Measuring the Board Gain Using Oscilloscope Application

You can find the documentation for the opAmp board here:

Inverting network

• Feedback Resistor (Rf): A resistor connected from the output to the inverting input, Rf, plays a pivotal role in determining the gain of the amplifier. The gain in this configuration is given by $$R_f/R_{in}$$ , where $$R_{in}$$ is the resistor chosen in the inverting input network and the $$R_f$$ is the resistor chosen in the feedback Network.

• Signal Inversion: The primary characteristic of this network is signal inversion, accompanied by amplification based on the resistor values.

What is an Inverting Operation Amplifier?

An inverting amplifier utilizes an operational amplifier (op-amp) with two key external components: the input resistor (Rin) and the feedback resistor (Rf). The input signal is applied to the inverting (-) input of the op-amp, while the non-inverting (+) input is typically grounded. The feedback resistor connects the output of the op-amp back to the inverting input. This configuration creates a closed-loop feedback, which is essential for controlling the gain and stability of the amplifier.

The output voltage (Vout) of an inverting amplifier is given by the formula:

$$V_{out}=-\frac{R_f}{R{in}}V_{in}$$

where Vin is the input voltage. The negative sign indicates that the output is inverted relative to the input.

Key Features and Advantages

• Phase Inversion: The inverting amplifier reverses the phase of the input signal, a characteristic exploited in signal processing tasks such as generating antiphase signals or implementing subtractive mixing.

• Adjustable Gain: The gain of an inverting amplifier is easily adjusted by changing the ratio of Rf to Rin, providing flexibility in designing circuits to meet specific amplification needs.

• Impedance Matching: These amplifiers can also be used for impedance matching, ensuring maximum power transfer between circuits with differing impedances.

• Signal Conditioning: Inverting amplifiers are commonly used in signal conditioning, where signals need to be amplified, filtered, or otherwise modified before being used by the next stage in a system.

Applications

The inverting amplifier configuration finds applications in various areas including, but not limited to:

• Audio Electronics: For mixing signals, phase inversion, or creating balanced audio lines.

• Analog Computing: Used in operations such as integration, differentiation, and other mathematical functions.

• Data Acquisition: To amplify small sensor signals to levels suitable for digitization.

• Signal Processing: For dynamic range adjustment, filtering, and constructing active filters.

• Instrumentation: In the design of precision measurement devices and systems.

Inverting amplifiers, with their straightforward design and operational flexibility, are indispensable in both educational settings for teaching fundamental electronics concepts and in industry for developing sophisticated electronic systems. Their simplicity, coupled with the vast range of possible applications, underscores the importance of understanding and utilizing inverting amplifiers in the field of electronics and electrical engineering.

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Press the on the toggle arrow to extend the theory on Inverting Amplifiers

Materials Required

• Red Pitaya STEMlab board

• Operational amplifier board in inverting configuration

• Oscilloscope probes

• Jumper wires

Connection Guide

1. Signal and Power Connections:

• Connect the output of the Red Pitaya's signal generator to the IN- terminal on the op-amp PCB (J4 connector).

• Move the Bottom jumper 1k||10k to the middle of the connector(pin2,pin3).
  

• Connect the oscilloscope's Channel 1 probe to the same point (IN-) to monitor the input signal to the op-amp.

• Connect the oscilloscope's Channel 2 probe to the OUTPUT terminal on the op-amp PCB to observe the amplified signal.

• Power the op-amp by connecting the 5V supply from the Red Pitaya to the positive power rail Vs+ and the -4V to the negative power rail Vs- on the op-amp PCB.



• Change Ratio of Rin and Rf - By moving the Bridge connectors on the inverting input network, which represents Rin and by moving the bridge connectors on the feedback network, which represents Rf, you can change the gain of the circuit.
$$V_{out}=-\frac{R_f}{R_{in}}V_{in} \longrightarrow A_u=\frac{V_{in}}{V_{out}}=-\frac{R_f}{R_{in}}$$

Click on the Toggle button to check out some of the different gain setting available with picture examples:

Rin=1kOhm, Rf=1kOhm

$$A{u}=-(\frac{Rf}{Rin})=-(\frac{1}{1})=-1$$



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Rin=10kOhm, Rf=2kOhm

$$A{u}=-(\frac{Rf}{Rin})=-(\frac{2}{10})=-0.5$$



 

Rin=1kOhm, Rf=2kOhm

$$A{u}=-(\frac{Rf}{Rin})=-(\frac{2}{1})=-2$$



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Red Pitaya Configuration:

• Set up the Red Pitaya's web applications to control the signal generator and oscilloscope.

