Patent Description:
Radio communications occur using different radio access technologies (RAT). A single radio access technology can use one or more frequency bands for transmitting/receiving radio signals. Different RATs can use the same or different frequency bands for transmitting/receiving radio signals.

It can be desirable to filter a transmitted or received signal so that it is limited to a specific frequency range or frequency ranges. This allows the signal to noise ratio of the analogue radio signal to be improved.

A filter is a frequency selective impedance. A filter can be configured as a pass band filter that has a relatively low impedance for a band of frequencies and relatively high impedance for adjacent frequency bands. A filter can be configured as a band stop filter that has a relatively high impedance for a band of frequencies and a relatively low impedance for adjacent frequency bands.

<CIT> discloses a filter circuit comprising a first impedance element disposed in an input side, a second impedance element disposed in an output side, having an input end connected to an output end of the first impedance element, and made of the same component as that of the first impedance element, a distributed constant resonance circuit having one end connected to a junction between the output end of the first impedance element and the input end of the second impedance element, and a third impedance element having one end connected to the input end of the first impedance element and the other end connected to the output end of the second impedance element. The first and second impedance elements and the distributed constant resonance circuit are each constituted by a transmission line having a predetermined distributed constant, and the third impedance element is constituted by a capacitor having a predetermined concentrated constant.

<CIT> discloses a variable filter including, on a dielectric substrate including ground conductor, first resonator including a transmission line connected to input terminal, second resonator including a transmission line connected to output terminal, and coupling portion including a transmission line having one end connected to the first and second resonators and another end being an open end, or structure having one end connected to the first and second resonators, including a serial connection of a transmission line and a variable capacitor, another end of the variable capacitor connected to the ground conductor, and adjusting means capable of changing electric length, in the first and second resonators and the coupling portion, wherein pass band width can be changed by changing ratio of electric transmission length of the coupling portion to electric transmission lengths of transmission line including the coupling portion, and the first and second resonators.

<CIT> discloses a filter circuit including a plurality of elementary Fano resonator circuits electrically coupled to each other. Each elementary Fano resonator circuit can include a closed loop circuit including a combination of at least three inductive and/or capacitive components and at least two ports. At least one port of the at least two ports can correspond to a node of the filter circuit not within the closed loop circuit. The elementary Fano resonator circuit can also include a branch including at least one other inductive or capacitive component and extending between a node of the closed loop circuit and a port of the at least one port corresponding to a node of the filter circuit not within the closed loop circuit.

<CIT> discloses a two-port tunable or reconfigurable network having a filter transfer function including: a network input port; a network output port; a hybrid coupler having a hybrid input port, a hybrid isolated port, a hybrid through port, and a hybrid coupled port; a first internal two-port network connected between the network input port and the hybrid input port; a second internal two-port network connected between the network output port and the hybrid isolated port; and a third internal two-port network connected between the hybrid through port and the hybrid coupled port. At least one of the first internal two-port network, the second internal two-port network, the third internal two-port network, and the hybrid coupler may be tunable or reconfigurable in response to an electrical signal or a user-operated control in a way that tunes or reconfigures the filter transfer function of the two-port tunable or reconfigurable network.

According to various, but not necessarily all, embodiments there is provided circuitry comprising:.

In some but not necessarily all examples, the circuitry comprises:.

In some but not necessarily all examples, the first resonant radio frequency conductive path between the first node and the third node has a single zero transfer function; the second resonant radio frequency conductive path between the first node and the third node has a single zero transfer function;
the phase shift element separates the zero of the transfer function for the first resonant radio frequency conductive path from the zero of the transfer function for the second resonant radio frequency conductive path.

In some but not necessarily all examples, the first resonant radio frequency conductive path comprises a first radio frequency conductive path between a first node and ground via the shunt resonant element; and the second resonant radio frequency conductive path comprises a second radio frequency conductive path between the second node and the ground via the shunt resonant element.

In some but not necessarily all examples, the shunt resonant element has a single zero transfer function.

