阅读说明：本技术 用于在射频操作i中操作平面变压器上的可变阻抗负载的装置和方法 (Apparatus and method for operating a variable impedance load on a planar transformer in radio frequency operation I ) 是由 克里斯托夫·布拉姆伯格 于 2019-07-22 设计创作，主要内容包括：本发明涉及一种在装置上操作可变阻抗负载的方法,所述装置包括平面变压器,所述平面变压器至少包括初级侧和次级侧,所述初级侧和次级侧可以作为输入侧或输出侧操作,所述方法包括将在所述次级侧对称点之一处的虚拟RF接地端映射到第一阻抗。(The invention relates to a method of operating a variable impedance load on an apparatus comprising a planar transformer comprising at least a primary side and a secondary side, which primary and secondary sides are operable as input side or output side, the method comprising mapping a virtual RF ground at one of the secondary side symmetry points to a first impedance.)

1. A method for operating a variable impedance load in a planar transformer, the planar transformer comprising at least a primary side and a secondary side, the primary and secondary sides being operable as input side or output side, characterized in that the method comprises mapping a virtual RF ground at a point of symmetry of one of the secondary sides to a first impedance.

2. The method of claim 1, further comprising:

selecting a distance to a point of symmetry along an output direction of the secondary side to the secondary side, the distance of the secondary side to the output of the secondary side being equal to an odd (or even) multiple of a quarter of a wavelength of a desired harmonic; and/or terminating the output of the secondary side with an open circuit (or short circuit).

3. A method for operating a planar transformer comprising a primary side and a secondary side, wherein the primary side has at least one first coil and the secondary side has at least one second coil, the second coil being symmetrically constructed and having a point of symmetry and a differential output of two branches, the second coil having a distributed inductance and a distributed capacitance to the first coil between the point of symmetry and the first branch of the differential output, the method comprising:

a resonant frequency between the distributed inductance and the distributed capacitance is selected that is equal to a multiple of the preferred operating frequency.

4. A method of operating a planar transformer comprising a primary side and a secondary side, wherein the primary side has at least one first coil and the secondary side has at least one second coil, the second coil being symmetrically constructed and having a virtual radio frequency ground at the point of symmetry when the planar transformer is operated in a differential mode, the method comprising:

selecting an electrical length of the second coil that is less than half of a wavelength at a preferred operating frequency and equal to an integer multiple of half of the wavelength at the preferred operating frequency.

5. A method for operating a planar transformer, characterized in that the planar transformer has a preferred operating frequency and consists of a primary side and a secondary side, the primary side having an input with a first input impedance at the preferred operating frequency and the secondary side having an output with a first output impedance at the preferred operating frequency, the output having a first supply impedance and a first load impedance, wherein at the preferred operating frequency the first supply impedance is the complex conjugate of the first load impedance of the input impedance at termination of the output and the first load impedance is the complex conjugate of the first supply impedance of the output impedance at termination of the input; wherein the primary side has at least one first coil, the secondary side has at least one second coil, the second coil being symmetrically configured and having a virtual radio frequency ground at a point of symmetry, when the planar transformer operates in a differential mode, the method comprising:

selecting an electrical length of the second coil that is less than half of a wavelength at the operating frequency and equal to an integer multiple of half of the wavelength at the operating frequency.

6. The method according to any of the preceding claims, wherein the planar transformer operates in radio frequency operation.

7. The method of claim 6, wherein the radio frequency operation is f ≧ 10 MHz.

8. The method of claim 6, wherein the radio frequency operation is 50kHz ≦ f ≦ 10 MHz.

9. Planar transformer, characterized in that it has at least a primary side and a secondary side operable as input side or output side, and a controller, wherein the controller has a programming with the steps according to one of the preceding claims.

10. A planar transformer having a preferred operating frequency and comprising a primary side having at least one first coil and a secondary side having at least one second coil, the second coil being symmetrically configured and having a virtual radio frequency ground at the point of symmetry when the planar transformer is operated in a differential mode, the second coil having an electrical length less than half of a wavelength at the operating frequency and equal to an integer multiple of half of a wavelength at the operating frequency.

