Analog Sensing
Single-channel inverting amplifier using the Texas Instruments LM358 dual op-amp providing -3.6 V/V closed-loop gain from a ±12 V split supply.
Circuit overview
Click any component in the schematic above to inspect its electrical ratings, function, and connections.
This circuit implements the classic inverting amplifier from Texas Instruments LM358 datasheet SLOS068AB Figure 8-1. Operating from symmetrical ±12 V rails, it provides a closed-loop inverting gain of Av = -RF / RI = -36 kΩ / 10 kΩ = -3.6 V/V. Symmetrical dual supplies allow true bipolar signal amplification (±0.5 V input produces ∓1.8 V output) centered around ground. High open-loop gain forces the inverting terminal into a virtual ground (0 V), while negative feedback establishes high linearity, predictable frequency response up to 152 kHz, and low output impedance.
| Closed-Loop Voltage Gain (Av) | -3.6 V/V (-11.13 dB, 180° phase inversion) |
|---|---|
| Input Resistor (RI / R1) | 10 kΩ, 1%, 0.125 W |
| Feedback Resistor (RF / R2) | 36 kΩ, 1%, 0.125 W |
| Input Signal Range (VI) | ±0.5 V nominal (1.0 V p-p) |
| Output Signal Range (VO) | ∓1.8 V nominal (3.6 V p-p) |
| Power Supply Rails (V+ / V-) | ±12 V split supply (operates from ±1.5 V to ±16 V) |
| Small-Signal Bandwidth (-3 dB) | ≈ 152 kHz (GBW = 0.7 MHz, noise gain = 4.6) |
| Input Impedance (ZIN) | 10 kΩ (defined by R1) |
The LM358 operational amplifier is powered from symmetrical ±12 V supplies (+12 V connected to pin 8 V+, -12 V connected to pin 4 V-). Symmetrical rails ensure that the internal class-AB output stage can swing undistorted in both positive and negative directions relative to the 0 V circuit ground, enabling clean AC and bipolar DC signal amplification.
The non-inverting input (IN+ / pin 3) connects directly to circuit ground (0 V). The op-amp internal differential input stage and high open-loop gain (A_OL ≈ 100 dB) act through the negative feedback loop to drive the differential input voltage V_ID = V+ - V- to virtually zero volts. Consequently, the inverting summing node at pin 2 is maintained at 0 V, forming an ideal virtual ground.
Because the LM358 PNP Darlington input transistors draw minimal bias current (I_B ≈ 20 nA typical), signal current arriving from input resistor R1 must flow entirely through feedback resistor R2. Applying Kirchhoff's Current Law at the inverting summing junction gives:
IIN = (VIN - 0V) / (RI) = (0V - VOUT) / (RF)Solving for output voltage V_OUT yields the ideal inverting amplifier transfer equation:
VOUT = -VIN × (RF) / (RI) = -VIN × (36kΩ) / (10kΩ) = -3.6 × VINAn input signal of ±0.5 V produces an inverted output of ∓1.8 V (180° phase inversion).
At the inverting terminal, the virtual ground sets the circuit input impedance to exactly the value of the input series resistor:
ZIN = RI = 10kΩUnlike non-inverting configurations with gigohm input resistance, the inverting amplifier draws a signal current of I_IN = ±0.5 V / 10 kΩ = ±50 µA from the input source. Upstream signal generators must have low internal impedance (< 10 Ω) to avoid gain attenuation errors.
The LM358 provides a unity-gain bandwidth product (GBW) of 0.7 MHz (700 kHz) and a slew rate of 0.3 V/µs. With a closed-loop noise gain of A_N = 1 + R_F / R_I = 1 + 3.6 = 4.6 V/V, the small-signal -3 dB bandwidth is:
f-3dB ≈ (GBW) / (1 + (RF) / (RI)) = (700kHz) / (4.6) ≈ 152 kHzFor large output swings (3.6 V peak-to-peak), the full-power bandwidth is constrained by the 0.3 V/µs slew rate to approximately 26.5 kHz before triangular wave distortion occurs.
