Motorola Corporation

Ronald H Chapman

Kenneth A Hansen

Paul H Gailus

Richard S Kommrusch

William J Turney

Walter J Rozanski, Jr

Anthony P Van Den Heuvel

Jeffrey B Wilhite

Gary A Cannalte

John Stephen Ruppel

Kermit Myles Beseke

Percy P Batlivala

Jona Cohn

James Robert Johannsen

Robert M Bennett

Andrew F Peterson

A linear amplifier (103) has a negative feedback loop that has a closed loop gain and a forward path gain. The negative feedback loop is closed, such that quick changes in the closed loop gain are prevented, thereby reducing splatter. When the negative feedback loop is opened, quick changes in the closed loop gain are also prevented, thereby reducing splatter.

Feedback loop closure in a linear transmitter

A feedforward distortion cancellation circuit active control of both cancellation loops and a pilot signal and using least means squared circuits in both cancellation loops is disclosed. According to the invention, by using a pilot signal as the reference signal in a least means squared cancellation circuit, the required level of cancellation is reduced and thus it is easier to fabricate the circuit and the circuit is more stable.

Feedforward distortion cancellation circuit

An amplifier circuit uses a microprocessor to count occurrences of the output stage going into saturation to decide when to control input levels to the amplifier. When the output amplifier stage saturates too frequently, the microprocessor controls a scaling line that effectively attenuates input levels to the amplifier, eliminating saturation levels. When the output stage saturates too infrequently, input levels to the amplifier are increased.

Splatter controlled amplifier

An adaptive range circuit (10) suitable for use with an analog to digital convertor (11) having operating range control inputs. The invention includes a peak detection unit (12) that can include a positive peak detector (13) and a negative peak detector (14) that provide signals representative of positive and negative peaks for the incoming analog signal to be digitized. These representative signals can be utilized to control the operating range of the A/D convertor (11).

Adaptive range/DC restoration circuit or use with analog to digital

An improved arrangement and method for use in a radio communication system is disclosed which makes possible mobile radio channel assignments on narrower channel spacings with a minimum amount of adjacent channel interference or splatter occurring at an included base station receiver. In a first embodiment, the mobile radios modify at least one transmission parameter, such as maximum allowable deviation, a given amount of transmitter output power, and a modulation limiting bandwidth, if a processed value of receive signal strength exceeds at least one predetermined threshold value. The processed value of receive signal strength is taken from a plurality of sampled and stored receive signal strength values in the mobile radio. By determining that the processed value of receive signal strength exceeds a predetermined threshold value, the mobile radio is able to adaptively control the amount of splatter caused at the base station, thus keeping the amount of splatter within acceptable levels. In a second embodiment, the improved arrangement and method incorporated in a mobile radio progressively adapts the transmission parameters upon determining that the processed value of receive signal strength exceeds a first, a second, and a third threshold value to effect reduced maximum allowable deviation only, reduce the maximum allowable deviation and power output only, or to reduce the maximum allowable deviation, power output, and modulation limiting bandwidth upon exceeding one, two, or all of these threshold values. Moreover, in each of these embodiments, the base station includes apparatus and a method for compensating the level and bandwidth of recovered audio by sensing the relative level of received signal strength in the base station receiver.

Adaptive splatter control

An incoming signal is received and processed through a discriminator function. A reference signal is generated corresponding to the incoming signal. First and second difference signals, corresponding to the frequency difference between the reference signal and the incoming signal are generated, each having a unique phase. A direction signal is generated from the first and second difference signals to indicate if the incoming signal frequency is greater than or less than the reference signal frequency. Pulses are generated which relate to the difference in frequency between the reference signal and the incoming signal, and a recovery circuit is used for recovering modulation from the generated pulses and the direction signal.

Digital frequency discriminator

An improved encoder/decoder circuit which utilizes a phase locked loop frequency synthesizer configuration to permit both encoder and decoder operation. In addition, a sampling filter detector is employed to permit monolithic integration of the circuit and minimize sensitivity to vibration. The sampling filter detector has digitally controlled bandwidth which permits rapid response to reverse burst turn-off. In addition, the circuit includes a pulse adder to implement an energy limited reverse burst turn-off mode.

Continuous tone decoder/encoder

An apparatus for minimizing the spillover signal from the transmitter to the receiver in a same frequency repeater includes a mechanism for generating a receiver first injection signal carrying the modulation component of the transmitter signal, and a first mixer for mixing the received signals and the first injection signal to produce a first IF signal having one unmodulated IF component signal and another modulated IF component signal. A correlation and cancellation circuit is utilized to cancel the unmodulated IF component signal. A mechanism is provided for generating a second injection signal which carries the modulation component of the transmitter signal. A second mixer mixes the first IF signal and the second injection signal to produce a second IF signal such that the modulation component of the spillover signal is substantially cancelled. Time synchronization mechanisms are preferably provided to adjust the phase of the modulation component of the transmitted signal as carried by the first and second injection signals such that it arrives at the first and second mixers in phase synchronization with the modulation component of the spillover signal. This invention also contemplates a method for canceling the modulation component of the spillover signal.

