Patent Description:
Electromagnetic interference suppression circuits are known and are commonly used for suppressing conducted electromagnetic interference signals present on signal or power lines. These conducted electromagnetic interference signals can be classified into differential mode electromagnetic interference signals, which are conducted on the power supply line and the power return line in opposite directions, and common mode electromagnetic interference signals, which are conducted on the power supply line and the power return line in the same direction.

In theory, an electromagnetic interference suppression circuit is able to generate a suppression signal that can reduce or even eliminate the unwanted electromagnetic interference signal. For the best suppression performance, the generated suppression signal should be a negative of the electromagnetic interference signal (e.g., equal in magnitude and anti-phase) so that the two always completely cancel each other. In practice, however, a substantial or complete cancellation can be difficult to achieve.

<FIG> shows an existing electromagnetic interference suppression circuit <NUM> arranged to suppress differential mode electromagnetic interference signals between a power source <NUM> and an electronic circuit <NUM> (as a load). A shunt capacitor Cx is connected across the power lines, in parallel between the power source <NUM> and the electronic circuit <NUM>. The circuit <NUM> includes a sensing circuit <NUM> connected across the power lines, in parallel between the capacitor Cx and the electronic circuit <NUM>, to sense a conducted electromagnetic interference signal Vn generated by the electronic circuit <NUM>. The circuit <NUM> also includes an amplifier <NUM> that connects with the sensing circuit <NUM>, and a voltage source <NUM> that connects with and controlled by the amplifier <NUM>. The amplifier <NUM> amplifies the signal obtained from the sensing circuit <NUM> and provides a control signal to control the voltage source <NUM> such that the voltage source <NUM> outputs a suppression signal Vn' that counteracts the interference signal Vn to prevent the interference signal Vn from passing into the power source <NUM>. One potential problem with circuit <NUM> is that during operation the sensing circuit <NUM> will pick up not only the electromagnetic interference signals Vn generated by the electronic circuit <NUM> but also the electromagnetic interference signals from the power source <NUM>. The electromagnetic interference signals from the power source <NUM>, detected by the sensing circuit <NUM> and subsequently amplified by the amplifier <NUM>, will inevitably affect or degrade the suppression performance of the circuit <NUM>.

<CIT>) relates to a control circuit for suppressing electromagnetic interference signals. According to the abstract of this document there is provided a control circuit for suppressing electromagnetic interference signal has an input and an output and a variable gain filter circuit with a first gain factor that is variable. The variable gain filter circuit receives a signal indicative of an electromagnetic interference signal and outputs a signal to a controlled signal source, which a second gain factor. The control circuit also has a controller operably connected to the variable gain filter circuit. The controller receives a signal indicative of an output signal at the output of the control circuit and outputs a control signal to the variable gain filter circuit. The control signal is based on the signal indicative of the output signal at the output of the control circuit, and the control signal controls the first gain factor and reduces the electromagnetic interference signal.

<CIT>) relates to a high frequency current reduction device. According to the abstract of this document there is provided a system line for supplying power from an AC power source to a load through a converter and an inverter, in which a noise reduction unit is connected to a single connection line between the AC power source and the converter. In the noise reduction unit, a current transformer detects a noise current flowing through the connection line after converting it to a voltage, and the detected voltage V1 is supplied through a filter device to a voltage amplifier followed by being voltage-amplified and applied to a capacitor. The capacitor is connected to an injection point on the connection line, so that a high-frequency current in the same direction as the noise current is supplied to the converter from the connection line, to thereby reduce a high-frequency noise current at the AC power source side.

<CIT>) relates to an Active Compensation Circuit and System. According to the abstract of this document there is provided a circuit which includes a first compensation stage and at least one other compensation stage, wherein each of the first compensation stage and the at least one other compensation stage includes a sensor configured to provide a sensor signal being representative of a current flowing in one or more phases, a controlled current sink configured to supply a compensation current as a function of the sensor signal and an active amplifier element configured to provide a frequency response of an open circuit voltage amplification and/or is to supply a maximal output current, wherein the frequency response differs from a frequency response of at least one other active amplifier and/or wherein the maximal output current differs from a maximal output current of at least one other active amplifier.