In some but not necessarily all examples, the circuitry is configured to control the phase shift element to change the relative phase shift between the first resonant radio frequency conductive path and the second resonant radio frequency conductive path.

In some but not necessarily all examples, the circuitry is configured to control the phase shift element to select one of a plurality of predefined phase shifts.

In some but not necessarily all examples, the circuitry comprises: one or more additional first resonant radio frequency conductive paths between the first node and the third node each comprising a phase shift element for introducing a relative phase shift to the respective resonant radio frequency conductive path relative to the second resonant radio frequency conductive path.

In some but not necessarily all examples, a band stop filter comprises the circuitry in an in-line series configuration wherein input/output nodes of the filter are coupled to the first and second nodes of the circuitry.

In some but not necessarily all examples, a bandpass filter comprises the circuitry in a shunt configuration to ground wherein input/output nodes of the filter are coupled to the first node of the circuitry and wherein the second node of the circuitry is coupled to ground via an impedance and the third node of the circuitry is coupled to ground.

According to various, but not necessarily all, embodiments there is provided a filter comprising:.

Some examples which all fall within the scope of the present invention as defined by the appended claims will now be described with reference to the accompanying drawings in which:.

The drawings illustrate, and the following description describes, various examples of circuitry <NUM> comprising:.

<FIG> illustrates circuitry <NUM> for providing a band-stop resonance. The circuitry <NUM> has a triangular network topology. The circuitry <NUM> comprises three nodes <NUM>, <NUM>, <NUM> which form the vertices of a triangle-like topology.

The circuitry <NUM> has a first radio frequency conductive path <NUM> between the first node <NUM> and an intermediate node <NUM>. This forms one edge of the triangle-like topology.

The circuitry <NUM> has a second radio frequency conductive path <NUM> between the second node <NUM> and the intermediate node <NUM>. This forms another edge of the triangle-like topology.

The circuitry <NUM> has an internode radio frequency conductive path <NUM> between the first node <NUM> and the second node <NUM>. This forms a further edge of the triangle-like topology.

The first node <NUM> and second node <NUM> are input/output nodes of the circuitry <NUM>. In the example illustrated the first node <NUM> is an input node and the second node <NUM> is an output node. However, in other examples, the first node <NUM> is an output node and the second node <NUM> is an input node.

The circuitry <NUM> has a third radio frequency conductive path <NUM> between the intermediate node <NUM> and a third node <NUM>. In some examples, the third node is held at a constant potential such as a ground potential. The third node <NUM> can be described, in some examples, as a ground node indicating that it is or is intended to be grounded.

The circuitry <NUM> comprises: a first resonant radio frequency conductive path <NUM> between the first node <NUM> and the third node <NUM>; a second resonant radio frequency conductive path <NUM> between the second node <NUM> and the third node <NUM>; and the internode radio frequency conductive path <NUM> between the first node <NUM> and the second node <NUM>.

A shunt resonant element <NUM> is coupled to the third node <NUM> and shared by the first resonant radio frequency conductive path <NUM> and the second resonant radio frequency conductive path <NUM>. The third radio frequency conductive path <NUM> comprises the shunt resonant element <NUM>. The shunt resonant element is configured to operate as a frequency selective impedance Z that provides a lower impedance path between the intermediate node <NUM> and the third node <NUM> for a narrower band of frequencies and a higher impedance path between the intermediate node <NUM> and the third node <NUM> for wider bands of frequencies adjacent the narrower band of frequencies. This is illustrated by a transfer function (S-parameter S21) for the shunt resonant element <NUM>.

The circuitry <NUM> comprises a phase shift element <NUM> for introducing a relative phase shift to the first resonant radio frequency conductive path <NUM> relative to the second resonant radio frequency conductive path <NUM>. The first radio frequency conductive path <NUM> comprises the phase shift element <NUM>.

The first resonant radio frequency conductive path <NUM> between the first node <NUM> and the third node <NUM> comprises the first radio frequency conductive path <NUM> between the first node <NUM> and the intermediate node <NUM> and comprises the third radio frequency conductive path <NUM> between the intermediate node <NUM> and the third node <NUM>.

