# Resistor 'absorbs' oscillation?

#### lennybogzy

I have a tiny bit of current fluctuation on one of my lines. If i put a lil 500ohm resistor in the line the osillations on the other end substantially decrease.

Why?

Does the resistor effectively 'absorb' these oscillations?

Related Electrical Engineering News on Phys.org

#### Integral

Staff Emeritus
Gold Member
It is hard to say much without some knowledge of the circuit. If you could tell us more it would help.

#### Bob S

If you are talking about standing waves (oscillations) in transmission lines, then terminate the t-line with its characteristic impedance; e.g., 50 ohms for RG-58. A t-line that is open at one end has a current node (voltage maximum) at the end, and reflects the forward signal..
Bob S.

#### lennybogzy

Thanks for the replies.

Specifically I'm talking about a X96010 programmable current generator. My suspicion is that the analog temperature driven Vsense for this device is a bit unstable, normally unnoticable, but because there is a high speed LT1394 comparator with a relatively small hysteresis in the design, becomes a problem right around the switch point (otuput oscillates).

Might also have to do with the fact that the X96010 basically acts as an ADC, and I might be flopping between bytes.

Eithe way it is causing some current fluctuation, which seems to be improved if i put an (arbitrary) 499ohm resistor in the line. I'm trying to understand the fundamental reason for the improvement.

#### famousken

Depending on how long your line is, you could be suffering from oscillation between the source and line. Every line has a capacitance and if you switch a voltage vary quickly into that line, a current spike can be created. What it seems like is happening is that spike is bouncing back and forth between the line and your source; by adding the resistor (in series right?), you are slowing the rate at which the capacitance is charged, reducing the oscillation.

#### lennybogzy

Depending on how long your line is, you could be suffering from oscillation between the source and line. Every line has a capacitance and if you switch a voltage vary quickly into that line, a current spike can be created. What it seems like is happening is that spike is bouncing back and forth between the line and your source; by adding the resistor (in series right?), you are slowing the rate at which the capacitance is charged, reducing the oscillation.
Yes the resistor is in series. Very interesting, thank you.

#### lennybogzy

heres the pic, the current from the x96010 is what i believe osillates

#### Attachments

• 15.3 KB Views: 168

#### Bob S

If the line from the x96010 is a twisted pair, I would out a ~70 ohm resistor upstream of the 0.1 uF capacitor. This plus the capacitor will be an effective termination for the twisted pair.
Bob S

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving