Abstract: A processor capable of independently adding a specified level of noise to each different frequency-based channel signal of a composite signal, where the specified levels of noise for at least two channel signals are different. In one embodiment, the processor operates in the digital domain after the composite signal can been channelized using a single set of time-multiplexed circuitry for all channel signals.

Abstract: Two or more digital-input RF amplifiers are configured in parallel such that a combiner combines their respective outputs to generate a relatively large composite RF output signal. A feedback control architecture minimizes the phase differences between the various amplifier outputs so that the outputs can be efficiently combined. The feedback control can measure the return loss for each amplifier to determine how to adjust each amplifier's phase. In some embodiments, the feedback control can also measure the composite RF output signal for use in phase adjustment. In certain implementations, phase adjustment is implemented by an iterative coarse phase-adjustment mode (e.g., based on either the return loss or the composite output signal) followed by an iterative fine phase-adjustment mode (e.g., based on the return loss).

Abstract: A received analog spread-spectrum signal is selectively attenuated prior to digitization, where the amount of attenuation is based on the amplitude of the digitized signal before the digitized signal is filtered to compensate for interference that may exist in the received signal. By selectively attenuating the signal only when the digitized signal is relatively large, the receiver can be implemented using a relatively small analog-to-digital converter (ADC) than would otherwise be the case for a particular signal processing application. Taking advantage of the signal-concentration characteristics of spread-spectrum receivers, embodiments of the present invention can be designed to operate with signal having negative signal-to-noise ratios at the A/D conversion step.

Abstract: In a receiver of a transmission system in which the data transmission rate is not an integer multiple of the spacing between transmission channels, a single oscillator is used to generate both the system clock used to process the data signal as well as the mixing signal used to downconvert the received RF signal to an intermediate frequency (IF). The frequency error in the IF signal that results from mixing the RF signal at a less-than-ideal mixing frequency is compensated by selecting an appropriate mixing signal frequency applied when downconverting the IF signal to baseband. In a transmitter, the mixing signal frequency used to upconvert the outgoing baseband signal to IF is selected to pre-compensate for the frequency error resulting from upconverting the IF signal to RF using a less-than-ideal mixing frequency. In either case, the receiver/transmitter can be implemented without having to provide a dedicated reference oscillator for converting signals between RF and IF.

Abstract: A frequency upconverter using mixers operating on one or more signals and inverted versions thereof and a subtractor, such as a balun, for subtractively combining the mixer outputs to produce an upconverted signal.

Abstract: A radio transmitter for transmitting signals in a predetermined frequency band has a transmit filter and a compensating filter. The transmit filter filters a signal to be transmitted from the transmitter to suppress the transmission of parts of the signal outside the band. The compensating filter, e.g., operating in the digital domain, filters the signal upstream from the transmit filter, wherein the compensating filter is arranged to alter the signal to counteract at least one of a phase ripple, an amplitude ripple, and a group delay variation of the transmit filter within the band.

Abstract: The insertion phase or delay of an amplifier can be controlled by comparing signals from the amplifier path with signals from a corresponding reference path without requiring the overall signal delay through the reference path to nominally match the overall signal delay through the amplifier path. Amplifier and reference path signals can be combined to form a combined signal whose power is detected using a narrow-band, frequency-selective power detector. For given phase and delay offsets between the amplifier and reference paths, cancellation (i.e., perfectly destructive interference) will occur at a series of different frequencies. By operating the power detector at one of these cancellation frequencies, a variable phase or delay adjuster in the amplifier path can be controlled to minimize the detected power level in order to achieve a desired level of insertion phase for the amplifier, without having to implement an expensive delay element in the reference path.

Abstract: A power amplifier's complex pre-distortion curve is generated by decomposing a representation of an input signal, processing the resulting decomposed signals using analog techniques, and performing signal re-composition. In one implementation, two different halves of a transfer function corresponding to the amplitude characteristics of the amplifier are separately modeled and then combined to generate a control signal used to control a voltage-controlled attenuator that attenuates the input signal, while two different halves of a transfer function corresponding to the amplifier's phase characteristics are separately modeled and then combined to generate a different control signal used to control a voltage-controlled phase shifter that adjusts the phase of the input signal. The resulting output signal corresponds to an amplitude-and-phase pre-distorted signal that can be applied to linearize a corresponding (high power) amplifier.

Abstract: In an amplifier system having two or more different amplifier sub-systems, the input signal to at least one of the amplifier sub-systems is pre-distorted based on the combined output signal from the two or more amplifier sub-systems. In one embodiment, each other amplifier sub-system pre-distorts its input signal based on only its own output signal. In one operational scenario, during initial operations, each amplifier sub-system separately pre-distorts its input signal based on only its own output signal. After pre-distortion has settled, one of the amplifier sub-systems is switched to pre-distort its input signal based on the combined output signal, while the other amplifier sub-systems continue to pre-distort their input single based on only their own output signals.

Abstract: Pre-distortion, whose magnitude—and preferably phase—are frequency-dependent, is applied to an input signal in order to reduce spurious emissions resulting from subsequent amplification of the signal. In preferred embodiments, the pre-distortion technique of the present invention is implemented in combination with the (frequency-independent) magnitude and phase pre-distortion technique described in U.S. patent application Ser. No. 09/395,490 (“the '490 application”), where the frequency-dependent pre-distortion corresponds to amplifier distortion that has a magnitude that is proportional to the frequency offset from the carrier frequency and a phase shift of ±90° on either side of the carrier frequency. The frequency-dependent pre-distortion is generated by differentiating waveforms corresponding to two different sets of pre-distortion parameters with respect to time.

