Abstract: An analog-to-digital converter (10) comprises a set of comparators (12a-12f) for providing a set of different output signals whose logic states are a function of an analog input signal voltage and one or more reference voltage signals supplied by a resistive network (16). The comparators are connected to a decoder (20) for processing the thermometer code outputs of the comparators to generate a digital word output corresponding to the voltage amplitude of the analog signal. Several of the comparators are also connected to an error checking network (22), including a preconditioning circuit (100) and a detection circuit (102) for processing these comparator outputs to provide an error signal whenever one or more of the comparators are not operating properly. The error checking network and decoder are connected to an error correction circuit (26) for correcting the digital word signal in accordance with the error signal.

Abstract: In a multiple trace oscilloscope wherein separate traces displayed on a cathode ray tube screen are updated in succession, a random access memory is addressed by the count output of a programmable counter which increments its count each time the oscilloscope finishes updating one trace prior to updating a next trace. Data stored in the random access memory at the storage location addressed by the count is utilized to control attributes of the next trace to be updated by controlling the switching positions of attribute control switches which select the horizontal, vertical and intensity control signals controlling the appearance of each trace.

Abstract: A pattern of conductive material is formed on a substrate of dielectric material. The substrate comprises a layer of flexible dielectric material having a layer of dimensionally-stable material adhered to one main face. The pattern is formed on the opposite main face of the layer of flexible dielectric material.

Abstract: A frequency-compensated transistor feedback amplifier provides relatively wide bandwidth and relatively large phase and gain margins, irrespective of the transconductance of the transistors in the amplifier. Each one of three preferred embodiments (10, 50, 104) of the invention includes a transconductance stage (20, 68, 68) and an amplifier stage (12 and 14, 54, 54 and 14). The transconductance stage delivers an input signal to the amplifier stage, which produces an amplified replica of the input signal. A feedback capacitor (24, 88, 24 and 88) connected between the output and the input of the amplifier stage provides dominant pole compensation by which the magnitude of the loop gain diminishes by 6 dB/octave with increasing frequency. The capacitor provides a forward feedthrough path for any residual portion of the input signal so that the residual portion arrives at the output of the amplifier stage in substantially the same phase relation with that of the output signal of intermediate frequency.

Abstract: A digital-to-analog converter circuit (10) comprises a current switch (22) that has differential input conductors (16a, 16b, . . . , 16n and 18a, 18b, . . . , 18n) which receive complementary logic voltage signals corresponding to a digital input word (X.sub.1, X.sub.2, . . . , X.sub.n). The current switch synthesizes an output signal (V.sub.o -V.sub.o) whose magnitude corresponds to the weighted value of the digital input word. The circuit further comprises a current reference source (60) that develops a reference current (I.sub.REF) from which transistor constant-current sources (48a, 48b, . . . , 48n) in the current switch derive binary-weighted currents to synthesize the output voltage signal. The current reference source includes an impedance element or resistor (70) through which the reference current flows and which is scaled to the load impedance connected to the current switch.

Abstract: An improved differential f.sub.T doubler amplifier is provided having two error amplifiers in series connection with the main signal amplifier for cancelling the nonlinear currents generated by the main signal amplifier. The error amplifiers receive a differential error voltage provided by a pair of transistors which sense the error voltage in the main signal amplifier.

Abstract: For a computer system having peripheral devices coupled to a common bus through interface devices transmitting and receiving messages containing an address code matching a stored address code, a dynamic address assignment system stores a unique address code in each interface device following system startup. On system start up each interface device stores a type number and an adjustable serial number, type numbers for peripheral devices of the same type being identical while serial numbers for all peripheral devices of the same type are adjusted to different values. A master controller transmits to all peripheral devices a series of universally addressed count commands. Each interface device counts the count commands and, when the count reaches a poll number determined by the unique combination of stored type and serial numbers, requests and obtains a unique address code from the host computer.

