How can I reduce noises on opamp as an amplifier?

[payam.hs]

lm318n probleme

I use LM318N as an amplifier, but input signal has more SNR than output signal. Input signal is a narrow pulse (200ns) about 20mV and gain is about 12. Please help me!!!

 

[kevpat]

There can be several reasons for distortion at your input.

What is your source (pulse) generated from, can you look at the pulse on a scope without the op amp connected, is the pulse distorted.

How have you built the circuit, have you used long connecting wires for your breadboard and do you have a good ground connection.

The op-amp itself could be a problem, the relatively slow slew rate of the op-amp would indicate that you will get a fair bit of distortion through the amp, especially at such a small signal level.

The rise time of your pulse would indicate that you would need an absolute minimum bandwidth of a couple of meg to minimise distortion. The datasheet shows that at a gain of 12 the gain for this op amp is around about 2Meg so reducing the gain may give you a bit less distortion.

 

[payam.hs]

It is a small signal I amplified by a instrumental amplifier.Anyway I see a good (high SNR) signal on oscople before LM318N(40Mhz WB), but output signal is noisy. I check out some other opamps such as TL072(2MHz WB) and Lf356(5MHz WB) but there is no defferent. I confused.
Would u tell me more about good ground?!!!

 

[khotkar]

Please check the input offset and output offset voltage of opamp.

 

[payam.hs]

What do u mean? both input and output signals has no DC voltage. I use a highpass filter before this amplifier.

 

[raghuram_msc]

Hi all,

I guess what khotkar has to say is - "Did you Null-Offset your Op-Amp properly?" More so that the data sheet indicates that the Time constant of the device itself is ~ 50ns. This means fair amount of distortion w.r.t 200ns pulse. Also on the whole if you could tell what is your 'previous' and 'next' stage in your design may be we can zero upoun the best method to sort out with the noise...!

All the best..!
Sai

 

[johnyaya]

Have you checked the opamp output with and without your high-pass filter?

 

[ameed]

hi all,

It is a small signal ,amplified by a instrumental amplifier.Anyway I see a good

(high SNR) signal before LM318N(40Mhz WB), but output signal is

noisy. I check out some other opamps such as TL072(2MHz WB) and Lf356(5MHz

WB) but there is no defferent.

thanx....

 

[hanm]

Of cource it is! This is because the amplifer adds in noise. Things always like this!