With the development of digital signal processing technology, more and more electronic products use digital audio technology. Digital audio interfaces have become a trend of development, and ECM and MEMS digital microphones using pulse density modulation (PDM) interfaces have also been born. At present, ECM and MEMS digital microphones have become the mainstream of portable notebook computer pickup equipment.
Compared with traditional ECM microphones, digital ECM or MEMS microphones have irreplaceable advantages. First of all, mobile devices are moving towards miniaturization and digitization, and digital pickup devices and technologies are urgently needed. Second, the device contains more and more functional units, such as notebook computers, which integrate Bluetooth and WiFi wireless functions, and the microphone is very close to these interference sources. The requirements of equipment for anti-interference are getting higher and higher; third, the development of triple play requires Internet access, video and voice communication can be carried out at the same time, which is usually encountered by environmental noise and echo in mobile devices; fourth, from To improve production efficiency, I hope to use SMT welding for the microphone. The digital microphone is suitable for SMT welding, which can solve the noise caused by various radio frequency interference of the system to voice communication. Fudi Technology's digital array microphone pickup technology can suppress and eliminate echo and environmental noise during calls. The digital interface facilitates the connection with the digital system .
Analog microphone and digital microphone
Microphone structure: ECM analog microphone is usually composed of diaphragm, back plate, junction field effect tube (JFET) and shielding shell. The diaphragm is a thin film coated with metal. The back plate is made of electret material, which is charged after high-voltage polarization, and the two form a plate capacitor. When the sound causes the diaphragm to vibrate, the distance between the two changes, which causes a voltage change and completes the acoustic-electric conversion. Junction field effect tubes are used for impedance transformation and signal amplification. Some high-sensitivity microphones use op amps to increase the microphone sensitivity (see Figure 1a). The ECM digital microphone is usually composed of a diaphragm, a back plate, a digital microphone chip and a shielding shell. The digital microphone chip is mainly composed of a buffer stage, an amplification stage, a low-pass filter, and an analog-to-digital conversion. The buffer stage completes the impedance transformation, the amplification stage amplifies the signal, and the low-pass filter filters out the high-frequency signal to prevent aliasing during analog-to-digital conversion. The analog-to-digital conversion converts the amplified analog signal into a pulse density modulation (PDM) signal. Sampled 1-bit delta-sigma analog-to-digital conversion (see Figure 1b). MEMS analog microphones are mainly composed of MEMS sensors, charge pumps, buffer amplifiers, and shielded enclosures. Referring to FIG. 1c, the MEMS sensor is composed of a diaphragm made by a semiconductor process, a back plate and a bracket, and an appropriate polarization bias is applied to the back plate through a charge pump. The buffer amplifier completes the impedance transformation and amplifies the signal. The MEMS digital microphone is mainly composed of a MEMS sensor, a charge pump, a digital microphone chip and a shielding shell, refer to FIG. 1d. In order to improve the anti-interference ability of the microphone, a small filter capacitor is added between the internal power supply of the microphone and the ground, usually 10pF and 33pF in parallel.
Figure 1a ECM analog microphone Figure 1b ECM digital microphone
Figure 1c MEMS analog microphone Figure 1d MEMS digital microphone
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