Filter circuit in radio frequency power detection circuit

Abstract

A filter circuit in a radio frequency power detection circuit includes input and output lines, wherein: an input terminal of the input and output lines is connected with a first capacitor, the first capacitor is connected with a first filtering sub-circuit; the first filtering sub-circuit is connected with a third capacitor, the third capacitor is connected with a second filtering sub-circuit; the second filtering sub-circuit is connected with an output terminal of the input and output lines. The filter circuit of the present invention is able to effectively improve the detection accuracy of the radio frequency electric source output power, thereby improving the power output accuracy of the radio frequency electric source.

Claims

1. A filter circuit in a RF (radio frequency) power detection circuit comprising: input and output lines, wherein: an input terminal of the input and output lines is connected with a first capacitor, the first capacitor is connected with a first filtering sub-circuit; the first filtering sub-circuit is connected with a third capacitor, the third capacitor is connected with a second filtering sub-circuit; the second filtering sub-circuit is connected with an output terminal of the input and output lines.

2. The filter circuit in the RF power detection circuit, as recited in claim 1, wherein: the first LC filtering sub-circuit comprises a first inductor and a second to capacitor connected with the first inductor; and the second LC filtering sub-circuit comprises a second inductor and a fourth capacitor connected with the second inductor.

3. The filter circuit in the RF power detection circuit, as recited in claim 2, wherein: an inductance of the first inductor of the first LC filtering sub-circuit is 4.5 pH and a capacitance of the second capacitor thereof is 1100 pF.

4. The filter circuit in the RF power detection circuit, as recited in claim 2, wherein: an inductance of the second inductor of the second LC filtering sub-circuit is 6.7 pH and a capacitance of the fourth capacitor thereof is 272 pF.

5. The filter circuit in the RF power detection circuit, as recited in claim 1, wherein: a capacitance of the first capacitor is 100 pF and a capacitance of the third capacitor is 745 pF.

6. The filter circuit in the RF power detection circuit, as recited in claim 1, further comprising multiple resistors.

7. The filter circuit in the RF power detection circuit, as recited in claim 6, wherein: a first resistor is connected between the first capacitor and the first filtering sub-circuit in series, a second resistor is connected between the second filtering sub-circuit and an output terminal of the input and output lines in series, one end of a third resistor is connected with the output terminal of the input and output lines, and the other end of the third resistor is connected with ground.

8. The filter circuit in the RF power detection circuit, as recited in claim 7, wherein: a resistance of the first resistor is 100Ω, and a resistance of the second resistor and the third resistor is 2000Ω.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 is a change curve of an existing 2 MHz RF electric source output power.

[0019] FIG. 2 is a circuit diagram of a filter circuit according to a preferred embodiment of the present invention.

[0020] FIG. 3 is a change curve of an improved 2 MHz RF electric source output power according to the above preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Embodiment 1

[0021] FIG. 2 shows a 1.8 MHz-2.2 MHz RF (radio frequency) electric source filter circuit. In FIGS. 2, C1 and C3 are adapted for allowing AC (alternating current) to pass through, isolating DC (direct current) and coupling. An inductor L1 and a capacitor C2 form a first LC filtering sub-circuit (which is labeled as reference number 1 in FIG. 2); an inductor L2 and a capacitor C4 form a second LC sub-circuit (which is labeled as reference number 2 in FIG. 2); resistors R1, R2 and R3 are adapted for limiting current and dividing voltage.

[0022] The coupling amounts of the LC filtering sub-circuits in the detection circuit at the high, medium and low frequency points are different from each other, which causes the output power of the RF electric source is not balanced in the range of the operating frequency. A waveform of general LC filter circuits is that: a coupling amount of a center frequency is slightly higher than frequencies at both ends, which results in larger differences at high, medium and low frequency points. To equalize the coupling amounts at the three frequency points as far as possible, the coupling amount of the center frequency needs to be reduced, or the coupling amounts of the frequencies at both ends need to be increased.

[0023] The present invention adopts two groups of LC filter circuits connected with each other in series, so as to improve the problem that one group of LC filter circuit has the larger difference in the electric source output power at the lower frequency end and the higher frequency end.

[0024] However, if the two groups of LC filter circuits are directly connected with each other in series, the obtained waveform is as same as that obtained from one group of LC filter circuit, and the coupling amounts of the three frequency points have larger differences. Therefore, the key of the present invention lies in utilizing a medium coupling capacitor C3 which is adapted for connecting the two LC filter circuits in series, for finally increasing the output accuracy of the three frequency points from ±5% to ±2%.

[0025] In addition, the specifications of the components, the capacitance of the capacitors, the inductance of the inductors, the resistance of the resistors, etc. also need to cooperate with each other to achieve the best results. The inductance of the inductor L1 in the first LC filtering sub-circuit is 4.5 pH, a capacitance of the capacitor C2 is 1100 pF; the inductance of the inductor L2 in the second LC filtering sub-circuit is 6.7 pH, a capacitance of the capacitor C4 is 272 pF. The capacitance of C1 is 100 pF, the capacitance of C3 is 745 pF. The resistance of R1 is 100Ω, the resistance of R2 and R3 is 2000Ω.

[0026] Simulation results of this embodiment are shown in FIG. 3, which achieves the design purpose that the coupling amount of the intermediate frequency point is below the coupling amounts of the frequency points at two ends. In the practical testing, when the frequency is 1.8 MHz, the output power is 2976 W which has a difference of 24 W from a rated output power; when the frequency is 2 MHz, the output power is 3012 W which has a difference of 12 W from the rated output power; when the frequency is 2.2 MHz, the output power is 3028 W which has a difference of 28 W from the rated output power. Through testing results, it can be seen that the output power accuracies at three frequency points are all controlled within ±2% of the rated output power. Therefore, the improved filter circuit plays a very obvious role in improving the output accuracy.

[0027] One skilled in the art will understand that the embodiment of the present invention as shown in the drawings and described above is exemplary only and not intended to be limiting.

[0028] It will thus be seen that the objects of the present invention have been fully and effectively accomplished. Its embodiments have been shown and described for the purposes of illustrating the functional and structural principles of the present invention and is subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.