Processing chip for a digital microphone and related input circuit and a digital microphone

A processing chip for a digital microphone and related input circuit and a digital microphone are described herein. In one aspect, the input circuit for a processing chip of a digital microphone includes: a PMOS transistor, a resistor, a current source, and a low-pass filter. The described processing chip possesses high anti high-frequency interference capabilities and the described input circuit possesses high high-frequency power supply rejection ratio.

RELATED APPLICATIONS INFORMATION

The application claims priority under 35 U.S.C. 119(a) to Chinese application number 201010505911.1, filed on Oct. 9, 2010, which is incorporated herein by reference in its entirety as if set forth in full.

BACKGROUND

1. Technical Field

The embodiments described herein relate to electronic circuits, and more particularly, to a processing chip for a digital microphone and related input circuit and a digital microphone.

2. Related Art

Digital microphone is the electro-acoustic component of microphone for directly outputting the digital pulse signal. Digital microphone has the characteristics of high anti-interference capacities, high integration, and ease of use. As a result, it has been widely used for power and size sensitive portable devices.

FIG. 1is a structure diagram showing a digital microphone under the existing technologies. The digital microphone includes a microphone11and a processing chip12, in which the processing chip12may include an input circuit120, an amplifier circuit121and an analog-to-digital conversion circuit122. In particular, the microphone11converts sound signals into analog electronic signals and sends the analog electronic signals to the processing chip12. Then the input circuit120in the processing chip12receives the analog electrical signals and the amplifier circuit121amplifies the analog signals, and the analog-to-digital conversion circuit122converts the amplified analog electronic signals into digital signals and then outputs the digital signals.

Under the existing technologies, the analog electronic signals outputted by the microphone11carry high-frequency interference signals, the analog electronic signals outputted to the amplifier circuit121by the input circuit120carry relatively strong high-frequency interference signals, resulting in poor anti-high-frequency interference capabilities for the processing chip12. Moreover, the power supply of the input circuit120also carries high-frequency interference signals, resulting in low high-frequency power supply rejection ratio for the input circuit120.

SUMMARY

A processing chip for a digital microphone and related input circuit and a digital microphone are described herein and the described processing chip possesses high anti high-frequency interference capabilities and the described input circuit possesses high high-frequency power supply rejection ratio.

In one aspect, an input circuit for a processing chip of a digital microphone includes:

A PMOS transistor, wherein the gate of the PMOS transistor includes a first branch and a second branch and said first branch being configured to receive the analog electronic signals outputted by the microphone, the source of said PMOS transistor includes a third branch and a fourth branch, and the drain of the PMOS transistor is configured to connect to a ground signal;

A resistor, wherein one end of the resistor is configured to connect to the second branch of the gate of said PMOS transistor and the other end of the resistor is configured to connect to the ground signal;

A current source, wherein the current source is configured to connect to the fourth branch of the source of said PMOS transistor;

A low-pass filter, wherein one end of the low-pass filter is configured to connect to the third branch of the source of said PMOS transistor and the other end of the low-pass filter is configured to connect to an amplifier circuit;wherein the source of the PMOS transistor further comprises a fifth branch connected with a metal layer underneath a pad of the first branch, wherein the area of the metal layer is larger than the area of the pad.

In another aspect, a processing chip for a digital microphone includes an input circuit, an amplifier circuit, and an analog-to-digital conversion circuit, wherein the input circuit includes:

A PMOS transistor, wherein the gate of the PMOS transistor includes a first branch and a second branch and said first branch being configured to receive the analog electronic signals outputted by the microphone, the source of said PMOS transistor may include a third branch and a fourth branch, and the drain of the PMOS transistor is configured to connect to a ground signal;

A resistor, wherein one end of the resistor is configured to connect to the second branch of the gate of said PMOS transistor and the other end of the resistor is configured to connect to the ground signal;

A current source, wherein the current source is configured to connect to the fourth branch of the source of said PMOS transistor;

A low-pass filter, wherein one end of the low-pass filter is configured to connect to the third branch of the source of said PMOS transistor and the other end of the low-pass filter is configured to connect to an amplifier circuit;wherein the source of the PMOS transistor further comprises a fifth branch connected with a metal layer underneath a pad of the first branch, wherein the area of the metal layer is larger than the area of the pad.

In yet another aspect, a digital microphone includes a microphone and a processing chip, wherein the processing chip includes an input circuit, an amplifier circuit and an analog-to-digital conversion circuit, wherein the input circuit includes:

A PMOS transistor, wherein the gate of the PMOS transistor includes a first branch and a second branch and said first branch being configured to receive the analog electronic signals outputted by the microphone, the source of said PMOS transistor may include a third branch and a fourth branch, and the drain of the PMOS transistor is configured to connect to a ground signal;

A resistor, wherein one end of the resistor is configured to connect to the second branch of the gate of said PMOS transistor and the other end of the resistor is configured to connect to the ground signal;

A current source, wherein the current source is configured to connect to the fourth branch of the source of said PMOS transistor;

A low-pass filter, wherein one end of the low-pass filter is configured to connect to the third branch of the source of said PMOS transistor and the other end of the low-pass filter is configured to connect to an amplifier circuit;wherein the source of the PMOS transistor further comprises a fifth branch connected with a metal layer underneath a pad of the first branch, wherein the area of the metal layer is larger than the area of the pad.

