Electronic device for processing radio frequency signals and matching circuit for providing variable impedance

1. Field of the Invention

The disclosure generally relates to an electronic device and a matching circuit, and more particularly, relates to an electronic device for processing radio frequency (RF) signals and a matching circuit for providing variable impedance.

2. Description of the Related Art

Compact portable devices usually have smaller antennas, resulting in poor antenna performance and OTA (Over-The-Air) performance. There are two main methods to solve the problem. One is to enhance antenna efficiency, and the other is to increase antenna bandwidth.

FIG. 1 is a diagram illustrating a traditional matching circuit 100 with variable impedance. As shown in FIG. 1 , an antenna 102 is coupled to the matching circuit 100 , which includes inductors 104 , 110 and variable capacitors 106 , 108 . With different capacitances, the variable capacitors 106 , 108 are the primary tuning elements to increase the antenna bandwidth. Different capacitances can be obtained according to controlled voltages of the variable capacitors 106 , 108 . However, the impedance of the matching circuit 100 cannot be tuned by the inductors 104 , 110 , such that freedom of design is limited.

In one exemplary embodiment, the disclosure is directed to an electronic device for processing radio frequency (RF) signals, which comprises an antenna, an RF circuit, and a matching circuit configured to provide variable impedance between the antenna and the RF circuit, wherein the antenna is capable of operating in a first frequency band or a second frequency band according to the variable impedance. The matching circuit comprises a first element having a first terminal and a second terminal, wherein the first terminal is coupled to the antenna; a second element having a third terminal connected to the second terminal of the first element and a fourth terminal coupled to the RF circuit; a first tuning cell connected to the second terminal of the first element and the third terminal of the second element. The first tuning cell comprises a first tuning element, a second tuning element and a first control element, wherein the first control element determines whether to make a first node connected between the first and second tuning elements couple to a voltage level according to a first control signal; and a selecting circuit coupled to the first control element and configured to generate the first control signal so as to adjust the variable impedance.

In another exemplary embodiment, the disclosure is directed to a matching circuit configured to provide variable impedance between an antenna and a RF circuit. The matching circuit comprises a first element having a first terminal and a second terminal, wherein the first terminal is coupled to the antenna; a second element having a third terminal connected to the second terminal of the first element and a fourth terminal coupled to the RF circuit; a first tuning cell connected to the second terminal of the first element and the third terminal of the second element. The first tuning cell comprises a first tuning element, a second tuning element and a first control element, wherein the first control element determines whether to make a first node connected between the first and second tuning elements couple to a voltage level according to a first control signal; and a selecting circuit coupled to the first control element and configured to generate the first control signal so as to adjust the variable impedance.

The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:

FIG. 1 is a diagram illustrating a traditional matching circuit with variable impedance;

FIG. 2A is a diagram illustrating an electronic device according to an embodiment of the invention;

FIG. 2B is a diagram illustrating a tuning cell according to an embodiment of the invention;

FIG. 3 is a diagram illustrating an electronic device according to an embodiment of the invention;

FIG. 4 is a diagram illustrating return loss of an antenna according to an embodiment of the invention.

FIG. 2A is a diagram illustrating an electronic device 200 according to an embodiment of the invention. As shown in FIG. 2A , the electronic device 200 comprises an antenna 202 , an RF circuit 204 , and a matching circuit 210 . The matching circuit 210 is electrically connected between the antenna 202 and the RF circuit 204 , and comprises a plurality of elements 212 - 1 , 212 - 2 , . . . , 212 -N, one or more tuning cells 214 - 1 , 214 - 2 , . . . , 214 -M, and a selecting circuit 216 , wherein N is an integer which is greater than or equal to 2, M is an integer which is greater than or equal to 1, and N is greater than or equal to M. Each of the plurality of elements 212 - 1 , 212 - 2 , . . . , 212 -N may comprise one or more electronic components, such as capacitors, inductors, or resistors. The selecting circuit 216 may transmit one or more control signals S 1 , S 2 , . . . , SM according to a setting signal SSI or a default value so as to adjust impedances of the one or more tuning cells 214 - 1 , 214 - 2 , . . . , 214 -M, respectively. Therefore, the matching circuit 210 can provide variable impedance between the antenna 202 and the RF circuit 204 . It is noted that each of the one or more control signals S 1 , S 2 , . . . , SM may comprise one or more sub-signals. For example, the control signal S 1 may comprise sub-signals S 1 - 1 , S 1 - 2 . The antenna can be operated in a plurality of frequency bands, such as 3G, LTE (Long Term Evolution), DCS (Distributed Control System) Band, or WCDMA (Wideband Code Division Multiple Access) BC1, according to the variable impedance of the matching circuit 210 .