One of the objectives of the invention is to address the above needs, to overcome or substantially ameliorate the above disadvantages or, more generally, to provide an improved or otherwise alternative electromagnetic interference suppression circuit that can effectively reduce or even substantially eliminate conducted differential mode electromagnetic interference signals in a circuit, e.g., generated at an electronic circuit on a load side.

In a first aspect of the invention, there is provided an electromagnetic interference suppression circuit as set out in claim <NUM>.

Various optional feature of the invention are set out in the dependent claims.

Terms of degree such as "about", "substantially", or the like, are used herein to account for the general tolerances and non-ideal characteristics associated with the various circuit components and inevitable signal fluctuation in practice. The expressions "gain factor" or the like is used herein to generally indicate a multiplication factor, which may take any number larger than <NUM>, equal to <NUM>, or smaller than <NUM>.

Other feature, aspects, objectives, and advantages of the invention will become apparent to the skilled person by considering the detailed description and accompanying drawings. For example, any feature(s) described herein in relation to one aspect or embodiment may be combined with any other feature(s) described herein in relation to any other aspect or embodiment as appropriate and applicable, as long as this is covered by the appended claims.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:.

<FIG> shows a control circuit <NUM> for suppressing differential mode electromagnetic interference signals in one embodiment of the invention. The control circuit <NUM> is arranged between the power source <NUM> and the electronic circuit <NUM> (as a load). The power source <NUM> is adapted to power the electronic circuit <NUM>. In one application the control circuit <NUM> can suppress differential mode electromagnetic interference signals generated by the electronic circuit <NUM>.

The control circuit <NUM> includes a shunt circuit and an electromagnetic interference suppression circuit. The shunt circuit is formed by a capacitor C connected between the power source <NUM> and the electronic circuit <NUM>. The electromagnetic interference suppression circuit includes a sensing circuit <NUM> that is connected on a supply power line and is arranged in series between the capacitor Cx and the electronic circuit <NUM>. The sensing circuit <NUM> has a gain factor Ks and includes an input (e.g., input terminals/nodes) on the power line and an output (e.g., output terminals/nodes). The input and output of the sensing circuit <NUM> may be isolated (i.e., the input terminals/nodes are different from the output terminals/nodes), or may not be isolated (i.e., the input terminals/nodes are the same as the output terminals/nodes), as explained in greater detail below. The sensing circuit <NUM> is adapted to detect the electromagnetic interference signal Vn to be suppressed across the capacitor Cx as a result of the noise signal Vno generated by the electronic circuit <NUM> so as to prevent the interference signals from reaching the power source <NUM>. Based on the detection, the sensing circuit <NUM> is adapted to output a signal Vs associated with (e.g., correlated to) the electromagnetic interference signal Vn. In one example, the signal Vs equals to the interference signal Vn times the gain factor Ks of the sensing circuit <NUM>. If the factor Ks is about <NUM>, the signal Vs is substantially the same as the electromagnetic interference signal Vn.

The electromagnetic interference suppression circuit also includes regulator circuit, in the form of an amplifier <NUM>, and a controlled voltage source <NUM>. The amplifier <NUM> has a gain factor Ka, and includes two input terminals connected with the output terminals of the sensing circuit <NUM>, and an output terminal connected with the controlled voltage source. The amplifier <NUM> may take the signal Vs as input, regulate it by a gain factor Ka, and produce an output signal equals to the signal Vs times the gain factor Ka of the amplifier <NUM>. The controlled voltage source is connected the supply power line and is arranged in series between the power source <NUM> and the capacitor Cx. The controlled voltage source <NUM> has a gain factor Kv, and includes an input connected with the output of the amplifier <NUM> and an output connected on the supply power line between the power source <NUM> and the capacitor Cx. The output signal Vn' of the controlled voltage source <NUM> equals to the signal outputted from the amplifier <NUM> times the gain factor Kv of the controlled voltage source <NUM>. In one implementation, the controlled voltage source <NUM> is formed by a transformer, with a primary coil as the input and the secondary coil as the output, and the turns ratio N of the transformer (number of turns of secondary coil divided by number of turns of primary coil of transformer) defining the gain factor Kv. In one example, the signal Vs is substantially the same as the electromagnetic interference signal Vn, and the product of the gain factors Ks, Ka and Kv has a magnitude of about <NUM> and a phase difference of about <NUM> degrees from the electromagnetic interference signal Vn. This prevents the interference signal Vn from propagating into the power source <NUM>. In this embodiment, the electromagnetic interference suppression circuit forms a loop.

