Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By amplitude
Reexamination Certificate
2002-10-07
2004-05-25
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By amplitude
C327S307000, C327S531000
Reexamination Certificate
active
06741103
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device which uses a detection circuit to determine whether an output current thereof is source-induced or load-induced, and the method therefor, and more particularly, to a device which performs some type of operation based upon the determination as to whether the output current thereof is source-induced or load-induced, and method therefor. Such a device may have many applications, including use in systems where distinctions between source and load-induced currents are employed in feedback systems to control the system voltage source, systems where the system voltage source is not controlled, but other sources are controlled to influence a summation of voltages and currents at sensing locations, and systems for measurement instrumentation.
2. Description of the Related Art
An electronically programmable output impedance circuit is described in U.S. Pat. No. 5,708,379, issued Jan. 13, 1998 to Yosinski. The electronically programmable output impedance circuit therein is employed in a very specific manner in an AC source/analyzer product family, but has broader application.
The AC source/analyzer product family includes models which are DC-coupled and which also employ a novel feedback circuit, an output impedance circuit, which is described in U.S. Pat. No. 5,708,379 issued to Yosinski, which causes the source part of the product to exhibit a controlled non-zero output impedance. The output impedance may be set to be resistive or inductive. It may also be set to a complex value that is equivalent to series-connective resistive and inductive components. The magnitudes of the resistive and inductive components are programmable. For realizations in the AC source/analyzer products, the resistive component may be set to values between zero and one ohm, and the inductive component to values between 20 uH and 1 mH. Different ranges are possible subject to constraints imposed by necessity of maintaining stability in feedback loops.
DC-coupled members of the AC source/analyzer product family also employ another feedback circuit, a DC offset elimination circuit used as a DC servo control loop that may be enabled to eliminate unwanted DC offset voltages at the product's output.
As will be shown below, the output impedance circuit and the DC offset elimination circuit, when active simultaneously, interact in an undesired manner that compromises the functionality and performance of the output impedance circuit at low frequencies including DC.
Practical applications for DC-coupled laboratory grade AC sources require simultaneous operation of both the output impedance circuit and the DC offset elimination circuit mentioned above. When AC sources are used to simulate AC power systems, it is desirable to have both resistive and inductive source impedances, since real systems exhibit a finite source impedance which includes both components. The magnitudes of the impedance components vary widely in real systems, making programmability highly desirable.
Aside from the effects of source impedance, actual AC power systems appear as nearly ideal sources for loads of the size that may powered by all but the very largest laboratory grade AC sources. To the extent that the source acts ideally, it will be capable of supplying any amount of current at any frequency. For this reason, it is essential for the output impedance circuit to work properly at very low frequencies including DC. Loads with varying current consumption, for example, may exhibit “beat-frequency” effects that produce AC power system currents at low frequencies and/or DC. Adjustable speed drives (ASDs) are a commonly encountered example of such loads. Another common example is a half-wave rectified load which draws DC current from an AC power system.
Aside from the desired property of correctly simulating effects of source impedance and DC load current, it is otherwise essential to have as little DC voltage present at the output of laboratory grade sources as possible since equipment with line-connected power transformers may exhibit very little tolerance for DC voltage. DC levels of just a few millivolts can cause power transformers in the supplied equipment to saturate.
On the other hand, it is undesirable for the source to actually be AC-coupled using, for example, an output transformer since practically-sized output transformers exhibit properties that preclude proper simulation of many events with DC content that occur in AC power systems. Examples include partial cycle dropouts, non-symmetrical voltage waveforms, etc.
To assist in an understanding of the present invention, it is helpful to understand the operation of the output impedance and DC offset elimination circuits. In the discussion that follows, operation of the circuits is considered independently and then in combination. Highly simplified circuits imported from a circuit simulator and scaled to nominal values will be used to develop an understanding of the essential concept of the present invention.
FIG. 1A
shows a very basic voltage source
100
which includes an inverting power amplifier
102
. A DC voltage source
104
is shown to represent an accumulated effect of undesired offset voltage sources encountered in practical devices. For the sake of simplicity, the overall gain to the output of the basic voltage source
100
is set to −1. A current sensing element, or shunt, identified as
106
, is coupled to 1000× differential gain block
108
(hereinafter referred to as “differential gain block”) to provide a voltage output proportional to output current. Actual implementations may use differential amplifiers, but otherwise, the function and value for the current sensing element
106
and associated differential gain block
108
are as might be encountered in practice.
Feedback is provided through an operational amplifier
110
which is configured as a unity gain follower. The voltage at the output side of the current sensing element
106
is connected to the positive terminal of the operational amplifier
110
. The feedback sensing point is selected to cause voltage drops across the current sensing element
106
to be inside of the feedback loop, so that the voltage at the right hand, or output, side of current sensing element
106
is regulated by the action of the feedback. A resistor
114
is connected between the output terminal of the operational amplifier
110
and the negative terminal of the inverting amplifier
102
. A resistor
116
is connected between the DC voltage source
104
and the negative terminal of the differential amplifier
102
. A circuit comprising power amplifier
102
, operational amplifier
110
, and associated input and feedback resistors
114
,
116
, and current sensing element
106
are thus configured to function as an ideal voltage source. As an example, current sensing element
106
, and resistors
114
and
116
have the values 0.001 ohm, 10 k ohm and 10 k ohm, respectively.
Typically, another differential amplifier would be used in a voltage feedback signal path, but for purposes of this example, it is useful to include the operational amplifier (configured as a unity gain follower)
110
as shown since it is functionally transparent except for its action to prevent current flowing in the feedback resistor
114
from becoming part of the total current sensed by the current sensing element
106
. Thus, only the load current is shown in meter
122
. One volt displayed in meter
122
corresponds to one ampere of load current. All of the meters
120
,
122
,
124
shown in
FIG. 1A
are DC sensing.
A one-ampere current sink
118
is connected to the output node of the voltage source
100
in FIG.
1
A. The resulting current flow develops a voltage across current sensing element
106
which is amplified by the associated differential gain block
108
and displayed as 1 volt in meter
122
. As would be expected with an ideal voltage source, the load current produces a negligible voltage drop at the voltage source output as shown by
Agilent Technologie,s Inc.
Cunningham Terry D.
Nguyen Long
LandOfFree
Device using a detection circuit to determine whether an... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Device using a detection circuit to determine whether an..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Device using a detection circuit to determine whether an... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3217890