FIG. 2B is a diagram illustrating the tuning cell 214 - 1 according to an embodiment of the invention. As shown in FIG. 2B , the tuning cell 214 - 1 comprises a plurality of tuning elements 218 - 1 , 218 - 2 , . . . , 218 -K and one or more control elements 220 - 1 , 220 - 2 , . . . , 220 -(K− 1 ), wherein K is an integer that is greater than or equal to 2. The plurality of tuning elements 218 - 1 , 218 - 2 , . . . , 218 -K and the one or more control elements 220 - 1 , 220 - 2 , . . . , 220 -(K− 1 ) are electrically coupled between a ground voltage VSS (e.g., 0V) and a work voltage VDD (e.g., 1.8V or 3V). It is noted that each of the other tuning cells 214 - 2 , . . . , 214 -M may comprise the same components as those of the tuning cell 241 - 1 . The control signal S 1 , generated by the selecting circuit 216 , comprises one or more sub-signals S 1 - 1 , S 1 - 2 , . . . , S 1 -(K− 1 ) for controlling the one or more control elements 220 - 1 , 220 - 2 , . . . , 220 -(K− 1 ), respectively. For example, the control element 220 - 1 determines whether to make a node NT 1 , which is electrically connected between the tuning elements 218 - 1 , 218 - 2 , electrically connect to the ground voltage VSS according to the sub-signal S 1 - 1 . The control element 220 - 1 may be a switch or a diode. In one embodiment of the invention, if the sub-signal S 1 - 1 is equal to the work voltage VDD, the control element 220 - 1 electrically connects the node NT 1 to the ground voltage VSS, and if the sub-signal S 1 - 1 is equal to the ground voltage VSS, the control element 220 - 1 does not electrically connect the node NT 1 to the ground voltage VSS or opens the node NT 1 . The other control elements 220 - 2 , . . . , 220 -(K− 1 ) may have similar features to that of the control element 220 - 1 , so they will not be described again.

FIG. 3 is a diagram illustrating an electronic device 300 according to another embodiment of the invention. As shown in FIG. 3 , the electronic device 300 comprises an antenna 302 , an RF circuit 304 , and a matching circuit 310 .

The matching circuit 310 is configured to provide variable impedance between the antenna 302 and the RF circuit 304 . The antenna 302 is capable of operating in at least a frequency band F 1 or a frequency band F 2 according to the variable impedance provided by the matching circuit 310 . The matching circuit 310 comprises at least two elements 312 - 1 , 312 - 2 , at least one tuning cell 314 - 1 , and a selecting circuit 316 . The elements 312 - 1 , 312 - 2 are electrically coupled between the antenna 302 and the RF circuit 304 . The element 312 - 1 has two terminals T 1 and T 2 , wherein the terminal T 1 is coupled to the antenna 302 . The element 312 - 2 has two terminals T 3 and T 4 , wherein the terminal T 3 is electrically connected to the terminal T 2 , and the terminal T 4 is coupled to the RF circuit 304 . Each of the elements 312 - 1 , 312 - 2 may comprise one or more electronic components, such as capacitors, inductors, or resistors. The tuning cell 314 - 1 is electrically connected to the terminal T 2 of elements 312 - 1 and the terminal T 3 of the element 312 - 2 , and comprises at least two tuning elements 321 and 322 and at least one control element 331 . The control element 331 determines whether to make a node N 1 , which is electrically connected between the tuning elements 321 and 322 , couple to a voltage level according to a control signal S 1 . In an embodiment, the voltage level is the ground voltage VSS. The selecting circuit 316 is configured to generate at least the control signal S 1 according to a setting signal SSI or a default value so as to adjust the variable impedance of the matching circuit 310 .

