Non-Inverting Amplifier using Op-Amp

Adapted from the ExpEYES blog lab on the non-inverting op-amp. For the inverting companion experiment, see Inverting Amplifier using Op-Amp.

1. Aim

To build a non-inverting op-amp amplifier using OP07, verify its voltage gain (same phase as the input), and study output clipping when the required output exceeds the supply rails.

2. Apparatus / Components Required

3. Theory & Principle

In the non-inverting configuration the signal is applied to the non-inverting (+) input. Feedback from the output to the inverting (−) input forms a voltage divider with $R_f$ and $R_i$ (to ground).

Ideal closed-loop gain:

\[A_v = \frac{V_{out}}{V_{in}} = 1 + \frac{R_f}{R_i}\]

With $R_i = 1\text{ k}\Omega$ and $R_f = 10\text{ k}\Omega$:

\[A_v = 1 + 10 = 11\]

So the output should be:

If $V_{in}$ is too large, $A_v\cdot V_{in}$ exceeds the supply swing and the output clips.

4. Circuit Diagram / Setup

  1. Power the OP07 with dual rails (about $+6\text{ V}$ and $-6\text{ V}$).
  2. Apply the WG sine to the non-inverting (+) input.
  3. Connect $R_i = 1\text{ k}\Omega$ from the inverting (−) input to GND.
  4. Connect $R_f = 10\text{ k}\Omega$ from the op-amp output back to the inverting (−) input.
  5. Measure input on A1 (WG / input node) and output on A2 (op-amp output).
  6. Start with WG amplitude about 80 mV (try ~1 V later to see clipping).

Non-inverting amplifier breadboard

5. Procedure

  1. Wire the circuit and check supply polarity before applying WG.
  2. Set WG to a sine (e.g. 200 Hz–1 kHz) at about 80 mV.
  3. Observe A1 (input) and A2 (output) on the oscilloscope.
  4. Record $V_{in,pp}$, $V_{out,pp}$, and confirm they are in phase.
  5. Compute $A_v = V_{out,pp}/V_{in,pp}$ and compare with 11.
  6. Increase amplitude toward ~1 V and note the onset of clipping.

Non-inverting amplifier oscilloscope

Optional — Python capture

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import eyes17.eyes
from pylab import *

p = eyes17.eyes.open()
p.set_sine(200)

t, v, tt, vv = p.capture2(500, 20)  # A1 and A2

xlabel("Time (ms)")
ylabel("Voltage (V)")
plot([0, 10], [0, 0], "black")
ylim([-4, 4])
plot(t, v, linewidth=2, color="blue", label="A1 input")
plot(tt, vv, linewidth=2, color="red", label="A2 output")
legend()
show()

6. Observation Table

Trial $V_{in,pp}$ (V) $V_{out,pp}$ (V) Calculated $A_v$ Phase (same / inverted) Waveform quality
1 (small signal)          
2          
3 (near clipping)          

7. Results and Discussion

8. Precautions

  1. Confirm OP07 pinout before wiring.
  2. Use correct dual-supply polarity.
  3. Start near 80 mV input; increase gradually.
  4. Keep SEELab and amplifier grounds common.
  5. Do not confuse with the inverting topology (input must go to +, not through $R_i$ into −).

9. Troubleshooting

Symptom Possible Cause Corrective Action
No output Missing rails / wrong pins Check power and output pin
Gain ≈ −10 or inverted Built the inverting circuit by mistake Move signal to +; $R_i$ to GND from −
Gain not near 11 Wrong $R_f$/$R_i$ Recheck 10 kΩ / 1 kΩ
Clipping at low input Rails too low or wiring error Verify $\pm 6\text{ V}$ and feedback

10. Viva-Voce Questions

Q1. Why is this called a non-inverting amplifier?

Ans: The output is in phase with the input; a positive input excursion produces a positive output excursion.

Q2. Derive $A_v = 1 + R_f/R_i$.

Ans: With ideal feedback, $V_+ = V_- = V_{in}$. The divider on the feedback path gives $V_- = V_{out}\cdot R_i/(R_i+R_f)$. Setting $V_- = V_{in}$ yields $V_{out}/V_{in} = 1 + R_f/R_i$.

Q3. What happens if $R_f < R_i$?

Ans: Gain is still $1 + R_f/R_i$, so it remains greater than 1 but closer to unity (e.g. $R_f = R_i$ gives $A_v = 2$).

Q4. How does this differ from the inverting amplifier?

Ans: Inverting: signal into − via $R_i$, + grounded, $A_v = -R_f/R_i$. Non-inverting: signal into +, feedback divider on −, $A_v = 1 + R_f/R_i$, same phase.