Abstract: A clock changeover device comprising a first input port for accepting a first external clock signal, a second input port for accepting a second external clock signal, and an output port for outputting a selected one of the clock signals. The clock changeover device also comprises a circuit for generating a control signal as a function of one of the external clock signals. The control signal has a first state and a second state, the control signal being at the second state when the second external clock signal is coupled to the second input port, the control signal being at the first state when the second external clock signal is not coupled to the second input port. The clock changeover device further comprises an output circuit responsive to the control signal for coupling the first input port to the output port when the control signal is in the first state and for coupling the second input port to the output port when the control signal is in the second state.

Abstract: A circuit for utilizing the magnetizing current in the transformer of a converter to reset the transformer's core and to provide a zero-voltage-switching condition on the converter's primary switch and to regulate the output voltage is disclosed. The power converter includes a transformer having a primary winding and a secondary winding, the secondary winding being coupled to an output load and a primary switch connected in series between the primary winding and a voltage source. The closing of the primary switch causes energy to be stored in the transformer and the opening of the primary switch causes the energy to be released from the transformer. The utilization circuit includes a series combination of a storage capacitor and a first switch coupled in parallel with one of the transformer's windings to capture the energy released from the transformer. The captured energy is used to reset the transformer's core and to create a zero voltage switching condition across the primary switch.

Abstract: An electronic device has a circuit whose operation is adjustable by changing a variable component responsive to stored data. The electronic device also has a processor responsive to a stored program for controlling the circuit by receiving new input data and changing the variable component by replacing the stored data with the new input data. Preferably the electronic device has radio frequency circuits for transmitting and receiving a radio frequency signal, and audio frequency circuits for relaying and reproducing an audio signal. For calibration and adjustment during assembly or servicing, the electronic device is connected to automatic testing, checking and adjustment equipment including a computer that provides the input data to change the variable component as required. The calibration or adjustment is made as a series of progressively better approximations to the required valve.

Abstract: An adjustable power converter which allows the output voltage of the power converter to be controlled linearly by a programming resistor or a programming voltage is provided. The adjustable power converter includes a linear programming circuit which generates a current as a linear function of the programming voltage or the resistance of the programming resistor. The current is connected to the feedback loop of a conventional power converter such that the output voltage of the power converter is a linear function of the current. As a result, the output voltage of the power converter can be linearly adjusted by adjusting the programming voltage or the programming resistor.

Abstract: The present invention provides a power transformer having a low profile and low overall volume. The power transformer also has improved isolation between the primary and the secondary windings, while at the same time providing improved electromagnetic coupling between these windings. The power transformer comprises an insulating enclosure for encapsulating a primary winding wound therein. The secondary winding comprises two electrically connected planar windings stamped from a conductive foil sheet. The insulating enclosure is positioned between the two planar windings of the secondary winding. The power transformer also comprises a core for coupling magnetic flux from the primary winding to the secondary winding.

Abstract: A circuit for utilizing the magnetizing current in the transformer of a converter to reset the transformer's core and to provide a zero-voltage-switching condition on the converter's primary switch is disclosed. The power converter includes a transformer having a primary winding and a second winding, the secondary winding being coupled to an output load and a primary switch connected in series between the primary winding and a voltage source. The closing of the primary switch causes energy to be stored in the transformer and the opening of the primary switch causes the energy to be released from the transformer. The utilization circuit includes a series combination of a storage capacitor and a first switch coupled in parallel with one of the transformer's windings to capture the energy released from the transformer. The captured energy is used to reset the transformer's core and to create a zero voltage switching condition across the primary switch.

Abstract: A control circuit for a radio frequency (rf) amplifier having multiple selectable power output levels in response to a plurality of input control signals is presented. The rf amplifier includes a variable gain input which is responsive to the control circuit. The control circuit includes an attenuator coupled to the output of the rf amplifier for providing an attenuated rf signal and an detector coupled to the output of the attenuator for generating a DC output signal which is substantially linearly related to the magnitude of the rf signal output by the rf amplifier. The control circuit also includes a means coupled to the input control signals for selecting one of a plurality of amplification factors. An amplifier is used to amplify the DC output signal generated by the detector using the selected amplification factors. The amplified output is coupled to the variable gain input of the rf amplifier.