The second resonant radio frequency conductive path <NUM> between the second node <NUM> and the third node <NUM> comprises the second radio frequency conductive path <NUM> between the second node <NUM> and the intermediate node <NUM> and comprises the third radio frequency conductive path <NUM> between the intermediate node <NUM> and the third node <NUM>.

The first resonant radio frequency conductive path <NUM> and the second resonant radio frequency conductive path <NUM> share the intermediate node <NUM> and the third radio frequency conductive path <NUM>, comprising the shunt resonant element <NUM>, between the intermediate node <NUM> and the third node <NUM>.

The operation of the circuitry <NUM> is schematically illustrated in <FIG> illustrates that current I1 carried by the first radio frequency conductive path <NUM> and current I2 carried by the second radio frequency conductive path <NUM> join at the intermediate node <NUM> to create the current I1 + I2 carried by the third radio frequency conductive path <NUM> through shunt resonant element <NUM> of impedance Z to the third node <NUM>.

When I2=p*I1 where p is a factor, the input impedance Zin, <NUM> at the first node <NUM> is (<NUM> +p). Z , and the input impedance Zin, <NUM> at the second node <NUM> is ((<NUM> +p)/p). The circuitry <NUM> therefore has two current paths to the third node <NUM> with potentially different impedance.

When I1 =I2, then p=<NUM>, and Zin, <NUM> = Zin, <NUM>. This occurs when the phase shift provided by the phase shift element <NUM> is equal to the phase delay provided by the internode radio frequency conductive path <NUM>. When I1 =I2, it appears as if one resonator is "replicated", and the combined resonant structure (band-stop behaviour) operates at exactly the same frequency. This condition is called "double zero" and is illustrated in <FIG>.

By imposing the condition that p ≠ <NUM>, the first resonant radio frequency conductive path <NUM> and the second resonant radio frequency conductive path <NUM> have different impedances. Two separate zeroes at different frequencies are achieved as illustrated in <FIG>. The frequency separation between these two resonant frequencies is proportional to <MAT> where φshift is the phase shift (delay) introduced by the phase shift element <NUM>, and φinternode_path is the phase delay provided by the internode radio frequency conductive path <NUM>.

One can model the result as replicated resonators coupling to each other where the extent of coupling is determined by |φshift - φinternode_path|. The extent of coupling also effectively determines a bandwidth of the obtained band-stop filter.

The operational bandwidth of the filter response illustrated in <FIG> is between <NUM> and <NUM> at -20dB to -40dB.

The first resonant radio frequency conductive path <NUM> between the first node <NUM> and the third node <NUM> has a single zero transfer function. The second resonant radio frequency conductive path <NUM> between the second node <NUM> and the third node <NUM> has a single zero transfer function. The phase shift element <NUM> separates the zero of the transfer function for the first resonant radio frequency conductive path <NUM> from the zero of the transfer function for the second resonant radio frequency conductive path <NUM>.

The first resonant radio frequency conductive path <NUM> comprises a first radio frequency conductive path <NUM> between a first node <NUM> and the third node <NUM> via the shunt resonant element <NUM>. The second resonant radio frequency conductive path <NUM> comprises a second radio frequency conductive path <NUM> between the second node <NUM> and the third node <NUM> via the same shunt resonant element. The shunt resonant element <NUM> has, in this example, a single zero transfer function.

The first radio frequency conductive path <NUM> comprises a first transmission line, the second radio frequency conductive path <NUM> comprises a second transmission line; and the internode radio frequency conductive path <NUM> comprises a third transmission line. The first transmission line and the second transmission line are identical branches from the third transmission line except that the first transmission line comprises the phase shift element <NUM>.

In some examples, the phase shift element <NUM> has a fixed value of phase shift introduced to the first radio frequency conductive path <NUM>. In other examples, the phase shift element <NUM> is configured to vary the value of a phase shift introduced to the first radio frequency conductive path <NUM>. For example, circuitry <NUM> can be configured to control the phase shift element <NUM> to change the relative phase shift between the first resonant radio frequency conductive path <NUM> and the second resonant radio frequency conductive path <NUM>. The circuitry <NUM> can be configured to control or enable control of the phase shift element <NUM> to select one of a plurality of predefined phase shifts.

