Abstract: A variable attenuation signal acquisition probing system and voltage measurement system uses an optical cavity to acquire a signal under test. The probing system has an optical transmitter and receiver that are coupled to the optical cavity via an optical transmission system. The optical cavity has an electrode structure having apertures formed in the optical cavity that are parallel to propagation path of the optical signal within the cavity. A modulated optical signal is generated by the optical cavity in response to the signal under test creating an electromagnetic field distribution in electro-optic material in the optical cavity that overlaps the optical path of the optical signal propagating in the optical cavity which varies the index of refraction of electro-optic material in the optical path. Changes in the polarization state of the optical signal attenuates the magnitude of the output electrical signal of the optical receiver.

Abstract: A communications bus management circuit for a current probe system detects the connection of the current probe system to an instrument and the connection of a current probe to a current probe amplifier of the system. A controller generates a probe enable signal in the presence of the detected connection to the instrument that is coupled to a switching circuit. Switch elements couple the communications bus of the instrument to the communications bus of the current probe amplifier in the presence of the probe enable signal. The controller further generates a current probe present signal in the presence of the detected current probe that is also coupled to the switching element. A further switch element couples the data line of the instrument to ground via a resistive element in the presence of the current probe present signal and floats the data line when the current probe present signal is absent.

Abstract: A macro-level digital data event display provides event-based views of the digital, either in the form of a state machine representation or in the form of events versus time. Events within the digital data are defined, including assigning a specific color as desired. The digital data is parsed to locate each of the defined events, to determine the number of times unique transitions between events occur, and to measure the amount of time spent within each defined event. The events may be displayed as a graph with event labels along one axis representing lines that extend along another axis representing time, with a bar that transitions between lines when one event changes to another in sequence within the digital data, the length of the bar indicating the time spent in each event.

Abstract: An apparatus and method for demultiplexing sampled data at a first data rate on a data line using a non-standard demultiplex mode is achieved by first demultiplexing the sampled data using a standard, factor of two, demultiplex mode, to produce n data lines at 1/n time the first data rate, and then down-converting n data lines to m data lines at 1/m times the first data rate to produce the non-standard demultiplex mode. As a specific example sampled data is demultiplexed using a standard 4× mode and then converted to a non-standard 3× mode.

Abstract: A measurement instrument is provided with an FFT module providing a frequency domain output; and a power calculator connected to the frequency domain output to measure power statistics for a test signal of arbitrary length. In some embodiments, a spectrum integration module is provided to calculate the power contained within a frequency band. In an embodiment, a filter/averaging module is provided to compute signal power statistics over an arbitrary time period. Accumulators may be provided to store data related to maximum power, minimum power, average power, or peak to average power. A CCDF module may be provided in some embodiments to calculate CCDF related measurements. Also provided are methods of making power statistic measurements.

Abstract: A multiband amplifier for a test and measurement instrument includes a splitter to split an input signal into split signals, amplifiers, and means for combining and digitizing the amplified signals into a digitized signal. Each amplifier is configured to amplify an associated split signal over an amplifier passband. The amplifier passband of at least one amplifier is different from the amplifier passband of another amplifier.

Abstract: A current probing system has a current probe and a detachable adapter. The current probe has a probe body with electrically conductive contacts that mate with electrically conductive contacts on the adapter. Leads extend from the adapter for coupling to a current carrying conductor. The leads can connect to a plug that is coupled to a current diverting device for coupling a current signal to the current probe. The adapter may also include a switch that selectively couples the current signal to the current probe when the adapter is mated with the current probe. The contacts of the current probe are coupled to a current sensing circuit which generates a voltage output representative of the current signal. The voltage output is coupled to an oscilloscope via an electrical cable.

Abstract: A triggered data generator reduces timing jitter at the start of serial data output from arrival of a trigger signal. A trigger detecting circuit 8 produces trigger phase information indicating the phase relationship between the trigger signal and a reference clock. A data pattern generating circuit 10 generates parallel data bits according to the reference clock in response to the trigger signal. A data shifting circuit 11 rearranges the parallel data bits in a predetermined order to produce shifted parallel data bits in which data bit order is shifted relative to the reference clock as a function of the trigger phase information. A parallel to serial converter 16 converts the shifted parallel data bits into serial data bits.

Abstract: A messaging system and method for creating a messaging hierarchy in a computer network are described. The network is made up of multiple network entities, which include both publishing entities and subscribing entities, where the publishing entities have data of which the subscribing entities may have need. The messaging system and method for creating a messaging hierarchy also include a data hierarchy applied to the data exchanged between the publishing entities and subscribing entities.

Abstract: A method of non-invasive estimation of round trip time (RTT) between a sender and receiver in a packet oriented acknowledgment based transmission system uses a probe to monitor signals transmitted between the sender and receiver at any point in the transmission system. For a presetable number of acknowledgments in a sequence of acknowledgments received by the probe within a time interval, the time stamps of the acknowledgments are compared (i) with the timestamps of the packets received before the acknowledgments to determine an estimated value for the round trip time between the probe and receiver, and (ii) with the timestamps of the packets received after the acknowledgments to determine an estimated value for the round trip time between the probe and sender. Also sequence numbers of the same group of acknowledgments are compared with the packets encountered to perform a distance function along the sequence numbers themselves.

