Patent Description:
Ideally, a test and measurement system would have the bandwidth and large input dynamic range that would allow users to measure signals with wide voltage swings and then be able to zoom in on the finer details of that signal to look at the small voltage components of that signal that are in the 1mVs - 100mVs range. A good use case of this is trying to measure the dynamic ON resistance of a switching device (such as a diode, a FET, an IGBT, and so on). Trying to look at the voltage Vds(on) and the switching/conduction losses associated with the Vds(on) state after it has come out of and going into the Vds(off) state (i.e., high voltage) has been an ongoing challenge and a key measurement for users, especially as users need to achieve higher efficiencies and understanding of the losses in their systems (such as SMPS, Inverters, Motor drives, and so on).

Thus, a needs remains to introduce a break-through measurement solution to address these measurement challenges.

<CIT> concerns a probe for a measurement instrument comprising an input terminal configured to receive an input signal from a device under test, an output terminal configured to transmit an output signal to a measurement instrument, and a clamping circuit disposed in a signal path between the input terminal and the output terminal and configured to clamp an internal probe signal between an upper clamping threshold and a lower clamping threshold to produce the output signal, wherein the clamping circuit operates with substantial gain and amplitude linearity throughout a range between the upper clamping threshold and the lower clamping threshold.

In the drawings, which are not necessarily to scale, like or corresponding elements of the disclosed systems and methods are denoted by the same reference numerals.

The invention is defined by the electrical test and measurement system according to claim <NUM> and the method for an electrical test and measurement instrument according to claim <NUM>. Further aspects are defined by the corresponding dependent claims.

<FIG> illustrates an example of a test and measurement system <NUM> that uses a probe <NUM> or other accessory. Initially, a signal may be measured from a device under test (DUT) <NUM> by the probe <NUM>. The measurement from the probe <NUM> may then be sent to a controller <NUM> or oscilloscope <NUM>, e.g., through a communication link <NUM>. The controller <NUM> may be connected to a test instrument such as an oscilloscope <NUM> in order to display the measurement on a display (not shown) of the oscilloscope <NUM>.

It should be noted that certain alternative implementations of the test and measurement system <NUM> may not include the controller <NUM>. In such implementations, the probe <NUM> may be electrically coupled directly with the oscilloscope <NUM>.

Probe and accessory outputs, especially power probes, have strived to achieve a fast over-drive recovery when the probe/accessory's input exceeds its input limits, trying to recover in tens of nanoseconds (ns). While a given probe or accessory can usually recover within tens of nanoseconds, the oscilloscope input generally takes several times that, e.g., tens of microseconds (µsec) in some cases, to recover. So, the probe or accessory tends to recover after its input limits have been exceeded but the oscilloscope input may lag due to the slower over-drive recovery of the oscilloscope input. A typical power probe or accessory output may swing between +/- 1V to +/- 10V on the output of the probe or accessory during these measurements, which may exceed the input level of the oscilloscope's front end when the oscilloscope's vertical input sensitivity is increased.

In certain implementations, a probe or accessory dynamically limits/clamps its output voltage swing in order to prevent the oscilloscope's front end from saturating/clipping, thereby maintaining its ability to zoom in and see the finer details of a large signal. This can be accomplished by a variety of clamping/limiting schemes incorporated somewhere in the probe/accessory's signal path that can be adjusted based on the desired output clamping levels required. These clamping/limiting circuits advantageously clamp/limit the peak voltage of the output waveform to a specific/defined voltage envelope that will generally not exceed the linear input range of the oscilloscope, thus preventing the oscilloscope input from being overdriven. These clamping/limiting upper and lower threshold levels can be made to track each other or be controlled independently of each other.

Implementations of the disclosed technology may include a probe or accessory having a user selectable output clamping/limiting feature that, when enabled, may serve to limit the output voltage swing of the measurement system into the oscilloscope's input and thus allow the user to increase the vertical sensitivity on the oscilloscope without it being overdriven/saturated. While this may generally be a user selectable function, it may be incorporated into the overall measurement system in alternative embodiments such that it would be dynamically controlled by the oscilloscope, e.g., as the user changes the oscilloscope input sensitivity, offset, etc. This may serve to make the feature transparent to the user and also assist the user with avoiding the trap of having to deal with distorted and/or rolled-off waveforms by not understanding that the front end of the oscilloscope may become saturated/over-driven when the user is changing the measurement system settings. The probe or accessory may be configured to never drive the oscilloscope input into a saturation or clipping condition.

<FIG> illustrates an example of a test and measurement system <NUM> in accordance with certain implementations of the disclosed technology.

In the example, a probe <NUM> or other accessory is electrically coupled between a device under test (DUT) <NUM> and an oscilloscope <NUM> or other suitable measurement instrument. The probe <NUM> receives an input signal from the DUT <NUM> and provides an output signal to the oscilloscope <NUM>. The probe <NUM> or accessory includes a clamp/limit control block <NUM> that is configured to control a positive (+) clamp/limit level <NUM> and a negative (-) clamp/limit level <NUM>.