11. Planar transformer, characterized in that it has a preferred operating frequency and comprises a primary side with at least one first winding and a secondary side with at least one second winding, which is symmetrically constructed and has a point of symmetry and a differential output with two branches, the second winding between the point of symmetry and the first branch of the differential output having a distributed inductance and a distributed capacitance to the first winding, characterized in that the resonance frequency between the distributed inductance and the distributed capacitance is equal to a multiple of the preferred operating frequency.

12. A planar transformer having a preferred operating frequency and consisting of a primary side having an input with a first input impedance at the preferred operating frequency and a secondary side having an output with a first output impedance at the preferred operating frequency, the output having a first supply impedance and a first load impedance, wherein at the preferred operating frequency the first supply impedance is the complex conjugate of the first load impedance of the input impedance at termination of the output and the first load impedance is the complex conjugate of the first supply impedance of the output impedance at termination of the input, wherein the primary side has at least one first winding and the secondary side has at least one second winding symmetrically configured and having a virtual radio frequency ground at a point of symmetry, when the planar transformer operates in a differential mode, an electrical length of the second coil is less than half of a wavelength at the operating frequency and equal to an integer multiple of half of the wavelength at the operating frequency.

13. Planar transformer according to claims 10-12, characterized in that it has a controller with programming with the steps according to one of the preceding claims.

Technical Field

The present invention relates to an apparatus and method for operating a variable impedance load on a planar transformer in radio frequency operation.

Background

In the prior art, an apparatus is disclosed in which a signal power source is connected to a load through a transmission path. In the high power range, a low impedance power supply (e.g., 1 Ω) is typically connected through a higher impedance transmission path (e.g., 50 Ω) to a low impedance load, which is typically variable (e.g., variable around a value of 1 Ω). For impedance matching, a first matching network with a (e.g. fixed) first impedance ratio is typically used between the power supply and the transmission path, and a second matching network with a (e.g. variable) second impedance ratio is typically used between the transmission path and the load. A signal is transmitted from a power source to a load via a first matching network, a transmission path, and a second matching network. A signal typically has a fundamental frequency component and a harmonic component, i.e. integer multiples of the fundamental frequency.

The prior art treats transformers as matching networks with a fixed impedance ratio. The transformer comprises an input coil ("primary winding") with a first number of windings and an output coil ("secondary winding") with a second number of windings, and a ratio between the second number of windings and the first number of windings, called the winding ratio.

In the case of a low frequency signal, a transformer with a winding ratio of N down-converts the voltage between the input and output by a factor of N, but conversely up-converts the current by a factor of N, so that the ratio of the supply to load impedance of N2 can be adjusted with the transformer.

A planar transformer is a special embodiment of a transformer. A planar transformer has primary and secondary coils that are substantially parallel planes separated by a dielectric.

In the case of radio frequency technology, a planar transformer is an element that transmits a signal from an input terminal to an output terminal using distributed inductance and distributed capacitance, and has a desired variation in signal impedance. Although in the low frequency range the ratio of change between the two actual impedances is the square of the winding ratio, in the higher frequency range this relationship is more complicated due to the fact that the radio frequency impedance is not an actual resistance, and the distributed capacitance and inductance coating is present in nature.

From the prior art, it is known to construct mirror-symmetrical primary coils ("primary side symmetry plane transformers"). It is also unambiguously derivable from the prior art that in the case of an even number of secondary coil windings, the planar transformer is adapted to evaluate the winding direction from a first point of view of the planar transformer, with half of the secondary coil windings being arranged above the primary coil in a first winding direction and the other half of the windings being arranged below the primary coil in the opposite winding direction ("secondary-side symmetrical planar transformer"). From a first perspective, the first half-winding and the second half-winding of the secondary coil are conductively connected to each other in a rotational center region of the secondary coil. Finally, according to the prior art, it is possible to construct a planar transformer completely symmetrically, that is to say symmetrically on the primary side and on the secondary side.

If the power supply is a differential amplifier arrangement, in the case of a planar transformer with symmetrical primary side, there is a point in the middle of the primary winding, which is grounded according to the radio frequency technique and through which the supply voltage can be supplied, with very low requirements for blocking the output signal from the supply voltage. In the case of a planar transformer with symmetrical secondary sides, in the same way, there is a point in the middle of the secondary coil, which is grounded according to the radio frequency technique; according to the prior art, this is used, for example, to apply a DC voltage to the antenna connection or to tap a DC voltage from the antenna connection.