The circuitry <NUM> can operate as a bandstop filter <NUM>. In this example, the circuitry <NUM> is arranged in an in-line series configuration where input/output nodes <NUM>, <NUM> of the filter <NUM> are coupled to the respective first and second nodes <NUM>, <NUM> of the circuitry <NUM>. In the example illustrated in <FIG> and <FIG>, when the third node <NUM> is connected to ground, the band stop filter <NUM> provides a frequency selective low impedance path to ground via the intermediate node <NUM>, shunt resonant element <NUM>, and the third node <NUM>.

The circuitry <NUM> can operate as a band pass filter <NUM> (e.g. <FIG>). In this example, the circuitry <NUM> is arranged in a shunt-to-ground configuration where input/output nodes <NUM>, <NUM> of the filter are coupled to the first node <NUM> of the circuitry <NUM> and the second node <NUM> of the circuitry <NUM> is coupled to ground via an impedance <NUM>. The third node <NUM> of the circuitry <NUM> is coupled to ground.

<FIG> illustrates an example of a filter <NUM> configured as a band pass filter. The filter <NUM> comprises first circuitry <NUM><NUM> comprising circuitry <NUM> as previously described. The filter <NUM> comprises second circuitry <NUM><NUM> comprising circuitry <NUM> as previously described.

The filter <NUM> comprises a four-port cross-coupler <NUM> comprising four ports. One of the ports is coupled to the first node <NUM> of the first circuitry <NUM>, and another of the ports is coupled to the first node <NUM> of the second circuitry <NUM><NUM>. The remaining two ports connect directly inside the cross coupler to provide input/output ports <NUM>, <NUM> of the filter <NUM>.

The first circuitry <NUM><NUM> is configured as a first band stop filter connected via an impedance <NUM> to ground. The first circuitry <NUM><NUM> is arranged in an in-line series configuration where the first and second nodes <NUM>, <NUM> of the first circuitry <NUM><NUM> are input/output nodes of the first band stop filter. The third node <NUM> is connected to ground. The second node <NUM> is connected to ground via an impedance <NUM>.

The second circuitry <NUM><NUM> is configured as a second band stop filter connected via an impedance <NUM> to ground. The second circuitry <NUM><NUM> is arranged in an in-line series configuration where the first and second nodes <NUM>, <NUM> of the second circuitry <NUM><NUM> are input/output nodes of the second band stop filter. The third node <NUM> is connected to ground. The second node <NUM> is connected to ground via an impedance <NUM>.

Thus the second order band-stop filter can be transformed into a band-pass filter <NUM>.

The use of a <NUM>-dB coupler as the four-port cross-coupler <NUM> can produce a reflection-less band-pass filter <NUM>. The creation of the reflection-less bandpass filters is enabled by the constitutive relationship inherent to <NUM>-dB couplers, given by: <MAT>.

Where Γ<NUM> and Γ<NUM> represent the reflection coefficient of the two loads (first and second band-stop filters). Under the condition that they are identical, i.e. Γ<NUM> = Γ<NUM>= Γ , the reflection coefficient, S<NUM> vanishes, while the transmission coefficient, S<NUM> becomes equal to jΓ.

<FIG> illustrates an example of circuitry <NUM> as previously described and comprising one additional first resonant radio frequency conductive path <NUM>a between the first node <NUM> and the third node <NUM>. The additional first resonant radio frequency path <NUM>a comprises an additional radio frequency conductive path <NUM>a to the intermediate node <NUM> and the previously described third radio frequency conductive path <NUM> between the intermediate node and the third node <NUM>. The third radio frequency conductive path <NUM>, comprising the shunt resonant element <NUM>, is shared by the first resonant radio frequency conductive path <NUM>, the additional first resonant radio frequency conductive path <NUM>a and the second resonant radio frequency conductive path <NUM>.

