Abstract: A direct current offset correction system is disclosed for use in an analog signal processing system. The offset correction system includes a comparator unit for comparing the polarity of signals from an analog signal channel and producing a binary output signal. The system also includes a digital accumulator unit that is coupled to the comparator output signal for providing an accumulated average signal over a predetermined period of time. The system also includes a threshold window digital comparator unit for determining whether the accumulated signal is within a defined threshold window of acceptable values. The system further includes a correction unit for applying a corrective signal to the analog signal channel.

Abstract: A crystal oscillator circuit is disclosed including a differential amplifier, a positive feedback assembly, and a series resonant crystal assembly. The differential amplifier includes a first transistor and a second transistor. The positive feedback assembly is coupled to each of the first and second transistors, and has a loop gain of greater than unity. The series resonant crystal assembly is coupled to one of the first and second transistors, and includes a crystal and a capacitor.

Abstract: A variable gain amplifier system for radio frequency signals is disclosed. The system provides a relatively constant gain change in decibels responsive to an incremental change in control voltage. The system includes two or more cascaded gain stage amplifiers. Each gain stage amplifier is adjustable between a first gain setting and a second gain setting.

Abstract: A transceiver circuit is disclosed for use in radio frequency communication systems. The circuit includes a transmitter circuit, a receiver circuit and a local oscillator circuit. The local oscillator circuit includes at least one oscillator input signal having a frequency that is a non-integer multiple of the transmission frequency of the radio frequency communication system. The oscillator input signal is used to produce a transmitter local oscillator signal and a receiver local oscillator signal.

Abstract: A direct conversion circuit for radio frequency signals is disclosed. The circuit includes a pair of quadrature related mixers, a phase shift unit, and a local oscillator. The pair of quadrature related mixers is coupled to a radio frequency signal input port for mixing down a radio frequency input signal. The phase shift unit is in communication with at least one of the pair of mixers for phase shifting a local oscillator signal. The local oscillator produces the local oscillator signal. The local oscillator includes a non-integer frequency multiplier for multiplying the frequency of a first voltage controlled oscillator signal by a non-integer value to produce the local oscillator signal.

Abstract: A direct conversion circuit for radio frequency signals is disclosed. The circuit includes a pair of quadrature related mixers, a phase shift unit, and a local oscillator. The pair of quadrature related mixers is coupled to a radio frequency signal input port for mixing down a radio frequency input signal. The phase shift unit is in communication with at least one of the pair of mixers for phase shifting a local oscillator signal. The local oscillator produces the local oscillator signal. The local oscillator includes a non-integer frequency multiplier for multiplying the frequency of a first voltage controlled oscillator signal by a non-integer value to produce the local oscillator signal.

Abstract: A power amplifier, especially for mobile radio systems, achieves high efficiency while maintaining stability by frequency translating the input signal during the power amplification process. Two class C amplifiers (q5,q6) have their outputs coupled together and have their inputs driven differentially. The transistors (q5,q6) are biassed for optimum efficiency and to ensure unsaturated class C operation.

Abstract: A sinewave oscillator and a quadrature phase shift network fabricated as an integrated circuit for a Barber radio receiver comprising, in order that the network and oscillator be simply adjustable to provide an accurate 90.degree. shift and a sinewave of accurate frequency and high spectral purity, a first capacitance means (C1, C2; C4, C5) coupled to the input of a gyrator (G1; G2) comprising first and second amplifiers (10, 12; 22, 24) connected in feedback configuration with a capacitance (C3; C6) connected to the output of the first amplifier. The oscillator network may be adjusted by current control of transconductance of the amplifiers, and the amplifiers include input signal limiting means to limit the input signal to a linear operating region. An output load resistance (R) may be simulated using a further amplifier connected in feedback configuration.

Abstract: A bias circuit (FIG. 5) of the type comprising a bias transistor (T1) having a pair of resistors (R1, R2) in its collector path, the junction of these two resistors (R1 and R2) being connected to the transistor base. The base of a drive transistor (T2), of like polarity type, is connected to the collector of the bias transistor (T1), this serving as current source or sink. To provide and increase extended operation, operation at supply voltages lower than usual and current regulation from low supply voltage (0.9V) to much high voltage, this circuit is modified by the provision of a third resistor (R3) in the collector path and a diode shunt (T3) between the base of the drive transistor T2 and the junction of the third and first resistors (R3 and R1). The polarity inverse of this modified circuit is also effective and may be combined, in cascade or in ring feedback loop configuration, with the aforementioned modified circuit. These latter combinations serve to provide yet higher order current regulation.