Why is the non-inverting amplifier's bandwidth rating lower than expected?

AI Thread Summary
The discussion centers on the unexpected lower bandwidth of a non-inverting amplifier compared to its rated 1.5MHz. Testing revealed that the non-inverting configuration only achieved 29KHz before distortion occurred, while the inverting configuration performed as expected up to 1.6MHz. The difference in performance is attributed to the gain bandwidth product and feedback factors, which vary between configurations. The LM741 op-amp's slew rate of 0.5V/μs also limits the maximum frequency without distortion, suggesting that the non-inverting setup's gain affects its bandwidth. Overall, the findings highlight the complexities of op-amp behavior in different configurations.
tomizzo
Messages
113
Reaction score
2
Hello, I have a question that I thought some of you may know an answer to.

I was recently testing an op amp is several closed-loop feedback configurations. Primarily inverting, and non-inverting.

When testing the output voltage of an invertin amplifier, I found that the output signal became attenuated at around 1.6MHz. The op-amp's data sheet says the bandwidth is 1.5MHz so this makes sense.

However, when I did the similar test with a non-inverting amplifier, I could only get up to 29KHz before bad deformation occurred. Why is this? I thought the op-amp was rated at 1.5MHz?

Does it have something to do with how many capacitors within the op-amp are being used in a non-inverting configuration?

I haven't been able to find a good answer so I will appreciate any help!
 
Engineering news on Phys.org
tomizzo said:
Hello, I have a question that I thought some of you may know an answer to.

I was recently testing an op amp is several closed-loop feedback configurations. Primarily inverting, and non-inverting.

When testing the output voltage of an invertin amplifier, I found that the output signal became attenuated at around 1.6MHz. The op-amp's data sheet says the bandwidth is 1.5MHz so this makes sense.

However, when I did the similar test with a non-inverting amplifier, I could only get up to 29KHz before bad deformation occurred. Why is this? I thought the op-amp was rated at 1.5MHz?

Does it have something to do with how many capacitors within the op-amp are being used in a non-inverting configuration?

I haven't been able to find a good answer so I will appreciate any help!

What gains were you testing at? Can you share the schematics of your test configurations?
 
The closed loop gain capabilities are a function of the input frequency. If I am not mistaken what would be supplied to you on the specification sheets are the gain bandwidth product of the chip. This can be used, along with your resistors (see 'feedback factor') to find the gain for varying input frequency. The derivation is a little cumbersome, especially in the case of the inverting amplifier, but the end result is that closed loop gain for both configurations only differs by 1 for the same feedback factor. So, for different instances of the same chip, it is odd I believe that you have received such a dramatic bandwidth decrease. As berkeman said it would be a good idea to post how the circuits are connected, I expect these feedback factors are wildly different. The feedback factor is calculated as one divided the non-inverting gain for both an inverting and non inverting amplifier arrangement. This is an oddity but not a unique one in electronics, many things that are common to both configurations (inverting and non inverting) are determined by the non-inverting configuration only. It appears not only here in frequency response but also in noise calculations and beyond.

Hopefully I didn't lead you astray if I did I am sure someone will set us both straight
 
The LM741 op-amps were powered with +/ 15V. The gain for the inverting amplifier was -3 and the non-inverting was 4.

I've posted images below of the circuits.

For the inverting op-amp, Rin = 3.3K ohm and Rf = 10K ohm.

Here is a screen shot of the output being shifted/deformed at 1.75 MHz which is outside the bandwidth of the op-amp. Refer to the attached screenshots from the oscilloscope.


The non-inverting op amp has Rg = 3.3K ohm and Rf = 10K ohm. The non-inverting output became deformed at 29Khz. The op-amp is rated at 1.5Mhz. Why is the output signal being distorted this much? Refer to the second attached screenshot from the oscillscope featuring the triangle wave.

images?q=tbn:ANd9GcQD70c1nUYza0Ed6zb6IPRKS1YZSqSrOaxcPkzstrbafsl0wpMe.png


220px-Operational_amplifier_noninverting.svg.png
 

Attachments

  • scope_2.png
    scope_2.png
    14.9 KB · Views: 538
  • scope_12.png
    scope_12.png
    10.9 KB · Views: 508
Strange. If you use smaller signals, like around 1V max output voltage swing, what do you get for the bandwidths?
 
LM741 has a slew rate around 0.5V/us So the Fmax without distortion for 6V peak output is equal to
Fmax = (0.5V/us)/( 2 * pi * 6V) = 13.4KHz
So your op amp has slightly better SR then 0.5V/us.
Also the small signal bandwidth should be equal to.
fc = 1.5MHz/gain = 1.5MHz/4 = 375kHz
 

Thread 'What happens if shielded cable has a short to the shield?'

While I was rolling out a shielded cable, a though came to my mind - what happens to the current flow in the cable if there came a short between the wire and the shield in both ends of the cable? For simplicity, lets assume a 1-wire copper wire wrapped in an aluminum shield. The wire and the shield has the same cross section area. There are insulating material between them, and in both ends there is a short between them. My first thought, the total resistance of the cable would be reduced...
View full post »

Thread 'Underwater piezoelectric sensor array receive sensitivity'

Hi all I have some confusion about piezoelectrical sensors combination. If i have three acoustic piezoelectrical sensors (with same receive sensitivity in dB ref V/1uPa) placed at specific distance, these sensors receive acoustic signal from a sound source placed at far field distance (Plane Wave) and from broadside. I receive output of these sensors through individual preamplifiers, add them through hardware like summer circuit adder or in software after digitization and in this way got an...
View full post »

Thread 'Question about bonding ground and neutral'

I am not an electrical engineering student, but a lowly apprentice electrician. I learn both on the job and also take classes for my apprenticeship. I recently wired my first transformer and I understand that the neutral and ground are bonded together in the transformer or in the service. What I don't understand is, if the neutral is a current carrying conductor, which is then bonded to the ground conductor, why does current only flow back to its source and not on the ground path...
View full post »

Similar threads

How Do Op Amps Respond to Inverting and Non-Inverting Inputs?
Replies
12
Views
2K
Op-amp compensation of cascade fudges audio signal oddly
Replies
3
Views
2K
How to clasify if it's an inverting/non-inverting op amp
Replies
33
Views
6K
Clarifying the Confusion: Op Amp Gain in Non-Inverting Amplifier Circuits
Replies
5
Views
2K
How does an opamp work as non-inverting amplifier
Replies
11
Views
3K
Op-amp: Current and bandwidth question
Replies
8
Views
3K
How do I get a DC difference amplifier working?
Replies
15
Views
3K
Confusion on: High Pass Filter at Op Amp Input
Replies
6
Views
3K
Engineering Why is the voltage source high potential into node 1 at -12 V in this op amp problem?
Replies
15
Views
2K
Low voltage op amp to control high voltage series pass transistor
2
Replies
53
Views
10K

Hot Threads

Recent Insights

Back
Top