Abstract: A transmitter that includes an amplifying element, an antenna, a gain stage, and a closed loop feedback may compensate for varying antenna loads without an isolator. This may be accomplished by determining the effects of the varying loading on overall loop gain. Knowing the effects, the transmitter adjusts the gain of the gain stage to maintain a constant overall loop gain, thus eliminating the need for an isolator.

Abstract: A transmitter has an oscillator (101, 201, 303, 401, 501) that operates at frequency k multiplied by f.sub.c, thus the oscillator (101, 201, 303, 401, 501) outputs a signal at an output frequency, kf.sub.c. Coupled to the oscillator (101, 201, 303, 401, 501) is a frequency modifier (103, 205, 307, 405, 505), for modifying the oscillator output frequency by factor 1/k, thereby producing a signal at frequency f.sub.c at the frequency modifier output. Coupled to the frequency modifier output is a modulator (105, 215, 301, 407-417, 507-517) for producing a modulated output signal substantially centered at frequency f.sub.c.

Abstract: A power amplifier is described, such as an amplifier employing closed loop feedback (e.g. Cartesian feedback) as well as a radio transmitter incorporating such an amplifier. The amplifier circuit has an amplifier control loop and a loop closing element (18, 107) for selectively opening and closing the control loop in response to a loop closing signal (40). One or more gain elements (30, 31, 32, 33, 101, 102, 110, 111) external to the control loop is adjusted responsive to the loop closing signal so as to maintain approximately constant gain between the input and the output of the amplifier during opening and closing of the loop, Because the gain adjustment is carried out external to the loop, any negative impact on the phase shift or phase stability is reduced or eliminated, and the circuit can be designed with reduced phase margin and greater simplicity.

Abstract: A transmitter that includes an amplifying element, an antenna, a gain stage, and a closed loop feedback may compensate for varying antenna loads without an isolator. This may be accomplished by determining the effects of the varying loading on overall loop gain. Knowing the effects, the transmitter adjusts the gain of the gain stage to maintain a constant overall loop gain, thus eliminating the need for an isolator.

Abstract: An analog signal having an input level is provided. The analog signal is converted into a digitized representation of the analog signal in an analog to digital converter (105) that uses an operating range. The digitized representation of the analog signal is processed (107) to determine the input level for the analog signal. The input level for the analog signal is compared (109) with a reference signal to provide a comparison signal. The comparison signal is manipulated (111) to adjust the operating range.

Abstract: An analog-to-digital (A/D) circuit comprising a multi-pole gain stage, a quantizer, and a feedback stage is stabilized when an analog input signal is excessive in the following manner. A stabilization detector continually samples a representation of stabilization of the A/D circuit. When the representation of stabilization is unfavorable, the stabilization detector increases, via a stabilizer, phase margin by adjusting the pole locations of the multi-pole gain stage based on the degree of unfavorability of the representation of stabilization. With the increased phase margin, the A/D circuit continues to provide digital representations of the analog input signal.

Abstract: An amplifier level-setting apparatus is provided for obtaining the maximum power output and highest efficiency allowable for a predetermined level of distortion. According to the invention, a training signal is applied to the input of the amplifier prior to the desired signal. The training signal level is increased while the output distortion is measured. When the output distortion level reaches a predetermined limit, the corresponding training signal input level is saved. The input signal level is then adjusted to this saved level value, thereby resulting in the maximum amplifier output level possible that is still within the distortion limit.

Abstract: A method and device are set forth for, where a linear transmitter has inphase and quadrature modulation paths for an input signal and at least one open feedback signal path is provided, substantially correcting an initial phase relationship between an input signal having an input signal vector with a phase and a magnitude, and an input feedback signal having an input feedback signal vector with a phase and a magnitude. The present invention provides a more time-efficient phase correction to at least one feedback signal path.

Abstract: A linear transmitter having both an open loop and a closed loop training mode capability functions to schedule and facilitate these training modes in a manner that reduces adjacent channel splatter. A training waveform can be utilized to enhance these operational objectives. Scheduling of the open loop and closed loop training modes can be ordered, in a TDM system, in a variety of ways.

Abstract: An adjustable slew rate amplifier in the input stage of an amplifier circuit helps reduce off-channel frequency splatter. In instances where test sequences are input to an amplifier circuit that are used to measure maximum permissible input levels to the amplifier, inclusion of a low slew rate amplifier in the input loop further prevents the production of off-channel frequency splatter caused even by the input test sequence. The adjustable slew rate amplifier is run at full slew rate, providing full-bandwidth amplification, during periods of normal circuit operation.

