s******e
发帖数: 2181 | 1 First of all, thank fku0000 to settle my power amplifier question.
Does there exist ultra frequency amplifer? I mean ranges from 0Hz to higer.
Since I want to receive respiration signals, whose frequency is normally 0.2
-0.5Hz.
I found the lowest frequency for TDAs is 10 Hz unfortunately. |
a*******e
发帖数: 62 | |
f*****0
发帖数: 489 | 3 most opamp will have no problem handling that, including the TDA. you just
don't need the input/output capacitors.
now, if you are very particular about output DC drifting, you should stay
with voltage feedback opamps (most opamps are like that). current feedback
opamps tend to have serious DC drifting issues.
if you look for speed of a current feedback opamp but the DC performance of
a voltage feedback opamp, look into ths4012 from TI. |
s******e
发帖数: 2181 | 4 ultra low frequency dosn't mean DC.
The human respiration frequency is very low - under 1Hz. Zero means the
person is dead! I don't want DC signal either.
What I need is to seek an amplifier whose frequency range covers 0.1 to 1Hz.
If I move away the input/output capacitoes of TDA circuit, DC component
will enter. |
s******e
发帖数: 2181 | 5 ultra low frequency dosn't mean DC.
The human respiration frequency is very low - under 1Hz. Zero means the
person is dead! I don't want DC signal either.
What I need is to seek an amplifier whose frequency range covers 0.1 to 1Hz.
If I move away the input/output capacitoes of TDA circuit, DC component
will enter. |
f*****0
发帖数: 489 | 6 you wanted an analog amplifier that has a frequency response from 0.1hz -
1hz, but a cut-off at 0hz.
such a thing has not been invented and will probably never be invented.
you are much better off rethinking your whole architecture or using a
computer on the back-end to solve that problem.
two potential but dumb solutions:
1) use a manually generated DC potential to offset the DC content in the
input signal. the opamp remains a DC amplifier.
2) use a servo (with extremely long time constant) to |
s******e
发帖数: 2181 | 7 Thank you upstairs!
Can I increase the input capacitor to 22 uF so that the impedience for low
frequency attenuates? The original input capacitor was 1 uF. |
s******e
发帖数: 2181 | 8 Thank you upstairs!
Can I increase the input capacitor to 22 uF so that the impedience for low
frequency attenuates? The original input capacitor was 1 uF. |
s******e
发帖数: 2181 | 9 Thank you upstairs!
Can I increase the input capacitor to 22 uF so that the impedience for low
frequency attenuates? The original input capacitor was 1 uF. |
f*****0
发帖数: 489 | 10 you will never be able to find a high quality 22uf capacitor to do what you
wanted to do. electrolytic capacitors are surprisingly leaky and resistive.
your likely best solution is in the digital domain. |
|
|
r*****e
发帖数: 620 | 11 check this, amplifier with bandwidth of 0.025Hz-7.2kHz，and dc offset
rejected
should be OK in your case
R. R. Harrison and C. Charles, "A low-power low-noise cmos amplifier for
neural recording applications" IEEE Journal of Solid-State Circuits, vol. 38
, pp. 958 -965, 2003. |
s******e
发帖数: 2181 | |
f*****0
发帖数: 489 | 13
I would be interested in knowing how they did that.
【在 r*****e 的大作中提到】
: check this, amplifier with bandwidth of 0.025Hz-7.2kHz，and dc offset
: rejected
: should be OK in your case
: R. R. Harrison and C. Charles, "A low-power low-noise cmos amplifier for
: neural recording applications" IEEE Journal of Solid-State Circuits, vol. 38
: , pp. 958 -965, 2003.
|
r******w
发帖数: 13 | 14 How about modulate the ultra low frequency signal to high frequency signal?
After amplified, demodulate the output signal and low pass filter it. |
f*****0
发帖数: 489 | 15 I am not sure if that would have solved the problem. the issue here is that
the useful signal (0.1hz - 1hz) is too close to DC for any analog filter to
work. |
