Resistor Network Parameters
Input Signal Potentials
Power Rails Headroom
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Input Parameters Specification
Resistors (R1, R2, R3, R4)Feedback divider network resistors (R1, R2) and input divider network resistors (R3, R4) in kΩ.
Input Voltages (V1 & V2)Voltage signals applied to the inverting (V1) and non-inverting (V2) amplifier terminals.
Rails Headroom (Vp & Vn)The supply voltage limits. The actual physical output of the op-amp cannot swing beyond these boundaries.
Feedback TopologyFeedback loop R2 runs from Pin 1 back to Pin 2, while R4 ties Pin 3 to reference ground.
Practical Operational Examples
Summing / Differential Amplifiers
Analyze differential operational stages where signals are subtracted to eliminate common-mode noise across sensing lines.
ADC Scaling Interface
Verify whether your sensor amplification gain factors saturate microchip ADC pins under dynamic input sweeps.
DAC Bias Tuning
Design a gain stage to shift and scale low-voltage DAC outputs up to industrial bipolar actuator system demands.
Analog Comparator Pre-Match
Evaluate threshold levels for active op-amp comparators by examining gains before implementing hysteresis loops.
Diagrams & Theory
This amplifier operates as a combined inverting and non-inverting stage. Signals applied to V1 are scaled by the inverting gain ratio (-R2/R1). Signals applied to V2 are scaled down by the input voltage divider R4/(R3+R4) before undergoing non-inverting amplification. The resulting output voltage is the superposition of both amplified paths, limited by power supply saturation thresholds.
Formulas & Mathematical Logic
Inverting amplification ratio: Gain_inv = -R2 / R1
Non-inverting path multiplier: Factor_noninv = 1 + R2 / R1
Non-inverting amplification ratio: Gain_noninv = Factor_noninv * (R4 / (R3 + R4))
Unclipped Output Voltage: Vout_raw = (Gain_noninv * V2) + (Gain_inv * V1)
Clipped Output: Vn <= Vout <= Vp
Step-by-Step Example
Example values: R1 = 10 kΩ, R2 = 20 kΩ, R3 = 10 kΩ, R4 = 10 kΩ, V1 = 1 V, V2 = 2 V, Vp = 15 V, Vn = -15 V.
Step 1: Calculate inverting path gain: Gain_inv = -20 / 10 = -2.000 V/V.
Step 2: Calculate non-inverting gain multiplier: Factor_noninv = 1 + 20 / 10 = 3.000.
Step 3: Calculate non-inverting path gain: Gain_noninv = 3 * (10 / (10 + 10)) = 1.500 V/V.
Step 4: Compute final output: Vout = (1.500 * 2) + (-2.000 * 1) = 3 - 2 = 1.000 V.
Step 5: Verify that the 1V output falls safely within the Vn (-15V) and Vp (15V) limits.
How to Use This Calculator
Enter the values for resistors R1, R2, R3, and R4 in kΩ.
Input signal voltages V1 and V2 in volts.
Set the power supply rail voltages Vp (positive) and Vn (negative) to establish the output voltage swing limits.
Click Calculate to run the equations.
Review the output voltage, path gains, and check if the amplifier output is saturated.
About This Calculator
Determine the output voltage and channel gains of dual-input summing operational amplifiers.
The CalcBoy Op-Amp Voltage and Gain Calculator simplifies the design of differential and scaling analog stages by computing channel-specific gains, evaluating total output potentials, and monitoring power supply rail limits.
Operational amplifiers configured with concurrent inverting and non-inverting pathways are common in analog circuit design. This specific topology is widely used to scale and combine two distinct signals, offset baseline voltages, or function as a differential receiver stage. Calculating the output of this circuit involves using superposition to find the gain of each path independently.
This calculator handles these equations automatically while accounting for the physical voltage limits imposed by the power supply rails (Vp and Vn). If the calculated output voltage exceeds these limits, the tool flags that the circuit is saturated. Any calculated negative values—including the naturally negative inverting gain—are displayed directly without modification, providing an accurate, unmasked view of the circuit's electrical performance.
Typical UseDifferential receiver conditioning, analog signal offset shifting, and sensor scaling.
Rail Splay CheckChecks if the ideal computed output falls outside the real-world boundaries of the supply rails.
SuperpositionEnables simultaneous gain analysis of both input terminals.
Resistor TipSelect low-drift thin-film metal resistors to minimize gain drift and common-mode errors.
Tip: Standard operational amplifiers cannot pull their outputs fully to the supply rails. For high-precision applications near the power limits, consider using a specialized rail-to-rail operational amplifier.
Frequently Asked Questions
1. What happens if the ideal output voltage exceeds the supply rails?
The operational amplifier will saturate, and its output voltage will clip at the limit of the respective supply rail (Vp or Vn). This calculator automatically accounts for this limit and displays a warning if saturation occurs.
2. Why is the inverting path gain displayed as a negative number?
The negative sign indicates a 180-degree phase shift. An increase in the input voltage at V1 produces a proportional decrease in the output voltage.
3. How do you balance this circuit to function as a pure differential amplifier?
To configure this circuit as a standard differential amplifier where Vout = (R2/R1) * (V2 - V1), select resistor values such that the ratio R2/R1 equals R4/R3.
4. Can this calculator be used with a single-supply op-amp?
Yes. For single-supply designs, set the negative supply rail Vn to 0V (ground), and ensure all input and output signals remain within the positive supply headroom.
5. What is common-mode rejection ratio (CMRR)?
CMRR is the amplifier's ability to reject input signals common to both terminals. Matching the resistor ratios (R2/R1 = R4/R3) is critical to maximize CMRR and cancel common-mode noise.
6. Why is the input impedance of the non-inverting terminal lower than an un-loaded terminal?
In this circuit, the input impedance of the non-inverting path is limited by the resistor divider network (R3 + R4) connected to ground, which draws signal current from V2.
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