Comparator Threshold Calculator
This Comparator Threshold Calculator estimates the ideal reference voltage generated by a resistor divider and determines whether a single-threshold comparator output is HIGH or LOW.
Use it for first-pass threshold checks, sensor trip points, voltage monitor circuits, simple level detection, and design reviews where the ideal comparator model is appropriate.
Engineering tool
Comparator Threshold Calculator
Calculate comparator reference threshold voltage from a divider and determine ideal HIGH or LOW output state.
Comparator supply or divider excitation voltage.
Divider resistor from Vcc to the reference node.
Divider resistor from the reference node to ground.
Signal voltage compared against the reference threshold.
Reference voltage (Vref)
2.5 V
Output: HIGH
Result console
- Reference voltage (Vref)
- 2.5V
- Comparator state
- HIGH
- Threshold condition
- Vin > Vref
- Input margin
- 500mV
- Input voltage (Vin)
- 3V
- Supply voltage (Vcc)
- 5V
- Upper resistor R1
- 10kΩ
- Lower resistor R2
- 10kΩ
Result is valid for the ideal single-threshold comparator model.
Formula reference
Comparator Threshold Formula
The ideal single-threshold comparator model assumes a divider-generated reference voltage and instant HIGH or LOW switching when Vin crosses Vref.
Vref = Vcc × R2 / (R1 + R2)Non-inverting: Vin > Vref → Output = HIGHNon-inverting: Vin < Vref → Output = LOWInverting: Vin > Vref → Output = LOWInverting: Vin < Vref → Output = HIGHVariable definitions
- Vcc
- Supply voltage applied to the reference divider
- R1
- Upper divider resistor from Vcc to Vref
- R2
- Lower divider resistor from Vref to ground
- Vref
- Comparator reference threshold voltage
- Vin
- Input voltage being compared
- Output
- Ideal HIGH or LOW comparator state
Variable Description
- Comparator mode
- Selects whether the input is applied to the non-inverting or inverting comparator input.
- Supply voltage Vcc
- The voltage that excites the divider used to create the reference threshold.
- Upper resistor R1
- The resistor from Vcc to the reference node. It forms the top half of the divider.
- Lower resistor R2
- The resistor from the reference node to ground. Increasing R2 raises the threshold.
- Input voltage Vin
- The signal voltage compared against the reference threshold.
- Comparator state
- The ideal HIGH or LOW output state predicted by the selected comparator mode.
Worked Examples
Example 1: Non-Inverting Comparator
- Mode
- Non-Inverting
- Vcc
- 5 V
- R1
- 10 kΩ
- R2
- 10 kΩ
- Vin
- 3 V
Vref = Vcc × R2 / (R1 + R2)
Vref = 5 V × 10 kΩ / (10 kΩ + 10 kΩ) = 2.5 V; Vin = 3 V
Vin > Vref, Output = HIGH
In non-inverting mode, an input above the reference threshold drives the ideal output HIGH.
Example 2: Inverting Comparator
- Mode
- Inverting
- Vcc
- 12 V
- R1
- 20 kΩ
- R2
- 10 kΩ
- Vin
- 5 V
Vref = Vcc × R2 / (R1 + R2)
Vref = 12 V × 10 kΩ / (20 kΩ + 10 kΩ) = 4 V; Vin = 5 V
Vin > Vref, Output = LOW
In inverting mode, an input above the reference threshold drives the ideal output LOW.
Comparator basics
A comparator is used as a switching circuit, not a linear amplifier. It decides whether Vin is above or below a reference.
Reference voltage
The reference threshold can come from a divider, voltage reference, DAC, or sensor bias network.
Voltage divider
R1 and R2 set the ideal reference level, but tolerance, leakage, and input bias current affect real thresholds.
Input threshold
A single threshold can chatter if Vin moves slowly or contains noise near Vref.
Output saturation
Op-amps used as comparators may saturate and recover slowly compared with dedicated comparators.
Comparator vs operational amplifier
Dedicated comparators are usually better for speed, logic outputs, saturation recovery, and input overdrive behavior.
Open-loop operation
The comparator is normally operated without linear negative feedback, so small input differences can produce full output changes.
Common Mistakes
Confusing linear amplifier mode with comparator mode
Comparator circuits are switching circuits. They are not intended to produce a proportional analog output.
Calculating the reference voltage incorrectly
R1 and R2 positions matter. Vref equals Vcc times the lower resistor divided by the total resistance.
Ignoring output saturation
An op-amp used as a comparator can saturate and recover slowly, especially with large overdrive.
Mixing up inverting and non-inverting logic
The same Vin and Vref relationship produces opposite output states depending on comparator mode.
Using a general op-amp as a comparator without checking speed
Real switching applications should verify propagation delay, slew behavior, input range, and output logic compatibility.
Support reference
FAQ
What is a comparator?
A comparator compares an input voltage against a reference threshold and drives its output HIGH or LOW depending on which voltage is greater.
How is the threshold voltage calculated?
This calculator uses a resistor divider reference: Vref = Vcc × R2 / (R1 + R2), where R1 is the upper resistor and R2 is the lower resistor.
What is the difference between an inverting and non-inverting comparator?
For a non-inverting comparator, Vin above Vref produces HIGH. For an inverting comparator, Vin above Vref produces LOW.
Can an operational amplifier be used as a comparator?
Sometimes, but a dedicated comparator is usually better for switching speed, saturation recovery, input range, and output stage behavior.
Why is my output always HIGH?
The input voltage may be consistently on the HIGH side of the threshold, or the selected comparator mode may invert the logic compared with your expectation.
Why is the threshold not equal to half the supply voltage?
The threshold is half the supply only when R1 and R2 are equal. Unequal divider resistors intentionally create a different reference voltage.
Does this calculator include hysteresis?
No. This first version models a single-threshold comparator. Real noisy signals often need hysteresis to prevent output chatter near the threshold.
Related Engineering Guides
Dedicated op-amp guides are planned for this topic cluster. These guide topics are reserved for future publication and are shown without links until the pages exist.
Planned Engineering Guide
Comparator Basics
Planned guide covering open-loop comparison, HIGH/LOW output behavior, input thresholds, and practical comparator circuits.
Planned Engineering Guide
Voltage Divider Design
Planned guide explaining divider references, resistor selection, loading, tolerance, and threshold accuracy.
Planned Engineering Guide
Comparator vs Op-Amp
Planned guide comparing dedicated comparators with op-amps used in open-loop switching applications.
Planned Engineering Guide
Reference Voltage Design
Planned guide covering resistor dividers, references, noise, filtering, tolerance, and threshold stability.
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Engineering Disclaimer
This calculator uses an ideal single-threshold comparator model for estimation and education. Real designs must verify input common-mode range, output stage behavior, hysteresis, propagation delay, saturation recovery, noise, offset, divider tolerance, loading, supply rails, and device-specific datasheet limits before hardware release.