Part Number: AFE5808A
Other Parts Discussed in Thread: AFE5809, AFE5818
Hi,
We have in the past successfully used the AFE5808A in sonar applications. We normally operate in the 80 to 400KHz range. However we wish to go to even lower frequencies for a new design, as low as 4 kHz. However, the 5808A has a DC offset correction in the LNA which acts like a HPF. Cbypass is a capacitor that affects the HPF corner frequency. By default, the specifications specify the 5808A with a Cbypass of 15nF, which gives the HPF a corner frequency of 100 KHz. In our old designs we used 22nF to lower that a bit to around 70KHz.
However to achieve a corner frequency of 4KHz or lower, Cbypass would have to be very large, something like 1uF. The spec sheet does not seem to suggest a limit to Cbypass.
If I compare the 5808A to the AFE5809 spec sheet, the 5809 suggest that a 1uF could be used for Cbypass for low frequency operations. The 5809 spec sheet also suggest disabling the PGA integrator. However these suggestions are not present in the 5808A spec sheet.
The 5809 spec sheet also has a PGA response curve shown for Cbypass = 1uF.
Even with the integrator disabled, the low frequency response may not be good enough for our application.
The AFEs are attractive to us because of the level of integration. Our devices use large array of tightly packed ceramic receiver elements, and using the AFEs with built-in multi-channel LNA/LPF/ADC is necessary to fit everything together. Being able to operate at a large range of frequencies is also attractive.
Our questions are, is it possible to use the 5808A or similar AFE device for our low frequency (4Khz+) application? If so, does using a large Cbypass degrade the performance of the 5808A?
Alternate suggestions are welcome.
Thanks!
