Patent ID: 12249910

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The drawings as referred to throughout the description of the present invention are for illustration only, to show the interrelations between the circuits and the signal waveforms, but not drawn according to actual scale of circuit sizes and signal amplitudes and frequencies.

FIG.2shows a schematic diagram of a preferred embodiment of the switching power converter of the present invention. The switching power converter102comprises a power stage circuit10and an AEF circuit30. The power stage circuit10includes at least one transistor which is configured to operably switch an inductor L to convert an input power to an output power. The AEF (Active EMI Filter) circuit30is configured to sense a noise input signal Vnoise which is related to a switching noise caused by the switching of the power stage circuit10(for example when switching the switch QH or QL), and amplify the noise input signal Vnoise to generate a noise cancelling signal I_inj. In one embodiment, the noise cancelling signal I_inj is injected into an input node NII of the switching power converter102, so as to suppress the switching noise and thus reducing EMI. In this embodiment, the input power is provided through the input node to the power stage circuit.

In one embodiment, the input power for example can be provided by a battery90. The input power includes input voltage Vin and input current Iin. In one embodiment, the output power includes output voltage Vout and provides an output current Iout to a load.

In one embodiment, the power stage10includes a high side switch QH and a low side switch QL which are configured to switch the inductor Lx by control signals HG and LG. In this embodiment, the power stage10is a buck converter. However, the present invention can also be applied in other types of switching converters such as boost, buck-boost, flyback converters, and etc.

Note that a line impedance stabilization network (LISN)50is coupled between the input power and an input node NII where the input power is provided through to the power stage10. The LISN and the analyzer are utilized for measuring the level of the switching noise caused by the power stage circuit10and the EMI suppression efficacy achieved by the AEF circuit30. Note that the LISN can be removed and the input power can be directly connected to the input node NII during actual applications in one embodiment.

More specifically, in one embodiment, the AEF circuit30includes at least one amplifier, wherein the at least one amplifier is configured to operably sense the noise input signal Vnoise and amplify the noise input signal Vnoise to generate the noise cancelling signal I_inj.

Still referring toFIG.2, in this embodiment, the switching power converter102further comprises a sensing resistor Rs. A first terminal of the sensing resistor Rs is coupled to the input node NII, and a second terminal of the sensing resistor is coupled to the power stage circuit10. The noise input signal Vnoise is generated according to a voltage across the sensing resistor Rs.

Still referring toFIG.2, in one embodiment, the AEF circuit30includes an amplifier310, which is configured as a differential amplifier stage collaborating the passive components shown inFIG.2. More specifically, an inverting input terminal of the amplifier310is coupled to the second terminal of the sensing resistor Rs through an input capacitor CS1, and a non-inverting input terminal of the amplifier310is coupled to the first terminal of the sensing resistor Rs through an input capacitor CS2, such that an AC (alternating current) component of the noise input signal Vnoise are differentially coupled from the sensing resistor Rs. In one embodiment, the AEF circuit30further includes an input resistor Ri1and an input resistor Ri2which are coupled in series with the input capacitor CS1and the input capacitor CS2respectively.

Still referring toFIG.2, in one embodiment, the noise cancelling signal I_inj is generated from an output terminal of the amplifier310. In one embodiment, the noise cancelling signal I_inj is coupled to the first terminal of the sensing resistor Rs through an injection capacitor CINJ, such that an AC component of the noise cancelling signal I_inj is injected into the input node NII of the switching power converter102. In one embodiment, the at least one amplifier is arranged to make the phase of the noise cancelling signal I_inj is inverse to the phase of the noise input signal Vnoise.

Note that, in this embodiment, the DC component of the noise input signal Vnoise is blocked by the input capacitors CS1and CS2and the DC component of the output signal of the amplifier310is blocked by the injection capacitor CINJ. In one embodiment, a feedback capacitor CFB1and a feedback resistor are coupled in parallel between the output terminal and the inverting terminal for feedback configuration, and a feedback capacitor CFB2and a feedback resistor are coupled in parallel from the non-inverting terminal to a DC reference voltage Vref.