In this embodiment, the signals Vn, Vno, Vs, and Vn' are in the form of voltage signals. The sensing circuit <NUM> achieves its function to sense the interference voltage signal Vn based on the Kirchhoff's voltage law. Referring to <FIG>, according to Kirchhoff's voltage law, the sum of the voltage across the input of the sensing circuit <NUM> and the interference voltage signal Vn across capacitor Cx should equal the interference signal Vno appearing across (e.g., generated by) the electronic circuit <NUM>. In one embodiment in which the input and the output of the sensing circuit <NUM> are not isolated, the output voltage signal Vs from the sensing circuit <NUM> is the same as the signal at the input of the sensing circuit <NUM>. In one embodiment in which the input and the output of the sensing circuit <NUM> are isolated, the output voltage signal Vs from the sensing circuit <NUM> equals the signal at the input of the sensing circuit <NUM> times the gain factor of the sensing circuit <NUM>. The arrangement of the electromagnetic interference suppression circuit, in particular the sensing circuit <NUM>, minimizes the influence of the interference signals from the power source <NUM> on the electromagnetic interference suppression performance. The relatively high immunity to the interference signals from the power source <NUM> is due to capacitor Cx providing a low impedance path for the interference signal from the power source <NUM> (which are high frequency signals). Such path has relatively low impedance compared with the impedance of the input of the sensing circuit <NUM> in series with the impedance across the electronic circuit <NUM>. In addition, the interference signals from the power source <NUM> seen by the sensing circuit <NUM> is substantially reduced, as the interference signals appearing at capacitor Cx due to the interference signal from the power source <NUM> are divided based on the ratio of the impedance of sensing circuit <NUM> to the sum of impedance of sensing circuit <NUM> and the input impedance of the electronic circuit <NUM>. This arrangement provides improved electromagnetic interference suppression performance over some existing circuits such that in <FIG>.

<FIG> shows an implementation of the sensing circuit 102A not forming part of the claimed invention. The input and the output of the sensing circuit 102A are not isolated. The terminals/nodes of the sensing circuit 102A are connected in series between the interference signal source Vno and the capacitor Cx. The sensing circuit 102A includes a capacitor Cs and an inductor Lp connected in parallel forming a resonator circuit. The resonance frequency of the resonator circuit is arranged below the minimum frequency of the electromagnetic interference signal Vn to be suppressed across the capacitor Cx and above a frequency of the power source <NUM> such that the sensing circuit 102A can provide high pass and low pass functions as needed, e.g., be considered as capacitor for high frequency signals and inductor for low frequency signals.

The interference signal Vn to be suppressed across the capacitor Cx and the signal Vs outputted by the sensing circuit 102A can be considered as a capacitive voltage divider of the noise signal Vno according to Kirchhoff's voltage law as in the following expressions: <MAT> <MAT> Hence <MAT> Or <MAT>.

In this example, the gain factor Ks of the sensing circuit 102A equals to a capacitance of the capacitor Cx divided by capacitance of the capacitor Cs. The inductor Lp may enable the flow of power (e.g., current, low frequency in nature) from the power source <NUM> to the electronic circuit <NUM> while the capacitor Cs presents a high impedance to prevent the flow of power (e.g., current, low frequency in nature) from the power source <NUM> to the electronic circuit <NUM>.

<FIG> shows another implementation of the sensing circuit 102B in one embodiment. In this embodiment, the input and the output of the sensing circuit 102B are isolated. The input terminals/nodes of the sensing circuit 102B are connected in series between the interference signal source Vno and the capacitor Cx. The sensing circuit 102B includes a capacitor Cs and an inductor Lp connected in parallel forming a resonator circuit and arranged at the input of the sensing circuit 102B, and a transformer connected in parallel to the resonator circuit and arranged at the output of the sensing circuit 102B. The transformer includes primary coil with Np turns and a secondary coil with Ns turns, defining a turns ratio N (Ns/Np). The primary coil is connected directly in parallel with the inductor Lp. The transformer provides isolation between the input and output of the sensing circuit 102B, and an additional voltage gain factor equals to the turns ratio N. The resonance frequency of the resonator circuit is arranged below the minimum frequency of the electromagnetic interference signal Vn to be suppressed across the capacitor Cx and above a frequency of the power source <NUM> such that the sensing circuit 102B can provide high pass and low pass functions as needed, e.g., can be considered as capacitor for high frequency signals and inductor for low frequency signals. In this implementation, the inductance of the primary coil of transformer is much greater than the inductance of inductor Lp such that there exists negligible parallel resonance effect.

