TW201517638A - Microphone circuit - Google Patents

Abstract

The present invention provides a microphone circuit including a microphone, an anti-noise module and a CODEC. The anti-noise module couples to the microphone. The CODEC has a positive input node and a negative input node. The positive input node couples to an output node of the anti-noise module, and the negative input node connects to the output node through a capacitor. The capacitor decreases the interference of radio noise of the microphone within at least one predetermined frequency.

Description

Microphone circuit

The present invention relates to a microphone circuit, and more particularly to a microphone circuit that eliminates noise caused by resonance between a microphone and an antenna.

In general, mobile devices (eg, cell phones, tablets, etc.) that comply with the Global System for Mobile Communications (GSM) specifications typically use Time Division Multiple Access (TDMA) technology to generate high power RF signals. The microphone in the mobile device is often interfered with by the radio frequency signal from the antenna, thus reducing the quality of the call and recording. Especially in the path along the connected area in the circuit board of the mobile device, when the characteristic impedance of the path matches the impedance of the antenna, resonance is caused, so that the microphone is interfered by the radio frequency signal. Therefore, a microphone circuit is needed to improve the noise interference caused by the resonance between the microphone and the antenna.

The invention provides a microphone circuit comprising a microphone, an anti-noise module and a codec. The anti-noise module is coupled to the microphone. The codec has a positive input terminal and a negative input terminal, and the positive input terminal is coupled to one of the output terminals of the anti-noise module, and the negative input terminal is coupled to the output terminal through a capacitor, wherein the capacitor is used to reduce the Interference from at least one specific frequency of radio frequency noise.

100‧‧‧Microphone circuit

120‧‧‧Microphone

122‧‧‧ positive end point

124‧‧‧negative endpoint

150‧‧‧Anti-noise module

152‧‧‧ Output

156‧‧‧ input

160‧‧‧ codec

162‧‧‧ positive input

164‧‧‧negative input

170‧‧‧ Capacitance

1 is a schematic diagram of a microphone circuit provided by the present invention;

2 is a comparison diagram of noise between the microphone circuit provided by the present invention and a conventional microphone circuit.

The apparatus and method of use of various embodiments of the present invention are discussed in detail below. However, it is to be noted that many of the possible inventive concepts provided by the present invention can be implemented in various specific ranges. These specific examples are only intended to illustrate the apparatus and methods of use of the present disclosure, but are not intended to limit the scope of the invention.

FIG. 1 is a schematic diagram of a microphone circuit 100 provided by the present invention. As shown in FIG. 1, the microphone circuit 100 includes a microphone 120, an anti-noise module 150, and a codec (CODEC) 160. In one embodiment, the microphone 120 has a positive terminal 122 and a negative terminal 124, wherein the positive terminal 122 is coupled to the input 156 of the anti-noise module 150 and the negative terminal 124 is coupled to ground. In another embodiment, an impedance element is disposed between the negative terminal 224 and the ground to prevent the microphone 120 from resonating with an antenna at at least one particular frequency. It is worth noting that the impedance component is an inductor, or a resistor, or a combination of an inductor and a resistor.

In this embodiment, the anti-noise module 150 is used to eliminate noise interference between the microphone 120 and the antenna. The anti-noise module 150 includes a filter, or a circuit layout, or a combination of the two. In general, both the microphone 120 and the antenna are located directly below the mobile device. It is worth noting that when the characteristic impedance of the path of the microphone 120 and the antenna feed point is matched to the impedance of the antenna, resonance occurs, so that the microphone 120 is interfered by the noise of the radio frequency signal. In detail, The specific frequencies of the above-described resonant RF signals include 850 Mhertz (Hz), 900 MHz, 1800 MHz, and 1900 MHz.

It is to be noted that the codec 160 has a positive input terminal 162 and a negative input terminal 164, and the positive input terminal 162 is coupled to one of the output terminals 152 of the anti-noise module 150, and the negative input terminal 164 is coupled to a capacitor 170. Connect to ground. That is, the capacitor 170 is disposed between the output terminal 152 and the negative input terminal 164 for improving radio frequency noise caused by resonance between the microphone and the antenna. In detail, since the sound signal received by the microphone 120 cannot pass through the capacitor 170, the sound signal only enters the positive input terminal 162. However, the RF noise will pass through the capacitor 170 into the positive input 162 and the negative input 164, allowing the codec 160 to utilize differential techniques to cancel the RF noise, leaving only the acoustic signal. In addition, it should be noted that the configuration of the microphone 120 is a single mode, and the configuration of the codec 160 is a differential mode.

