To: epic@ti.com
Subject: susana - amplifier for electret mic
 
Elite program : ESIEE - Noisy le grand France
Research Program : Meniere Desease Diagnose (intracranial pressure 
estimation)
 
Context : ADC 200kHz 24 bits (probably PCM4202)
Electret Microphone in the auditory canal (ear)
Emitter : sine wave 1kHz
We study only the ear response @ 800Hz
Recorded signal : 10 micro Vrms (for 800Hz) + 1milliVrms (for 1kHz)
 
Amplification chain
1- Electret microphone (2 wires)
2- Amplifier (G=1000) (signal ~ 1V)
3- high pass filter (50Hz rejection)
4- high order low pass filter (to reject 1kHz and keep the 0.8kHz)
5- Amplifier (G=1000) (to amplify the signal at 800Hz)
6- ADC
 
Different questions
 
* In TI Home > Amplifiers and Linear > Audio Amplifiers
http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?family=analog&familyId=20&uiTemplateId=NODE_STRY_PGE_T
Two categories appear : 
- microphone preamplifier (INA 103, INA 163, INA 166, INA 217, PGA 2500)
- signal conditionning preamplifier (OPA1632)
We do not see which family we have to choose and why ?
The electret microphone can be considered as a single-ended source.
 
*Ground
Our device will be portable and so there is not a "real ground",
I mean a wire with quasi null resistance connected to the ground.
Is that a problem for such application ? Audio professional apps are
always connected to the electricity network that can offer a "real ground".
 
*Power
We will work with batteries. Last year we test the 4202 using your 
PCM4202 EVM.
We notice that the noise present in the +5 -5 was producing 
misbaheviors. Is there
a technical note of TI for that, in order to use the best and most 
correct capacitors
for decoupling and the best linear regulators for such audio applications.
 
Thx

Brgs Lilian Buzer