Abstract: A circuit board assembly for a cellular telephone system or the like is described. A housing encloses a printed circuit board. The housing comprises a frame including an outer wall surrounding the periphery of the printed circuit board and a pair of cover plates engaging the outer edges of the outer wall of the frame. The printed circuit board is secured to the frame, and the frame is secured between the cover plates by fasteners which pass through holes in the printed circuit board. A plurality of internal walls on the frame isolate components on the printed circuit board and engage a ground line on the printed circuit board. The printed circuit board is a multi-layer board designed to permit signal lines to pass underneath the ground lines. Components are amounted on both sides of the printed circuit board.

Abstract: A current-sensing rectifier for current rectification and measurement applications is described. The current-sensing rectifier comprises a current-sensing device for rectifying the current in a selected circuit branch and an active-sense comparison circuit to measure the sense current provided by the current-sensing device. The current-sensing device and active measurement circuit are operated such that the current-sensing device rectifies the current of a selected circuit branch. No negative voltage supplies are required for rectification or for the measurement of the branch current. Further embodiments of the present invention include sample-and-hold circuits which sample the value of the rectified current during an ON-period of operation and maintain the sampled value during a subsequent OFF-period.

Abstract: A programmable temperature detector for simple detection applications is described. The programmable temperature detector has three terminals and a plurality of temperature-transitions points from which to choose. A first terminal receives power from a supply, a second terminal receives a ground reference, and a third terminal provides an indication of an object's temperature crossing a selected temperature-transition point. The desired temperature transition point is specified by a single non-precision resistor coupled in series with the power terminal of the detector. The non-precision resistor and a power supply set a program signal, in the form of a current, into the power terminal of the detector. The programmable temperature detector comprises circuitry for quantizing the program signal into a discrete signal level and for selecting a temperature transition point in response.

Abstract: An improved radio frequency (RF) coupler for providing two or more secondary signals from a primary RF signal. The RF coupler has a primary coupling element and two or more secondary coupling elements for providing the two or more secondary signals. The secondary RF coupling elements are offset and nonoverlapping with respect to one another along the axis of the primary coupling element so as to reduce the cross coupling and interference between the secondary elements. The offset relationship between secondary coupling elements allows for optimal design control over the coupling between each secondary coupling element and the primary coupling element. In one embodiment, the spatial area required for the coupling elements is reduced by introducing U-shaped portions in the primary coupling element and at least one of the secondary coupling elements. In another embodiment, the secondary coupling elements are provided on separate substrates to further reduce cross interference.

Abstract: A magnetically actuated information display device is disclosed which includes a rigid, permanently magnetized display segment movably mounted in a non-magnetic chamber having a transparent viewing window and containing an opaque fluid whose color contrasts with the color of the display device. A core affixed to the rear of the chamber is capable of being selectively magnetized so as to repel or attract the display segment, according to the selected magnetic polarity of the core. Repulsion of the display segment by the core causes the display segment to move toward the transparent window through which the color of the display segment may be viewed as the opaque fluid is displaced away from the transparent window. Attraction of the display segment by the core causes the display segment to move away from the transparent window thereby allowing the opaque fluid to obstruct viewing of the display segment. In this position, the color of the opaque fluid is viewed through the transparent window.

Abstract: A data input device includes a pair of resistive sheets positioned so as to overlap one another to define a common writing area. These sheets are separated from one another by a layer of material that is only electrically conductive under pressure. An energizing voltage is alternatively applied to each sheet such that the pressure of a stylus or the like at a contact point on the surface of the writing area generates first and second output voltages representative of the X and Y coordinates of the contact point. A circuit periodically biases one of the resistive sheets. The bias circuit causes an overvoltage outside of the normal range of voltages to be generated on this resistive sheet when no electrical contact presently exits between the two resistive sheets, indicating that a stylus is not presently applying pressure to a contact point on the surface of the data input device.

Abstract: A start circuit for starting the generation of pulse width modulated switching pulses is disclosed for use in a DC/DC switching converter power supply. The starting circuit is responsive to the initiation of a DC voltage source and starts the operation of a pulse generator. The starting circuit also includes a relaxation oscillator connected to the DC voltage source for periodically generating a start pulse at a predetermined frequency. Ongoing power is coupled to the pulse generator once the generator begins operation. The relaxation oscillator is selectively disabled when the pulse generator is powered by the ongoing power supplied by the power supply during normal operation. The start circuit further includes a delay function for delaying the disabling of the relaxation oscillator for a preselected period after shutdown of the power supply and includes a rapid start function for reducing the time between restoration of input power and the operation of the start circuit.