and output limited mixer linearity, the echo can be cancelled in analog baseband directly at the mixer output using an out-of-channel signal indicator as the error signal for an echo control loop.