The harmonic matching structure is also referred to in the prior art as a first matching network, by means of which, depending on the number and phase, desired values of the load impedance for the fundamental and the harmonic can be achieved. The control of the impedance can also be used advantageously in the case of harmonics, in order to obtain a time profile of the current and voltage at the output of the power supply, by means of which a particularly efficient operation of the power supply can be achieved.

Loads with variable impedance generally exhibit variations in input impedance not only for the fundamental wave of the signal but also for the harmonics. The second matching network with variable impedance ratio according to the prior art is generally only adapted to absorb variations in load impedance at the fundamental frequency of the signal, but it generally does not allow impedance matching of any harmonics.

Then, at a fundamental frequency with a prescribed impedance, without further measures on the side facing the transmission path, a harmonic matching structure is derived as a first matching network; however, at multiples of the fundamental frequency, there is a variable impedance. Such variable harmonic terminals have an adverse effect on the time distribution of the current and voltage at the power supply output.

In order to achieve reproducible harmonic termination at the power supply even with variable loads, it is known from the prior art to design the arrangement consisting of the second matching network, the transmission path and the first matching network so as not to be permeable to harmonic frequencies: as a result, a reproducible impedance ratio can be achieved at the output of the amplifier device with the power supply components, thereby achieving a high efficiency of the power supply, which is largely independent of the impedance of the load.

In particular, structures are known from the prior art, such as frequency-selective suction circuits or frequency dividers, by means of which the harmonics are deflected to ground. Such a deviation from ground represents, for example, a short circuit in the respective harmonic and provides a defined impedance in the respective harmonic; based on this, the first matching network may be designed such that the power supply can always operate efficiently.

A disadvantage of the prior art is, in particular, that such measures for deviating harmonics are associated with high expenditure. Another disadvantage of the prior art is that such measures for deviating harmonics always involve a loss of signal power, which reduces the overall efficiency.

It would therefore be an object of development to provide a measure by which consistent high efficiency of the power supply can be achieved by harmonic matching even though the power supply is operated to drive a variable impedance load, while reducing the disadvantages of the prior art.

It is therefore desirable to provide a method that addresses the low loss operation of variable impedance loads without the disadvantages of the prior art.

Disclosure of Invention

The opaque planar transformer I with selectable frequency of the invention solves the defects of the prior art and realizes the aim of low-loss operation of the variable impedance load. The invention relates to a method for operating a variable impedance load in an apparatus, the apparatus comprising a planar transformer, the planar transformer comprising at least a primary side and a secondary side, the primary side and the secondary side being operable as input side or output side, the method comprising mapping a virtual RF ground at one of the secondary side symmetry points to a first impedance.

A "planar transformer" is a special type of transformer that is characterized by a planar design. In terms of radio frequency, a planar transformer is a distributed structure with capacitive and inductive components. The inductance component is led by the coil; the capacitive component comprises on the one hand a capacitive coating between the primary coil and the secondary coil and on the other hand a possible capacitance between two windings within the primary coil or the secondary coil itself, as long as these windings comprise (parts of) a coil with more than one winding.

The inductive coating along the coil together with the capacitive coating between the primary and secondary coils forms a strip line with a given line impedance and a given wire length. The wire length in turn depends on the geometric wire length and the propagation speed of the signal in the dielectric.

At the signal frequency, the virtual RF ground is mapped onto a first impedance at a point of symmetry of the secondary coil. If the electrical length of the path from the point of symmetry along the secondary to the output of the secondary is chosen to be equal to an odd (even) multiple of a quarter wavelength of the desired harmonic, the transmission of the signal from the output to the input of the perfectly symmetrical planar transformer has the largest loss if the output is terminated with an open circuit (short circuit). For all load impedances normally expected at the output side of the planar transformer, which impedance is terminated by the transmission path, the second matching network and the load, the amount of transmission from the output to the input is low, and therefore the planar transformer will provide at the input side an impedance of the desired harmonic, which impedance is not dependent on the ("reflected") signal impinging on the output of the planar transformer: the planar transformer is opaque to these harmonics and the harmonic termination at the input side is independent of the state of the load and the second matching network.

