IM73D122V01 ultrasonic frequency range, does aliasing occur in Low Power Mode?

[greg120]

According to the data sheet, the IM73D122V01 has a frequency range extending out to 80KHz in the Ultrasonic mode. If I'm using the microphone in the "Low Power Mode" (eg. 666KHz clock in my case) - will a loud ultrasonic tone (eg. ~40KHz) alias into the normal audio range?

I'm hoping/assuming there is some sort of Low Pass filtering based on the microphone mode/clock. I have a product idea that will be mainly interested in tones less than 2000Hz for most of the time, but the "Ultrasonic Mode" could be useful for providing some other features  too. Assuming there is a LPF in the "Low Power Mode", what would be the cut-off frequency for 666KHz? If there is application note or paper that describes how the filtering works in different modes and clock frequencies please let me know.

Thanks.

[George_T]

Hi @greg120,

Please note that IM73D122 is suitable for audio bandwidth of 20 Hz to 20 kHz, as mentioned in the datasheet. All the specifications mentioned in the datasheet are for this specific range.

The performance can not be guaranteed for operation outside the operating ranges mentioned in the datasheet. 

Thanks and regards,

George

[greg120]

Hi George,

I'm a bit confused by your statement "suitable for audio bandwidth of 20 Hz to 20 kHz".

The data sheet mentions an "Ultrasonic mode" on page 7. Figure "3" on page 4 is titled "Typical free field ultrasonic response" which shows a graph indicating a response up to 80KHz.  The "Acoustic characteristics" on page 6 specify that the "Test conditions" were from "20Hz to 20KHz" but does not say that the microphone is only suitable for "20Hz to 20KHz". So for me, all the above indicates that this microphone will do something in the Ultrasound range.
I presently use the IM69D120 and I'm pretty happy with it (especially its low frequency roll-off), I will buy some of the IM73D122V01 and do some testing with them too.

[George_T · Accepted solution]

Hi @greg120,

Please note that the microphone is not characterized completely for the frequency ranges beyond the mentioned range in the datasheet. So the specifications mentioned in the datasheet are valid only for the specific test conditions specified. Hence if you are planning to use the microphone for ultrasonic range, characterization/testing is required at user end to evaluate the performance.

Infineon is currently developing microphones for ultrasonic applications. More information can be found in the link below. 

https://www.infineon.com/cms/en/product/promopages/mems-microphones/

Thanks and regards,

George