Abstract: A direct conversion FM receiver that comprises a quadrature mixer, an A to D converter, a digital demodulator, a digital phase lock loop, and frequency offset setting means is disclosed. The quadrature mixer receives FM signals and mixes them with a local oscillator signal to produce an analog in-phase baseband signal and an analog quadrature baseband signal. The analog in-phase baseband signal and the analog quadrature baseband signal are converted into digital signals by the A to D converter. The digitally converted baseband and quadrature signals are digitally demodulated and filtered by the digital demodulator such that modulation information is produced. The modulation information is used, at least in part, to control the phase lock loop means.

Abstract: A low power digital receiver (10) is provided that contemporaneously selects the lowest possible sampling signal frequency (34) (from a plurality of available sampling signals), and received signal level (28) to properly digitize (32) and recover a desired signal. Digitization is performed after the first IF using broadband stages (28, 30, and 32) that are temporarily enabled (44) to rapidly digitize the first IF signal. This, together with the low sampling rate, minimizes the power consumption of the receiver (10) thereby permitting portable and mobile digital receiver embodiments.

Abstract: An improved apparatus and method for a sigma delta converter for bandpass signals is disclosed, suitable for use in mobile radio applications, between the front end and digital signal processing stages, that includes at least one bandpass filter, an n-level quantizer, an n-level digital-to-analog (D/A) converter, and a direct current (DC) feedback network. The sigma delta converter for bandpass signals may be configured in a second order or a fourth order embodiment and achieves analog-to-digital conversion of a signal having a non-zero frequency carrier or suppressed carrier with improved signal-to-noise ratio performance and with minimal quantization error. As a result, the sigma delta conversion occures earlier in a receiver chain and a dynamic range of about 95-98 dB is achieved.

Abstract: A low power digital receiver (10) is provided that contemporaneously selects the lowest possible sampling signal frequency (34) (from a plurality of available sampling signals), and received signal level (28) to properly digitize (32) and recover a desired signal. Digitization is performed after the first IF using broadband stages (28, 30, and 32) that are temporarily enabled (44) to rapidly digitize the first IF signal. This, together with the low sampling rate, minimizes the power consumption of the receiver (10) thereby permitting portable and mobile digital receiver embodiments.

Abstract: A method and means for reducing noise in a GaAs FET oscillator circuit is described. The circuit of the present invention achieves low noise oscillator operation by driving the gate input of the GaAs FET oscillator circuit with a source of voltage which exhibits a low impedance at baseband frequencies and driving the drain input with a source of current which exhibits a high impedance at said frequencies. The present invention further operates to control the D.C. voltage present on the drain terminal of the GaAs FET device regardless of the drain current, while simultaneously maintaining a constant D.C. drain current at some predetermined value which corresponds to optimum low-noise operation.

Abstract: A improved microwave dielectric oscillator module which is provided with a removable temperature compensated dielectric resonator channel element is described. The removable temperature compensated dielectric resonator channel element cooperates with an electrically shielded housing. A substrate is mounted within the housing. Microstrip or stripline conductive patterns deposited on the substrate couple energy from the removable dielectric resonator to the remainder of the oscillator circuitry. The oscillator achieves wideband operation utilizing a GaAs FET transistor as the oscillators active element in conjunction with an intergral trombone-line phase adjuster.

Abstract: A modulated elongate cavity oscillator with minimized modulation nonlinearities includes a first cavity having dimensions which determine the fundamental resonant frequency of the oscillator, a gain element disposed in said first cavity that provides amplification to sustain oscillation, and a varactor diode disposed in said first cavity for modulating the fundamental frequency. A first waveguide is coupled to the first cavity for absorbing modes higher than the mode of the fundamental frequency which have an electric field maxima concurrent with the longitudinal center line of the first cavity. A second waveguide is coupled to the first cavity for absorbing modes higher than the mode of fundamental frequency which have an electric field minima concurrent with the longitudinal center line of the first cavity, whereby the first and second waveguides provide effective attenuation of higher order modes such that modulation nonlinearities due to the existence of higher order modes are substantially eliminated.

Abstract: A quadrature combiner circuit is provided which employs a quadrature coupler to split an input radio frequency signal into split radio frequency signals which are amplified by respective amplifiers and recombined in a second quadrature coupler in such a manner as to minimize intermodulation distortion products. A feedback loop is employed to assure that the split amplified radio frequency signals incident upon the second quadrature combiner are maintained in quadrature relationship to assure intermodulation product cancellation.

Abstract: A variable impedance synthesis circuit is provided for generating a selected impedance, whether real or complex, at a predetermined port. The variable impedance synthesis circuit exhibits the selected impedance in response to control signals applied thereto.

Abstract: Apparatus is provided for inhibiting the generation of intermodulation products in a radio frequency amplifier coupled to a circulator. A control circuit generates a control signal exhibiting indicia of the amount of isolation provided by the circulator. The control signal is provided to a variable impedance synthesis circuit coupled to the circulation isolation port such that the impedance synthesis circuit exhibits the appropriate impedance to maximize circulation isolation. Intermodulation is thus minimized.