Hello,
Overview: I have implemented the forward path of this circuit as shown here except ONE change: Instead of using 6k|| 60k, I have used two 2.7k resistors (G=10). The total gain of the circuit is supposed to be 1010 or 1V/1mV over the entire range of 0.3 Hz to 1 kHz. I have a Rigol DG4062 function generator which generates EMG signal. I used that as input signal to the circuit.
Issue:
When I measure the output signal amplitude, the signal is substantially lower than expected. The gain is 320 to 500 for frequencies >200 Hz. As the frequency reduces, the gain tends towards 1k.
I measured the individual gain of each stage.
The InAmp Stage provides a gain of 6-10 in the freq range 1 Hz to 1 kHz.
The BPF stage shows a gain of 65- 100 range.
If I measure the combined gain of both stages, I am unable to achieve the highest desired gain.
I thought the feedback path is not necessary for benchtop testing. Is that wrong?
Could anyone please help me understand why there is a gain reduction during the implementation of the circuit?
Thank you.
Hi Bhaskar Ravishankar ,
instead of an answer three questions ;-) :
- Do I understand correctly that you replaced R3, R4, R5 by by two 2.7k resistors in series = 5.4k?
- Does the function generator deliver a sinusoidal signal or does it imitate real EMG signals? In the second case, when you speak of 1 kHz, do you mean the frequency of the spikes (not the upper limit of the associated frequency spectrum)?
- How did you determine the value of C3?
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