Op amp noise reduction

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Interference can appear as spikes, steps, sine waves, or random noise, and it can come from anywhere : machinery, nearby power lines, r-f transmitters and receivers, computers, or even circuitry within the same equipment for example, digital circuits or switching-type power supplies. If all interference could be eliminated, there would still be random noise associated with the operational amplifier and its resistive circuits. But it is generated by both voltage and current sources.

All internal sources are generally referred to the input, i. Voltage noise is the noise specification that is more usually emphasized, but, if impedance levels are high, current noise is often the limiting factor in system noise performance. That is analogous to offsets, where offset voltage often bears the blame for output offset, but bias current is the actual guilty party. Bipolar op-amps have traditionally had less voltage noise than FET ones, but have paid for this advantage with substantially greater current noise --today, FET op-amps, while retaining their low current noise, can approach bipolar voltage-noise performance.

Many noise sources are, for practical purposes i. White noise is noise whose power within a given bandwidth is independent of frequency.

Gaussian noise is noise where the probability of a particular amplitude, X, follows a Gaussian distribution. Gaussian noise has the property that when the rms values of noise from two or more such sources are added, provided that the noise sources are uncorrelated i. A useful consequence of RSS summation is that if two noise sources are contributing to the noise of a system, and one is more than 3 or 4 times the other, the smaller is often ignored, since.

The current noise of simple i. Schottky noise is current noise due to random distribution of charge carriers in the current flow through a junction. The Schottky noise current, In, in a bandwidth, B, when a current, I, is flowing is obtained from the formula. Bias-compensated op-amps have much higher current noise than one can predict from their input currents. The reason is that their net bias current is the difference between the base current of the input transistor and the compensating current source, while the noise current is derived from the RSS sum of the noise currents.

Traditional voltage-feedback op-amps with balanced inputs almost always have equal though uncorrelated current noise on both their inverting and non-inverting inputs.

Noise Reduction Amplifiers

Current-feedback, or transimpedance, op-amps, which have different input structures at these two inputs, do not. Their data sheets must be consulted for details of the noise on the two inputs. The noise figure NF of an amplifier expressed in dB is a measure of the ratio of the amplifier noise to the thermal noise of the source resistance.

It is a useful concept for r-f amplifiers, which are almost always used with the same source resistance driving them usually 50 ohms or 75 ohmsbut it would be misleading when applied to op amps, since they are used in many different applications with widely varying source impedances which may or may not be resistive. For very low source resistance, the noise generated by the source resistance and amplifier current noise would contribute insignificantly to the total. In this case, the noise at the input will effectively be just the voltage noise of the op-amp.

op amp noise reduction

This is demonstrated by the figure nearby, which compares voltage and current noise noise for several Analog Devices op amp types, for a range of source-resistance values. The diagonal line plots vertically the Johnson noise associated with resistances on the horizontal scale.

Noise will not be reduced by say a ohms source impedance, but it will be increased by a 2-kohms source impedance. Remember that any resistance in the non-inverting input will have Johnson noise and will also convert current noise to a noise voltage; and Johnson noise in feedback resistors can be significant in high-resistance circuits.

All potential noise sources must be considered when evaluating op amp performance. At temperatures above absolute zero, all resistances have noise due to thermal movement of charge carriers. This is called Johnson noise. The phenomenon is sometimes used to measure cryogenic temperatures.

The voltage and current noise in a resistance of R ohms, for a bandwidth of B Hz, at a temperature of T kelvins, are given by:. All resistors in a circuit generate noise, and its effect must always be considered. In practice, only resistors in the input s and, perhaps, feedback, of high-gain, front-end circuitry are likely to have an appreciable effect on total circuit noise. Barrow, J.Remember Me? How to reduce noise from the amplifier s?

Hi everyone, I am a super novice at this stuff, but I have made a "sound system". A speaker unit with 3 channels, which can listen to the 3 channels simoutanously or by demand. On the microphone unit you can setup the channels. There are way too much noise, when all 3 channels are active at same time. How can I possible do this the easiest or the best way? I hope you understand the problem and you're able to help somehow. I am very thankful for any suggestions.

