Oscilloscope probe having output clamping circuit

Patent metadata

Field	Value
Publication number	US-9423422-B2
Application number	US-201313869774-A
Country	US
Kind code	B2
Filing date	Apr 24, 2013
Priority date	Apr 24, 2013
Publication date	Aug 23, 2016
Grant date	Aug 23, 2016

Abstract

A probe for a measurement instrument comprises an input terminal configured to receive an input signal from a device under test (DUT), 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.

First claim

The invention claimed is:

1. A probe for a measurement instrument, comprising:
an input terminal configured to receive an input signal from a device under test (DUT);
an output terminal configured to transmit an output signal to a measurement instrument; and
a clamping circuit comprising: a first precision rectifier configured to clamp a positive voltage portion of the internal probe signal to produce a first intermediate signal;
a first level shifter configured to adjust a direct current (DC) bias of the first intermediate signal to produce a second intermediate signal; a second precision rectifier configured to clamp a negative voltage portion of the internal probe signal to produce a third intermediate signal; and a second level shifter configured to adjust a DC bias of the third intermediate signal to produce the analog output signal, the clamping circuit being 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, the upper clamping threshold corresponding to a positive voltage level and the lower clamping threshold corresponds to a negative voltage level, wherein the clamping circuit operates with substantial gain and amplitude linearity throughout a range between the upper clamping threshold and the lower clamping threshold.

2. The probe of claim 1 , wherein the measurement instrument is an oscilloscope.

3. The probe of claim 1 , wherein each of the first precision rectifier, the first level shifter, the second precision rectifier, and the second level shifter comprises an operational amplifier arranged in an inverting configuration.

4. The probe of claim 1 , wherein the first precision rectifier performs clamping on the positive voltage portion by adjusting a DC bias of the internal probe signal, inverting the internal probe signal, and clamping a negative voltage portion of the adjusted and inverted internal probe signal.

5. The probe of claim 1 , further comprising:
an additional output terminal configured to transmit an additional output signal to the measurement instrument;
a first probe amplifier disposed in the signal path between the input terminal and the output terminal and located between the input terminal and the clamping circuit; and
a second probe amplifier disposed in an additional signal path between the input terminal and the additional output terminal.

6. The probe of claim 5 , wherein the first probe amplifier has a first gain and a first bandwidth, and the second probe amplifier has a second gain lower than the first gain and a second bandwidth higher than the first bandwidth.

7. The probe of claim 5 , wherein the first and second probe amplifiers are configured to amplify a voltage corresponding to a current through the DUT.

8. A measurement system, comprising:
a measurement instrument comprising an overdrive protection circuit having respective upper and lower overdrive protection thresholds; and
a measurement probe comprising an input terminal configured to receive an input signal from a device under test (DUT), an output terminal configured to transmit an output signal to the measurement instrument, and a clamping circuit comprising: a first precision rectifier configured to clamp a positive voltage portion of the internal probe signal to produce a first intermediate signal; a first level shifter configured to adjust a direct current (DC) bias of the first intermediate signal to produce a second intermediate signal; a second precision rectifier configured to clamp a negative voltage portion of the internal probe signal to produce a third intermediate signal; and a second level shifter configured to adjust a DC bias of the third intermediate signal to produce the analog output signal, the clamping circuit being 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, the upper clamping threshold corresponding to a positive voltage level and the lower clamping threshold corresponds to a negative voltage level, wherein the upper overdrive protection threshold is greater than or equal to the upper clamping threshold and the lower overdrive protection threshold is less than or equal to the lower clamping threshold.

9. The measurement system of claim 8 , wherein the clamping circuit operates with substantial gain and amplitude linearity throughout a range between the upper clamping threshold and the lower clamping threshold.

10. The measurement system of claim 8 , wherein the measurement instrument is an oscilloscope and the measurement probe is an oscilloscope probe.

11. The measurement system of claim 8 , wherein the measurement instrument comprises first and second channels configured to receive respective first and second input signals from the measurement probe, wherein the first channel receives an input signal through the signal path, and the second channel receives an input signal through an additional signal path of the measurement probe.

12. The measurement system of claim 11 , wherein the measurement probe further comprises a first probe amplifier disposed in the signal path and located between the input terminal and the clamping circuit, and a second probe amplifier disposed in the additional signal path between the input terminal and the additional output terminal.

13. The measurement system of claim 8 , wherein the overdrive protection circuit is configured to prevent overdriving of an input amplifier of the measurement instrument.

14. The measurement system of claim 12 , wherein the first probe amplifier has a first gain and a first bandwidth, and the second probe amplifier has a second gain lower than the first gain and a second bandwidth higher than the first bandwidth.

15. The measurement system of claim 8 , wherein the first precision rectifier performs clamping on the positive voltage portion by adjusting a DC bias of the internal probe signal, inverting the internal probe signal, and clamping a negative voltage portion of the adjusted and inverted internal probe signal.

16. The measurement system of claim 8 , wherein each of the first precision rectifier, the first level shifter, the second precision rectifier, and the second level shifter comprises an operational amplifier arranged in an inverting configuration.

17. The measurement system of claim 8 , further comprising:
an additional output terminal configured to transmit an additional output signal to the measurement instrument;
a first probe amplifier disposed in the signal path between the input terminal and the output terminal and located between the input terminal and the clamping circuit; and
a second probe amplifier disposed in an additional signal path between the input terminal and the additional output terminal.

18. A method of operating a measurement probe, comprising:
receiving an input signal from a device under test (DUT);
processing the input signal to produce an output signal; and
transmitting the output signal to a measurement instrument,
wherein processing the input signal comprises clamping the input signal between an upper clamping threshold and a lower clamping threshold to produce the output signal by operating a clamping circuit having substantial gain and amplitude linearity throughout a range between the upper clamping threshold and the lower clamping threshold, the clamping comprising: inverting the i

Assignees

• Keysight Technologies Inc

Inventors

• Brush Iv Edward Vernon
• Mctigue Michael T
• Johnson Kenneth W

Classifications

• G01R1/20

  Modifications of basic electric elements for use in electric measuring instruments; Structural combinations of such elements with such instruments · CPC title

• G01R1/06766 Primary

  Input circuits therefor · CPC title

• G01R1/06788

  Hand-held or hand-manipulated probes, e.g. for oscilloscopes or for portable test instruments (end pieces terminating in a probe H01R11/18) · CPC title

• H03K5/08

  by limiting; by thresholding; by slicing, i.e. combined limiting and thresholding (H03K5/07 takes precedence; comparing one pulse with another H03K5/22; providing a determined threshold for switching H03K17/30) · CPC title