A radio frequency planar transformer with a given number of windings in the secondary coil may typically consist of two layers, where a first layer may be the primary side and another layer, which for illustration is arranged parallel to the first layer, may be the secondary side. The planar transformer may also have various combinations of more than one primary or secondary layer. For example, a planar transformer according to the invention may have a primary side (here: "side" has the same meaning as "layer" or "coil") which is arranged in the middle of two secondary sides in a sandwich structure (here: "side" has the same meaning as "layer", "half" or "coil"). Half of the windings of the secondary coil are above the primary coil and the other half are below the primary coil. There is a "virtual ground" in the middle. When viewed from above, the two halves appear in two opposite winding directions; this must be done because in one half the current flows "from inside to outside" and in the other half the current flows "from outside to inside", but the (partial) voltages induced in the two halves should add up, rather than cancel each other out.

Drawings

Fig. 1 shows a planar transformer, an apparatus according to the invention.

Detailed description of the drawings

Fig. 1 has an apparatus according to the invention, which can carry out the method 100 of the invention. The apparatus 10 comprises a planar transformer 10. A radio frequency planar transformer 10 with a variable number of windings in the secondary coil may typically be composed of two layers, where a first layer may be the primary side and another layer, which is arranged parallel to the first layer for illustration purposes, may be the secondary side. The planar transformer in fig. 1 has more than one secondary winding. The planar transformer in fig. 1 according to the invention comprises one primary side 11 (thick outer line), which primary side 11, like the sandwich structure, is arranged centrally between two secondary sides 12, 12' (thin dashed line). Half of the winding of the secondary coil 12 is above the primary coil 11 and the other half 12' is below the primary coil 11. The two secondary coils 12, 12' have mutually opposite winding directions. In the middle, the windings of the secondary coil are also connected, there being a "virtual ground". When viewed from above, the two halves appear to have opposite winding directions to each other; this must be done because in one half the current flows "from inside to outside" and in the other half the current flows "from outside to inside", but the (partial) voltages induced in the two halves should add up, rather than cancel each other out.

List of reference numerals used

10 device according to the invention-planar transformer

11 primary coil of planar transformer

Secondary winding of 12 plane transformer

Symmetrical secondary winding of 12' planar transformer (lower)

100 method according to the invention

Detailed Description

A planar transformer extending over seven layers that are substantially plane-parallel to each other is used as an illustrative example; in a row of consecutive layers, perpendicular to the layers are referred to as a first layer S1, a second layer P1, a third layer S2, a fourth layer P2, a fifth layer S3, a sixth layer P3 and a seventh layer S4 in that order.

For example geometrically identical, the primary coils each having a first input and a second input are arranged in three layers, a second layer P1, a fourth layer P2 and a sixth layer P3, wherein the first inputs of all primary coils are electrically short-circuited to each other and the second inputs of all primary coils are electrically short-circuited to each other. The first secondary coil is composed of a first coil portion T1 having a first number of windings in a first winding direction in the first layer S1 and a fourth coil portion T4 having a first number of windings in a winding direction opposite to the first winding direction in the seventh layer S4; the second secondary coil is composed of the second coil portion T2 of the first winding in the first winding direction in the third layer S2 and the third coil portion T3 of the first winding in the winding direction opposite to the first winding direction in the fifth layer S3; the inner ends of the first coil portion T1, the second coil portion T2, the third coil portion T3 and the fourth coil portion T4 are electrically conductively connected to each other as viewed in the direction of rotation of the winding; the outer ends of the first coil portion T1 and the second coil portion T2 are conductively connected to each other as viewed in the direction of rotation of the windings; the outer ends of the third coil portion T3 and the fourth coil portion T4 are electrically conductively connected to each other as viewed in the direction of rotation of the windings.

A transistor with a relatively high output power and at the same time a relatively low operating voltage delivers its output power particularly efficiently to a low-resistance load: modern high voltage fets with 130V breakdown voltage typically operate at 50V supply voltage. When fully controlled, the RF output voltage swing is approximately between +/-50V of 50V. In order to obtain an output power of 1kW from the transistor, an output current of 40A is required, the output impedance is 50V/40A, i.e. in the range of 1 ohm: this is determined only by the operating voltage and the output power, so a load impedance of about 1 ohm is necessary.

In order to be able to provide a typical "real" load of 50 ohms to the transistor, a matching network that maps 50 ohms to 1 ohm is required. The planar transformer according to the invention may be part of the matching network.

