Mạch khuếch đại micro MAX9814 ( 1C4.1 )



Bộ khuếch đại micrô MAX9814 với AGC và âm thanh tiếng ồn thấp.
Tính năng, đặc điểm:
● Điều khiển tự động điều chỉnh độ khuếch đại  (AGC, 20dB-0dB)
● Fixed 12dB Pre-amp.
● Có thể lựa chọn mức tăng cố định 8dB (40dB), 18dB (50dB), hoặc 28dB (60dB).
●  Programmable Attack Time, Attack and Release Ratio
● Ngõ vào 2.7V đến 5.5VDC
● TDFN 14 chân.
● -40 ° C đến + 85 ° C.

Testing Setup:
MAX9814 module setup is similar to schematic.
5VDC operating from DC power supply.
A/R set at 1:2000 (+V).
Gain (total): +V=40dB, GND=50dB, open=60dB
Oscilloscope CH1: Output audio signal. 1kΩ on MAX9814 MICOUT.
1kHz tone from function generator connected to 8Ω speaker.
DMM =AC output voltage.
2x 1uF bypass/filter caps.

Testing Results:
Output is 1.25V DC offset.
Base noise is no sound (mVp-p)
Output holds steady with varying audio level by moving speaker closer/further from microphone. Acceptable output with frequency sweep from 400 to 12kHz. Still some pickup up to 20kHz. High output noise at high gain. Audio clipping is possible with loud sounds.

Recommendation: MAX9814 functions as designed. Good for general audio speech applications. 40dB gain is good for general talking close to microphone. 50dB is good for general talking within a few feet from the microphone. 60dB gain for 3-5' from microphone. 60dB also has high base noise that does not go away with higher output signals and may cause signal processing problems. A higher AGC control level is required for better attenuation of the varying audio sound levels.

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