OSCILLOSCOPE PROBE

• US 20100176795A1
• Filed: 07/16/2007
• Published: 07/15/2010
• Est. Priority Date: 08/14/2006
• Status: Active Grant

• Current Assignee: Rohde & Schwarz GmbH & Company KG
• Original Assignee: Rohde & Schwarz GmbH & Company KG
• Inventors: Schild, Alexander, Peschke, Martin
• Granted Patent: US 8,791,689 B2
• Time in Patent Office: Days
• US Class Current: 324/121.R
• CPC Class Codes: G01R 1/06 Measuring leads; Measuring probes G01R19/145, G01R19/165 take precedence
• CPC Class Codes: G01R 1/067 Measuring probes
• CPC Class Codes: G01R 1/06766 Input circuits therefor
• CPC Class Codes: G01R 1/30 Structural combination of electric measuring instruments with basic electronic circuits, e.g. with amplifier
• CPC Class Codes: G01R 13/20 Cathode-ray oscilloscopes
• CPC Class Codes: G01R 13/22 Circuits therefor
• CPC Class Codes: G01R 13/34 Circuits for representing a single waveform by sampling, e.g. for very high frequencies

Abstract

Disclosed is a probe for an oscilloscope comprising a multi-stage transistor amplifier that acts as an impedance transformer. Said amplifier is a d.c.-coupled emitter follower circuit that is composed of bipolar transistors or a d.c.-coupled source follower circuit which is composed of field effect transistors and the successive amplifier elements of which are dimensioned and tuned to each other in such a way that the resulting offset direct voltage between the input and the output is minimal.

Claims

1. Probe for an oscilloscope with a multi-stage transistor amplifier acting as an impedance converter, of which the output is connected to the oscilloscope,

characterized in that

the amplifier is a DC-coupled emitter-follower circuit constructed from bipolar transistors or a DC-coupled source-follower circuit constructed from field-effect transistors or a circuit composed of both of these circuits, of which the successive amplifier elements are dimensioned and matched to one another in such a manner that the resulting offset direct voltage between the input and the output is minimal.

2. Probe according to claim 1,

characterized in that

the transistors of the emitter-follower- and respectively source-follower-circuits are mixed with intermediate diodes and/or resistors connected in such a manner that the offset direct voltage is minimal.

3. Probe according to claim 1,

characterized in that

the amplifier is an emitter-follower circuit constructed from several bipolar transistors, and the successive transistors are selected from a mixture of the npn and respectively pnp conductor type in such a manner that the sum of the successive base-emitter voltages is minimal.

4. Probe according to claim 1,

characterized in that

the amplifier is a self-conducting source-follower circuit consisting of several field-effect transistors, of which the source currents are selected in such a manner that the gate-source voltages of the individual transistors and therefore also their sum is approximately 0 volts.

5. Probe according to claim 1,

characterized in that

the DC-coupled amplifier consists of a mixture of bipolar transistors and field-effect transistors and optionally diodes and/or resistors, which are dimensioned and matched to one another in such a manner that the sum of the successive base-emitter voltages, gate-source voltages and optionally rectified voltages of the diodes and voltages of the resistors is approximately 0 volts.

6. Probe according to claim 1,

characterized in that

a circuit connected to the input and output of the amplifier for measuring the offset and for generating a compensation value corresponding to the latter is allocated to the DC-coupled amplifier, with which compensation value the offset is compensated directly in the amplifier by means of a compensation circuit allocated to the amplifier.

7. Probe according to claim 6, characterized in that

the offset is measured by means of an operational amplifier comparing the input voltage and output voltage of the amplifier.

8. Probe according to claim 6,

characterized in that

the compensation value is supplied directly to the output of the amplifier as a compensation voltage for the compensation of the offset.

9. Probe according to claim 6,

characterized in that

the compensation value is supplied to the bias-current of one of the successive amplification elements of the amplifier as a compensation current for the compensation of the offset.

10. Probe according to claim 1,

characterized in that

a circuit connected to the input and output of the amplifier for measuring the offset and for generating a compensation value corresponding to the latter is allocated to the DC-coupled amplifier, which compensation value is provided via an additional conductor to the oscilloscope for the compensation of the offset in the oscilloscope.

11. Probe according to claim 10,

characterized in that

the offset is measured by means of an operational amplifier comparing the input and output voltage of the amplifier.

12. Probe according to claim 10,

characterized in that

the measured offset voltage is provided to the oscilloscope in digital form and taken into consideration accordingly in the evaluation of the measured voltage in the oscilloscope.

13. Probe according to claim 1,

characterized in that

a switching device capable of being controlled remotely or operated manually via the oscilloscope is allocated to the input of the DC-coupled amplifier, by means of which an earth potential can be connected to the amplifier input instead of the measured voltage of the probe tip, and accordingly, with the amplifier input connected to earth, the direct-voltage offset is measured in the oscilloscope and taken into consideration accordingly in the evaluation of the measured voltage in the oscilloscope.

14. Probe according to claim 1,

characterized in that

an input-voltage divider is connected upstream of the DC-coupled amplifier.

15. Probe according to claim 5,

characterized in that

the DC-coupled amplifier consists of a MOSFET transistor of the p-channel type followed by two bipolar npn transistors operated in an emitter-follower circuit.

16. Probe according to claim 15,

characterized in that

the adjustment of the gate-source voltage of the MOSFET transistor is implemented to match the base-emitter voltages of the npn transistors via a p-channel MOSFET transistor, of which the gate-source voltage is specified by two npn-base-emitter paths.