What is a non-inverting amplifier circuit?

This time, we'll start by explaining what a non-inverting amplifier circuit is! Its configuration is different from the inverting amplifier circuit we covered in the second lesson, so please pay close attention. In a non-inverting amplifier circuit, the input signal is directly connected to the non-inverting input terminal of the operational amplifier. On the other hand, the output voltage Vout is returned to the inverting input terminal via resistor R2, and the inverting input terminal is further connected to a reference voltage (generally GND) via resistor R1.

In this way, negative feedback is applied by feeding a portion of the output voltage back to the inverting input, limiting the output so that the voltage at the inverting input terminal approaches the voltage at the non-inverting input terminal. As a result, the output is amplified while maintaining the same polarity as the input signal, and is therefore called a "non-inverting amplifier circuit."

Non-inverting amplifier circuit using OP97

When the input voltage of a non-inverting amplifier circuit is Vin and the output voltage is Vout, the relationship between Vin and Vout is as follows:

Just like with inverting amplifiers, the values of R1 and R2 are important for the gain of a non-inverting amplifier circuit. However, unlike inverting amplifiers, the polarity does not invert, so be careful!

Let's try building a non-inverting amplifier circuit on a breadboard!

Now, let's build a non-inverting amplifier circuit, just like before.

The resistance values are set to [R1=1kΩ, R2=1kΩ, load resistance 10kΩ].

Breadboard connection example of a non-inverting amplifier circuit using OP97.

Actual non-inverting amplifier circuit

Thisis the pinout forthe ADALM2000.

This time, as with the first and second times,

• 1+/1-(Oscilloscope channel 1/​ ​GND of oscilloscope channel 1)

・ 2+/2-(Oscilloscope channel 2/​ ​GND of oscilloscope channel 2)

・GND

・ V+/V-(Positive power supply / Negative power supply)

• W1 (Signal Input 1)

We will use these pins. Connect ch1 of the oscilloscope to the input side and ch2 to the output side, and then observe the waveforms of each.

Once you've connected the jumper wires, connect the ADALM2000 to your PC and start measuring!

This time too

Input signal frequency: 1kHz (sine wave)

Input signal amplitude: 2Vp-p

Power supply voltage: ± 5V

Let's perform the measurement under the above conditions and examine the input and output voltage waveforms as before!

Under the conditions R1=1kΩ and R2=1kΩ in this case

Therefore, the amplification factor becomes 2 times. In other words, all we need is an output voltage waveform that is twice the amplification of the input signal!

Now, let's launch the familiar Scopy and proceed with the setup.

As with the previous time, we will configure two settings: "Signal Generator" and "Power Supply." The configuration conditions are as follows:

Power supply voltage: ± 5V

Input signal frequency: 1kHz (sine wave)

Input signal amplitude: 2Vp-p

For detailed setup instructions, please refer to the previous article.

Let's experiment with ADALM2000! Unity Gain Circuit

Actual measurement! Non-inverting amplifier circuit!

Now let's look at the waveform. Since it's twice 2Vp-p, we should get a waveform of approximately 4Vp-p.

Input/output voltage waveforms of a non-inverting amplifier circuit measured with Scopy

YES!!
As expected, I was able to obtain an output voltage waveform of approximately 4Vp-p. It feels great when you get the waveform you want!

LTspice waveform of a non-inverting amplifier circuit

I was able to get a perfect 4Vp-p output voltage waveform using LTspice as well!

*Since the OP97 component does not exist in LTspice, the evaluation was performed using the substitute component OP07.

Bonus: Let's try changing the resistance value!

In the bonus section on the inverting amplifier circuit, we were able to obtain a fully swinging waveform from a clipped waveform by reducing the input signal. Now that we already have a fully swinging waveform, let's tweak the conditions a bit and try clipping the output voltage waveform instead. This time, instead of changing the input signal, we'll use another approach: changing the resistance value!

In the evaluation of the non-inverting amplifier circuit we've been working with R1=1kΩ and R2=1kΩ, resulting in a gain of 2x. In this bonus section, we want to amplify the output voltage waveform enough to clip it, so we'll change the value of R2 (the numerator in the calculation formula) to 4.7kΩ and observe the waveform!

The gain of changing the resistance value is,

Therefore, a waveform with an amplitude 5.7 times that of the input signal should be obtained. Since the input signal is 2Vp-p, the calculation suggests that an output voltage waveform of approximately 11.4Vp-p should be obtained. However, due to the characteristics of the OP97, it can only track up to ± 4V, or about 8Vp-p, so we can expect to see a clipped waveform of about ± 1-2V. Now let's take a look at what the waveform actually looks like!

Circuit with the resistance value of R2 changed to 4.7kΩ

The waveform obtained by Scopy after changing the resistance value of R2 to 4.7kΩ

I was able to obtain the expected waveform with the output voltage clipped!

As you can see, the output voltage can be adjusted not only by changing the input signal, but also by changing the amplification factor through resistance changes, so please try experimenting with different resistance values!

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