TWI301390B - Printed circuit board having low-pass filtering function - Google Patents

Description

1301390

TRIA NUMBER: TW2385PA IX. DESCRIPTION OF THE INVENTION: TECHNICAL FIELD OF THE INVENTION The present invention relates to a circuit board, and more particularly to a circuit board having a low pass filter. [Prior Art], Figure 1 shows the equivalent electrical diagram of the traditional microstrip line low-pass filter: the microstrip line low-pass filter, 10 includes the inductor u, the inductor L2 and the capacitor rain six, L1 The ends of the inductor L2 and the capacitor ci are electrically connected to each other, and the other end is electrically connected to the ground. The conventional microstrip line low pass filter section, the other end of & 1 receives the signal S1' and removes the high frequency in the signal S1: =, and the low frequency part of S1 passes through the other end of the electrification to form the apostrophe S2. Step by step, 'the traditional microstrip line low-pass filter 1G inductor L1, inductor / a C1 system 'knife is formed by the microstrip line' and each microstrip line is engraved in the - power shortage, and the length of the microstrip line The width or capacitance needs to correspond to its inductance value or capacitance value. 'Because the traditional microstrip line low-pass filter 10 is composed of the inductor L1 and the inductor.α valley C1, the inductance L1 and the inductor L2 will cause an increase in the insertion loss _ L〇SS) and a second harmonic loss (2nd). The reduction of Harmonic Loss) makes the signal 82 susceptible to distortion. ^ Z 'Because the design of the inductor requires a considerable length of microstrip line, the length of the board needs to be relatively increased, resulting in an increase in production costs. SUMMARY OF THE INVENTION The purpose of this is to provide a low pass filter. Using a microstrip line to form two capacitors and an inductor to form a low-pass filter 1301390

Sanda number: TW2385PA to avoid signal distortion. In accordance with the purpose of the present invention, a circuit board having a low pass filter is proposed. The circuit board includes a substrate, a first microstrip line, a second microstrip line, and a third microstrip line. The first microstrip line and the third microstrip line are respectively formed on the substrate, and have a length of 8 mm to 8.8 mm and a width of 0.7 mm to 0.9 mm. The second microstrip line also forms _up, and the length is 7.9匪~8.1!^, and the width is 〇6 with ~〇8_. Second volume

One end of the line is electrically connected to one end of the first microstrip line, and the J-end of the second microstrip line is electrically connected to the end of the third microstrip line. #输人信号到第二微蛛 | The end of the line, the board filters out one of the high frequency parts of the signal and outputs it via the other end of the second line I. The above described objects, features, and advantages of the present invention will become more apparent and understood in the light of the description. Shown as an equivalent of a filter in accordance with the present invention. You, g, and also the low-pass 802 m / t system is suitable for the L3" of the wireless local area network. The low-pass filter 20 includes a capacitor C2, a capacitor C3, and an inductor. The terminal of the inductor C2 is electrically connected to the terminal of the inductor u. The other terminal is electrically connected to the terminal of the capacitor C3. One end of the capacitor C2 and the capacitor U are electrically connected to the ground end. Signal s 3 ^ In addition, the low-pass chopper (four) except 4.8 fine z ~ 4.968GHf of 2 = input signal - the low frequency part of the other through the inductor 使 S4. The M-formed signal has a low-pass "light (4) 2_ design - the tool-microstrip line technology; 饳:: = circuit layout diagram. The aforementioned low-pass filter is inscribed on the circuit board 30, the circuit board 3 For example, it is broken glass.

1301390 Sanda number: TW2385PA board (FR4 PCB), and its length and width are 19.5mm~20.5mm, and the thickness is 0.6mm~1mm. The circuit board 30 includes a substrate 210, a first microstrip line 220, a second microstrip line 230, a third microstrip line 240, a first pad 250 and a second pad 260, a first microstrip line 220, a second micro The strip line 230 and the third microstrip line 240 form a 7-turn type structure. The first microstrip line 220 and the third microstrip line 240 are respectively formed on the substrate 210 by etching, and have a length of 8 mm to 8.8 mm and a width of 0.7 mm to 0, 9 mm to be equivalent to the filter 20 described above. Medium capacitors C2 and C3. In addition, making the lengths of the first microstrip line 220 and the third microstrip line 240 inconsistent will effectively reduce the insertion loss (Insertion Loss) to improve the efficiency and increase the 2nd harmonic to enhance the filtering. Harmonic effect. The second microstrip line 230 is also formed on the substrate 210 in a meandering manner, and has a length of 7.9 mm to 8.1 mm and a width of 0.6 mm to 0.8 mm, which is equivalent to the inductance L3 of the filter and the filter 20. . One end of the first pad 250 is electrically connected to one end of the first microstrip line 220 and the second microstrip line 230, and one end of the second pad 260 is connected to the other end of the second microstrip line 230 and the third end. One end of the microstrip line 240 is electrically connected. The first pad 250 and the second pad 260 are respectively soldered to an SMA connector. After the signal S3 is input from the SMA connector on the first pad 250, the high frequency portion of 4.824 GHz to 4.968 GHz is filtered out through the circuit board 30. The low frequency portion of signal S3 is output via the SMA connector on second pad 260 to form output signal S4. Please refer to Fig. 4, which is a waveform diagram of the insertion loss and feedback loss measurement according to Fig. 3. The insertion loss curve 4 01 indicates the insertion loss of the board 30 as a function of frequency, and the feedback loss curve 402 indicates the change in the feedback loss of the board 30 with frequency. The circuit board 30 can avoid insertion loss and increase in second harmonic loss by the foregoing design. For example, when the length of the first microstrip line is 8 mm and the width is 0.8 mm, and the length of the second microstrip line is 8 mm, the width is 0.7 mm, and 1301390