The additional first resonant radio frequency path <NUM>a comprises a phase shift element <NUM>a for introducing a relative phase shift to the respective resonant radio frequency conductive path <NUM>a relative to the second resonant radio frequency conductive path <NUM>.

In the illustrated example, the additional radio frequency conductive path <NUM>a extends to the intermediate node <NUM> from a node part-way along the internode radio frequency conductive path <NUM>. In other examples, the additional radio frequency conductive path <NUM>a can extend to the intermediate node <NUM> from the first node <NUM>.

The operation of the 'triple path' circuitry <NUM> illustrated in <FIG> is schematically illustrated in <FIG> illustrates that a current I1 carried by the first radio frequency conductive path <NUM>, a current I3 carried by additional first radio frequency conductive path <NUM>a, and a current I2 carried by the second radio frequency conductive path <NUM> join at the intermediate node <NUM> to create the current I1 + I2 + I3 carried by the third radio frequency conductive path <NUM> through shunt resonant element <NUM> of impedance Z to the third node <NUM>.

The circuitry <NUM> therefore has three current paths to the third node <NUM> with potentially different impedance.

When I1 =I2=I3, then p1=p2=<NUM>, and Zin, <NUM> = Zin, <NUM> = Zin, <NUM>. This occurs when the phase shift provided via each path (including phase shifts introduced by the phase shift elements <NUM>, 40a, if any) between the first node <NUM> and the intermediate node <NUM> is equal. In this case, it appears as if one resonator is "replicated", and the combined resonant structure (band-stop behaviour) operates at exactly the same frequency. This condition is called "triple zero".

By imposing the conditions that p<NUM> ≠ p2 ≠ <NUM>, the first resonant radio frequency conductive path <NUM>, the additional first resonant radio frequency conductive path 11a and the second resonant radio frequency conductive path <NUM> therefore have different impedances. Three separate zeroes at different resonant frequencies are achieved. The frequency separation between these resonant frequencies is dependent upon the phase shifts introduced by the phase shift elements <NUM>, 40a.

<FIG> illustrates an extension of the circuitry <NUM> illustrated in <FIG> to have multiple additional first resonant radio frequency conductive paths 11i. If I1=pi * Ii, then imposing the conditions pi ≠ p(i + <NUM>) ≠ <NUM>, for all i=<NUM>,<NUM>. n, results in an "n-tuple" zero case.

<FIG> illustrates an example of a filter <NUM> configured as a band pass filter. The filter <NUM> comprises first circuitry <NUM><NUM> comprising circuitry <NUM> as previously described with reference to <FIG> and comprises second circuitry <NUM><NUM> comprising circuitry <NUM> as previously described with reference to <FIG>.

The filter <NUM> of <FIG> and/or <FIG> comprises a four-port cross-coupler <NUM> comprising four ports:
wherein a first one of the ports is coupled to the first node <NUM> of the first circuitry <NUM>, wherein a second one of the ports is coupled to the first node <NUM> of the second circuitry <NUM><NUM> and wherein the other two ports connect directly inside the cross coupler to provide input/output ports <NUM>, <NUM> of the filter <NUM>.

The first circuitry <NUM><NUM> is configured as a first band stop filter connected via an impedance <NUM> to ground. The first circuitry <NUM><NUM> is arranged in an in-line series configuration where the first and second nodes <NUM>, <NUM> of the first circuitry <NUM><NUM> are input/output nodes of the first band stop filter. The third node <NUM> is connected to ground. The second node is connected to ground via an impedance <NUM>.

The second circuitry <NUM><NUM> is configured as a second band stop filter connected via an impedance <NUM> to ground. The second circuitry <NUM><NUM> is arranged in an in-line series configuration where the first and second nodes <NUM>, <NUM> of the second circuitry <NUM><NUM> are input/output nodes of the second band stop filter. The third node <NUM> is connected to ground. The second node is connected to ground via an impedance <NUM>.

The use of a <NUM>-dB coupler as the four-port cross-coupler <NUM> can produce a reflection-less band-pass filter <NUM>.

