Linearize a standard NTC thermistor output using a voltage divider and a non-inverting Op-Amp amplifier. This tool automatically calculates the optimal Divider Resistor (R1) and the Bias/Gain Resistors (R2, R3) to map your specific temperature range to a full-scale ADC voltage range (e.g., 0V to 3.3V).

1. NTC Sensor & System

Supply (V_dd)

Beta (β)

R @ T_β

T_β

°C

2. Target Ranges

Temp Min

°C

Temp Max

°C

ADC V_{out_min}

ADC V_{out_max}

3. Circuit Tuning

Feedback (R4)

Higher R4 = higher gain needed

Divider R1 (Pull-up)

0 = Auto-calculate optimal

Rounding

4. Input Filter

Cutoff F_c

Filter R_f

Reference Circuit

NTC Op-Amp Signal Conditioning Schematic

Bias & Gain Resistors

Required Op-Amp Resistors

—

R2 (Pull-up)

—

R3 (Pull-down)

Divider Performance

R_NTC (Min / Max) / Ω

Divider R1 (Optimal) — Ω

V_in @ T_min — V

V_in @ T_max — V

Op-Amp Details

V_ref (Target vs Actual) / V

Gain (Ideal vs Actual) /

V_out @ T_min — V

V_out @ T_max — V

Filter Cap & Status

Filter C_f — μF

Settling Time (~5τ) — ms

Linearity Error —

Sanity Check —

Diagnostic Tests

Use Current Inputs Use Defaults

...

Frequently Asked Questions

Why use an Op-Amp for NTC Thermistors?

Standard NTC voltage dividers are non-linear and have high output impedance. An Op-Amp circuit provides linearization, impedance buffering, and gain/offset adjustment to match the full dynamic range of your ADC.

How is the optimal R1 calculated?

The calculator chooses R1 (the pull-up resistor) to be the geometric mean of the NTC resistance at Tmin and Tmax: R1 = √(R_min * R_max). This centers the non-linearity curve, providing the most linear voltage response possible before Op-Amp processing.

What does the schematic look like?

Divider Stage: Vdd connects to R1, which connects to the NTC and Ground. The center tap (Node A) provides the input voltage.
Gain Stage: Node A feeds the Non-Inverting Op-Amp input (via Rf). Resistors R2 and R3 set the DC bias point, while R4 sets the gain.

Why is the Cutoff Frequency (Fc) important?

NTC sensors often pick up high-frequency noise. The passive low-pass filter (Rf/Cf) removes this noise before amplification, preventing aliasing errors in your ADC readings.