After the analog electronic signals outputted by the microphone are put into the first branch of the gate of the PMOS transistor, and biased by the PMOS transistor, the analog electronics signals, which are outputted through the third branch of the source of the PMOS transistor, are filtered by the low-pass filter and then outputted to the amplifier circuit. Because the low-pass filter filters out the high-frequency interference signals in the analog electronic signals, the processing chip's anti high-frequency interference capabilities are improved. Meanwhile, the low-pass filter also filters out the high-frequency interference signals in the power supply of the input circuit, the high-frequency power supply rejection ratio of the input circuit is increased.

DETAILED DESCRIPTION

Referring now to the drawings, a description of embodiments will be made herein.

FIG. 2a schematic diagram showing an input circuit in a processing chip for a digital microphone according to one embodiment. The input circuit may include a PMOS transistor21, a resistor22, a current source23and a low-pass filter24.

In particular, the gate of the PMOS transistor21may include a first branch211and a second branch212, the source of the PMOS transistor21may include a third branch213and a fourth branch214. The first branch211may be configured to receive the analog electronic signals outputted by a microphone, the drain of the PMOS transistor21is connected with a ground signal. One end of the resistor22may be configured to connect with the second branch212and the other end of the resistor22may be configured to connect with the ground signal. The current source23may be configured to connect with the fourth branch214. One end of the low-pass filter24may be configured to connect with the third branch213of the source of the PMOS transistor21and the other end of the low-pass filter24may be configured to connect with an amplifier circuit.

In this embodiment, after the analog electronic signals outputted by the microphone are put into the first branch211of the gate of the PMOS transistor21, and biased by the PMOS transistor21, the analog electronics signals, which are outputted through the third branch211of the source of the PMOS transistor21, may be filtered by the low-pass filter24and then outputted to the amplifier circuit. Because the low-pass filter24filters out the high-frequency interference signals in the analog electronic signals, the processing chip's anti high-frequency interference capabilities are improved. Meanwhile, the low-pass filter24also filters out the high-frequency interference signals in the power supply of the input circuit, increasing the input circuit's high frequency power supply rejection ratio.

In addition, in order to reduce the parasitic capacitor between the pad of the first branch and the substrate, the source of the PMOS transistor21may further include a fifth branch215, the fifth branch215may be configured to connect with a metal layer underneath the pad of the first branch211, where the area of the metal layer may be larger than the area of the pad. Specifically, there may be more than one metal layer underneath the pad and the fifth branch215may be configured to connect with any of the metal layers.

In addition, in this embodiment, the resistance of the resistor22may be greater than or equal to 10 G ohms. In another embodiment, the resistance of the resistor22may be greater than or equal to 20 G.

FIG. 3is a schematic diagram showing a processing chip of a digital microphone according to another embodiment. The processing chip may include an input circuit31, an amplifier circuit121, and an analog-to-digital conversion circuit122. The amplifier circuit121may be configured to connect with the input circuit31, and the analog-to-digital conversion circuit122may be configured to connect with the amplifier circuit121. The input circuit31may include the aforementioned input circuit in the processing chips for the digital microphone.

In this embodiment, the input circuit31may be configured to receive the analog electronic signals outputted by a microphone, the analog electrical signals may be filtered by the low-pass filter24in the input circuit31and outputted to the amplifier circuit. Because the low-pass filter24filters out the high-frequency interference signals in the analog electronic signals, the processing chip's anti-high-frequency interference capabilities are improved. Meanwhile, the low-pass filter24also filters out the high-frequency interference signals in the power supply of the input circuit, the high-frequency power supply rejection ratio of the input circuit is increased.

FIG. 4is a schematic diagram showing a digital microphone according to another embodiment. The digital microphone may include a microphone11and a processing chip41. The processing chip41may include an input circuit31, an amplifier circuit121, and an analog-to-digital conversion circuit122, the input circuit31may be configured to connect with the microphone11, the amplifier circuit121may be configured to connect with the input circuit31, and the analog-to-digital conversion circuit122may be configured to connect with the amplifier circuit121. In particular, the input circuit31may include the aforementioned input circuit in the processing chips for the digital microphone.

In this embodiment, the input circuit31may be configured to receive the analog electronic signals outputted by a microphone, the analog electrical signals may be filtered by the low-pass filter24in the input circuit31and outputted to the amplifier circuit. Because the low-pass filter24filters out the high-frequency interference signals in the analog electronic signals, the processing chip's anti-high-frequency interference capabilities are improved. Meanwhile, the low-pass filter24also filters out the high-frequency interference signals in the power supply of the input circuit, the high-frequency power supply rejection ratio of the input circuit is increased.