FIG.3shows frequency response diagrams of FFT (Fast Fourier Transform) measured by the analyzer coupled from the LISN50of the prior art as shown inFIG.1and of the switching power converter102. Note that from the baseband to all the higher harmonics show improvements in the switching power converter102which includes the AEF circuit for suppressing the switching noise.

FIG.4shows a schematic diagram of a preferred embodiment of the switching power converter of the present invention. The switching power converter104inFIG.4is similar to the power converter102inFIG.2. In this embodiment, the switching power converter102includes amplifiers320and330. The amplifier320is configured as a differential amplifier stage. An inverting input terminal of the amplifier320is coupled to the first terminal of the sensing resistor Rs through an input resistor Ri1and an input capacitor CS1which are coupled in parallel, and a non-inverting input terminal of the amplifier320is coupled to the second terminal of the sensing resistor Rs through an input resistor Ri2and an input capacitor CS2which are coupled in parallel, such that an AC component of and a DC component of the noise input signal Vnoise are differentially coupled from the sensing resistor Rs. In one embodiment, a feedback resistor Rfb1is coupled between the output terminal and the inverting terminal of the amplifier320for feedback configuration, and a feedback resistor Rfb2is coupled from the non-inverting terminal to a DC reference voltage Vref. In one embodiment, the resistance of Rfb1is the same as Rfb2, and the resistance of Ri1is the same as Ri2.

From one perspective, the input capacitors CS1and CS2of the switching power converter102can be considered as feedforward capacitors, which prevents division of AC component by the resistor network. In other words, an AC coupling ratio is higher than a DC coupling ratio for coupling the noise input signal Vnoise to the inverting terminal and the non-inverting terminal of the amplifier320.

Still referring toFIG.4, the amplifier330is configured as an single-ended inverting amplifier. An inverting input terminal of the amplifier330is coupled to the output terminal of the amplifier320through the DC blocking capacitor Cdc. A non-inverting terminal of the amplifier330is coupled to the DC reference voltage Vref. The noise cancelling signal I_inj is generated from an output terminal of the amplifier330. The noise cancelling signal I_inj is coupled to the first terminal of the sensing resistor Rs through an injection capacitor CINJ, such that an AC component of the noise cancelling signal I_inj is injected into the input node NII of the switching power converter104. A feedback resistor Rfb3is coupled between the output terminal and the inverting terminal of the amplifier330for feedback control. Note that, in one embodiment, the amplifiers (e.g. amplifiers310,320and330) can be single supplied amplifiers, the same hereinafter.

Still referring toFIG.2andFIG.4, each of the switching power converters102and104further comprises a passive filter circuit80′. In one embodiment, the passive filter circuit80′ is coupled between the sensing resistor Rs and the power stage circuit10. The passive filter circuit80′ includes a filtering inductor Lf′, a damping capacitor Cd′ and a damping resistor Rd′ for further filtering the noise input signal Vnoise. Note that due to the EMI reducing efficacy provided by the AEF circuit, the inductance of the filtering inductor Lf′ and the capacitance of the damping capacitor Cd′ which are required in the passive filter circuit80′ can be greatly reduced compared to the prior art, and the filtering capacitor shown inFIG.1can be omitted and the cost can be saved according to the present invention. Also note that an input capacitor CIN can be arranged to be coupled to the joint node between the passive filter circuit80′ and the power stage circuit10.

FIG.5shows frequency response diagrams of FFT (Fast Fourier Transform) measured by the analyzer coupled from the LISN50of the prior art as shown inFIG.1and of the switching power converter104. Note that from the baseband to all the higher harmonics show improvements in the switching power converter104which includes the AEF circuit for suppressing the switching noise.

FIG.6shows a schematic diagram of a preferred embodiment of the switching power converter of the present invention. In one embodiment, noise input signal Vnoise is related to a switching node NLx of the power stage.

The switching power converter106further comprises a snubber circuit40. The snubber circuit40includes a snubber capacitor Csnub and a snubber resistor Rsnub which are coupled in series from the switching node NLx. The switching node NLx is coupled to one terminal of the inductor L.