The interference signal Vn to be suppressed across the capacitor Cx and the sensed sign Vs' at the input of sensing circuit 102B can be considered as a capacitive voltage divider of the noise signal Vno according to Kirchhoff's voltage law as in the following expressions: <MAT> <MAT> Hence <MAT> Or <MAT>.

The secondary coil of the transformer serves as the output of sensing circuit 102B with an output voltage Vs that equals to (N is the turns ratio of transformer): <MAT>.

In this example, the gain factor Ks of the sensing circuit 102B equals to the product of the turns ratio N of the transformer and the capacitance of the capacitor Cx, divided by the capacitance of the capacitor Cs. The inductor Lp may enable the flow of power (e.g., current, low frequency in nature) from the power source <NUM> to the electronic circuit <NUM> while the capacitor Cs presents a high impedance to prevent the flow of power (e.g., current, low frequency in nature) from the power source <NUM> to the electronic circuit <NUM>. The inductance of the transformer primary coil should be substantially larger than the inductance of inductor Lp such that resonant frequency will not be substantially affected and power current flows mainly through the inductor Lp.

<FIG> shows another implementation of the sensing circuit 102C in one embodiment. In this embodiment, the input and the output of the sensing circuit 102C are isolated. The input terminals/nodes of the sensing circuit 102C are connected in series between the interference signal source Vno and the capacitor Cx. The sensing circuit 102C includes a capacitor Cs arranged at the input of the sensing circuit 102C, and a transformer connected in parallel to the capacitor Cs and arranged at the output of the sensing circuit 102C. The transformer includes primary coil with Np turns and a secondary coil with Ns turns, defining a turns ratio N (Ns/Np). The transformer provides isolation between the input and output of the sensing circuit 102C. The primary coil of the transformer is connected directly in parallel with the capacitor Cs to form a resonator circuit. The resonance frequency of the resonator circuit is arranged below the minimum frequency of the electromagnetic interference signal Vn to be suppressed across the capacitor Cx and above a frequency of the power source <NUM> such that the sensing circuit 102C can provide high pass and low pass functions as needed, e.g., can be considered as capacitor for high frequency signals and inductor (primary side of the transformer) for low frequency signals.

The interference signal Vn to be suppressed across the capacitor Cx and the sensed signal Vs' at the input of sensing circuit 102C (the capacitor Cs) can be considered as a capacitive voltage divider of the noise signal Vno according to Kirchhoff's voltage law as in the following expressions: <MAT> <MAT>.

The secondary coil of the transformer serves as the output of sensing circuit 102C with an output voltage Vs that equals to (N is the turns ratio of transformer): <MAT>.

In this example, the gain factor Ks of the sensing circuit 102C equals to the product of the turns ratio N of the transformer and the capacitance of the capacitor Cx, divided by the capacitance of the capacitor Cs. The primary side of the transformer may enable the flow of power (e.g., current, low frequency in nature) from the power source <NUM> to the electronic circuit <NUM> while the capacitor Cs presents a high impedance to prevent the flow of power (e.g., current, low frequency in nature) from the power source <NUM> to the electronic circuit <NUM>.

<FIG> shows another implementation of the sensing circuit 102D in one embodiment. The sensing circuit 102D in <FIG> is similar to the sensing circuit 102C in <FIG>, except that the capacitor is moved to the output (<FIG>) of the sensing circuit 102D. In this embodiment, the input and the output of the sensing circuit 102D are isolated. The input terminals/nodes of the sensing circuit 102D are connected in series between the interference signal source Vno and the capacitor Cx. The sensing circuit 102D includes a transformer arranged at the input of the sensing circuit 102D, and a capacitor Cs' connected in parallel to the transformer and arranged at the output of the sensing circuit 102D. The transformer includes primary coil with Np turns and a secondary coil with Ns turns, defining a turns ratio N (Ns/Np). The transformer provides isolation between the input and output of the sensing circuit 102D. The secondary coil of the transformer is connected directly in parallel with the capacitor Cs' to form a resonator circuit. The resonance frequency of the resonator circuit is arranged below the minimum frequency of the electromagnetic interference signal Vn to be suppressed across the capacitor Cx and above a frequency of the power source <NUM> such that the sensing circuit 102D can provide high pass and low pass functions as needed, e.g., can be considered as capacitor for high frequency signals and inductor (primary and secondary sides of the transformer) for low frequency signals.

