National Instruments Corporation

Minnesota Mining and Manufacturing Company

Windrop Weather Devices

Mark Whittington

Zaher G Harb

Raffaele Cetrulo

Mohammadreza Samadiboroujeni

Niels Knudsen

Eric M Mullen

George H More, Iii

John Jeffries

A novel modular probe may include an interchangeable (connectable/disconnectable) probe-tip adaptor having a tip connector for coupling to a device under test, and further having a probe-tip terminal for coupling to a first assembly connector of a cable assembly, which further has a second assembly connector for coupling to a first build-out terminal of a build-out adaptor, which also has a second build-out terminal for coupling to an assembly connector of an interchangeable instrument connector cable assembly, which also has an instrument-end connector for coupling to a measurement instrument. The built-out adaptor may include a compensation adjustment circuit for compensating the probe for varying system capacitances. The probe may include one or more corrective circuits in the interchangeable probe-tip adaptor and/or in the build-out adaptor for at least partially terminating each end of the cable assembly with a characteristic impedance of the cable in the cable assembly to attenuate reflections.

Modular probe for automated test applications

A novel coupling system may include a head-end circuit for coupling a probe via a cable to an instrument, delivering power to the probe over the cable while the cable carries signal(s) from the probe to the instrument. The head-end circuit may include a first terminal for coupling to the probe via a cable, and may further include a second terminal for coupling to the instrument. The head-end circuit may apply direct-current (DC) power to the cable, and may remove a DC voltage offset resulting from the applied DC power before a signal from the probe reaches the instrument. The head-end circuit may include a common node coupled to the first terminal, a current source coupling the common node to a supply voltage, and a voltage source coupling the common node to a second terminal that couples to the instrument.

Active probe powered through driven coax cable

A front-end converter circuit may allow devices, e.g. oscilloscopes and digitizers, to receive input signals having a wide range of possible amplitudes while maintaining a high standardized input impedance. The converter may selectively couple, using low-voltage switches, a selected input network of two or more input networks to a virtual ground node, and a selected feedback network of two or more feedback networks to a transconductance stage input. The selected input network and selected feedback network together define a respective input signal amplitude range. The converter may also controllably adjust an AC gain of the converter to match a DC gain of the converter, and selectively couple non-selected input networks to signal ground. Output referred integrated resistor thermal noise may be reduced to a desired value by lowering the value of the transconductance stage coupled across the input of the converter (through an input resistance) and the virtual ground node.

Solid state wideband high impedance voltage converter

A front-end circuit for measurement devices, for example oscilloscopes or digitizers, may implement DC gain compensation using a programmable variable resistance. A MOS transistor may be configured and operated as a linear resistor with the ability to self-calibrate quickly, while compensating for temperature variations. An integrated CMOS-based variable resistor may be thereby used for an analog adjustable attenuator. Master and slave CMOS transistors may be operated in linear mode, and temperature effects on the linear transistors may be compensated for by using an integral loop controller (current controller) configured around the master MOS transistor. Circuits implemented with the compensated variable resistance have a wide range of adjustment with a control voltage, and may be used in the front-end (circuits) of an oscilloscope or digitizer, or in any other circuit and/or instrumentation benefitting from an adjustable attenuator.

Compensated temperature variable resistor

Various embodiments of an input protection circuitry may be configured with a variable tripping threshold and low parasitic elements, which may prevent a signal from propagating into the protected equipment/device if the voltage of the input signal exceeds a certain limit. The input protection circuit may operate to protect a measurement instrument, which may be an oscilloscope, early in the signal path leading into to the instrument, to avoid exposing sensitive circuitry to damaging voltage levels, and without introducing significant parasitic elements that would degrade the performance of the instrument. The protection circuit may be configured to include clamping to provide protection during the circuit response delay time. The input protection threshold of the protection circuit may be adaptive to a selected voltage range on the instrument without trading-off instrument performance and features.

Input protection method with variable tripping threshold and low parasitic elements

Various embodiments of a self-calibration circuit may solve the problem that arises in high performance oscilloscopes and in particular, RF oscilloscopes, of internally providing a precision calibration signal without degrading the bandwidth, flatness of the frequency response, and input return loss of the oscilloscope. The self-calibration circuit may be configured to implement an impedance transformation technique where active and passive circuit elements with carefully chosen values are configured in an impedance converter. During self-calibration, switching elements comprised in the self-calibration circuit may be toggled to create a servo loop comprising an amplifier within the circuit, with an attenuator and resistive component acting as feedback elements. The circuit may hence become an impedance gyrator and behave as a precision source with an impedance matching the input impedance of the load circuit.

Self-calibration circuit with gyrated output impedance

A system and method for overcoming the parasitic elements associated with off the shelf or general purpose solid-state devices configured to operate as RF AC/DC signal coupling networks. An AC/DC signal coupling network may comprise a general purpose solid-state relay device and two inductors having values carefully chosen to compensate for the imperfections and intrinsic parasitic elements associated with the solid-state relay. The inductors may also have values carefully chosen to compensate for the parasitic elements of the neighboring or coupled circuit, and for the capacitance that is associated with the printed circuit board bond pad that is directly dependent upon the area of the pad and distance to the neighboring conductors. The inductors may cause the input path to become inductive as the signal frequency increases, and also improve the input return loss over the RF input range.