Abstract: A method and apparatus is disclosed for the improved monitoring and detection of improper device operation. Operation of a prototype device is first modeled. In particular, a set of test vectors is selected to provide a desired degree of testing of the prototype unit. The expected response of the prototype to the selected set of test vectors is determined through the use of analytical prediction means, and stored for subsequent comparison with the operation of the prototype unit. Thereafter, the selected set of test vectors are applied to the prototype unit, and the response thereto compared in real time with the expected responses. Improper operation of the prototype device is thereby identified, and associate information recorded for subsequent analysis.

Abstract: In a color graphics display system, video analog self-test hardware for testing the system elements between the frame buffer and the CRT display monitor is provided including a bi-directional data bus between the graphics processor and the color map, an analog comparator, an integrator, and an analog multiplexor. The self-test method includes calibrating the self-test circuitry with respect to a reference voltage. The method next includes testing the DACs by outputting predetermined bit patterns to each of the DACs via the frame buffer, measuring each DAC output level in response to each input bit pattern, comparing the DAC output levels to predetermined limits, and reporting the results. Provision is made also for testing the system clock.

Abstract: A temperature compensated amplifier network for a fiber optical receiver includes a photodiode having an optical input and a current output, and a cascadable transimpedance amplifier having N stages, each stage having a common base-emitter voltage. An emitter-follower transistor is coupled to the last stage of the transimpedance amplifier network and has a base-emitter voltage of the same magnitude but of opposite polarity from the base-emitter voltage of each of the amplifier stages. Any DC drift of the amplifier stages is therefore offset by a compensating drift in the opposite direction by the output emitter-follower.

Abstract: A method and circuit employ digital techniques in processing an input signal of a first frequency to develop an output signal of a second frequency that is a multiple of the first frequency. During each cycle of the input signal, a presettable down counter (146) is decremented from its maximum value at a rate of 1/T.sub.1. The digital word appearing at the output of the down counter at the end of the cycle is programmed into an up counter (278) that is clocked at a rate of 1/T.sub.2. The frequency of the signal developed at the overflow output (336) of the up counter is divided by two by a flip-flop (342) whose output (348) provides a signal of a frequency which is T.sub.1 /2T.sub.2 times that of the input signal. The frequency of the output signal changes after one cycle of a change in frequency of the input signal. The frequency multiplication factor can be a noninteger value.

Abstract: A differential signal input is applied through two resistors to the two sides of a dual clamping circuit and the two current outputs of a current mirror. The dual clamping circuit prevents the voltage on either output of the current mirror from going above some reference value in response to the imbalance created by the differential input signal. With one side, the high side, of the differential signal output held to this reference value by the operation of the clamping transistor on that side, the whole voltage imbalance on the input appears on the other output as a result of the operation of the current mirror. Thus, the reference level of the differential signal is shifted at the output, while the amplitude of the signal is preserved. Alternative embodiments substitute a dual clamping circuit with an opposite polarity or an averaging circuit for the dual clamping circuit described, thereby referencing the output signal to the low side or an average instead of the high side as in the preferred embodiment.

Abstract: Optical detector storage effects reduction is achieved by inserting an optical modulator between the optical signal to be measured and the optical detector. The modulator is normally turned off, and is only turned on during the period when the output of the optical detector is being sampled by a sampling system.

Abstract: A current mirror includes first and second transistors having interconnected bases and having emitters respectively coupled through first and second resistors to a common potential source. A collector voltage of the first transistor is fed back to the transistor bases through a feedback capacitor, and through a unity gain amplifier and series resistor, to form a feedback loop for controlling the voltage at the transistor bases. A current source connected to the collector of the first transistor causes the second transistor to produce an output collector current substantially equal in magnitude to the input current. To prevent circuit instability, the feedback capacitor and the aforementioned series resistor are sized to reduce the frequency at which the open loop gain of the feedback loop is unity so that it does not exceed the short-circuit current gain-bandwidth product of the first transistor.