Abstract: An input signal is pre-distorted to reduce spurious emissions resulting from subsequent signal amplification. Frequency-dependent pre-distortion is preferably implemented in combination with frequency-independent pre-distortion, where the frequency-dependent pre-distortion corresponds to amplifier distortion that has a magnitude that is proportional to the frequency offset from the carrier frequency and a ±90° phase shift on either side of the carrier frequency. The frequency-dependent pre-distortion is generated by differentiating waveforms corresponding to two different sets of pre-distortion parameters with respect to time. In one embodiment, one of the differentiated waveforms is applied to a positive-frequency filter and the other to a negative-frequency filter to generate positive- and negative-frequency pre-distortion signals, respectively, to account for asymmetries in the amplifier characteristics.

Abstract: The signal generated by a high-power amplifier (HPA) operating in its non-linear region is linearized by an amplifier circuit using feed-forward compensation in which an auxiliary channel relies on a model of the HPA to generate an auxiliary signal that is combined with the HPA output to generate an amplified linearized output signal. The amplifier circuit may be implemented with a pre-distorter in the main amplifier channel to linearize the HPA using both pre-compensation and feed-forward compensation. Using the HPA model in the auxiliary channel enables the auxiliary signal to be generated without directly relying on the HPA output. This enables the amplifier circuit to be implemented without having to delay the high-power HPA output signal prior to being synchronously combined with the auxiliary signal. In preferred embodiments, the auxiliary channel signal is generated using a relatively low-power amplifier operating in its linear region.

Abstract: An input signal having amplitude information is pre-distorted and converted into two pre-distorted signals without amplitude information. The two pre-distorted signals are separately amplified and then recombined to generate a linearized amplified output signal having amplitude information. The pre-distortion and conversion may be implemented using a pre-distorter and a LINC modulator. Alternatively, the pre-distortion and conversion may be implemented in circuitry that combines the functions of a pre-distorter and a LINC modulator. The amplified, pre-distorted signals are preferably combined using circuitry that provides at least some impedance matching, such as a transformer or a transmission line tee with transmission line stubs.

Abstract: Pre-distortion, whose magnitude—and preferably phase—are frequency-dependent, is applied to an input signal in order to reduce spurious emissions resulting from subsequent amplification of the signal. In preferred embodiments, the pre-distortion technique of the present invention is implemented in combination with the (frequency-independent) magnitude and phase pre-distortion technique described in U.S. patent application Ser. No. 09/395,490 (“the '490 application”), where the frequency-dependent pre-distortion corresponds to amplifier distortion that has a magnitude that is proportional to the frequency offset from the carrier frequency and a phase shift of ±90° on either side of the carrier frequency. The frequency-dependent pre-distortion is generated by differentiating waveforms corresponding to pre-distortion parameters with respect to time and then applying the resulting differentiated pre-distortion parameters to the input signal.

Abstract: An automatic gain control (AGC) circuit for an RF amplifier (or other type of signal-processing module) has a single, switched, RF detector that selectively detects the instantaneous power level of either the sampled RF input signal or the sampled (and optionally attenuated) RF output signal. A processor uses the detected input and output power levels to generate control signals for a variable (e.g., voltage-controlled) attenuator that attenuates the RF input signal prior to being applied to the input of the RF amplifier. The processor is designed (eg., programmed) to control the variable attenuator to maintain a constant gain between the input and output terminals of the AGC circuit. In addition to this closed-loop mode of operation, the AGC circuit may also have a temperature sensor, where the processor controls the variable attenuator in an open-loop mode of operation based on the temperature of the RF amplifier.

Abstract: Signal handling equipment, such as a high power amplifier, is implemented with feed-forward compensation circuitry that adjusts the effective operation of the equipment (e.g., linearizes the amplifier). The compensation circuitry includes (i) a nulling loop, which generates an error signal based on the output from the amplifier, and (ii) an error loop, which generates, based on the error signal, a feed-forward compensation signal that is added to the output of the amplifier. The compensation circuitry is tuned by tuning the nulling loop and then iteratively tuning the error loop based on data generated by perturbing the tuning of the nulling loop. In one implementation, data corresponding to the amplitude of the output signal is analyzed to generate metric values that are used to iteratively adjust the tuning of the error loop.

Abstract: An enclosure for electronic components has a chassis, a cover mountable to the chassis, and a face plate mountable to the chassis/cover sub-assembly. The top side of the cover has a generally U-shaped groove running along three sides to receive a friction-fitted gasket that forms a portion of the environmental seal for the enclosure. Each end of the groove has a J-shaped portion within which the gasket loops back on itself. The bottom of each J-shaped portion is open on the cover's front side, such that the side of the gasket will protrude beyond the front side of the chassis/cover sub-assembly, thereby providing a portion of the seal when the face plate is mounted onto the chassis/cover sub-assembly. The J-shaped portions account for contraction of the gasket due to strain relief after the gasket is placed in the groove and provide increased frictional force that further inhibits such strain relief.