Op amp bandwidth analysis questions

Question

I have some questions about analyzing the bandwidth of an op amp circuit. In the attached circuit diagram, I understand that the low cutoff frequency is created by C1 and R3 and it's 1/(2*pi*RC), and it's about 22 Hz. This circuit is on a breakout board, which says on the product page that there is a "-3dB roll off at 100Hz", so how do you get 100 Hz from this?

Another question: what is the purpose of C3? I read that the R4/C3 combination creates a 16 KHz high frequency low pass filter, which I understand based on 1/(2*pi*RC). Why not just remove C3? What's the point of having this "extra filter" of R4 and C3?

I know the high cutoff frequency is the Gain Bandwidth Product/Gain, and I understand it's 15 kHz.

For a similar circuit, I saw a calculation for the cutoff frequency of the bias voltage divider (1/(2*pi*5k*1uF)). What is the significance of this cutoff frequency? What is the purpose of C2?

If someone asked "what is the bandwidth of this amplifier?", is there a straightforward answer with single lower and single upper cutoff (-3 dB) frequencies?

Answer 1

For the OPA344 I read a GBW = 1MHz typ. 2.7~5.5=Vs

I agree BW/Av= 1MHz/66.67 = 15kHz

The problem with uA rail to rail OA's is often driving a capacitive load ( as do most emitter followers). What happens is the phase margin reduces and a bit of overshoot may occur. So adding a pole at the GBW cuttoff helps improve the feedback and reduce the effects of a small capacitive load. I have not personally verified this on OPA344 but know this helps some uA OA's for stability and overshoot.

Answer 2

Tony has addressed the upper cut off frequency at 15 kHz. About your other question (lower cut off frequency)...
The product page claims that the MP401 MEMS microphone itself attenuates frequencies below about 100 Hz. Although they do not say, it is quite possibly a single-pole response. The MEMS microphone designers do not want frequency response to extend to zero, else it becomes a pressure sensor - it is meant for audio use only.
Your op-amp circuit must also include a high-pass filter, since this MEMS microphone emits a DC voltage of 0.8v to which is added the audio AC. You wish to amplify the AC, and reject the DC, which is accomplished by C1, R3. Since the output impedance of the MEMS microphone is 200 ohms, the actual lower cut-off frequency is:
1/(2 * PI * (R3+200) * C1)
This is close to 20 Hz.
The 200 ohm output Z also reduces op-amp gain slightly: 100k/(1500+200).
So you have two cascaded high-pass filters, one having a corner frequency of 100 Hz., the other having a corner frequency of 20 Hz. The composite corner frequency will be slightly higher than 100 Hz.