<FIG> demonstrate performance of the circuitry <NUM> configured as different filters. The results for three different topologies are illustrated.

The plots labelled A are single zero. The plots labelled B are double zero. The plots labelled C are triple zero. The resonator(s) <NUM> are configured to operate at a frequency of <NUM> and to have an unloaded Q-factor of <NUM>.

<FIG> demonstrate performance of the circuitry <NUM> configured as different band stop filters <NUM>. The plots labelled A are single resonance. The plots labelled B are double resonance. The plots labelled C are triple resonance. <FIG> plots the Transmission coefficient S21 of the three topologies. <FIG> plots the Reflection coefficient S11 of the three topologies. Increasing the number of resonances results in steeper filtering.

<FIG> demonstrate performance of the circuitry <NUM> configured as different band pass filters <NUM>. The plots labelled A are single resonance. The plots labelled B are double resonance. The plots labelled C are triple resonance. <FIG> plots the Transmission coefficient S21 of the three topologies. <FIG> plots the Reflection coefficient S11 of the three topologies.

The bandwidth of the band-stop and, hence, band-pass filters can be adjusted using the phase shifter(s) <NUM>.

<FIG> illustrates an example of a radio transceiver <NUM> and, in particular, a front end (radio frequency part) of a radio transceiver. The radio transceiver comprises an antenna <NUM>, a filter <NUM> and an additional filter <NUM> formed from circuitry <NUM>. In this example the additional filter <NUM> is a band stop filter <NUM>. In other examples it can be a band pass filter <NUM>.

In other examples, a radio transmitter can be used instead of a radio transceiver <NUM>. In other examples, a radio receiver can be used instead of a radio transceiver <NUM>.

The radio transceiver <NUM> can be a portable electronic apparatus. Examples of portable electronic apparatus include but are not limited to user equipment, mobile stations, hand-held telephones, watches, wearables etc..

The radio transceiver <NUM> can be a network access point such as a base station. Examples of base stations include NodeB (and evolutions NodeB such as gNB).

The circuitry <NUM> can therefore be combined with an existing filter <NUM> to further support alteration of the filter response in a desired system to achieve performance targets.

The filter <NUM> can, for example, be configured to have one or more operational frequency bands that cover a <NUM> NR n79 band between <NUM> and <NUM> and an IEEE <NUM> a/n/ac band between <NUM> and <NUM>.

The above described examples find application as enabling components of: automotive systems; telecommunication systems; electronic systems including consumer electronic products; distributed computing systems; media systems for generating or rendering media content including audio, visual and audio visual content and mixed, mediated, virtual and/or augmented reality; personal systems including personal health systems or personal fitness systems; navigation systems; user interfaces also known as human machine interfaces; networks including cellular, non-cellular, and optical networks; ad-hoc networks; the internet; the internet of things; virtualized networks; and related software and services.

The term 'a' or 'the' is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a/the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use 'a' or 'the' with an exclusive meaning then it will be made clear in the context. In some circumstances the use of `at least one' or `one or more' may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer any exclusive meaning.

Claim 1:
Circuitry (<NUM>) comprising:
a first resonant radio frequency conductive path (<NUM>) comprising a first transmission line between a first node (<NUM>) and a third node (<NUM>);
a second resonant radio frequency conductive path (<NUM>) comprising a second transmission line between a second node (<NUM>) and the third node (<NUM>);
an internode radio frequency conductive path (<NUM>) comprising a third transmission line between the first node (<NUM>) and the second node (<NUM>);
a shunt resonant element (<NUM>) coupled to the third node (<NUM>) and shared by the first resonant radio frequency conductive path (<NUM>) and the second resonant radio frequency conductive path (<NUM>); and
a phase shift element (<NUM>) for introducing a relative phase shift to the first resonant radio frequency conductive path (<NUM>) relative to the second resonant radio frequency conductive path (<NUM>);
wherein the first transmission line and the second transmission line are substantially identical branches from the third transmission line except that the first transmission line comprises the phase shift element (<NUM>).