High frequency, high output impedance amplifier for EMI active filter applications
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.
1. 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.
2. The high-frequency amplifier of claim 1 , wherein the voltage feedback loop is configured for feeding back potentials at both ends of the sense resistor to an inverting input and a noninverting input of the input stage, respectively.
3. The high-frequency amplifier of claim 1 , wherein the voltage reference is a Vbe multiplier.
4. The high-frequency amplifier of claim 1 , wherein the voltage reference is configured for operation in class B or AB, and a quiescent current of the high-frequency amplifier is less than 400 mA.
5. The high-frequency amplifier of claim 1 , having a unipolar power supply.
6. The high-frequency amplifier of claim 1 , having an output dynamic range between 1 A peak-to-peak and 10 A peak-to-peak a bandwidth of at least 10 MHz, or a bandwidth in the interval 10 kHz-100 MHz, and an output impedance of at least 1000 Ohm at 100 kHz.
7. The high-frequency amplifier of claim 1 , having a temperature operating range extending at least between −40° C. and 125° C.
8. 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.
9. The active EMI filter of claim 8 , comprising a sense unit configured to sense a noise signal circulating in a power line from a noise source to a load, control the high-frequency current source according to the noise signal, inject the high-frequency output current of the high-frequency current source into the power line through a current-inject unit.
10. The active EMI filter of claim 9 , wherein the noise signal is common-mode.
11. Use of the active EMI filter of claim 8 on a power bus of an electric or hybrid vehicle.
12. 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, the high-frequency amplifier of claim 1 , driven by the noise signal generating an output current, and a current-inject unit injecting the output current into the power line.