Coded data generation or conversion – Analog to or from digital conversion – Nonlinear
Reexamination Certificate
1999-09-28
2001-06-26
JeanPierre, Peguy (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Nonlinear
C381S106000, C381S107000
Reexamination Certificate
active
06252529
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to circuitry for conditioning alternating current waveforms to produce amplified and rectified waveforms. In particular, the invention relates to a technique for receiving AC waveforms of a fairly large dynamic range, rectifying the waveform, and amplifying the waveform by one of a plurality of discrete gain levels in a closed loop feedback configuration for obtaining waveforms suitable for input into downstream circuitry, such as an analog-to-digital converter.
2. Description of the Related Art
A variety of applications exist for signal processing of alternating current waveforms wherein the input waveform must be rectified and amplified for application to downstream circuitry. For example, in a current sensing relay, current sensors may be applied to one or more current-carrying conductors for outputting signals which are indicative of a level of current flow. Depending upon the type of downstream processing, the signal may need to be rectified and digitized, particularly where downstream circuitry includes digital signal processing circuitry such as microprocessors, digital signal processors, and the like. In such arrangements, circuitry must not only rectify the input signal, but may need to amplify the input signal to make best use of the dynamic range of an analog-to-digital converter. The amplification becomes somewhat more complex in applications where the dynamic range of the input signal itself may vary widely.
In applications including analog-to-digital converters and input signals comprising AC waveforms of a broad dynamic range, difficulties may be encountered in the scaling of the rectified waveform to make best use of the dynamic range of the analog-to-digital converter, while avoiding excessive amplification of noise. For example, where an input signal to such circuitry is an AC waveformn, a very low amplitude may result in output data from the analog-to-digital converter which is of little utility due to a lack of sufficient amplification. On the contrary, where an input signal has a dynamic range which may change substantially during operation, a fixed amplification level may cause the analog-to-digital converter output to saturate when the amplitude of the input signal increases substantially as compared to its normal amplitude levels, or at least to the amplitude levels at which the amplification gain was appropriate.
In monitoring and control equipment, such as microprocessor-based overload relays, very substantial dynamic ranges may be encountered in input levels of AC waveforms, such as from current sensors. To perform analysis of the input signals, however, the signals must be rectified and digitized. Accommodation of the large variations in the amplitude of the input signal requires a novel approach to both the rectification and the amplification of the signal prior to application of the output to the analog-to-digital converter.
In general, analog-to-digital converters may not sample negative portions of an input signal, such devices generally operating between an input range of 0 to 5 volts. Thus, precision full wave rectifiers are typically needed to provide an absolute value function, affording proper operation of the analog-to-digital converter. Traditional full wave rectifiers have been employed for this purpose, including a pair of cascaded amplifiers to produce the absolute value function. However, such devices often produce intolerable levels of error due to the amplification of the first stage amplifiers error by the second amplifier, and addition of this amplified error to the error of the second amplifier itself. Moreover, conventional precision full wave rectifiers may offer gain, but do not offer adjustable gain. Such adjustability in gain levels would be highly desirable to increase the dynamic range of the system, but such adjustability is difficult to synthesize in a non-cascaded amplifier approach.
There is a need, therefore, for a technique capable of rectifying and amplifying AC waveforms of varying amplitude. For practical applications, the technique should be relatively easy to implement and cost effective to manufacture. Moreover, there is a particular need for a technique which provides discrete levels of amplification based upon the level of an output waveform applied to downstream circuitry, such as an analog-to-digital converter. In circuits including a digital signal processor, a microprocessor or a similar programmable device, it would be particularly convenient to provide some degree of feedback control of the amplification level based upon detected and fed-back characteristics of the output waveform.
SUMMARY OF THE INVENTION
The present invention provides a technique for rectifying and amplifying an input waveform designed to respond to these needs. The technique may be implemented in a variety of devices, but is particularly well suited to devices in which an input waveform has a substantial dynamic range, requires rectification, and must be amplified to optimize a dynamic range of downstream circuitry. The technique makes use of inverting and noninverting amplifier circuits, such that rectification is performed by inverting negative polarity lobes of an input waveform, while passing positive polarity lobes without inversion. Amplification is performed by both the inverting and the non-inverting circuits. The gain of each of the amplifying circuits may be selected among a plurality of discrete gains as defined by a switchable resistance circuit associated with each amplifier. In a preferred configuration, solid state switches are employed for selecting the appropriate gain level.
Where a microprocessor or other programmable digital signal processing circuitry is employed in the device, the discrete gain may be selected by detecting the amplitude of the waveform, or of a digitized signal downstream of the amplifiers. The output signal amplitude, or the output of an analog-to-digital converter receiving the rectified and amplified signal is fed back to the microprocessor, which then generates command signals for placing the selector switches in conductive states appropriate for selecting the desired gain. Various schemes may be employed for selecting the appropriate gain. In a presently preferred configuration, for example, the circuitry may assume and lowest gain level, monitor output, and increase gain until the output reaches a level that does not saturate the downstream circuitry, particularly an analog-to-digital converter. The input signal is thus rectified, and amplified to make optimal use of the dynamic range of the downstream circuitry.
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Bolda Daniel J.
Haensgen Steven T.
Gerasimow A. M.
Horn John J.
Jean-Pierre Peguy
Jeanglaude Jean Bruner
Rockwell Technologies LLC
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