Balun device

This application claims the benefit of U.S. provisional application Ser. No. 61/136,504, filed Sep. 10, 2008, and Taiwan application Serial No. 98104245, filed Feb. 10, 2009, the subject matter of which is incorporated herein by reference.

1. Field of the Invention

The invention relates in general to a balun device, and more particularly to a balun device with wave-filtering function.

2. Description of the Related Art

Along with the booming growth in the industry of wireless communication, more and more communication products are developed and provided, and how to improve the function of a communication product has become one of imminent goals to be achieved. In a communication product, the radio frequency module of a communication device includes an antenna, a low noise amplifier, a filter, a balun device, and so on.

After a wireless signal is received by the antenna of the communication device, a single port electrical signal outputted from the antenna will be outputted to the balun device. Then, the balun device converts the single port electrical signal into a dual port electrical signal, and further outputs the dual port electrical signal to a next-stage circuit for further processing. If the wave-filtering effect of the filter is not good enough, the balun device needs to be equipped with wave-filtering function. Thus, how to provide a balun device with wave-filtering function has become one of the imminent goals to the manufacturers.

The invention is directed to a balun device, wherein the decay rate at the stopband of the balun device can be increased, so that the balun device produces excellent wave-filtering effect.

According to a first aspect of the present invention, a balun device is provided. The balun device includes a first inductance element, a second inductance element, a first capacitance element, a second capacitance element, a third capacitance element and a third inductance element. The first inductance element has a first end and a second end, wherein the first end is for receiving an input signal. The second inductance element has a third end and a fourth end, wherein the third end is for outputting a first output signal corresponding to the input signal, and the fourth end is for outputting a second output signal corresponding to the input signal. The first output signal and the second output signal substantially have the same amplitude but have opposite phases. The second inductance element and the first inductance element generate mutual inductance. The first capacitance element is coupled to the first end. The second capacitance element is coupled to the third end. The third capacitance element is coupled to the fourth end. The third inductance element is connected to one of the first capacitance element in series, the second capacitance element and the third capacitance element.

The invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings.

FIG. 1 shows a circuit diagram of a balun device according to an embodiment of the invention;

FIG. 2 shows a simulated circuit diagram of the balun device in FIG. 1 being in differential mode;

FIG. 3 shows a simulation result of the amplitude im-balance between a first output signal and a second output signal in FIG. 2 ;

FIG. 4 shows a simulation result of a phase difference between the first output signal and the second output signal in FIG. 2 ;

FIG. 5 shows a simulated circuit diagram of the balun device in FIG. 1 being in common mode;

FIG. 6 shows a simulated circuit diagram of the balun device in FIG. 1 being in common mode with the third inductance element L 3 being removed;

FIG. 7 shows a simulation result of the insertion loss according to the simulated circuit of the balun device in FIG. 5 and FIG. 6 ;

FIG. 8 shows a circuit diagram of a balun device according to another embodiment of the invention;

FIG. 9 shows a simulated circuit diagram of the balun device in FIG. 8 being in differential mode;

FIG. 10 shows a simulation result of the amplitude im-balance between a first output signal and a second output signal in FIG. 9 ;

FIG. 11 shows a simulation result of a phase difference between the first output signal and the second output signal in FIG. 9 ;

FIG. 12 shows a simulated circuit diagram of the balun device in FIG. 9 being in common mode;

FIG. 13 shows a simulation result of the insertion loss according to the simulated circuit of the balun device in FIG. 6 and FIG. 12 ; and

FIG. 14 shows a circuit diagram of a balun device according to further another embodiment of the invention.

The invention discloses a balun device including a first inductance element, a second inductance element, a first capacitance element, a second capacitance element, a third capacitance element and a third inductance element. The first inductance element has a first end and a second end, wherein the first end is for receiving an input signal. The second inductance element has a third end and a fourth end, wherein the third end is for outputting a first output signal corresponding to the input signal, and the fourth end is for outputting a second output signal corresponding to the input signal. The first output signal and the second output signal substantially have the same amplitude but have opposite phases. The second inductance element and the first inductance element generate mutual inductance. The first capacitance element is coupled to the first end. The second capacitance element is coupled to the third end. The third capacitance element is coupled to the fourth end. The third inductance element is connected to one of the first capacitance element in series, the second capacitance element and the third capacitance element. A number of embodiments are disclosed below for elaborating the invention.

Referring to FIG. 1 , a circuit diagram of a balun device according to an embodiment of the invention is shown. The balun device 100 includes a first inductance element L 1 , a second inductance element L 2 , a first capacitance element C 1 , a second capacitance element C 2 , a third capacitance element C 3 and a third inductance element L 3 . The first inductance element L 1 has a first end E 1 and a second end E 2 , wherein the first end E 1 is for receiving an input signal. The second inductance element L 2 has a third end E 3 and a fourth end E 4 , wherein the third end E 3 is for outputting a first output signal corresponding to the input signal, and the fourth end E 4 is for outputting a second output signal corresponding to the input signal. The first output signal and the second output signal substantially have the same amplitude but have opposite phases. The second inductance element L 2 and the first inductance element L 1 generate mutual inductance. The first output signal and the second output signal may be a pair of differential signals.

