MEMS Microphone

MEMS Microphone

NJR researched MEMS microphone transducer for smartphone microphone module etc. from 2010, and Mass-production has carried out since March 2013. MEMS microphones for smartphone headphone set etc. have been shipped smoothly after mass-production. The delivery quantity exceeded 200 million until November 2014.With the expansion of small microphone demand in the future, we are planning to improve the production capacity for production increase and stable supply. We are researching new products and will put on the market one by one.

【Market Trend of Small Microphone】

Even though ECM (Electret Condenser Microphones) had been used for small microphone, MEMS (Micro-Electrical-Mechanical System) microphones are replacing ECM recently. The reasons that ECM are being replaced by MEMS microphones are that MEMS have excellent heat resistance than ECM with hand soldering, can be reflow soldered and mounted with other semiconductors or electronic parts, and have high reliability and low cost implementation.

A MEMS microphone is one module that consists of MEMS microphone transducer and MEMS microphone amplifier. The MEMS microphone transducers and amplifiers are designed and manufactured in pair by NJR. Therefore that can make it easier to match the characteristics as microphone module for microphone module manufacturers.


MEMS Microphone Transducer

The size of NJR’s MEMS microphone transducer NJD3002 is 1.3mm (length) x 1.3mm (width) x 0.4mm (thickness). The diameter of membrane is 750um. The transducer is hollow under the membrane. Usually the sensitivity of MEMS transducer will reduce with the downsizing. NJR improved the vibration mode of the membrane, so established a technology to achieve both miniaturization and high sensitivity. That technology will be applied to the future products.

The structures of NJR’s MEMS microphone transducer NJD3002 are showed in the following figures.

microphone microphone

MEMS microphone transducer is actually condenser type microphone. It is composed of a top membrane and a back plate with a number of sound holes on both sides of the cavity. Sound pressure vibrates the membrane of MEMS microphone transducer, so the capacity of the condenser is changed. Therefore MEMS microphone transducer converts the sound pressure into an electrical signal. Then the electrical signal is processed by the following microphone amplifier.


MEMS Microphone Amplifier

MEMS Microphone Amplifier

NJR’s MEMS microphone amplifiers have analog output type and digital output type. NJR’s long-term analog technologies have strong competitive advantages, especially low power consumption, high SNR, and high integration, etc. That excellent performance advantages are also applied to the MEMS microphone amplifiers.

The inner structures of analog output and digital output MEMS microphone amplifiers are showed as follows.

Analog MEMS Microphone Amplifier Digital MEMS Microphone Amplifier
microphone microphone
NJU72084 NJU9553(Development)

The analog output MEMS microphone amplifier includes the following 3 blocks. Those are reference circuit (VREG), Charge Pump and preamplifier (PREAMP).
The reference circuit generates a reference voltage for charge pump. The charge pump can boost the reference voltage several times for driving MEMS microphone transducer. The preamplifier outputs analog signal from MEMS microphone transducer by impedance conversion. That makes a gain adjustment effect.

The digital output MEMS microphone amplifier adds a ΔΣ modulation circuit behind the preamplifier based the analog output amplifier, converts an analog signal into PDM (Pulse density modulation) signal and outputs, so directly connects encoder or DSP for digital processing.


Supply Chip Sets to Microphone Module Manufacturers

MEMS Microphone Module

Usually the characteristic of MEMS Microphone transducer will be changed along with membrane stress and thickness. Therefore it is necessary to develop a MEMS microphone amplifier matching the transducer. NJR designs and manufactures both MEMS microphone transducers and amplifiers. The characteristic matching work becomes easy by using those in pair. Furthermore it is the most important feature that can improve the capability and reliability of MEMS Microphone module.

As above, NJR supplies the MEMS Microphone transducers and amplifiers to microphone module manufacturers.

In the future, NJR will develop new higher sensitivity and smaller MEMS microphone transducers than NJD3002. Moreover we will introduce the digital output MEMS microphone amplifiers with a built-in ΔΣ modulator and PDM output in the next few days.



For MEMS Microphone

Analog Output



microphone microphone

NJU72090 (Development)

Pre Amp
(Adjustable gain)

Digital Output


NJU9553 (Development)

microphone microphone

◆Data Sheet
MEMS Microphone Transducer NJD3002PDF
◆Data Sheet
Analog MEMS Microphone Amplifier NJU72084PDF

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