Best Regards, Michael Trolle. Re: How to reduce noise from the amplifier s? I think you could start from replacing the s with better equivalents. IC is a very primitive and noisy op-amp.

Op-amp noise sources and minimizing system noise

Nice to hear, I appreciate. I am gonna order some right away to test that. Now I found this, it should be high-end? What about this electret microphone? The NE is a far better option compared to that of the ones I suggested above. I think any electret microphone will suit your application, mainly because of a less variety available in the lower priced ones. Just make sure that you have made the interconnections between the boards short, signals routed via shielded coaxial cables and proper grounding.

It will be better if you use the star grounding technique. This will avoid ground loops and hence reducing your overall system noise. Thanks a lot for the great advice! But as you say; Grounding and a quality shielded cable helps a lot.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It only takes a minute to sign up. I am using this op-amp circuit to buffer voltage V received from MCU. Resistors at the output are used to limit the current controlling the solid-state relay. This makes the operation of the SSR unstable. How can I reduce or avoid this noise.

Vin is an on-off square signal of maximum pulse duration of 20ms, to switch the SSR on and off. Next, a view of the noisy Vin signal taken from Oscilloscope is shown.

op amp noise reduction

And a zoomed view of this signal at the high-to-low change is also given. I am sorry for combining all images in a one, because I am not able to attach more than two images in this question. Now in case this is because you must use the op-amp please note that: by placing a resistor in the op-amp's input you are reducing its input impedance. This setup is inducing the ripple you see in the scope.

If by placing the input resistor it's your intention to reducing the current, you are doing quite the opposite because the opamp already has a high input impedance. Taking off the resistor will reduce the load on the microcontroller's output thus reducing the ripple. This will simplify your design as you won't have to worry about the reverse current on the LED. Even if noise is an issue, you could use an Schmitt trigger buffer like These circuits work well up to 15 volts but there are devices available with higher rated voltages.

Now, if you want to simplify even more. Use a transistor as others have suggested. I don't think you need a Op-amp to drive a SSR.

A NPN bipolar would do the job without the "noise" issue. Anyway, the question regarding the noise can be solved by replacing the op-amp stage by a Schmitt trigger nice comparator with hystersis. This will ensure zero false triggers for SSR. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Reduce noise in this op-amp buffer circuit Ask Question.

Asked 3 years, 7 months ago. Active 3 years, 7 months ago. Viewed 2k times. It would be unusual for an MCU output to be "noisy" unless there is something odd going on Ditch the op amp, use a mosfet or a bjt to drive the relay. Might help you. Active Oldest Votes. If an op-amp is not a must, an open collector digital driver like the old would be enough. Krauss Krauss 1 1 silver badge 11 11 bronze badges. This SSR need a deriving current of maximum 25mA. A larger current would damage the SSR.

The SSR works as a fast switch 2ms for current to another circuit.Welcome, Guest. Please login or register. Did you miss your activation email?

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This topic This board Entire forum Google Bing. Print Search. The noise level is around 40mVp-p and considering that my ADC resolution is around 0. The problem can be easily solved by a "heavy" low pass filter on the output, but I want the circuit to be fast plus I want first to eliminate any over sources of noise and then adjust the output filter. Can you suggest any noise filtering methods?

I will include the schematic below The sensor will be connected inside and H-bridge, in series with the motor. In the end, I will be redesigning the board, this first board was more a proof of concept.

If you are an engineer and you are not tired You are doing it wrong! Paul Price Super Contributor Posts: Noise figure is not quantified by a single unit of measure such as just using max acceptable noise voltage such as 1mV max you mention.

Without looking up any further details on the op-amp etc id speculate it being an oscillation which could be cured by ensuring that there is a sufficient amount of local decoupling to the chips and possibly a compensation cap on the feedback resistor in the opamp. You are going to use a motor, so you would do well to clearly define the type.

