Anyone tested the ADC for noise as I am looking at the datasheet again and now wondering on a second look the ADC on the original might not of been noisy as the example has far too big a cap as the input impedance could be even higher and 34Hz is far too low a cut-off.
Anyway I have ordered some 0.01uf/ 0.033uf caps than the 0.1uf example as if the impedance is higher I can work out from the cutoff of the sample I get.
Anyone else been using the ADC and got a good signal I am going to try some electrets and various other inputs.
8.3.2 Analog Interface
Fig. 8-7 Microphone Input
There are two microphone input pin, MICP and MICN. They can be configured as differential
inputs by the microphone PGA (MIC).
The signal of microphone output should be input to Audio Codec through DC-blocking
capacitor, as shown in following figure.
Fig. 8-8 Input DC-blocking capacitor
The capacitance and input resistance from a high pass filter. For example, when the gain of
the MIC module is 20dB, the input resistance is 45kΩ and 0.1uF DC-blocking capacitor is
used, the lower cut-off frequency is:
3 6
1 1 35.4
2 2 45 10 0.1 10
f Hz
The capacitance of the DC-blocking capacitor should be determined by the minimum input
impedance and application requirements. If the output of microphone is single-ended, the
audio ADC input should be connected as following figure.