Circuit for compensating an offset voltage in an amplifier

Abstract

A circuit for compensating an offset voltage in an amplifier or a DC component in a signal supplied to the amplifier comprises the amplifier and a first voltage source. The amplifier has at least one measurement signal port and at least two contacts for a supply voltage. Each of two contacts is connected to a different terminal of the first voltage source. The potential at each contact is separated from a ground potential and from an external supply potential.

Claims

1. A circuit for compensating an offset voltage in an amplifier or a DC component of a signal supplied to the amplifier, wherein the circuit comprises the amplifier and a first voltage source, wherein the amplifier has at least one measurement signal port and at least two power supply contacts for a supply voltage, wherein a dynamic voltage range at an output port of the amplifier has a potential which corresponds to the offset voltage or to the DC component of a measurement signal supplied to the measurement signal port plus half of voltage provided by the first voltage source, wherein each of the at least two power supply contacts is connected to a different terminal of the first voltage source, wherein each of the at least two power supply contacts is separated from a ground potential, wherein each of the at least two power supply contacts is also separated from any external supply potential, and wherein a potential at each of the at least two power supply contacts floats.

2. The circuit according to claim 1, wherein an amplified measurement signal is positioned at a mean in the dynamic voltage range at the output port of the amplifier.

3. The circuit according to claim 1, wherein the potential at each of the at least two power supply contacts is galvanically separated from a ground potential or from every external supply potential.

4. The circuit according to claim 1, wherein a contact of the at least two power supply contacts of the amplifier having a lower potential is additionally connected to a first terminal of a second voltage source, wherein a second terminal of the second voltage source is connected to the ground potential.

5. The circuit according to claim 4, wherein the second voltage source provides a voltage equivalent to the offset voltage or the DC component of the measurement signal supplied to the measurement signal port.

6. The circuit according to claim 1, wherein a contact of the at least two power supply contacts of the amplifier having a higher potential is additionally connected to a first terminal of a second voltage source, wherein a second terminal of the second voltage source is connected to the ground potential.

7. The circuit according to claim 6, wherein the second voltage source provides a sum of the offset voltage or of the DC component of the measurement signal supplied to the measurement port and of the voltage provided by the first voltage source.

8. The circuit according to claim 1, wherein the first voltage source is a battery.

9. The circuit according to claim 1, wherein the first voltage source is a voltage provided by AC voltage source via a transformer and a succeeding rectifying circuit.

10. An oscilloscope having at least one input port, whereby each input port is a measurement signal port in a circuit according to claim 1.

11. A probe having a tip, which is connected to a measurement signal port of a circuit according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the invention is described on the basis of the drawings which present advantageous exemplary embodiments of the invention by way of example only. The drawings show:

(2) FIG. 1 a circuit diagram with a circuit for compensating an offset voltage in an amplifier and/or a DC component in a signal supplied to the amplifier according to the state of the art,

(3) FIG. 2A a circuit diagram with a first variant of a first embodiment of an inventive circuit for compensating an offset voltage in an amplifier and/or a DC component in a signal supplied to the amplifier,

(4) FIG. 2B a circuit diagram with a second variant of a first embodiment of an inventive circuit for compensating an offset voltage in an amplifier and/or a DC component in a signal supplied to the amplifier,

(5) FIG. 3 a circuit diagram with a second embodiment of an inventive circuit for compensating an offset voltage in an amplifier and/or a DC component in a signal supplied to the amplifier and

(6) FIG. 4 a circuit diagram with a third embodiment of an inventive circuit for compensating an offset voltage in an amplifier and/or a DC component in a signal supplied to the amplifier.

DETAILED DESCRIPTION OF THE DRAWING

(7) In the following the embodiments of the invention and additional inventive variants are described in detail with reference to FIGS. 2A, 2B, 3 and 4.

(8) In the first variant of the first embodiment of the inventive circuit for compensating an offset voltage in an amplifier and/or a DC component in a signal supplied to the amplifier shown in FIG. 2A and in the other inventive variants and inventive embodiments shown in FIGS. 2B, 3 and 4 a single input port amplifier 1 for amplifying a common-mode measurement signal V.sub.in at the input of the inventive circuit is used. Alternatively, a differential amplifier for amplifying a common-mode measurement signal V.sub.in or a differential measurement signal can also be used and is thus within the scope of the invention.

(9) The common-mode measurement signal V.sub.in is referenced to a ground potential which represents the common ground potential. The voltage level of the measurement signal V.sub.in is provided through in a frequency dependent voltage divider comprising a parallel circuit of a resistor R.sub.1 and a capacitor C.sub.1 in series to a parallel circuit of a resistor R.sub.2 and a capacitor C.sub.2. The measurement signal is fed to an input port 9 of the amplifier 1. After amplification of the attenuated measurement signal a signal V.sub.out is generated at the output port 10 of the amplifier 1.

(10) The total dynamic voltage range of the output signal V.sub.out of the amplifier 1 is dependent on the voltage supplied between the contacts for a supply voltage 11 and 13 of amplifier 1. Each contact for a supply voltage 11 and 13 in the amplifier 1 is connected to a different terminal 12 and 14 of a first voltage source 15 generating a DC voltage V.sub.F. The total dynamic voltage range at the output 10 of the amplifier 1 depends on this voltage V.sub.F.