I assume you are interested in getting instantaneous motor current readings on a PWM on-time cycle by cycle basis. If you are using PWM drive for the motor, many more different effects need to be considered. To get any where near an idea of the average or RMS motor current you would have to sample the current only during the on period of the PWM pulse and integrate the result by software calculation.

The current sense resistor amplifier you are using would not be fast enough to capture these transients, and a KHz low-pass filter would only ring, maybe just smooth out an abundance of motor noise created, while distorting the instantaneous current peaks of interest. If you are using an induction motor or a capacitive start type of motor or a multi-phase motor or especially a brush-type motor, the readings you will get from your circuit would not very well reflect motor current.

op amp noise reduction

Quote from: Paul Price on September 30,pm. I was actually more interested in the form of the noise you are currently having a problem with. For example, is it by any chance at the same frequency of the PWM switching but not consistent with the expected current waveform, in which case it current be a problem due to common mode rejection. Does it have a dominant frequency, is it sinusoidal etc.

Quote from: dannyf on September 30,pm. No longer active here - try the IRC channel if you just can't be without me. Quote from: penfold on September 30,pm. Quote from: cp on September 30,pm.

I just wanted to post the schematics now, in case someone knew if the problem was inherit with my design. You obviously have detected the noise - you gave their measurements, using some means.

The same means would allow you to tell where the noise is from, step 1 in a long journey. Depending on your scope, scope bandwidth and way of probe use, the 40mV noise could just be a probe - oscilloscope type of artifact. Then, that only leaves as the cause the high gain setting of the sense resistor amp and the leads the instrumentation op-amp input acting as antennas.

The op-amp input pins of the op-amp must be close as possible to the sense resistor, symmetrical in length, a twisted pair, or otherwise both coaxial cable shielded. But you haven't really described the noise so carefully.Noise originates inside an op amp, in passive components, and from external radiation.

As noted by Daniel Defoe and Benjamin Franklin, there are only two things that are certain in life: death and taxes. Unfortunately for those that design or use electronics, there is another: noise. Although electrical noise cannot be avoided, a better understanding of the various noise sources and how they each contribute to the overall system noise level enables designers to minimize the impact.

From the system perspective, noise can originate from a variety of places. There are noise sources that are generated inside the operational amplifier, along with noise from the passive components that are used within the op-amp circuitry. There is also a wide variety of external sources, such as radio waves or ac mains. This article will review some of these noise sources, as they relate to the internal workings of op amps. This low-frequency noise can be very problematic if the input signal is near dc, as often occurs in the outputs from strain gauges, pressure sensors, thermocouples or any slow-moving sensor signal.

Although system designers cannot control the internal flicker noise of an amplifier, they can minimize this noise source by selecting the proper amplifiers for the application.

It appears to be a part of the amplifiers offset and gets compensated accordingly. Perhaps a lesser-known internal noise source is shot noise, or Schottky noise. This noise source is a result of imperfections in the conduction of charge carriers. Electrical current is electrons moving based on an applied potential.

As these electrons run into barriers imperfections in metals, etc. Since shot noise is associated with current flow, if there is no current flowing, there is no shot noise. Shot noise has a Gaussian probability density distribution and is independent of frequency and temperature. It is inversely proportional to the square root of the dc current, so less current means more shot-noise voltage. On the other hand, as the dc current increases the shot noise will go up, but its proportion to the overall current will actually decrease, raising the signal to noise ratio.

To determine whether shot noise is a factor within a given design, reduce or increase the dc current and see if the noise is affected. Also called Johnson noise, thermal noise is present in all active and passive circuit components.

Heat causes electrons to increase their movement, resulting in a random factor to their motion that produces noise.The purpose of this build is to show that Noise Cancellation is possible with basic parts like OP-Amp. And that application of fundamental physics of wave. Did you use this instructable in your classroom? Add a Teacher Note to share how you incorporated it into your lesson. Take a look at my "kids can understand too! The diagram shows red waves and blue waves.