• Set the signal generator to produce a clean sine wave at an initial frequency of 100Hz and an amplitude of 0.1V.

• Observe the signal on the Output of the board using the IN2 on the red pitaya oscilloscope app and the Input on the IN1.

• Increase the input signal frequency at gain 2 and 10, until you reach 70% of the initial gain which is defined as the -3dB point.
• Start with low frequency 100Hz
• Increase frequency until you find -3dB Point,
• Another measurement at High frequency 20kHz)

Results

Gain set to 1:

$$A{u}=-(\frac{Rf}{R_{in}})=-(\frac{1}{1})=-1$$$$f=100Hz \longrightarrow A_u\approx-1$$



$$f=8000Hz \longrightarrow A_u\approx-0.7 \newline This \space is\space the -3dB \space point$$



$$f=20kHz \longrightarrow A_u\approx -0.4$$



 

 

Gain set to 2:

$$A{u}=-(\frac{Rf}{R_{in}})=-(\frac{2}{1})=-2$$$$f=100Hz \longrightarrow A_u\approx-2$$



$$f=3900Hz \longrightarrow A_u \approx-1.4 \newline This \space is\space the -3dB \space point$$



$$f=20kHz \longrightarrow A_u\approx-0.4$$

Non Inverting Amplifier Experiment

• Feedback Loop: A feedback resistor (Rf) is connected from the output to the inverting input, along with a resistor (Rin) connected from the inverting input to the ground. This resistor network sets the gain of the amplifier.

• Amplifier Gain: The gain in a non-inverting configuration is given by the formula 1 + Rf/Rin, offering a minimum gain of 1 (unity gain). This allows for signal amplification without inversion.

• Phase Consistency: Unlike the inverting configuration, the non-inverting network retains the same phase between the input and output, making it ideal for applications where such consistency is critical.

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Press the on the toggle arrow to extend the theory on Non Inverting Amplifiers

Materials Required

• Red Pitaya STEMlab board

• Operational amplifier board in non-inverting configuration

• Oscilloscope probes (on the picture yellow and orange jumper are used instead of probes)

• Jumper wires

Connection Guide

Signal and Power Connections:

• Move the Bridge Connector and shortcut the inverting network like shown in the picture bellow. Also move the bottom bridge(non-inverting input) to the left side of the connector.

• Connect the Red Pitaya's signal generator output to the IN+ terminal on the op-amp PCB (often marked as the non-inverting input).

• Attach the oscilloscope's Channel 1 probe to the IN+ terminal to monitor the input signal. Attach the oscilloscope's Channel 2 probe to the OUTPUT terminal on the op-amp PCB to observe the amplified signal.

• Provide power to the op-amp by connecting the 5V and -4V supplies from the Red Pitaya to the appropriate power rails on the op-amp PCB. (same as in inverting configuration)

• Change Ratio of Rg and Rf - By moving the Bridge connectors on the inverting input network, which represents Rg and by moving the bridge connectors on the feedback network, which represents Rf, you can change the gain of the circuit.

Toggle the menu to check out some of the different gain setting available:

Rg=1kOhm, Rf=1kOhm

$$A{u}=(1+\frac{Rf}{R_{in}})=(1+\frac{1}{1})=2$$

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Rg=10kOhm, Rf=2kOhm

$$A{u}=(1+\frac{Rf}{R_{in}})=(1+\frac{2}{10})=1.2$$

Rg=1kOhm, Rf=2kOhm

$$A{u}=(1+\frac{Rf}{R_{in}})=(1+\frac{2}{1})=3$$

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Red Pitaya Configuration:

• Set up the Red Pitaya's web applications to control the signal generator and oscilloscope.

• Set the signal generator to produce a clean sine wave at an initial frequency of 1000Hz and an amplitude of 1V.

• Observe the signal on the Output of the board using the IN1 on the red pitaya oscilloscope app.

 

Results for Non-inverting Amplifier

Gain set to 2:

$$A_{u}=(1+\frac{R_f}{R_{in}})=(1+\frac{1}{1})=2$$$$f=100Hz \longrightarrow A_u\approx2$$

$$f=10800Hz \longrightarrow A_u\approx1.4 \newline This \space is\space the -3dB \space point$$

$$f=30kHz \longrightarrow A_u\approx1$$

 

 

 

Gain set to 11:

$$A_{u}=(1+\frac{R_f}{R_{in}})=(1+\frac{10}{1})=11$$$$f=100Hz \longrightarrow A_u\approx11$$

$$f=760Hz \longrightarrow A_u\approx8 \newline This \space is\space the -3dB \space point$$

$$f=30kHz \longrightarrow A_u\approx1$$