This guide covers the installation of silicon microphones on flexible PCBs, as well as structural design considerations for echo and noise cancellation in mobile devices.
1. Installation of Silicon Microphones on Flexible PCBs
Installation Space: When installing the silicon microphone on a flexible PCB, there must be more than 5mm of space between the edge of the flexible PCB and the microphone.
Reinforcement Requirements: To install the microphone on the flexible PCB, additional reinforcing ribs should be added to the PCB, and the thickness of these ribs must exceed 0.25mm for proper stability.
2. Echo Cancellation and Noise Reduction in Mobile Devices
Echo Cancellation in Mobile Devices
To reduce echo in mobile phone systems, the microphone must be isolated from the internal speaker cavity to minimize the amount of echo picked up by the microphone.
The speaker must be tightly integrated with the device housing, and a shock-absorbing, airtight gasket should be placed between the speaker assembly and the housing. Additionally, the microphone's silicone sleeve must form an airtight seal with the internal cavity, and the microphone needs its own isolated chamber to prevent echo from the speaker reaching the microphone. At least one of these methods must be implemented for effective echo cancellation.
Noise Cancellation with Two Omni-Directional Microphones
The main goal of noise cancellation is to preserve close-range voice signals while eliminating distant background noise. This is achieved using two microphones on the phone, which distinguish between the useful signal and noise by analyzing the difference in energy levels.
The microphone setup must first satisfy echo cancellation requirements (airtightness). Then, under normal handheld conditions, the two microphones should capture a difference in voice energy of at least 6dB (usually 8-10dB) and have parallel frequency spectra. The positions of the microphones on the phone determine these requirements.