Abstract: System and apparatus enabling the use of a single cable to communicate triggering information between each of a plurality of signal acquisition devices and, illustratively, an external trigger control unit. A combined trigger signal is produced only when each trigger condition of each signal acquisition device is true. Thus, all of the signal acquisition devices will be triggered substantially simultaneously.

Abstract: A DDS pulse generator has an accumulator that accumulates a phase increment value to produce phase accumulator values, and has a lookup table that contains a digital representation of a pulse waveform such that a pulse output signal is produced from the lookup table in response to the phase accumulator values. To change a period of the pulse output signal without changing edge positions a programmable modulo value is used. An address mapper is situated between the accumulator and address lines of the lookup table to map the rising and falling edge portions of the phase accumulator values into large regions of the lookup table, while phase accumulator values corresponding to high and low logic levels are mapped into small regions of the lookup table. The resulting pulse output signal has easily independently controlled period and pulse width as well as rising and falling edge speeds.

Abstract: A triggered DDS generator architecture accumulates a phase increment value in response to a DDS clock to generate phase accumulator values for addressing a waveform lookup table which contains a desired output signal. A time measurement circuit determines a time interval between the arrival of a trigger signal and a subsequent cycle of the DDS clock, which time interval is used to either adjust an initial phase accumulator value or delay the DDS clock so that a constant time is maintained between the arrival of the trigger signal and the desired output signal.

Abstract: A system, apparatus and method for performing differential return loss measurements and other measurements as a function of frequency uses a digital storage oscilloscope (DSO) having spectral analysis functions. A waveform generator generates a differential test signal in the form of a series of pulses where each pulse includes spectral components associated with each of a plurality of frequencies of interest. A test fixture presents the differential test waveform to a load including at least one of a device under test (DUT), a short circuit, an open circuit and a balanced load. A signal acquisition device differentially measures the test waveform during each of the load conditions. The signal acquisition device computes an error correction parameter using measurements made during the short circuit, open circuit and balanced load conditions. The correction parameter tends to offset signal acquisition errors within measurements made during the DUT load condition.

Abstract: A security block for securing I/O ports of an electronic instrument physically prevents any breach of data through a protected I/O port, such as a USB port, by securing cables that may be plugged into the port by means of a locked cover. The cables are prevented from being removed and USB memory devices are prevented from being connected in their place. In a second aspect, a portion of the security block covers unused I/O ports thereby preventing USB memory devices and other devices from being connected to unoccupied I/O ports. The locking mechanism can be either a padlock, or a locking screw, or the like.

Abstract: A test and measurement instrument such as a Logic Analyzer, or the like, has at least one Reloadable Word Recognizer whose reference value can be loaded by a trigger machine with a current acquired data sample while data is being acquired. In a second embodiment useful for performing memory testing, the reloadable word recognizer is used in cooperation with two conventional word recognizers. In a third embodiment, a delay unit is employed to provide delayed input data words as reference words. In a fourth embodiment, an offset register and adder are used to modify the input data words before storing them. A fifth embodiment provides for substantially immediate use of base addresses of relocatable subroutines and stack-based variables recovered from a data stream acquired from a system under test.

Abstract: Image alias rejection when converting a high resolution rasterized waveform to a lower resolution rasterized waveform for display uses a statistical filter. The statistical filter provides a shaped probability density function either by combining the outputs of multiple random number generators, such as linear feedback shift registers, or by using a corresponding look-up table to produce a dither signal. The statistical filter may be applied to one or both of the dimensional values for each data point of the high resolution rasterized waveform by combining the dimensional values with the dither signal. The resulting filtered dimensional values may then be subsampled, such as by truncation, to produce values for a lower resolution rasterized waveform display.

Abstract: A wide bandwidth attenuator input circuit for a measurement probe has a Z0 attenuator circuit coupled in series with a compensated RC attenuator circuit. The series attenuator elements of the Z0 and the compensated RC attenuator circuits are coupled via a controlled impedance transmission line to the shunt attenuator elements of the Z0 and the compensated RC attenuator circuits. The shunt element of the Z0 attenuator element terminates the transmission line in its characteristic impedance. The junction of the series and shunt attenuator elements are coupled to the input of a buffer amplifier. At low and intermediate frequencies, the compensated RC attenuator circuit attenuates an input signal while at high frequencies, the compensated RC attenuator circuit acts as a short and the Z0 attenuator circuits attenuates the input signal.

Abstract: An acquisition apparatus for a test and measurement instrument includes an input to receive an input signal, a digitizer to digitize a selected signal, a bypass path to selectively couple the input to the digitizer, a frequency shift path to frequency shift the input signal and selectively couple the frequency-shifted input signal to the digitizer, the frequency shift path including a means for frequency shifting, an input switch to switch the input signal to one of the bypass path and the frequency shift path, and an output switch to provide the selected signal to the digitizer by selectively coupling an output of one of the frequency shift path and the bypass path to the digitizer.

Abstract: A method and apparatus for decomposing timing jitter on arbitrary serial data sequences. Specifically, in one embodiment according to the present invention, a method is provided of decomposing timing jitter on a signal under test (SUT) comprising an arbitrary serial data stream. The method comprises performing a statistical analysis on a group of measurements, where each measurement comprises a timing jitter value and an associated bit pattern representing the bits falling within an analysis window, said window being successively located at a plurality of positions within the data stream.