NESTED AMMETER

Abstract

A nested ammeter for measuring the electrical current flowing through a device under test (DUT) can include an input configured to receive an input signal having a frequency within a frequency band and representing the electrical current flowing through the DUT. The nested ammeter can also include an output configured to generate an output voltage representing the electrical current flowing through the DUT. An active shunt can be used as the resistive feedback of the ammeter. A nested active shunt can be used as the resistive feedback element of the active shunt.

Claims

1. An ammeter for measuring current flowing through a device under test (DUT), the nested ammeter comprising: an input configured to receive an input signal having a frequency within a frequency band and representing the current flowing through the DUT; an output configured to generate an output voltage representing the current flowing through the DUT; a first operational amplifier (op-amp) electrically coupled between the input and the output; and a first active shunt electrically coupled with the first op-amp and used as a resistive feedback element for the ammeter.

2. The ammeter of claim 1, wherein the first active shunt includes a second op-amp.

3. The ammeter of claim 1, further comprising a capacitor electrically coupled in parallel with the first active shunt.

4. The ammeter of claim 2, wherein the first active shunt includes a second active shunt electrically coupled with the second op-amp and used as a resistive feedback element for the first active shunt.

5. The ammeter of claim 4, wherein the second active shunt includes a third op-amp.

6. The ammeter of claim 4, further comprising a capacitor electrically coupled in parallel with the second active shunt.

7. The ammeter of claim 5, wherein the second active shunt includes a third active shunt electrically coupled with the third op-amp and used as a resistive feedback element for the second active shunt.

8. The ammeter of claim 7, wherein the third active shunt includes a fourth op-amp.

9. The ammeter of claim 7, further comprising a capacitor electrically coupled in parallel with the third active shunt.

10. The ammeter of claim 4, wherein the first active shunt and second active shunt share a common power supply.

11. An ammeter for measuring current flowing through a device under test (DUT), the nested ammeter comprising: an input configured to receive an input signal having a frequency within a frequency band and representing the current flowing through the DUT; an output configured to generate an output voltage representing the current flowing through the DUT; a first operational amplifier (op-amp) electrically between the input and the output; an active shunt electrically coupled with the first op-amp and used as a resistive feedback element for the ammeter; and n nested active shunts within the active shunt, wherein each nested active shunt being one order higher than an other nested active shunt is used as a resistive feedback element for the other nested active shunt.

12. The ammeter of claim 11, further comprising a first capacitor electrically coupled in parallel with the first active shunt.

13. The ammeter of claim 12, further comprising n capacitors, each capacitor being used as a resistive feedback element for a corresponding nested active shunt.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 illustrates an example of a feedback ammeter configured with a high gain op-amp to pull the input circuit through a resistor R.sub.S.

[0014] FIG. 2A illustrates an example of an active shunt ammeter design using a controlled negative gain across a parallel RC feedback element.

[0015] FIG. 2B is a graph showing the gain B(s) of the fixed gain amplifier of the active shunt ammeter illustrated by FIG. 2A.

[0016] FIG. 3 illustrates an example of a feedback ammeter design in which an active shunt is used as the resistive feedback element in accordance with certain embodiments of the disclosed technology.

[0017] FIG. 4 illustrates an example of a nested ammeter with an active shunt using a second active shunt as its resistive feedback element in accordance with certain embodiments of the disclosed technology.

[0018] FIG. 5 illustrates an example of a nested ammeter using three active shunts where the 1.sup.st active shunt is in the feedback of the 2.sup.nd active shunt which is in the feedback of the 3.sup.rd active shunt in accordance with certain embodiments of the disclosed technology.

[0019] FIG. 6 illustrates an example of a nested ammeter in which an active shunt is the resistive element of another active shunt where both active shunts share a power supply in accordance with certain embodiments of the disclosed technology.

DETAILED DESCRIPTION

[0020] Embodiments of the disclosed technology generally pertain to electrical measurement equipment and, more particularly, to a nested ammeter suitable for use in measuring electrical current.

[0021] FIG. 3 illustrates an example of a feedback ammeter design 300 in which an active shunt 302 is used as the resistive feedback element in accordance with certain embodiments of the disclosed technology. This configuration generally results in a more stable behavior for the same value sense resistor.

[0022] FIG. 4 illustrates a first example of a nested ammeter configuration 400 in accordance with certain embodiments of the disclosed technology. In the example, an active shunt 404 can use another active shunt 402 as its feedback resistance. This results in an ammeter (i.e., a current-to-voltage converter) having a reduced input resistance. That is, the current sense resistor is reduced by the gains of both active shunt loops 402, 404. For example, if each active shunt has a loop gain of 100, the current sense resistor, R.sub.s, appears to the input as R.sub.s/(100×100). The result is a very low input impedance ammeter that is stable with virtually any size capacitive load. Thus, in the example, Z.sub.in=R.sub.S/(100×100).

[0023] Such configurations can be taken even further with the implementation of additional levels of nesting. For example, FIG. 5 illustrates a second example of a nested ammeter configuration 500 in accordance with certain embodiments of the disclosed technology in which an active shunt 502 is nested within another active shunt 504 that is nested in yet another active shunt 506. One having ordinary skill in the art will appreciate that such nesting of active shunts can be taken to virtually any order. If each active shunt has a gain of ×100 and Rs is the actual resistor in the feedback of active shunt #1, then Z.sub.in=R.sub.s/(100×100×100).

[0024] FIG. 6 illustrates an example of a nested ammeter 600 in which an active shunt 602 is the resistive element of another active shunt 604 where both active shunts 602, 604 share a power supply in accordance with certain embodiments of the disclosed technology. In the example, Z.sub.in=R.sub.in=R.sub.s/k.sub.1k.sub.2, where k.sub.1 and k.sub.2 are the gain of the active shunts.

[0025] Having described and illustrated the principles of the invention with reference to illustrated embodiments, it will be recognized that the illustrated embodiments may be modified in arrangement and detail without departing from such principles, and may be combined in any desired manner. And although the foregoing discussion has focused on particular embodiments, other configurations are contemplated.

[0026] In particular, even though expressions such as “according to an embodiment of the invention” or the like are used herein, these phrases are meant to generally reference embodiment possibilities, and are not intended to limit the invention to particular embodiment configurations. As used herein, these terms may reference the same or different embodiments that are combinable into other embodiments.

[0027] Consequently, in view of the wide variety of permutations to the embodiments that are described herein, this detailed description and accompanying material is intended to be illustrative only, and should not be taken as limiting the scope of the invention. What is claimed as the invention, therefore, is all such modifications as may come within the scope and spirit of the following claims and equivalents thereto.