RF AC/DC coupling circuit using general purpose solid-state relay

An attenuator circuit. The attenuator circuit includes a resistive divider coupled to a capacitive network including first and second capacitive dividers. The resistive divider is configured to perform an N:1 attenuation of a signal in a low frequency range. The first and second capacitive dividers are configured to perform an N:1 attenuation in the high frequency range that is a product of the attenuation provided by each (e.g., each performing an M:1 attenuation, where N=M&#xd7;M, with the total attenuation of the capacitive dividers being N:1 where N=M&#xd7;M). A variable capacitance divider is coupled in parallel with the second capacitive divider, and includes first and second variable capacitors that, when adjusted, change the high frequency attenuation of the attenuator circuit to match the value of the high frequency attenuation to that of the low frequency attenuation.

Compensated attenuator circuit and oscilloscope utilizing the same

A protection and voltage monitoring circuit that may provide the functionality of a diode without the typical large voltage drop and power dissipation. The protection and voltage monitoring circuit may include a first MOSFET, a second MOSFET, a first resistor, an input terminal, an output terminal, a diode, a BJT current source, and a voltage monitoring circuit. The BJT current source may limit a gate-to-source voltage of the two MOSFETs to a predetermined voltage that is less than a maximum allowed voltage by controlling a current flow through the first resistor to prevent damage to the MOSFETs. The voltage monitoring circuit may determine whether an external voltage is within an allowable range of voltages. If the external voltage is outside the predetermined voltage range, the voltage monitoring circuit turns off the BJT current source to block the external voltage from the output terminal of the protection and voltage monitoring circuit.

Protection and voltage monitoring circuit

A low power and high efficiency voltage-to-current (V/I) converter designed with few parts and having improved power supply rejection. The V/I converter may include an op-amp, a MOSFET, and a first and second voltage dividers. The first voltage divider circuit may include a first, second, third, and fourth resistors. A source terminal of the MOSFET may be connected to a junction of the third and fourth resistors and the fourth resistor may be connected to a positive supply rail. Also, an inverting input terminal of the op-amp may be coupled to a junction of the second and third resistors. Additionally, the second resistor may be coupled to the first resistor, which may be connected to an input terminal of the V/I converter. The V/I converter typically has very good DC rejection of the power supply because the first and second voltage dividers are designed to have the same ratios.

Low power and high efficiency voltage-to-current converter with improved power supply rejection

A system and method for reducing linearity errors in a delta-sigma converter. The linearity errors in the delta-sigma converter are modeled by generating a set of digital signals representative of an inputted sine wave. The set of digital signals are low-pass filtered and subjected to a fast Fourier transform algorithm to generate a frequency domain representation of the sine wave. Thereafter, a net linearity error spectrum is removed from the frequency domain representation and inverse Fourier transform back into the time domain. The filtered set of digital signals are also sorted into subsets of digital signals where each signal in a subset corresponds to a particular output of a delta-sigma modulator contained within the delta-sigma converter. A fast Fourier transform algorithm is applied to each of the filtered subsets of digital signals to generate a frequency domain representation thereof. Specific linearity errors are generated by applying an inverse Fourier transform algorithm to each of the specific linearity error spectrums in the frequency domain representations of the filtered subsets of digital signals. Thereafter, linearity error correction coefficients are generated as a function of the net linearity error and the specific linearity errors. The linearity error correction coefficients are used to generate entries in a look-up table where the entries are adjustable by digital outputs of the delta-sigma modulator. The look-up table is used to correct digital signals outputted by the delta-sigma modulator prior to decimation and digital filter.

System and method for generating a sigma-delta correction circuit using

A weather monitoring device includes a wind force receiving body supported by a support member and a wind velocity and direction measuring arrangement. The wind velocity and direction measuring arrangement, preferably includes strain gauges mounted upon the support member and measures the magnitude and direction of flex in the support caused by wind acting upon the wind receiving body. Wind direction and velocity are calculated from the flex measured in the support. The velocity and direction measuring arrangement also includes features to compensate for strain gauge offsets and temperature drift. Additionally, a rain monitoring arrangement may be included in the weather monitoring device to provide rain measurements in addition to the wind measurements. The rain monitoring arrangement includes a rain collection surface and a rain volume measuring device. The rain collection surface is completely contained within the wind force receiving body and directs water to the rain volume measuring device. The rain volume measuring device preferably causes droplets having a uniform and known volume to fall upon a piezoelectric transducer and calculates precipitation per unit area from drop signals by the piezoelectric element.

Weather monitoring apparatus and method

A circuit for selecting an input to a signal processing network from among several switchable antenna units. Each antenna unit includes a winding which is connected to a common signal bus. The switchable antenna units may be placed in 'on' or 'off' states in response to a controller, such as a microprocessor. One terminal of each winding is connected to a transistor which causes the terminal to be in an open condition when the unit is unselected, attenuating any signal which might otherwise be transmitted to the signal bus. A second winding is inductively coupled to the first winding and is used to improve attenuation of unselected signals.

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Austin, TX, United States of America

Mark Whittington