The efficiency of the amplifier, i.e. the combination of the transistor and the matching network, is determined by the operating efficiency of the transistor and the losses in the matching network, in particular in the planar transformer. Losses in the matching network are also affected by the impedance of the matching network at the input and output sides. For example, if the primary coil is driven by a push-pull amplifier, the differential output impedance of the push-pull amplifier may be seen at the input side as a termination of the primary coil. In contrast, for example, there is 50 ohms at the output side of the secondary coil.

The "winding ratio" is the number of windings of the secondary coil divided by the number of windings of the primary coil. If a power supply with very high supply power (e.g., 2500W from 36V) would operate with a moderate load impedance (e.g., 50 ohms) based on the operating voltage of the power supply, the windings would appear to be more favorable for matching than a planar transformer significantly larger than 1. For example, a planar transformer may be selected with one winding in the primary coil, three windings in the secondary coil, and each winding above and below the primary coil. It can be seen that such planar transformers with high winding ratios have minimal losses when terminated on the output side and the input side, each having an impedance that is disadvantageously high for the operation of the power supply or for the matching of the load, but disadvantageously high losses when terminated with existing load and power supply impedances.

The load impedance that minimizes losses in the matching network depends on the line impedance of the "line" secondary, with the primary as a reference ground. The present invention reduces this line impedance by connecting the two halves of the secondary coil in parallel. The advantages are that: the inductive coating is reduced (two coils are in parallel) and the capacitive coating is increased, the line impedance, which is the square root of the inductive coating, divided by the capacitive coating, and the two parallel secondary coils are reduced by half.

In the last-mentioned embodiment of the planar transformer (parallel connection), for example, the spaces between the first layer S1 and the second layer P1, the second layer P1 and the third layer S2, the third layer S2 and the fourth layer P2, the fourth layer P2 and the fifth layer S3, the fifth layer S3 and the sixth layer P3, the sixth layer P3 and the seventh layer S4 are filled with the same dielectric, respectively. The first distance between the second layer P1 and the third layer S2, between the third layer S2 and the fourth layer P2, between the fourth layer P2 and the fifth layer S3, and between the fifth layer S3 and the sixth layer P3 may be selected to be twice the second distance between the first layer S1 and the second layer P1, and between the sixth layer P3 and the seventh layer S4. As a result, all windings of the secondary coil have similar line impedances.

Thus, the device according to the invention can map the correct ratio of input to output impedance (e.g. 50 ohms) to the appropriate load impedance for the transistor and at the same time provide these 50 ohm low losses exactly as the load impedance.

The method according to the invention may further comprise selecting a path along one of the secondary sides to a point of symmetry of the output of the secondary side, the path being equal to an odd (or even) multiple of a quarter wavelength of the desired harmonic; and/or terminate the output of the secondary side with an open circuit (or short circuit).

A method for operating a planar transformer composed of a primary side and a secondary side, wherein the primary side has at least a first coil and the secondary side has at least a second coil, which is symmetrically constructed and has a point of symmetry and a differential output with two branches, the second coil between the point of symmetry and the first branch of the differential output having a distributed inductance and a distributed capacitance to the first coil, can be used to solve the object task. The second coil includes a selection of a resonant frequency between the distributed inductance and the distributed capacitance that is equal to a multiple of the preferred operating frequency.

The task is also solved by a method for operating a planar transformer consisting of a primary side and a secondary side, wherein the primary side has at least a first coil and the secondary side has at least a second coil, the second coil being symmetrically configured and having a virtual radio frequency ground at a point of symmetry when the planar transformer is operated in differential mode, the method comprising that the electrical length of said secondary coil is smaller than half the wavelength at said operating frequency and equal to an integer multiple of half the wavelength at said operating frequency.

A further solution to the objective task is provided by a method for operating a planar transformer. The scheme has a preferred operating frequency and consists of a primary side having an input with a first input impedance at the preferred operating frequency and a secondary side having an output with a first output impedance at the preferred operating frequency, the output having a first supply impedance and a first load impedance, wherein at the preferred operating frequency the first supply impedance is the complex conjugate of the first load impedance of the input impedance at termination of the output. The first load impedance is the complex conjugate of the first supply impedance of the output impedance at the termination of the input. The primary side has at least a first coil and the secondary side has at least a second coil, the second coil being of symmetrical construction and having a virtual radio frequency ground at a point of symmetry when the planar transformer is operated in a differential mode, the differential mode including selecting an electrical length of the secondary coil that is less than half of a wavelength at the operating frequency and is an integer multiple of half of the wavelength at the operating frequency.