In this embodiment, the amplifier340of the AEF circuit32is configured as a non-inverting amplifier stage. A non-inverting input terminal of the amplifier340is coupled to the switching node NLx through the snubber circuit40. An input capacitor CS1is coupled to a joint node Nsn where the snubber capacitor Csn and the snubber resistor Rsn is connected. The noise cancelling signal I_inj is generated from an output terminal of the amplifier340. The noise cancelling signal I_inj is coupled to the input node NII through an injection capacitor CINJ. More specifically, an AC component of the noise cancelling signal I_inj is injected into the input node NII of the switching power converter106.

Still referring toFIG.6, the switching power converter106further comprises a passive filter circuit80′. In one embodiment, the passive filter circuit80′ is coupled between the input node NII and the power stage circuit10.

FIG.7shows frequency response diagrams of FFT (Fast Fourier Transform) measured by the analyzer coupled from the LISN50of the prior art as shown inFIG.1and of the switching power converter106. Note that from the baseband to all the higher harmonics show improvements in the switching power converter106which includes the AEF circuit for suppressing the switching noise.

FIG.8shows a schematic diagram of a preferred embodiment of the switching power converter of the present invention.FIG.10shows a schematic diagram of a preferred embodiment of the switching power converter of the present invention.FIG.12Bshows a schematic diagram of a preferred embodiment of the switching power converter of the present invention. In these embodiments, the power stage circuit10of each of the switching power converters108,110and112includes a high side transistor QH and a low side transistor QL which are coupled to the switching node NLx for switching one terminal of the inductor L. In these particular embodiments, the power stage circuit10is configured as a buck converter. In this embodiment, the noise input signal is related to a drain-source current IdsH of the high side transistor QH, and/or a drain-source current IdsL of the low side transistor QL.

Referring toFIG.8, the AEF circuit33includes an amplifier340which is configured as a non-inverting amplifier stage. A non-inverting input terminal of the amplifier340is coupled to a sensing device for sensing the drain-source current of the high side transistor QH through an input capacitor CS1such that an AC component of the noise input signal Vnoise is coupled from the sensing device through the input capacitor CS1. In one embodiment, the sensing device can be for example a current mirror for mirroring a portion of the drain-source current IdsH and a resistor Rs1for converting the mirrored current to a sensed voltage related to the noise input signal Vnoise. In one embodiment, the sensing device can be for example a sensing resistor coupled in series with the high side transistor QH. An inverting input terminal of the amplifier340is coupled to a ground node through a DC blocking capacitor Cdc1.

Still referring toFIG.8, the noise cancelling signal I_inj is generated from an output terminal of the amplifier340. The noise cancelling signal I_inj is coupled to the input node NII through an injection capacitor CINJ. More specifically, an AC component of the noise cancelling signal I_inj is injected into the input node NII of the switching power converter108.

FIG.9shows frequency response diagrams of FFT (Fast Fourier Transform) measured by the analyzer coupled from the LISN50of the prior art as shown inFIG.1and of the switching power converter108. Note that from the baseband to all the higher harmonics show improvements in the switching power converter108which includes the AEF circuit for suppressing the switching noise.

Referring toFIG.10, the AEF circuit34includes an amplifier350which is configured as an inverting amplifier stage. An inverting input terminal of the amplifier350is coupled to a sensing device for sensing the drain-source current IdsL of the low side transistor QL through a second input capacitor CS2such that an AC component of the noise input signal Vnoise is coupled from the sensing device through the second input capacitor CS2. In one embodiment, the sensing device can be for example a current mirror for mirroring a portion of the drain-source current IdsL and a resistor Rs2for converting the mirrored current to a sensed voltage related to the noise input signal Vnoise. In one embodiment, the sensing device can be for example a sensing resistor coupled in series with the low side transistor QL. A non-inverting input terminal of the amplifier350is coupled to a DC reference voltage Vref.

Still referring toFIG.10, the noise cancelling signal I_inj is generated from an output terminal of the amplifier350. The noise cancelling signal I_inj is coupled to the input node NII through an injection capacitor CINJ. More specifically, an AC component of the noise cancelling signal I_inj is injected into the input node NII of the switching power converter110.

FIG.11shows frequency response diagrams of FFT (Fast Fourier Transform) measured by the analyzer coupled from the LISN50of the prior art as shown inFIG.1and of the switching power converter110. Note that from the baseband to all the higher harmonics show improvements in the switching power converter110which includes the AEF circuit for suppressing the switching noise.

