Hello I´m working on a medical device prototype, I had a lot of programed but now I having problems with the transducer conditioning for the ADC (I´have a lot experience in dsp but no in analog amplifiers ), I was reading and assembling a lot of circuits but only loosing time.
I was triying to take measurements betwin 100 to 10.000 Hz , using an electret microphone from knowles BEM-233446 is the first of the list, you can download specifications there:
http://www.knowles.com/eng/Products/Microphones/Hearing-instrument/EM-BEM-series
Basically the microphone (it has a fet inside) give me an lineal output of 0.6 volts (when there is no input signal), and it oscillate in frequency and voltage but always centred in 0.6volt like offset of 0.6 volts.
To condition these signal I had installed first of all one condenser of 100nF in serial with the microphone to put out the adc signal and it stabilize the signal in 0dB without offset. After that I connect this to an operational inverter amplifier single supplied obtaining the correct waves on mi oscilloscope.
The problem Starts when I connect mi ADC to the output of the amplifier because automatically it generates a new offset in the signal. Witch could be the reason of this last offset. I was using an TLV 2262 and it had an output impedance near 1ohm (I think). The impùt impedance of our ADC is 200 Ohms, could be this the reason????
I was trying a buffer before the adc but I can´t find the correct configuration. Do you have any idea or information for this?? I need to work with single supply and never more than 5 volts of supply.
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