sim ic tricks ..

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[SIZE="4"]BGF100 - EMI MIC FILTER IC[/SIZE]
BGF100-(EMI FILTER) Mic IC - Used in most BB5 phone that also used RETU 3.02 Audio / UI IC’s..this kind of IC was designed with differential microphone filter.
This one works same as EMIF01-SMIC01. but this one designed as a differential-meaning both positive at negative lines of the microphone were both filtered. the negative side of the microphone is not directly connected to ground…
. see picture below:


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[SIZE="3"]BGF100 in Mic Internal Circuit..[/SIZE]
Now, here how it works, when making a call a voltage / current will draw the line of R211 to supply the
Vcc (B+ terminal) A2 of the said IC to turn the microphone into active state. Once in active state the phone is now on capable of catching sounds and then feed it to the lines of B4 to B1, C4 to C1 and then send to C2100 and C2101 to purify the audio signal and send to RETU IC to amplify during transmission.

[SIZE="4"]BGF100[/SIZE]in Mic External Circuit When plugging an external headset the terminal or bump A4
Will react and send small signal to RETU to release the voltage/current of 2.1V to supply
the IC. And then the voltage / current will draw the line of R211 to supply the
Vcc (B+ terminal) A2 of the said IC to turn the microphone into active state. Once in active state the phone is now on capable of catching sounds and then feed it to the lines of B4 to B1, C4 to C1 and then send to C2100 and C2101 to purify the audio signal and send to RETU IC to amplify during transmission

(all credit goes to original poster)

thanks..