As indicated in FIG. 1 , the first capacitance element C 1 is coupled to the first end E 1 , the second capacitance element C 2 is coupled to the third end E 3 , and the third capacitance element C 3 is coupled to the fourth end E 4 . The third inductance element L 3 is connected to the first capacitance element C 1 in series, and one end E 5 of the third inductance element L 3 is grounded. One end E 6 of the second capacitance element C 2 and one end E 7 of the third capacitance element C 3 are grounded. Despite the third inductance element L 3 of the present embodiment is connected to the first capacitance element C 1 , the invention is not limited thereto. The third inductance element L 3 can also be connected to the second capacitance element C 2 or the third capacitance element C 3 in series. When the third inductance element L 3 is connected to the second capacitance element C 2 in series, the end of the third inductance element L 3 which is not connected to the second capacitance element C 2 will be grounded. When the third inductance element L 3 is connected to the third capacitance element C 3 in series, the end of the third inductance element L 3 which is not connected to the second capacitance element C 2 will be grounded.

Referring to both FIG. 1 and FIG. 2 . FIG. 2 shows a simulated circuit diagram of the balun device in FIG. 1 being in differential mode. During the simulation, it is assumed that the balun device 100 is electrically connected with the input end impedance R 1 , the load end impedance R 2 , and the load end impedance R 3 for performing simulation. One end of the input end impedance R 1 is coupled to the first end E 1 , and the other end of the input end impedance R 1 is grounded. One end of the load end impedance R 2 is coupled to the third end E 3 , and the other end of the load end impedance R 2 is grounded. One end of the load end impedance R 3 is coupled to the fourth end E 4 , and the other end of the load end impedance R 3 is grounded.

The following parameters are applied to the elements of FIG. 2 for simulation: L 1 =L 2 =3 nH, L 3 =0.45 nH, C 1 =1.5 pF, C 2 =2.3 pF, C 3 =2.7 pF, R 1 =R 2 =R 3 =50Ω.

Referring to FIG. 3 , a simulation result of the amplitude im-balance between a first output signal and a second output signal in FIG. 2 is shown. As indicated in FIG. 3 , within the frequency band of 2 GHz˜3 GHz, the curve 102 of the amplitude balance of the balun device 100 shows that the amplitude im-balance between the first output signal and the second output signal is about 1 dB to 1.2 dB and is within the tolerance range.

Referring to FIG. 4 , a simulation result of a phase difference between the first output signal and the second output signal in FIG. 2 is shown. As indicated in FIG. 4 , within the frequency band of 2 GHz˜3 GHz, the curve 104 of the amplitude balance of the balun device 100 shows that the phase difference between the first output signal and the second output signal is about 3 degrees to 4.5 degrees and is within the tolerance range.

Referring to FIG. 5 , a simulated circuit diagram of the balun device in FIG. 1 being in common mode is shown. During the simulation, it is assumed that the balun device 100 is electrically connected with the input end impedance R 4 and the load end impedance R 5 for performing simulation. One end of the input end impedance R 4 is coupled to the first end E 1 , and the other end of the input end impedance R 4 is grounded. One end E 6 of the second capacitance element C 2 and one end E 7 of the third capacitance element C 3 are respectively coupled to the two ends of the load end impedance R 5 .

Referring to FIG. 6 , a simulated circuit diagram of the balun device in FIG. 1 being in common mode with the third inductance element L 3 being removed is shown.

Referring to FIG. 7 , which shows a simulation result of the insertion loss according to the simulated circuit of the balun device in FIG. 5 and FIG. 6 . The curve 108 corresponds to FIG. 5 , and the curve 106 corresponds to FIG. 6 . The curve 108 of the insertion loss of the balun device 100 has a transmission zero around the frequency of 7.5 GHz, so that the decay rate at the stopband near the transmission zero is larger than the decay rate at the stopband on the curve 106 . Thus, the balun device 100 of the present embodiment indeed has wave-filtering function and its wave-filtering effect can compensate other filters for their deficiencies. Also, by adjusting the inductance value of the third inductance element L 3 of the balun device 100 , the frequency of the transmission zero can thus be adjusted.

However, the balun device of the present embodiment is not limited to use one inductance element being connected with one capacitance element in series, and several inductance elements can also be used to be connected with several capacitors in series respectively.