FIG.12Ashows a schematic diagram of a preferred embodiment of the switching power converter of the present invention. The switching power converter112A is a combination of the switching power converters108and110. In one embodiment, as shown inFIG.12A, the output signals of the amplifiers340and350are summed together and then injected into the input node NII of the switching power converter112A through the injection capacitor CINJ.

FIG.12Bshows a schematic diagram of a more specific embodiment of corresponding toFIG.12A.

Still referring toFIG.12B, the AEF circuit35of the switching power converter112B includes an amplifier360which is configured as a non-inverting adder circuit. A non-inverting input terminal of the amplifier360is coupled to the output terminal of the amplifier340through the DC blocking capacitor Cdc2and is coupled to the output terminal of the amplifier350through the DC blocking capacitor Cdc3such that an AC component of an output signal generated from the output terminal of the amplifier340and an AC component of an output signal generated from the output terminal of the amplifier350are superposed and amplified through the amplifier360. An inverting input terminal of the amplifier360is coupled to a ground node through a DC blocking capacitor Cdc4.

Still referring toFIG.12B, the noise cancelling signal I_inj is generated from an output terminal of the amplifier360. The noise cancelling signal I_inj is coupled to the input node NII through an injection capacitor CINJ. More specifically, an AC component of the noise cancelling signal I_inj is injected into the input node NII of the switching power converter112B.

FIG.13shows operation waveforms corresponding to the embodiment shown inFIG.8,FIG.10andFIG.12B. The first panel shows the switching node voltage VLx on the switching node NLX. The second panel shows the sensed signal VcsH which is related to the inductor current ILx and is sensed according to the drain-source current IdsH of the high side transistor QH. The third panel shows the sensed signal VcsL which is related to the inductor current ILx and is sensed according to the drain-source current IdsL of the low side transistor QL. The fourth panel shows the noise input signal Vnoise. The fifth panel shows the noise cancelling signal I_inj which is obtained by superposing and amplifying the sensed signal VcsH and the sensed signal VcsL, wherein the DC component is blocked by the injection capacitor (e.g. CINJ). The sixth panel shows the compensated signal Vcomp which is a cancellation result of the noise input signal Vnoise canceled by the noise cancelling signal I_inj. The level of the compensated signal Vcomp is much lower compared to the noise input signal Vnoise. Note that the switching frequency of the switching converter according to the present invention is Fsw. Tsw is the cycle period corresponding to the switching frequency Fsw, wherein Fsw=1/Tsw.

FIG.14shows frequency response diagrams of FFT (Fast Fourier Transform) measured by the analyzer coupled from the LISN50of the prior art as shown inFIG.1and of the switching power converter112B. Note that from the baseband to all the higher harmonics e switching power converter112B which includes the AEF circuit for suppressing the switching noise.

FIG.15shows a comparison table of the noise level of the prior art (noted as w/o AEF) and of all the aforementioned embodiments of the switching power converters having various AEF circuits according to the present invention. As shown in FIG.15, great improvements are achieved by all the embodiments according to the present invention compared over the prior art.

The present invention has been described in considerable detail with reference to certain preferred embodiments thereof. It should be understood that the description is for illustrative purpose, not for limiting the broadest scope of the present invention. An embodiment or a claim of the present invention does not need to achieve all the objectives or advantages of the present invention. The title and abstract are provided for assisting searches but not for limiting the scope of the present invention. Those skilled in this art can readily conceive variations and modifications within the spirit of the present invention. For example, to perform an action “according to” a certain signal as described in the context of the present invention is not limited to performing an action strictly according to the signal itself, but can be performing an action according to a converted form or a scaled-up or down form of the signal, i.e., the signal can be processed by a voltage-to-current conversion, a current-to-voltage conversion, and/or a ratio conversion, etc. before an action is performed. It is not limited for each of the embodiments described hereinbefore to be used alone; under the spirit of the present invention, two or more of the embodiments described hereinbefore can be used in combination. For example, two or more of the embodiments can be used together, or, a part of one embodiment can be used to replace a corresponding part of another embodiment. In view of the foregoing, the spirit of the present invention should cover all such and other modifications and variations, which should be interpreted to fall within the scope of the following claims and their equivalents.