Split-path linear isolation circuit apparatus and method
First Claim
1. A split-path amplifier apparatus for amplifying a wideband input signal voltage to provide a wideband output signal voltage that accurately represents the wideband input signal voltage, comprising:
- a high path amplifier that amplifies the wideband input signal voltage and couples a low-frequency to high-frequency portion thereof to a signal combiner;
a low path amplifier that amplifies the wideband input signal voltage and couples a DC to low-frequency portion thereof to the signal combiner; and
the signal combiner having a transformer with a primary winding and first and second secondary windings that receives the DC to low-frequency portion and the low-frequency to high-frequency portion of the amplified input signal voltage with the first and second secondary windings co-acting with the primary winding to produce a substantially zero net magnetic flux in the transformer over the DC to high-frequency range of the wideband output signal voltage, the frequency portions being substantially overlapped in a crossover frequency region such that the signal combiner produces the wideband output signal voltage having a substantially flat amplitude response without requiring frequency response adjustments in the crossover frequency region.
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Accused Products
Abstract
A split-path isolation amplifier (10) employs a transformer (30) in a high path (26) and a single-input, dual-output closed-loop optocoupler (66) in a low path (24) to achieve a flat, wide frequency response without need for frequency compensation adjustments. In a low path frequency region (106), the optocoupler provides all or most of the signal to the output. The isolation amplifier employs a substantially overlapped crossover frequency region (104) in which the high path signal is applied to a primary winding (28) of the transformer, and the low path signal is applied differentially to secondary windings (40, 42) of the transformer. At frequencies below the crossover frequency range, the signal from the optocoupler dominates as the signal coupled from the primary winding rolls off. At frequencies above the crossover frequency range, the signal coupled from the primary winding dominates as the signal from the optocoupler rolls off. At frequencies within the crossover frequency range magnetic flux components generated by the primary and secondary transformer windings co-act to provide a combined output signal having a flat frequency response. The only adjustments are those required to match the gain of the low path to the gain of the high path and to compensate for any offset in the low path.
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Citations
33 Claims
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1. A split-path amplifier apparatus for amplifying a wideband input signal voltage to provide a wideband output signal voltage that accurately represents the wideband input signal voltage, comprising:
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a high path amplifier that amplifies the wideband input signal voltage and couples a low-frequency to high-frequency portion thereof to a signal combiner; a low path amplifier that amplifies the wideband input signal voltage and couples a DC to low-frequency portion thereof to the signal combiner; and the signal combiner having a transformer with a primary winding and first and second secondary windings that receives the DC to low-frequency portion and the low-frequency to high-frequency portion of the amplified input signal voltage with the first and second secondary windings co-acting with the primary winding to produce a substantially zero net magnetic flux in the transformer over the DC to high-frequency range of the wideband output signal voltage, the frequency portions being substantially overlapped in a crossover frequency region such that the signal combiner produces the wideband output signal voltage having a substantially flat amplitude response without requiring frequency response adjustments in the crossover frequency region. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A split-path isolation apparatus for receiving a wideband input signal voltage referenced to a first ground and accurately amplifying the input signal voltage to provide a wideband output signal voltage referenced to a second ground that is isolated from the first ground by an isolation barrier, comprising:
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a high path amplifier that amplifies the wideband input signal voltage and couples a low-frequency to high-frequency portion thereof through a transformer having a primary winding and first and second secondary windings that forms a first portion of the isolation barrier; a low path amplifier that amplifies the wideband input signal voltage and couples a DC to low-frequency portion thereof through a single-input, multi-output optocoupler, a first output of which forms a linearity controlling feedback path around the low path amplifier and a second output of which forms a second portion of the isolation barrier; and a signal combiner including the transformer that receives the DC to low-frequency portion and the low-frequency to high-frequency portion of the amplified input signal voltage that is coupled across the isolation barrier with the first and second secondary windings co-acting with the primary winding to produce a substantially zero net magnetic flux in the transformer over the DC to high-frequency range of the wideband output signal voltage, the frequency portions being substantially overlapped in a crossover frequency region such that the signal combiner produces the wideband output signal voltage having a substantially flat amplitude response without requiring frequency response adjustments in the crossover frequency region. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A method for accurately amplifying a wideband input signal voltage referenced to a first ground to provide a wideband output signal voltage referenced to a second ground that is isolated from the first ground by an isolation barrier, comprising:
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splitting the wideband input signal voltage into a low path signal having a first 3-db rolloff frequency and a high path signal having a second 3-db rolloff frequency, the first and second rolloff frequencies being substantially overlapped in a crossover frequency region; coupling the high path signal across the isolation barrier with a transformer having a primary winding and first and second secondary windings; coupling the low path signal across the isolation barrier with a first output of a single-input, multi-output optocoupler; closing a feedback loop of an amplifier in the low path with a second output of the optocoupler; and combining the low path signal and high path signal coupled across the isolation barrier via the transformer to generate the wideband output signal voltage having a substantially flat amplitude response without requiring frequency response adjusting steps in the crossover frequency region with the first and second secondary windings co-acting with the primary winding to produce a substantially zero net magnetic flux in the transformer over the DC to high-frequency range of the wideband output signal voltage. - View Dependent Claims (24, 25, 26)
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27. In an oscilloscope having a chassis ground, an improved apparatus for accurately displaying an amplitude response versus time of a first input signal that is referenced to a first isolated ground, comprising:
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a first isolation barrier that separates the first isolated ground from the chassis ground; a first split-path isolation amplifier receiving the first input signal and including a high path amplifier employing a transformer having a primary winding and first and second secondary windings to couple a high-frequency portion of the first input signal across the first isolation barrier, and a low path amplifier that employs a single-input, multi-output optocoupler to couple a DC portion of the first input signal across the first isolation barrier; a first signal combiner including the transformer combining the DC and high-frequency portions of the first input signal coupled across the first isolation barrier to produce a first wideband output signal that is referenced to the chassis ground and that accurately represents the first input signal with the first and second secondary windings co-acting with the primary winding to produce a substantially zero net magnetic flux in the transformer over the DC to high-frequency range of the wideband output signal voltage; and a display subsystem electrically connected to the first wideband output signal for rendering an amplitude response versus time display of the first input signal. - View Dependent Claims (28, 29, 30, 31, 32, 33)
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Specification