Hello,
I have some questions regarding op amps, and how to reduce noise.
My circuit is built on a breadboard. (Yes, the nylon plastic things, and it is a larger, 3 ic wide board.)
I'm using TL081 op amps in a circuit. The first is configured as a wien oscillator. It puts out a nice sine wave at around 5 kHz, about 10 volts peak to peak. I then pass this signal through a resistor network; a 100 k to an amp configured as a non inverting amplifier, and a 560 ohm resistor to ground.
The second stage has a 6.1 - 10k feedback resistor to the inverting input. A pair of probes measures a resistance which is connected between the inverting input and ground (in the feedback loop.) It all works very well, except there is a lot of noise, coming from the non inverting amp.
I had the circuit working, and left it run while I went to work. When I returned home that evening, and was all set to show a friend, the output was bouncing wildly. It stopped when I shut down the power supply for a few minutes. I then added a few .01uF caps at all my V+ and V- supplies for the chips. Also, I found I could reduce the noise a bit further by adding a .01uF cap across the probes.
I disconnected the oscillator, and the output of the non inverting amp was bouncing with only the power to the chip, and the feedback resistor.
What is most troubling, is that if I just power up a TL081, no resistors at all, or just a 560 ohm on the non inverting input, the chip is still putting out some erratic pulses on pin 6 (output.)
Are these pulses normal in these op amps? How does one deal with this noise? Is it because my circuit is on the breadboard, and it should work better when I try the same circuit on a prototype board? I could handle a bit of noise, but the output is bouncing 50 - 100 milli-volts every time this noise occurs, which will make reading it with an ADC very difficult.
Can anyone shed some light for me?
Thanks for listening,
Robert
I have some questions regarding op amps, and how to reduce noise.
My circuit is built on a breadboard. (Yes, the nylon plastic things, and it is a larger, 3 ic wide board.)
I'm using TL081 op amps in a circuit. The first is configured as a wien oscillator. It puts out a nice sine wave at around 5 kHz, about 10 volts peak to peak. I then pass this signal through a resistor network; a 100 k to an amp configured as a non inverting amplifier, and a 560 ohm resistor to ground.
The second stage has a 6.1 - 10k feedback resistor to the inverting input. A pair of probes measures a resistance which is connected between the inverting input and ground (in the feedback loop.) It all works very well, except there is a lot of noise, coming from the non inverting amp.
I had the circuit working, and left it run while I went to work. When I returned home that evening, and was all set to show a friend, the output was bouncing wildly. It stopped when I shut down the power supply for a few minutes. I then added a few .01uF caps at all my V+ and V- supplies for the chips. Also, I found I could reduce the noise a bit further by adding a .01uF cap across the probes.
I disconnected the oscillator, and the output of the non inverting amp was bouncing with only the power to the chip, and the feedback resistor.
What is most troubling, is that if I just power up a TL081, no resistors at all, or just a 560 ohm on the non inverting input, the chip is still putting out some erratic pulses on pin 6 (output.)
Are these pulses normal in these op amps? How does one deal with this noise? Is it because my circuit is on the breadboard, and it should work better when I try the same circuit on a prototype board? I could handle a bit of noise, but the output is bouncing 50 - 100 milli-volts every time this noise occurs, which will make reading it with an ADC very difficult.
Can anyone shed some light for me?
Thanks for listening,
Robert