<FIG> illustrates an example of an input signal <NUM> for a test and measurement system in accordance with certain implementations of the disclosed technology such as the test and measurement system <NUM> illustrated by <FIG>.

<FIG> illustrates an example of an output signal <NUM> for a test and measurement system in accordance with certain implementations of the disclosed technology such as the test and measurement system <NUM> illustrated by <FIG>. In the example, the impact by the positive (+) clamp/limit level <NUM> and the negative (-) clamp/limit level <NUM> on the input signal can be readily ascertained by a user of the oscilloscope displaying the signal <NUM>.

The dynamic output clamping scheme, such as that implemented by the system <NUM> of <FIG>, advantageously enables the user of the probe <NUM> or accessory to measure the small level signals by clamping the output voltage that is fed into the input, e.g., front end, of the oscilloscope <NUM> and prevent it from saturating/overdriving the oscilloscope <NUM> input when the user tries to zoom in (e.g., increase vertical sensitivity) and maintain a fast settling time (e.g., over-drive recovery (ODR).

This implementation of output clamping/limiting could be implemented into the front end of the oscilloscope <NUM> to increase its over-drive recovery (ODR) performance which allows the oscilloscope <NUM> to be capable of withstanding large input voltages.

Clamping/gating/limiting the input voltage by the probe <NUM> may advantageously prevent the oscilloscope <NUM> front end from being driven into saturation and, consequently, needing a significant amount of time to recover from it.

Examples provide a probe for use with an electrical test and measurement instrument, comprising an input configured to receive an input signal from a device under test (DUT), a clamp control unit configured to apply at least one clamping/limiting level to the input signal to generate an output signal, and an output port configured to provide the clamped/limited output signal to an oscilloscope.

In some examples, the at least one clamping/limiting level includes a positive clamping/limiting level.

Some examples further comprise a diode implemented with the positive clamping level.

In some examples the at least one clamping/limiting level includes a negative clamping/limiting level.

Some examples further comprise a diode implemented with the negative clamping level.

In some examples the at least one clamping level includes a positive clamping/limiting level and a negative clamping/limiting level.

Some examples further comprise a first diode implemented with the positive clamping level and a second diode implemented with the negative clamping level.

Examples provide an electrical test and measurement system, comprising a device under test (DUT), an oscilloscope, and a probe, the probe including an input configured to receive an input signal from the DUT, a clamp control unit configured to apply at least one clamping/limiting level to the input signal to generate an output signal, and an output port configured to provide the clamped/limited output signal to the oscilloscope.

Some examples further comprise a first diode configured to implement a positive clamping level and a second diode configured to implement a negative clamping level.

Examples provide a method for an electrical test and measurement instrument, the method comprising receiving an input signal from a device under test (DUT), applying at least one clamping/limiting level to the input signal to generate an output signal, and providing the clamped/limited output signal to an oscilloscope.

In some examples the applying includes applying a positive clamping/limiting level to the input signal, and applying a negative clamping/limiting level to the input signal.

Examples provide a method for an electrical test and measurement instrument, the method comprising receiving an input signal from a device under test (DUT), and applying at least one clamping/limiting level at an input of an oscilloscope to prevent an overdrive/saturating condition.

Examples provide an accessory for use with an electrical test and measurement instrument, comprising an input configured to receive an input signal from a device under test (DUT), a clamp control unit configured to apply at least one clamping/limiting level to the input signal to generate an output signal, and an output port configured to provide the clamped/limited output signal to an oscilloscope.

In some examples the at least one clamping/limiting level includes a positive clamping/limiting level.

The term "controller" and "processor" as used herein is intended to include microprocessors, microcomputers, ASICs, and dedicated hardware controllers. One or more aspects of the invention may be embodied in computer-usable data and computer-executable instructions, such as in one or more program modules, executed by one or more computers (including monitoring modules), or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types when executed by a processor in a computer or other device.

The computer executable instructions may be stored on a non-transitory computer readable medium such as a hard disk, optical disk, removable storage media, solid state memory, RAM, etc. As will be appreciated by one of skill in the art, the functionality of the program modules may be combined or distributed as desired in various embodiments. In addition, the functionality may be embodied in whole or in part in firmware or hardware equivalents such as integrated circuits, field programmable gate arrays (FPGA), and the like. Particular data structures may be used to more effectively implement one or more aspects of the invention, and such data structures are contemplated within the scope of computer executable instructions and computer-usable data described herein.

Claim 1:
An electrical test and measurement system (<NUM>), comprising:
a device under test, DUT, (<NUM>);
an oscilloscope; and
a probe (<NUM>) for use with the oscilloscope,
where the probe (<NUM>) comprises:
an input configured to receive an input signal (<NUM>) from the DUT (<NUM>);
a clamp control unit (<NUM>) configured to apply at least one clamping/limiting level to the input signal to generate an output signal (<NUM>), wherein the at least one clamping/limiting level is dynamically controlled by the oscilloscope based on one or more changes to vertical sensitivity on the oscilloscope; and
an output port configured to provide the clamped/limited output signal to the oscilloscope (<NUM>).