Abstract: An improved mesh lens for PDA-type cathode-ray tubes is constructed in a manner that permits deformation into a concavo-convex shape with a substantially shorter radius of curvature than heretofore obtainable with prior art devices. A mesh lens (12) formed in accordance with this invention particularly comprises of multitude of interconnected webs (58) forming an array of apertures (60). Each web (58) has opposing ends and a midline (62) extending between those ends. The mesh (12) is configured so that an individual aperture (60) of the array is formed by a set of webs (58) interconnected at their ends. The midline (62) of each web in the undeformed mesh defines a bent line. The mesh can be deformed into a concavo-convex shape having a relatively short radius of curvature. This is so because the individual webs of the mesh respond to the application of deformation forces by initially straightening, thereby effectively delaying the development of tensile stresses in the webs.

Abstract: A high-speed, supply independent level shifter is implemented in bipolar, JFET, MOSFET or MESFET integrated circuit technology. A level shift circuit having a desired input potential V.sub.1 and a required output potential V.sub.2, is incorporated into a first current leg connected between first and second supply voltages. A second current leg in parallel with the first leg establishes a reference current. The two current legs are coupled by a current mirror to establish a fixed, preferably equal, relationship between the currents in the two legs. Each current leg includes a reference resistor. A buffered, floating voltage source is coupled in series with the resistor in the first leg to the control conductor of the current mirror. The voltage source is designed and the resistor values selected to provide a potential V.sub.3 that is an additive function of potentials V.sub.1 and V.sub.2 such that V.sub.1 is independent of the supply voltages.

Abstract: An analog signal multiplexer for differential signals comprises a plurality of channels, each channel having a pair of differential amplifiers forming an input stage for receiving a differential input signal and a pair of output transistors for forming an output stage producing a differential output signal. Each differential amplifier has a pair of emitter-coupled transistors, with each transistor having an additional emitter cross-coupled to the additional emitter of the opposite transistor of the other emitter-coupled pair. A plurality of current sources are provided to bias the emitter-coupled and emitter cross-coupled pairs. By selectively enabling the current sources, the input signals forming the differential input signal can be applied with normal polarity or inverted polarity to a respective transistor of the output stage to produce a normal or inverted differential output signal or to both transistors of the output stage to produce no differential output signal.

Abstract: A constant carrier watchdog circuit for an r.f. modem detects an anomalous constant "carrier on" condition in the modem. In response to this anomalous condition a signal is generated and output to the modem. The signal causes the carrier frequency to shift out of the data channel frequency bands so that the anomalous modem does not affect other users on a telecommunication network.

Abstract: For an oscilloscope capable of simultaneously displaying a plurality of waveforms on a screen and capable of performing operations with respect to a selected one of the displayed waveforms, a method and apparatus for permitting an operator to select a waveform. A touchscreen mechanism provides input signals to the oscilloscope indicating when and where an operator touches the surface of the screen and a microcomputer within the oscilloscope determines from data controlling the display of each waveform and from the data provided by the touchscreen whether the operator is touching any portion of a displayed waveform. If so, the microcomputer assumes that the operator has selected the waveform touched and reconfigures oscilloscope operation such that operations are performed with respect to the waveform touched by the operator.

Abstract: An electron beam addressed liquid crystal light modulator or "valve" includes a liquid crystal cell having a target surface which a writing electron beam and an erasing electron beam address to provide a display image. The writing electron beam and the erasing electron beam sequentially strike preselected locations on the target surface to cause an emission of secondary electrons and, thereby, develop an electrostatic potential at such preselected locations. A secondary electron collector electrode positioned over and above the target surface collects in a uniform manner the secondary electrons emitted by all regions of the target surface. A collector electrode controller circuit sequentially applies first and second potential differences between the target surface and the collector electrode in synchronism with the striking of the preselected locations by the respective writing and erasing beams.