With reference to the below small datasheet:

https://www.limpkin.fr/public/HB100/HB100_Microwave_Sensor_Application_Note.pdf

I have created the two stage pre-amplifier and it appears to work great. I have paired it with matlab and generated script which logs the data. However, I have found that the IF output from the amplifier (10,000 times greater than input) is 1.6V and It fluctuates slightly depending on the doppler effect on the radar module.

Can anyone explain why the output is 1.6V? I imagine it would be much, much lower and would only fluctuate when movement was detected.

The reason being is I have just fried my 16bit ADC converter by inputting those very large values and amplifying it again by 8. OOPS!

Thanks for reading!

Regards

Rich

 

hi 87,
There is a Vsup/2 resistive divider on the +inp of the output amp, this sets the OPA output above 0v.
E

EDIT:
What is the part number of your A2D IC.?

 

Of course, yes I see. However, with a 5V input should it not be 2.5V output instead of the 1.6V I am seeing?

The ADC is a cheap ADS1115 16bit ADC with programmable gain upto 16x, see datasheet below:

http://www.ti.com/lit/ds/symlink/ads1115.pdf

Max voltage it can tolerate is 5V which isn't a problem, but I was using the programmable gain which increased 1.6V to 12.8V or so.

RIch

 

hi 87,
If you have the space on your PCB, you could add another LM324 configured as a level shifter.
Will also look thru the ADC d/s, it may have a Vref offset feature.
E
EDIT:
No Vref, but it will accept +/-V inputs, so why not AC couple the amp output to the ADC input.??

 

hi 87,
This LTSpice sim shows the Vout for Vin =0, ie: ~ +2.5v.
Have you scoped the Vout signal.?
E
Added: 100Hz Doppler sine at 10uV