Isolation method and apparatus for a same frequency repeater

A circuit for changing the frequency of a pulse train in response to a change in the average value of an applied digital signal applies the signal to be changed to a pulse subtractor. Application of a predetermined number of digital data signals of one sign causes the periodic subtraction of a pulse at the subtractor, thus reducing the average frequency at the output from the pulse subtractor. The signal at the output from the subtractor is applied to a pulse adder which adds a pulse to the subtracted pulse train in response to a predetermined number of data pulses of the opposite sign. The output pulse train is thus varied in frequency in respose to variation in the average value of the digital data input. The order of addition and subtraction may be reversed, and one of the functions can be performed in the feedback loop of a frequency synthesizer which receives the output pulse train as a reference signal.

Variable frequency reference source responsive to digital data

An improved phase locked loop receiver for use in a simulcast transmission system is disclosed whereby the phase locked loop receiver is used as a means to distribute a common reference frequency to all of the transmitters in a simulcast system. By phase locking the link receivers at each of the simulcast transmitters to the carrier of the link transmitter, a common reference is obtained. This allows each of the synthesized simulcast transmitters to be phase locked to a common reference. The Phase Locked Receiver (PLR) uses a reference frequency derived from the receiver IF frequency. The injection oscillator of the receiver is phase locked to this reference.

Phase-locked receiver with derived reference frequency

A low frequency oscillator of the astable type having good frequency stability, fast starting, good immunity to DC loading, and suitable for fabrication in integrated circuit form. First and second switching transistors of the astable multivibrator are cross-coupled by a coupling capacitor and a frequency determining crystal. Base drive to the respective switching transistors and charging current to the capacitor and crystal are provided by a pair of differential amplifiers which are referenced to a forward biased diode. The differential amplifiers are also connected to respective collector terminals of the switching transistors. The capacitor is of small value suitable for containment within an integrated circuit with the oscillator circuit. The differential amplifiers substantially increase the impedance levels in the oscillator and shift base drive to the switching transistors to minimize the effects of DC loading at the output terminals of the oscillator.

Low frequency astable oscillator having switchable current sources

A wide frequency range current-controlled oscillator (CCO) provides a digital output signal that is frequency controllable by an input control current. The CCO includes a differential voltage comparator coupled to a timing capacitor for controlling charging and discharging currents applied to the timing capacitor. The charging and discharging currents are dependent on the input control current. The magnitude of the discharging current may be varied to control the duty cycle of the digital output signal.

Wide frequency range current-controlled oscillator

A simulcast transmission system is provided where a reference signal transmitted from a central station is utilized to phase-lock transmitters located at remote stations. The remote stations include a receiver for receiving the transmitted reference signal and a signal conditioner for conditioning the received reference signal for application to the transmitters. The transmitters include a phase-locked loop which may be followed by a multiplier for providing transmitter signals of predetermined frequencies. All the transmitters at the remote stations are phase locked to the reference signal transmitted from the central station. In the event that the reference signal transmitted by the central station is interrupted, the signal conditioner of the remote stations will operate in an open-loop fashion to provide the conditioned reference signal during the interruption. After the interruption has cleared, the signal conditioner is automatically phase synchronized to the reference signal and closed-loop operation is resumed.

Simulcast transmission system having phase-locked remote transmitters

A few cycles of an input signal are correlated, or compared, with a few cycles of the input signal received at a previous interval and the interval is varied when correlation, or a positive comparison, has been obtained with the apparatus providing an output or detection signal after a predetermined number of correlations have occurred.

Sampled signal detector

In combination with an asynchronous detector for detecting a particular digital word within a train of signals wherein the detector samples each bit in the train a plurality of times and provides a comparison signal in response to a predetermined number of correlations between the samples and a stored word, an analog to digital converter including signal conditioning means having first and second modes of operations for converting a received analog signal to a digital signal in both modes of operation and inserting periodic error pulses in the digital signal in the first mode of operation and switch means coupled to the signal conditioning means and the detector for switching the signal conditioning means between the first and second modes of operation in response to a comparison signal from the detector. The signal conditioning means includes either a phase locked loop or a digital circuit which counts the time between transitions of the digital signal and inserts error pulses when the time between transitions exceeds a predetermined time.

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Wheaton, IL, United States of America

Ronald H Chapman