An apparatus which can use the above-described method to achieve the object according to the invention is a planar transformer having at least one primary side and one secondary side, which primary side and secondary side can be operated as input side or output side, and a controller, wherein the controller comprises a programming according to the steps of one of the preceding claims.

Furthermore, a planar transformer as the apparatus according to the invention may have a preferred operating frequency and comprise a primary side and a secondary side, wherein, when the planar transformer is operated in differential mode, the primary side has at least a first coil and the secondary side has at least a second coil, the second coil being symmetrically configured and having a virtual radio frequency ground at a point of symmetry. This embodiment is characterized in that the electrical length of the secondary coil is less than half the wavelength at the operating frequency and equal to an integer multiple of half the wavelength at the operating frequency.

Another embodiment of the device is a planar transformer having a preferred operating frequency and comprising a primary side and a secondary side, wherein the primary side has at least a first coil and the secondary side has at least a second coil, the second coil being symmetrically constructed and having a point of symmetry and a differential output having two branches, the second coil between the point of symmetry and the first branch of the differential output having a distributed inductance and a distributed capacitance between its windings. This embodiment is characterized in that the resonance frequency between the distributed inductance and the distributed capacitance is equal to a multiple of the preferred operating frequency, thereby optimizing the efficiency.

Another embodiment of the apparatus for applying the method according to the invention is a planar transformer having a preferred operating frequency and comprising a primary side and a secondary side, the primary side having an input with a first input impedance at the preferred operating frequency and the secondary side having an output with a first output impedance at the preferred operating frequency, the output of the first output impedance having a first supply impedance and a first load impedance. Wherein at the preferred operating frequency the first supply impedance is the complex conjugate of the first load impedance of the input impedance at termination of the output. The first load impedance is the complex conjugate of the first supply impedance of the output impedance at the termination of the input. The primary side has at least a first coil and the secondary side has at least a second coil, which is of symmetrical design. When the planar transformer operates in differential mode, there is a virtual radio frequency ground at the point of symmetry. The apparatus is further characterized in that the electrical length of the secondary coil is less than half of the wavelength at the operating frequency and equal to an integer multiple of half of the wavelength at the operating frequency.

The above embodiments with respect to the device may also have a controller, wherein the controller comprises programming with steps according to one of the steps in the preceding claims.

Various embodiments of the planar transformer according to the present invention may also be operated in radio frequency operation using the method according to the present invention. Although in the low frequency range the ratio between the two actual impedances is the square of the winding ratio, in the higher frequency range this relationship is more complicated due to the fact that the radio frequency impedance is not an actual resistance, and the distributed capacitance and inductance coatings are present in nature. The radio frequency operation may be f ≧ 10 MHz. In addition, the radio frequency operation may also be 50kHz < f < 10 MHz.

In one embodiment, the capacitance between the primary and secondary windings forms a blocking circuit with an inductance of a respective half of the secondary winding of a fully symmetrical planar transformer. In terms of radio frequency technology, "symmetrically constructed" means: if the planar transformer is differentially fed, this symmetry results in a virtual earth at the point of symmetry of the respective coil.

The device according to the invention and the method according to the invention may also be combined with further, optional and advantageous features. For the purpose of illustration, it is again noted that it is an object of the present invention to achieve high efficiency with variable impedance loads in the RF range. The above-described methods, apparatus and embodiments thereof relate to using capacitance between a primary coil and a secondary coil to ensure efficiency. Other embodiments may combine the use of these with the use of capacity within the coil(s) to achieve improved efficiency.

In a combinable embodiment, the capacitance between the two windings of the coil of the planar transformer and the inductance of the coil form a resonant circuit. In the method according to the invention, the resonance frequency of the resonance circuit is selected such that it falls at the frequency of the harmonics of the signal to be suppressed. As a result, no signal can be transmitted from the output of the planar transformer to the input of the planar transformer with harmonics suppressed. On the input side, the planar transformer provides an impedance for the harmonics to be suppressed, which impedance is independent of the (reflected) signal hitting the output of the planar transformer: the planar transformer is opaque to these harmonics and the harmonic termination at the input side is independent of the state of the load and the second matching network.