In some embodiments, the tuning elements 321 and 322 are two capacitors C 1 and C 2 . The control element 331 comprises an RF chock inductor LF 1 and a diode D 1 . The RF chock inductor LF 1 is electrically connected to the node N 1 and receives the control signal S 1 . Inductance of the RF chock inductor LF 1 is greater than 33 nH, such as 56 nH, so as to block signals in high frequency bands. The diode D 1 has an anode electrically connected to the node N 1 and a cathode electrically connected to the voltage level. In an embodiment, the voltage level is the ground voltage VSS.

In another embodiment, the matching circuit 310 may further comprise another tuning cell 314 - 2 which is electrically connected to the terminal T 4 of the element 312 - 2 and the RF circuit 304 . Similarly, the tuning cell 314 - 2 comprises at least two tuning elements 323 and 324 and at least one control element 332 . The control element 332 determines whether to make a node N 2 , which is electrically connected between the tuning elements 323 and 324 , couple to the voltage level according to another control signal S 2 . In an embodiment, the voltage level is the ground voltage VSS. The selecting circuit 316 is further configured to generate the control signal S 2 according to the setting signal SSI or the default value so as to adjust the variable impedance of the matching circuit 310 .

In some embodiments, the tuning elements 323 and 324 are two inductors L 1 and L 2 . The control element 332 comprises an RF chock inductor LF 2 , a diode D 2 , and a blocking capacitor CB. The RF chock inductor LF 2 is coupled to the node N 2 and receives the control signal S 2 . Inductance of the RF chock inductor LF 2 is greater than 33 nH, such as 56 nH, so as to block signals in high frequency bands. The diode D 2 has an anode coupled to the node N 2 and a cathode electrically connected to the voltage level. In an embodiment, the voltage level is the ground voltage VSS. The blocking capacitor CB has one terminal connected to the node N 2 and the other terminal connected to the RF chock inductor LF 2 and the anode of the diode D 2 so as to block DC signals.

The elements 312 - 1 may be an inductor L 3 , and the element 312 - 2 may be a capacitor C 3 .

It is noted that the tuning cells 314 - 1 , 314 - 2 can be swapped with each other. In other words, the tuning cells 314 - 1 may be electrically connected to the element 312 - 2 and the RF circuit 304 , and the tuning cell 314 - 2 may be electrically connected to the elements 312 - 1 , 312 - 2 . The matching circuit 310 may also comprise the same two tuning cells; that is, the tuning cell 314 - 1 is replaced with another tuning cell 314 - 2 or the tuning cell 314 - 2 is replaced with another tuning cell 314 - 1 , so that the two tuning cells are identical.

In one embodiment of the invention, if the control signal S 1 generated by the selecting circuit 316 is equal to the work voltage VDD, the diode D 1 is turned on so as to electrically connect the node N 1 to the ground voltage VSS, and if the control signal S 1 is equal to the ground voltage VSS, the diode D 1 is turned off so as not to electrically connect the node N 1 to the ground voltage VSS. Similarly, if the control signal S 2 generated by the selecting circuit 316 is equal to the work voltage VDD, the diode D 2 is turned on (closed); and if the control signal S 2 is equal to the ground voltage VSS, the diode D 2 is turned off (open).

FIG. 4 is a diagram 400 illustrating return loss of the antenna 302 according to an embodiment of the invention. FIG. 4 is utilized for illustrating measured return loss (unit: dB) over frequency (unit: GHz). If the control signals S 1 , S 2 are both equal to the work voltage VDD, the diodes D 1 , D 2 are both turned on, and the matching circuit 310 can provide first impedance so that the antenna 302 is operated in the frequency band F 1 , DCS Band, which is approximately from 1.71 GHz to 1.88 GHz. On the other hand, if the control signals S 1 , S 2 are both equal to the ground voltage VSS, the diodes D 1 , D 2 are both turned off, and the matching circuit 310 can provide a second impedance so that the antenna 302 is operated in the frequency band F 2 , WCDMA BC1, which is approximately from 1.92 GHz to 2.17 GHz.

Use of ordinal terms such as “first”, “second”, “third”, etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.