(11) The first voltage source 15 in the first variant of the first embodiment is realized as a battery. Both terminals 12 and 14 of the battery and consequently both contacts for a supply voltage 11 and 13 of the amplifier 1 are not referenced to the common ground potential and also not to an external supply potential and are thus float.

(12) Consequently, the amplified measurement signal V.sub.out is positioned in the mean of the dynamic voltage range at the output 10 of the amplifier 1, i.e. in the optimal operating point in the center of the linear range of the amplifier. The AC component of the amplified measurement signal is now completely within the total dynamic voltage range at the output 10 of the amplifier 1. Thus, a DC component of the measurement signal and an internal offset voltage of the amplifier 1 are no more present in the amplified measurement signal. This means that the amplified measurement signal is cleared from the DC component of the measurement signal and from an internal offset voltage of the amplifier 1.

(13) In a second variant of the first embodiment of the invention shown in FIG. 2B the two contacts 11 and 13 for a supply voltage are connected to corresponding contacts 17 and 18 of capacitor 16. The voltage across the capacitor 16, which defines the total dynamic voltage range at the output 10 of the amplifier 1, is provided by an AC voltage V.sub.F between the two input ports 19 and 20 of a transformer 21. The transformed AC voltage V.sub.F at the output ports 22 and 23 of the transformer 21 are fed via a succeeding rectifier circuit 24 being a Graetz circuit comprising four rectifying diodes D.sub.1, D.sub.2, D.sub.3 and D.sub.4 for rectifying the transformed AC voltage to a corresponding DC voltage V.sub.F to the both contacts 17 and 18 of the capacitor 16.

(14) The voltage across the capacitor 16 does not have any reference to the common ground potential and to an external supply potential, because secondary side of the transformer 21 is not referenced to any reference potential.

(15) Equivalently to the first inventive variant in FIG. 2A, both contacts for a supply voltage 11 and 13 of the amplifier 1 in the second inventive variant in FIG. 2B are not referenced to the common ground potential and also not to an external supply potential and are thus float. Consequently, the amplified measurement signal V.sub.out is positioned in the mean of the dynamic voltage range at the output 10 of the amplifier 1, i.e. in the optimal operating point in the center of the linear range of the amplifier. The signal at the output 10 of the amplifier 1 contains only the AC component of the amplified measurement signal. Thus the amplified measurement signal is cleared from the DC component of the measurement signal and from an internal offset voltage of the amplifier 1.

(16) In the second embodiment of the invention shown in FIG. 3 the contact for a supply voltage 13 having a lower potential is additionally connected to the first terminal 25 of a second voltage source 26, whereas the second terminal 27 of the second voltage source 26 is connected to the common ground potential. The second voltage source 26 represents a voltage source with adjustable voltage level for compensating the DC component of the measurement signal and the internal offset voltage in the amplifier 1 at the output 10 of the amplifier 1. Consequently, the voltage level to be adjusted at the second voltage source 26 corresponds to the DC component of the measurement signal and to the internal offset voltage in the amplifier 1.

(17) Consequently, the mean of the dynamic voltage range at the output 10 of the amplifier 1 corresponds to the sum of the DC component of the measurement signal and the internal offset voltage in the amplifier 1 plus half of the voltage generated by the first voltage source 15. The total dynamic voltage range at the output 10 of the amplifier 1 covers only the AC component of the amplified measurement signal. Thus the amplified measurement signal is cleared from the DC component of the measurement signal and from an internal offset voltage in the amplifier 1.

(18) In the third embodiment of the invention shown in FIG. 4 the contact for a supply voltage 11 having a higher potential is additionally connected to the first terminal 28 of a second voltage source 26, whereas the second terminal 29 of the second voltage source 26 is connected to the common ground potential. The second voltage source 26 also represents a voltage source with adjustable voltage level for compensating the DC component of the measurement signal and the internal offset voltage in the amplifier 1 at the output 10 of the amplifier 1.

(19) Consequently, the voltage level to be adjusted at the second voltage source 26 corresponds to sum of the voltage V.sub.F provided by the first voltage source 15 plus the DC component of the measurement signal and the internal offset voltage in the amplifier 1.

(20) Consequently, the mean of the dynamic voltage range at the output 10 of the amplifier 1 corresponds to the sum of the DC component of the measurement signal and the internal offset voltage in the amplifier 1 plus half of the voltage generated by the first voltage source 15. In other words the mean of the dynamic voltage range is the voltage generated by the second voltage source 26 minus half of the voltage generated by the first voltage source 15. The total dynamic voltage range at the output 10 of the amplifier 1 covers only the AC component of the amplified measurement signal. Thus the amplified measurement signal is cleared from the DC component of the measurement signal and from an internal offset voltage in the amplifier 1.

(21) The invention is not restricted to the exemplary embodiments and exemplary variants. Advantageously, all the features described above or features shown in the figures of the drawing or features claimed in all the claims can be combined with one another arbitrarily within the scope of the invention.

(22) While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Numerous changes to the disclosed embodiments can be made in accordance with the disclosure herein without departing from the spirit or scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above described embodiments. Rather, the scope of the invention should be defined in accordance with the following claims and their equivalents.

(23) Although the invention has been illustrated and described with respect to one or more implementations, equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application.