# Which of these op amp configurations has the least noise?

• Yarger
In summary, the conversation discusses ways to minimize noise for a low frequency input with a gain of 1/2. Three possible methods are suggested: using a voltage divider into a voltage follower, measuring the input with a negative voltage and running it through a 1/2 inverting op amp, or using two inverting op amps with gains of -1 and -1/2. The speaker also mentions the option of using a switched capacitor, specifically the LTC1043 or LTC6934 from Linear Technology, for a very precise ratio of 1/2 with an accuracy of one part per million.
Yarger
I need to run a signal through a configuration so that it has a gain of 1/2. I'm trying to figure out what the best way to minimize the noise for a low frequency input. So far I've only really thought of 3 ways to do this:

1. Voltage divider into a voltage follower

2. Measure the input so that I get a negative voltage, and run it through a 1/2 inverting op amp

3. Run the input through an inverting op amp of -1 gain and then through another one of -1/2 gain

I believe that, since the frequency is low, I can be very generous with the low pass filter afterwords. Price and (for the most part) power consumption are not factors here, only the accuracy of the signal. I'm pretty new to board level design so any advice would be helpful.

Thanks!

Yarger said:
Price and (for the most part) power consumption are not factors here, only the accuracy of the signal.
For accuracy and a very precise ratio of ½ you should consider using switched capacitors.
Linear Technology makes the LTC1043 and the LTC6943.

Then look at the applications, “Divide by 2”, page 8, top left.
Notice the accuracy specified is one part per million.

## 1. What are the different types of op amp configurations?

There are three main types of op amp configurations: inverting, non-inverting, and differential. Inverting and non-inverting configurations are single-ended, while differential is a dual-ended configuration.

## 2. What is noise in an op amp?

Noise in an op amp is any unwanted or random signal that interferes with the desired output. It can come from internal and external sources, such as thermal noise, power supply fluctuations, and electromagnetic interference.

## 3. Which op amp configuration has the least noise?

The differential op amp configuration has the least noise because it uses two inputs to cancel out any common-mode noise, resulting in a cleaner output signal.

## 4. How does the inverting op amp configuration affect noise?

The inverting op amp configuration has a gain of -1, which amplifies both the signal and the noise. This means that the noise is also inverted and can potentially cancel out the original signal, resulting in a lower overall signal-to-noise ratio.

## 5. What are some ways to reduce noise in op amp circuits?

Some ways to reduce noise in op amp circuits include using a differential configuration, using low-noise components, adding filtering and decoupling capacitors, and using proper grounding techniques. It is also important to minimize the length and impedance of the signal path to reduce noise.

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