Calculates the inverted output voltage based on the feedback-to-input resistance ratio.
| Symbol | Parameter | Typical value |
|---|---|---|
| VOUT | Amplified output voltage | -1.8V |
| VIN | Input signal voltage | 0.5V |
| RF | Feedback resistor | 36kΩ |
| RI | Input resistor | 10kΩ |
Calculates the high-frequency -3 dB cutoff based on op-amp gain-bandwidth product and noise gain.
| Symbol | Parameter | Typical value |
|---|---|---|
| f_{ − 3dB} | High-frequency -3 dB cutoff | 152.2kHz |
| GBW | Gain-bandwidth product | 700kHz |
| RF | Feedback resistor | 36kΩ |
| RI | Input resistor | 10kΩ |
Calculates the maximum frequency achievable at peak output amplitude without slew-rate distortion.
| Symbol | Parameter | Typical value |
|---|---|---|
| fFPBW | Full-power bandwidth | 26.5kHz |
| SR | Op-amp slew rate | 0.3V/µs |
| VP | Peak output voltage amplitude | 1.8V |
Every part needed to build this circuit. Select a reference designator to inspect it on the schematic.
| RefDes | Component | Value / rating | Package | Role in circuit | Reference |
|---|---|---|---|---|---|
| Dual Operational Amplifier Texas Instruments LM358P, SLOS068AB Rev. AB; Pin 1 OUT1, Pin 2 IN1-, Pin 3 IN1+, Pin 4 GND/V-, Pin 8 V+. | LM358P | PDIP-8 | Inverting operational amplifier (Channel A used) | Dual Operational Amplifier pinout & datasheet | |
| Input Series Resistor 10 kΩ, 1%, 0.125 W metal film resistor. Sets input impedance to 10 kΩ. | 10kΩ | Axial / 0805 | Input signal scaling and impedance definition | — | |
| Feedback Resistor 36 kΩ, 1%, 0.125 W metal film resistor. Establishes closed-loop gain of -3.6 V/V. | 36kΩ | Axial / 0805 | Closed-loop negative feedback | — |
Traps found in real builds, with the fix for each.
When output current reverses direction across 0 V between sourcing and sinking, the LM358 complementary output stage exhibits a deadband that creates high-frequency crossover spikes on sinusoidal signals.
Connect an external pull-down resistor (2 kΩ to 10 kΩ) from the output (pin 1) to the negative rail (-12 V). This keeps the top NPN transistor sourcing current continuously, forcing class-A operation and eliminating crossover distortion.
The LM358 input PNP Darlington transistors have an input bias current (IB ≈ 20 nA to 100 nA) flowing out of both inputs. Tying IN+ directly to ground with 0 Ω causes an unequal DC voltage drop across RI || RF (7.83 kΩ), generating an uncompensated output offset.
Insert a bias compensation resistor RP = RI || RF ≈ 7.5 kΩ to 8.2 kΩ in series between IN+ (pin 3) and ground to equalize the source resistance seen by both differential inputs.
With a 0.3 V/µs slew rate, driving large-amplitude output signals (3.6 V p-p) above 26 kHz causes slew-rate limiting, turning smooth sinusoidal waves into distorted triangular waveforms.
Limit large-amplitude high-frequency signals below 25 kHz. For wider bandwidth applications, substitute a pin-compatible higher-speed op-amp such as the TL072 (13 V/µs) or OPA2134 (20 V/µs).
Because circuit input impedance is defined solely by RI (10 kΩ), any internal source impedance R_source of the driving signal generator adds directly to RI, reducing effective circuit gain to -RF / (RI + R_source).
Drive the inverting stage from a low-impedance buffer (< 10 Ω), or calibrate RI by subtracting known source resistance so the combined sum equals 10 kΩ exactly.
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