Blue wave represents noise captured and processed. The microphone will capture the ambient noise. Then it goes through a pre-amp to inverting OP-Amp. At this phase, the wave is inverted. Finally, inverted sound will be played at the earbud, effectively cancelling out the ambient noise.

Ask the Applications Engineer—7: Op-amp Noise

Build an inverting OP-Amp. For this particular build, an was used. It is untested but any inverting OP-Amp should work.

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Obviously, if you amplify way too much, it will amplify noise, which means more noise. But if not enough will unable to cancel ambient noise. Do note, There are few factors that plays a role: earbud's acoustic properties, Acoustic properties of head, and acoustic properties of the mic. The reason why I chose this earbud is because the acoustic property was accurately measured by innerfidelity.

As shown, RE does not change original sound source's phase up to 1kHz. Since we are aiming to cancel noise around Hz to Hz, this shouldn't be a problem. When dealing with Hz and Hz, your head vibrates and creates interesting sound acoustics. This is a reason why fine tuning with your head is the best.

Because ear canal is slightly angled, I found aiming microphone slightly angled towards back of my head worked better.

Impossible Active Audio Noise Cancelling by Muzo

I mentioned acoustic properties of the mic but most mics won't change phase significantly. Although I found x10 amplification through pre-amp created significant distortion. Distortions are not good.

My circuit made various kinds of white noise from many different things and so noise killing journey is on. Initially I had a giant breadboard with ground wire around it and it made strange white noise.

op amp noise reduction

Turns out, was picking on Assuming the ground wires acted as antenna, I built exactly same circuit on a smaller breadboard with shorter running wire. From recent testing, it was picking on random morse-code like sounds, which is likely to be transmitted by car remote. This meant the was picking on radio signals around mHz. I can't explain this strange phenomenon and I don't think anybody can but it happens randomly and rarely so I let it pass.

On the other hand, I found increase in white noise as human body touches running wire to the microphone. The wire to the microphone has to be long and because it has to be next to ear, the only way to solve this is to shield the wire. This solution kind of worked.Unfortunately, every time I tried to play some music, I jumped in shock, as the volume control defaults are pretty loud. Op amp PCB layout guidelines are particularly helpful devices within a Printed Circuit Board design; however, they can be difficult to use effectively and without causing undue errors within your device.

Having a basic understanding of how they might fail will inhibit mistakes in your designing. Operational amplifiers are signal conditioning components capable of filtering and amplifying signals through basic arithmetic operation. An operational amplifier has three terminals: an inverting input, a non-inverting input, and an output which forms the basis of many configurations.

All operational amplifiers display these characteristics: high open loop gain, high input impedance, low output impedance, and a limited bandwidth. A typical amplifier can have a gain of 10, or more.

The input resistance is less than ohms and the output resistance is often in the range of 0. Operational amplifier: a simple but versatile electronics component. Understanding the basic working of an operational amplifier is easy enough. If you apply a positive input to the non-inverting input, the operational amplifier will produce a positive swing at the output. Similarly, if you apply a positive voltage to the inverting input, a negative swing will occur at the output.

In short, the output is proportional to the difference between the voltages on both inputs. By connecting the output and input of the operational amplifier with feedback components like resistors and capacitors, you can derive different functions and gain. The list of operational amplifier applications can go on forever, but the most ones include voltage comparators, active rectifiers, signal filters, and voltage followers.

One use of operational amplifiers is amplifying raw analog signals from sensors before being processed by a microcontroller.

They are also commonly used in audio applications. When designing with operational amplifiers, it is important to be aware of the following PCB design guidelines:. The operational amplifier needs a stabilized voltage to produce the right output signal. To reduce the noise produced when switching the power supply, place a bypass capacitor close to the supply pin of the operational amplifier. This will also reduce the possibility of harmonic distortions.

This prevents the introduction of stray capacitance and ground noise that may significantly affect the output of the operational amplifier.


When using a power operational amplifier, thermal stability is crucial to maintaining a low-temperature junction for stable operations.