Referring to FIG. 8 , a circuit diagram of a balun device according to another embodiment of the invention is shown. The balun device 100 A includes a first inductance element L 1 A, a second inductance element L 2 A, a first capacitance element C 1 A, a second capacitance element C 2 A, a third capacitance element C 3 A, a third inductance element L 3 A and a fourth inductance element L 4 A. The first inductance element WA has a first end E 1 A and a second end E 2 A, wherein the first end E 1 A is for receiving an input signal, and the second end E 2 A is grounded. The second inductance element L 2 A has a third end E 3 A and a fourth end E 4 A, wherein the first capacitance element C 1 A is coupled to the first end E 1 A, and one end E 5 A of the first capacitance element C 1 A is grounded. The second capacitance element C 2 A is coupled to the third end E 3 A, and the third capacitance element C 3 A is coupled to the fourth end E 4 A. The third inductance element L 3 A is connected to the second capacitance element C 2 A in series, and one end E 6 A of the third inductance element L 3 A is grounded. The fourth inductance element L 4 A is connected to the third capacitance element C 3 A in series, and one end E 7 A of the fourth inductance element L 4 A is grounded.

Referring to both FIG. 8 and FIG. 9 . FIG. 9 shows a simulated circuit diagram of the balun device of FIG. 8 being in differential mode. During the simulation, it is assumed that the balun device 100 A is electrically connected with the input end impedance R 1 A, the load end impedance R 2 A and the load end impedance R 3 A for performing simulation. One end of the input end impedance R 1 A is coupled to the first end E 1 A, and the other end of the input end impedance R 1 A is grounded. One end of the load end impedance R 2 A is coupled to the third end E 3 A, and the other end of the load end impedance R 2 A is grounded. One end of the load end impedance R 3 A is coupled to the fourth end E 4 A, and the other end of the load end impedance R 3 A is grounded.

The following parameters are applied to the elements in FIG. 9 for simulation: L 1 A=3 nH, L 2 A=3 nH, L 3 A=0.45 nH, L 4 A=0.175 nH, R 1 A=R 2 A=R 3 A=50Ω, C 1 A=1.5 pF, C 2 A=2.3 pF, C 3 A=2.7 pF.

Referring to FIG. 10 , a simulation result of the amplitude im-balance between a first output signal and a second output signal in FIG. 9 is shown. Within the frequency band of 2 GHz˜3 GHz, the curve 110 of the amplitude balance of the balun device 100 A shows that the amplitude im-balance between the first output signal and the second output signal is about 0.4 dB to −0.9 dB and is within the tolerance range.

Referring to FIG. 11 , a simulation result of a phase difference between the first output signal and the second output signal in FIG. 9 is shown. As indicated in FIG. 11 , within the frequency band of 2 GH˜3 GHz, the curve 112 of the amplitude balance of the balun device 100 A shows that the phase difference between the first output signal and the second output signal is about 1.5 degrees to −1.5 degrees and is within the tolerance range.

Referring to FIG. 12 , a simulated circuit diagram of the balun device in FIG. 9 being in common mode is shown. During the simulation, it is assumed that the balun device 100 A is electrically connected with the input end impedance R 4 A and the load end impedance R 5 A for performing simulation. One end of the input end impedance R 4 A is coupled to the first end E 1 A, and the other end of the input end impedance R 4 A is grounded. One end E 6 A of the third inductance element L 3 A and one end E 7 A of the fourth inductance element L 4 A are respectively coupled to the two ends of the load end impedance R 5 A.

Referring to FIG. 13 , which shows a simulation result of the insertion loss according to the simulated circuit of the balun device in FIG. 6 and FIG. 12 . The curve 114 corresponds to FIG. 6 , and the curve 118 corresponds to FIG. 12 . The curve 118 of the insertion loss of the balun device 100 A has a transmission zero at the frequency of 5.7 GHz so that the decay rate at the stopband around the transmission zero is larger than the decay rate at the stopband on the curve 116 . Also, by adjusting the inductance value of the third inductance element L 3 and the fourth inductance element L 4 of the balun device 100 A, the frequency of the transmission zero can thus be adjusted.

Referring to FIG. 14 , a circuit diagram of a balun device according to further another embodiment of the invention is shown. FIG. 14 differs with FIG. 1 in that the balun device 100 B further includes a fourth inductance element L 4 B and a fifth inductance element L 5 B. The fourth inductance element L 4 B is connected to the second capacitance element C 2 in series, and one end E 6 B of the fourth inductance element L 4 B is grounded. The fifth inductance element L 5 B is connected to the third capacitance element C 3 in series, and one end E 7 B of the fifth inductance element L 5 B is grounded. If the third inductance element L 3 and the fourth inductance element L 4 B of the present embodiment are different, two transmission zeros at different frequencies are generated in a frequency response of the insertion loss for the balun device.

The balun device of the invention has excellent wave-filtering function so as to increase the decay rate at the stopband of the balun device to produce excellent wave-filtering effect for compensating other filters for their deficiencies. Thus, the communication products using the balun device of the invention has even better efficiency in use and its market competiveness is improved.

While the invention has been described by way of example and in terms of a preferred embodiment, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.