The method according to the invention can thus be combined with a method for operating a variable impedance load in a planar transformer comprising at least a primary side and a secondary side, which primary and secondary sides can be operated as input or output sides, which input or output sides comprise a primary coil and a secondary coil. Wherein a capacitance between the winding of the coil and the inductor of the coil forms a resonant circuit comprising a selection of a resonant frequency of the resonant circuit. Wherein the resonance frequency falls at a frequency of a harmonic of the input signal to be suppressed. Furthermore, the combined method may have a feature of providing an impedance at the input side of the planar transformer that is independent of the signal reflected at the output, so that the planar transformer appears opaque to harmonics.

According to the invention, a method for operating a planar transformer comprises a primary side and a secondary side, wherein the primary side has at least one first coil and the secondary side has at least one second coil, which is symmetrically formed and has a point of symmetry and a differential output having two branches, the second coil having a distributed inductance and a distributed capacitance between the point of symmetry and a winding between the first branches of the differential output. The method can also comprise the following steps: the feature that the resonance frequency between the distributed inductance and the distributed capacitance is equal to a multiple of the preferred operating frequency is chosen.

Another possible combination is to add a method for operating a planar transformer having a preferred operating frequency and comprising a primary side and a secondary side, the primary side having an input with a first input impedance at the preferred operating frequency and the secondary side having an output with a first output impedance at the preferred operating frequency, the output having a first supply impedance and a first load impedance, wherein in case of the preferred operating frequency the first supply impedance is the complex conjugate of the first load impedance of the input impedance at termination of the output; the first load impedance is the complex conjugate of the first supply impedance of the output impedance at the termination of the input. Wherein the primary side has at least one first coil and the secondary side has at least one second coil, which are symmetrically formed. And when the planar transformer operates in a differential mode, including selecting a resonant frequency between the distributed inductance and the distributed capacitance equal to a multiple of the preferred operating frequency, with a virtual radio frequency ground at the point of symmetry.

Various combined embodiments of the planar transformer according to the invention may also be operated in radio frequency operation using the method according to the invention. The radio frequency operation may be f ≧ 10 MHz. In addition, the radio frequency operation may also be 50kHz < f < 10 MHz.

The device according to the invention may comprise a planar transformer having at least a primary side and a secondary side, which primary side and secondary side may be operated as input side or output side, and a controller, wherein a program of said controller implements the steps of one of the aforementioned methods.

The device according to the invention may comprise a planar transformer having a preferred operating frequency and comprising a primary side and a secondary side, wherein the primary side has at least one first coil and the secondary side has at least one second coil, which is constructed symmetrically and has a point of symmetry and a differential output with two branches, the second coil between the point of symmetry and the first branch of the differential output having a distributed inductance and a distributed capacitance between its windings, characterized in that the resonance frequency between the distributed inductance and the distributed capacitance is equal to a multiple of the preferred operating frequency.

The apparatus according to the invention may comprise a planar transformer having a preferred operating frequency and comprising a primary side and a secondary side, the primary side having an input of a first input impedance at the preferred operating frequency and the secondary side having an output of a first output impedance at the preferred operating frequency, the output having a first supply impedance and a first load impedance, wherein in the case of the preferred operating frequency the first supply impedance is the complex conjugate of the first load impedance of the input impedance at termination of the output; the first load impedance is the complex conjugate of the first supply impedance of the output impedance at the termination of the input. Wherein the primary side has at least one first coil and the secondary side has at least one second coil, which are symmetrically formed. And a virtual radio frequency ground at the point of symmetry when the planar transformer operates in differential mode, characterized in that the resonance frequency between the distributed inductance and the distributed capacitance is equal to a multiple of the preferred operating frequency.

In contrast to the above-described structure, the skilled person, due to the greatest possible simplicity of presentation, can also apply the teaching disclosed in the present invention in such a way that the radio frequency ground, which is located at a point of symmetry of one secondary coil in the presently described structure, is located at another point, for example, when a first number of windings of a first winding direction are arranged in a first layer of the secondary coil, a second number of windings of a winding direction opposite to the first winding direction, which is different from the first number, are arranged in a second layer of the secondary coil.

It should be expressly noted that combinations of these features may be combined with combinations of features from the patent claims.