1. Home
  2. Electronics Design
  3. Amplifier Noise

Amplifier Noise

Hello ,

Please go to the following link

formatting link

and then go page# 13, figure#16. I tied pin#2 of INA133 to +15volts through a 2MegaOhm variable resistor. pin#3 is connected to a voltage ouput DAC ( AD5532HS ) producing a sine wave of 0 to +5volts unipolar with a offset of zero volts. I adjusted +2.5 volts at the pin#2 inorder to make the sine wave bipolar ( +2.5 volts to -2.5 volts peak to peak). There is a capacitor ( 0.1 uF) between the load and OPA131's non-inverting input inorder to stop DC going to the load. I added the variable resistor so that I can adjust the voltage at the input of the capacitor. Because the capacitor was getting biased with the -15volts supply( When there was no output from the DAC). But now when DAC is not giving any signal to the INA133 ( ZERO) the INA133 is producing a noise or sine wave kind of signal and its also passing through the capacitor to the load. The pin#5 of the INA133 is connected to pin #6 of the OPA131. The Reference pin ( pin#1 ) of the INA133 is connected to ground. The output pin#6 of INA133 is connected to the resistor "R". My load is resistive. My supply is plusminus 15 volts. My variable resistor is surface mount one turn variale resistor.

Regards John

Reply to
john
Loading thread data ...

I read in sci.electronics.design that john wrote (in ) about 'Amplifier Noise', on Thu, 6 Oct 2005:

Don't. Put a 10 kohm pot between +15 and ground and connect the slider to pin 2. Even better, put a 22 kohm resistor between the +15 V and the hot end of the pot, so that 2.5 V happens with the slider near the middle of its range.

If you do that, a 0 V signal from you DAC will give you maximum negative output current. Is that what you really want?

Have you got any DC path from the + input to anywhere? If not, the op-amp will not work.

If you really do want a bipolar current, I suggest you don't bias up the in-amp to get it, but accept a unipolar output from your current

-converter and then convert it to bipolar in a further stage. That eliminates the capacitor you put on the + input of the op-amp.

So you've grounded the feedback signal from the op-amp!

How do you come to have this task? It is clearly taxing your understanding a great deal.

--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
Reply to
John Woodgate

Reply to
john

selection.

Reply to
john

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.