The interference signal Vn to be suppressed across the capacitor Cx and the sensed signal Vs' at the input of sensing circuit 102D (primary side of the transformer) can be considered as a capacitive voltage divider of the noise signal Vno according to Kirchhoff's voltage law as in the following expressions: <MAT> <MAT> Hence <MAT> Or <MAT>.

The secondary coil of the transformer serves as the output of sensing circuit 102D with an output voltage Vs that equals to (N is the turns ratio of transformer): <MAT>.

In this example, the gain factor Ks of the sensing circuit 102D equals to capacitance of the capacitor Cx divided by the product of the turns ratio N of the transformer and the capacitance of the capacitor Cs'. The primary side of the transformer may enable the flow of power (e.g., current, low frequency in nature) from the power source <NUM> to the electronic circuit <NUM> while the capacitor Cs' presents a high impedance to prevent the flow of power (e.g., current, low frequency in nature) from the power source <NUM> to the electronic circuit <NUM>. Compared with the embodiment of <FIG>, in this embodiment, arranging the capacitor Cs' at the output instead of at the input of the sensing circuit can scale the capacitance of the capacitor Cs' by the square of the transformer turns ratio N, thus enabling the capacitor Cs' to have a small capacitance.

The control circuit and the electromagnetic interference suppression circuit in the above embodiments can be applied to circuit applications not specifically illustrated in the description and/or drawings.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as illustrated with respect to the specific embodiments without departing from the scope of the invention as defined in the claims. The described embodiments of the invention are therefore in all respects illustrative and not restrictive.

For example, the shunt circuit need not be formed by a single capacitor, but can be formed by different electronic component (s) forming a high pass circuit. The sensing circuit may include different constructions of resonator circuits and/or transformers. The resonator circuits may be formed from different capacitive and inductive circuits. The resonant frequency of the resonator circuit need not be strictly below a frequency of the electromagnetic interference signal Vn and above a frequency of the power source.

The amplifier can be replaced with other regulator circuit and/or the controlled voltage source can be replaced with other circuit components, so long as they serve the purpose to cooperate with the sensing circuit and the controlled voltage source to suppress electromagnetic interference signals. The sensing circuit and/or the controlled voltage source can be connected on the supply line or the return line; the sensing circuit and the controlled voltage source can be connected on different lines or on the same line. The illustrated capacitor can be embodied by any capacitive circuit(s) or circuit component(s); the illustrated inductors can be embodied by any inductive circuit(s) or circuit component(s). In embodiments where a transformer is used, the turns ratio can be chosen depending on needs, so long as the overall circuit can suppress the electromagnetic interference signals. Likewise, the gain factors of the sensing circuit, the amplifier, and the controlled voltage source can be any values provided that the overall circuit can suppress the electromagnetic interference signals.

Claim 1:
An electromagnetic interference suppression circuit, comprising:
a sensing circuit (<NUM>) with
an input adapted to be connected on a power line and in series between a load and a shunt circuit connected across power lines between a power source (<NUM>) and the load;
an output operatively coupled with the input, and adapted to provide a signal (Vs) associated with an electromagnetic interference signal (Vn) generated by or at the load and arranged to be experienced by the shunt circuit for determining a suppression signal (Vn') for reducing, or substantially eliminating, the electromagnetic interference signal (Vn);
a transformer with primary and secondary coils; and
a capacitive circuit;
a regulator circuit adapted to regulate the signal (Vs) provided by the sensing circuit to provide a regulated signal; and
a controlled signal source adapted to provide, based on the regulated signal, a suppression signal (Vn') for reducing, or substantially eliminating, the electromagnetic interference signal (Vn);
characterized in that:
the capacitive circuit is connected in parallel with the transformer;
one of the transformer and the capacitive circuit provides the input and the other one of the transformer and the capacitive circuit provides the output; and
the transformer and the capacitive circuit define a resonator circuit providing the input, the output, or both the input and the output.