High frequency, high output impedance amplifier for EMI active filter applications
AssigneeSchaffner EMV AG
InventorsAlessandro Amaducci, Enrico Mazzola
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Abstract
A high-frequency amplifier for an active EMI filter with a symmetric class B emitter-follower output stage driven by a driver stage, with a sense output resistor. Both terminals of the sense resistor are brought to the noninverting, respecting inverting input of the driver stage through two dividers of the same ratio, in a global voltage feedback loop. The amplifier is configured to provide a high output impedance at 10 kHz and up to 100 MHz, a peak-to-peak output current of 2-10 ampere and a low quiescent current of less than 400 mA. The invention includes EMI filters with such a high-frequency current source, for example in the current-sense current-inject feedback configuration.
Claims12
A high-frequency amplifier for an active EMI filter comprising a symmetric emitter-follower output stage for providing an output current with two bipolar transistors in a symmetric complementary pair configuration, an input stage driving the output stage, a sense resistor through which the output current flows, a voltage feedback loop for feeding back a voltage measured across the sense resistor to the input stage, wherein the high-frequency amplifier comprises a voltage reference defining a potential difference between bases of the bipolar transistors, wherein the voltage reference has a negative temperature coefficient.
An active EMI filter comprising a sense unit configured to sense a noise signal circulating in a power line from a noise source to a load, a high-frequency amplifier comprising a symmetric emitter-follower output stage for providing an output current with two bipolar transistors in a symmetric complementary pair configuration, an input stage driving the output stage, a sense resistor through which the output current flows, a voltage feedback loop for feeding back a voltage measured across the sense resistor to the input stage, the high-frequency amplifier is driven by the noise signal generating an output current, and a current-inject unit injecting the output current into the power line, wherein the sense unit is a current transformer coupling to a noise current on the power line.
Dependencies are inferred from the claim text.