Sanda number·· TW2385PA The length of the third microstrip line is 8.8mm, and the width is 〇.8mm, the energy change of the electrical signal is measured, and the insertion loss is in the working frequency. The board 30 is only 2.422GHz~2.484. Kirin' and the second harmonic loss is about _3〇dB at 4.824GHz~4.968GHz. A board having a low pass filter as disclosed in the above embodiments of the present invention. The invention has the following advantages by combining a low-pass filter and a waveband from two microstrip lines equivalent to a capacitor and an inductive microstrip line. The first advantage is to reduce insertion loss and Secondary spectral wave loss; '. By using the difference between the younger brother-microstrip line and the second microstrip line, the insertion and second harmonic loss will be effectively reduced. The two advantages of Beitian are to reduce the length of the microstrip line. If the inductance and capacitance are made of micro: and silk, respectively, it will be found that the length of the microstrip line of the inductor will be longer than that of the capacitor. Therefore, an inductor and two capacitors form a waver, which will relatively reduce the length required for the microstrip line. In the above description, the present invention has been described as being "preferably implemented", but its dreams are limited by the fact that any skilled person is skilled in the art, without departing from the scope of the invention. Various modifications and refinements are possible, and the scope of the invention is defined by the scope of the appended claims. , 1301390

Erda number: TW2385PA [Simple description of the diagram] Figure 1 shows the equivalent circuit diagram of the traditional microstrip line low-pass filter. - Figure 2 is a diagram showing an equivalent circuit of a low pass filter in accordance with a preferred embodiment of the present invention. As shown in FIG. 3, a circuit layout diagram of a circuit board having a low-pass filter 'as' is designed according to FIG. - The figure 4 is shown as the waveform of the insertion loss measurement according to Fig. 3.

[Main component symbol description] !〇: conventional microstrip line low-pass filter 20: low-pass filter 3 of the present embodiment: circuit board 210 • substrate 220: first microstrip line 230: second microstrip line 24 〇: third microstrip line 250: first pad 260: second pad 塾 LI, L2, L3: inductor

Cl, C2, C3: Capacitor 10

Claims (1)

1301390 Sanda number: TW2385PA X. Patent application scope: 1 · A circuit board with low-pass filtering function, including a substrate; a first microstrip line formed on the substrate and having a length of substantially 8 mm ~8.8mm, the width is substantially 0.7mm~0.9mm; Bay-a second microstrip line is formed on the substrate, and the length is substantially _7.9mm~8.1mm, and the width is substantially 〇6mm~〇 8mm, one end of the second microstrip line is electrically connected to one end of the first microstrip line; and a third microstrip line is formed on the substrate, and the length is substantially 8mm~8.8mm' The width is substantially 〇7mm~〇9mm, and one end of the third microstrip line is electrically connected to the other end of the second microstrip line; wherein when a signal is input to one end of the second microstrip line, the One of the high frequency portions of the signal is filtered out, and the filtered signal is output through the second microstrip: the other end. 2. The circuit board according to claim 1, wherein the circuit board is a fiberglass board (FR4PCB), and the thickness of the fiberglass board is substantially 0.6 mm to 1 mm. 3. The circuit board of claim 1, wherein the circuit board is used to filter out signals in the 4.824 GHz to 4.968 GHz band. The circuit board of claim 1, wherein the length of the first microstrip line is different from the length of the third microstrip line. 5. The circuit board of claim 3, wherein the length of the circuit board is substantially 19, 5 mm to 20.5 mm. 6. The circuit board of claim 2, wherein the width of the circuit board is substantially 19.5 mm to 20.5 mm. 7. The circuit board of claim 1, wherein the circuit board 11 1301390 has a number: TW2385PA further includes a first pad and a second pad, the first pad and the first The microstrip line and one end of the second microstrip line are electrically connected, the first pad is coupled to a first connector, the second pad and the other end of the second microstrip line One end of the third microstrip line is electrically connected, and the second pad is coupled to a second connector. 8. The circuit board of claim 1, wherein the first, second and third microstrip lines form a 7-inch structure. 12