The signal is a low duty cycle (~0.1%) periodic pulse at 10 Hz. Using a non-inverting amplifier with op amp, the gain should be (1+Rf/R). Ideally, the pulse would get amplified no matter how weak it is, but realistically there's always some noise, and once the pulse becomes too weak it doesn't get amplified (no amplified pulse at output). Which parameters of an op amp should I be checking for in order to tolerate as low a pulse amplitude as possible?It totally depends on the technique used to recover the signal.
Tell us more about the problem? what signal? what purpose?
A small correction on your view of amplification. Signal of any size will be amplified but it can be too small to use because of the noise. The correct way to think about it is the ratio of the size of the signal to the size of the noise (S/N). You want to make this ratio as large as possible. Too small a ratio and the pulse cannot be seen but it is there at the output.The signal is a low duty cycle (~0.1%) periodic pulse at 10 Hz. Using a non-inverting amplifier with op amp, the gain should be (1+Rf/R). Ideally, the pulse would get amplified no matter how weak it is, but realistically there's always some noise, and once the pulse becomes too weak it doesn't get amplified (no amplified pulse at output). Which parameters of an op amp should I be checking for in order to tolerate as low a pulse amplitude as possible?
Noise figure is not an op amp specification. CMRR would only apply if you use an Instrumentation Amplifier instead of a non-inverting op amp circuit. The op amp specs are Input Voltage Noise and Input Current Noise. TI and Analog Devices have many application notes about op amp noise. An example, of noise analysis and use of op amp noise specs for a non-inverting op amp circuit is this article.Hi guys
I want to be able to amplify a weak periodic pulse signal in the presence of noise. What are the key figure of merits I should be looking out for when selecting an op amp? e.g noise figure, CMRR, etc.
1. Small correction sorry: it's closer to 0.2% -> pulse width of 200 usecSome questions:
1. Your 0.1% duty cycle at 10 Hz infers a pulse width of 100 usec. Is this correct?
2. What are the rise and fall times of the pulse?
3. Do you care about the shape and amplitude or just want to know if a pulse is present?
4. Is your main concern noise produced by the circuit or getting rid of noise which comes into the circuit with the signal? Or both?
5. If noise coming in with the signal, what type of noise is it? Power line interference (50 or 60 Hz), RF pickup, etc.
6. Can you say what type of sensor you are using? What is the source of the pulse?
Yes, the phototransistor is shielded and has an optical bandpass filter in front of its active region. Modulating the LEDs is not an option, unfortunately - I'm working on extending the range of detection solely from the receiving end.Now we're getting somewhere.
You are using a photo-transistor. Is the photo-transistor shielded from ambient light and has a filter that allows IR only?
It is common practice to modulate the IR LED at 38kHz or 40kHz. Have you considered this option?
There are IR receiver modules that are readily available that will detect the 38kHz or 40kHz IR signal for you and give you a logic output.
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by Aaron Carman