In detail, when the specific frequency is 850 MHz or 900 MHz, the capacitance value of the capacitor 170 is between 25 pFad (pF) and 35 pFad. In a preferred embodiment, the capacitance of capacitor 170 is 33p Farad. When the specific frequency is 1800M Hz or 1900M Hz, the capacitance value of the capacitor 170 is between 15p farad and 25p farad. In a preferred embodiment, the capacitance of capacitor 170 is 22p Farad. It is worth noting that the capacitance value of the capacitor 170 is related to the specific frequency of the radio frequency signal and the distance between the microphone 120 and the antenna feed point. In other words, the capacitance value of the capacitor 170 is a function of various parameters such as the frequency, the board material of the microphone circuit 130, the distance between the microphone 120 and the antenna feed point, and the like. Therefore, the optimum capacitance value for eliminating radio frequency noise can be calculated by the above parameters.

Figure 2 is a microphone circuit 100 and a conventional wheat provided by the present invention. The noise comparison diagram of the gram circuit, wherein the solid line is the microphone circuit provided by the present invention, and the broken line is the microphone circuit of the prior art. As shown in FIG. 2, the radio frequency noise of the microphone circuit of the present invention is about -84 dB at a frequency of 217 Hz, and the radio frequency noise of the conventional microphone circuit is about -69 dB, so that the microphone circuit of the present invention is effectively reduced. The interference of radio frequency noise. In addition, observing other multipliers of 217 Hz can also find that the radio frequency noise interference of the conventional microphone circuit is more serious. It can be seen that the microphone circuit of the present invention does reduce the noise interference caused by the resonance between the microphone 120 and the antenna.

The above is only the preferred embodiment of the present disclosure, and the scope of the disclosure is not limited thereto, that is, the simple equivalent changes and modifications made by the disclosure of the patent application scope and the description of the invention, All remain within the scope of this disclosure. In addition, any of the embodiments or advantages of the present disclosure are not required to achieve all of the objects or advantages or features disclosed in the present disclosure. In addition, the abstract sections and headings are only used to assist in the search of patent documents and are not intended to limit the scope of the disclosure.

100‧‧‧Microphone circuit

120‧‧‧Microphone

122‧‧‧ positive end point

124‧‧‧negative endpoint

150‧‧‧Anti-noise module

152‧‧‧ Output

156‧‧‧ input

160‧‧‧ codec

162‧‧‧ positive input

164‧‧‧negative input

170‧‧‧ Capacitance

Claims (9)

A microphone circuit includes: a microphone; an anti-noise module coupled to the microphone; and a codec having a positive input terminal and a negative input terminal, and the positive input terminal is coupled to the microphone An output of the anti-noise module, wherein the negative input is coupled to the output through a capacitor, wherein the capacitor is configured to reduce interference of the radio frequency noise of the at least one specific frequency received by the microphone. The microphone circuit of claim 1, wherein the microphone has a positive end and a negative end, the negative end is coupled to a ground, and the anti-noise module is coupled to the positive end . The microphone circuit of claim 1, wherein the at least one specific frequency comprises 850 MHz, 900 MHz, 1800 MHz, and/or 1900 MHz. The microphone circuit of claim 3, wherein when the specific frequency is 850 MHz or 900 MHz, the capacitance of the capacitor is between 25 pF and 35 p farad. The microphone circuit of claim 3, wherein when the specific frequency is 1800 MHz or 1900 MHz, the capacitance of the capacitor is between 15 pFad and 25p farad. The microphone circuit of claim 1, wherein the capacitance value of the capacitor is related to the specific frequency and a distance between the microphone and an antenna feed point. The microphone circuit of claim 1, wherein the anti-noise module is a filter and/or a circuit layout. The microphone circuit of claim 2, wherein an inductor is disposed between the negative terminal and the ground. The microphone circuit of claim 2, wherein a resistor is disposed between the negative terminal and the ground.