THS3491 Amplifier Instability Issues

  • Thread starter Thread starter Aryia
  • Start date Start date
  • Tags Tags
    Amplifier
AI Thread Summary
The discussion revolves around amplifying a -6 dBm 75MHz signal to at least 31 dBm using THS3491 evaluation boards. The user removed an attenuation circuit but encountered instability when attempting to increase the gain beyond 10 by adjusting feedback resistors. A second approach using two amplifiers in series yielded lower than expected output (23 dBm instead of 26 dBm) with irregular waveform shapes observed on the oscilloscope. Questions were raised regarding supply voltages and physical layout, indicating potential factors contributing to the instability. The user seeks guidance on their approach and understanding of amplifier behavior.
Aryia
Messages
1
Reaction score
0
TL;DR Summary
Trying to amplify a -6 dBm 75MHz signal but encountering amplifier stability issues
Hello all,
I'm currently trying to amplify a -6 dBm 75MHz signal to at least 31 dBm by using THS3491 evaluation boards. The boards came with an attenuation circuit which I have removed, currently there is only a 50 ohm resistor in series with the output (output-6 dBm). Initially our approach was to tweak the gain by changing the feedback resistors RF/RG but the amplifier seems to become unstable at a gain over 10. Is this normal behavior?

Our second approach was to use two gain amplifiers in series (one 8x with no output resistor into a 10x with a 50 ohm resistor). We received somewhat promising results. We expected 26 dBm output but only measured 23 dBm and the oscilloscope sine wave reading has an irregular shape. *Hopefully I can attach some images*.

I have limited experience with amplifiers, am i approaching the issue wrong?
 
Engineering news on Phys.org
Welcome to PF.

Aryia said:
to at least 31 dBm
And what output voltage does that correspond to?

What are your supply voltages and how are you laying this out physically?

TI datasheet attached for reference...

EDIT -- the datasheet is too large to attach. Let me find a link...

https://www.ti.com/lit/gpn/ths3491
 

Attachments

Last edited:
Hey guys. I have a question related to electricity and alternating current. Say an alien fictional society developed electricity, and settled on a standard like 73V AC current at 46 Hz. How would appliances be designed, and what impact would the lower frequency and voltage have on transformers, wiring, TVs, computers, LEDs, motors, and heating, assuming the laws of physics and technology are the same as on Earth?
I used to be an HVAC technician. One time I had a service call in which there was no power to the thermostat. The thermostat did not have power because the fuse in the air handler was blown. The fuse in the air handler was blown because there was a low voltage short. The rubber coating on one of the thermostat wires was chewed off by a rodent. The exposed metal in the thermostat wire was touching the metal cabinet of the air handler. This was a low voltage short. This low voltage...
Thread 'Electromagnet magnetic field issue'
Hi Guys We are a bunch a mechanical engineers trying to build a simple electromagnet. Our design is based on a very similar magnet. However, our version is about 10 times less magnetic and we are wondering why. Our coil has exactly same length, same number of layers and turns. What is possibly wrong? PIN and bracket are made of iron and are in electrical contact, exactly like the reference design. Any help will be appreciated. Thanks. edit: even same wire diameter and coil was wounded by a...
Back
Top