Documentation sections

MOSFET Operating Point Calculator

POSThttps://rftools.io/api/py/v1/calculate

Slug mosfet-operating-point. Calculate MOSFET drain current, saturation voltage, transconductance, and operating region (cutoff, triode, saturation) for NMOS transistors

Inputs

Send every one of these in inputs, in the units shown. Most are required: a call without one is refused (400) and costs nothing; one the calculator can do without takes the default shown. An input outside its range is still computed and flagged in the provenance.

Inputs of mosfet-operating-point
Name	Unit	Range	Default	Description
vgsnumber	V	at least 0	5	Gate-Source Voltage
vthnumber	V	at least 0.1	2	Threshold Voltage
knnumber	mA/V²	at least 0.001	100	Process parameter kn = μ_n × Cox × W/L
vdsnumber	V	at least 0	10	Used only when Bias Mode is 1; by default V_DS is solved from V_DD and R_D
vddnumber	V	at least 0.1	12	Supply Voltage
rdLoadnumber	kΩ	at least 0.001	1	Drain Load Resistance
biasModenumber	none	0 … 1	0	Load line solves V_DS = V_DD − I_D·R_D; the other mode uses the V_DS enteredOne of: 0 Load line · 1 V_DS as entered

Outputs

Returned in values, by key. A value that is unbounded or undefined is null.

Outputs of mosfet-operating-point
Field	Unit	Description
idheadline	mA	Drain Current
vdsSat	V	Saturation Voltage
powerDissipation	mW	Power Dissipation
gm	mA/V	Transconductance
region	none	Operating Region (0=Off, 1=Triode, 2=Sat)
vdsOperating	V	V_DS at the Operating Point

Calling it

Calculate: one call, the request and response in full, and its errors.
Batch: this calculator with others, or a sweep, in one request.
Solve for a target: the value of one input that brings an output to a target.

curl -X POST https://rftools.io/api/py/v1/calculate \
  -H "X-API-Key: $RFTOOLS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "slug": "mosfet-operating-point",
    "inputs": {
      "vgs": 5,
      "vth": 2,
      "kn": 100,
      "vds": 10,
      "vdd": 12,
      "rdLoad": 1,
      "biasMode": 0
    }
  }'

import rftools

client = rftools.Client()  # reads RFTOOLS_API_KEY, or the key `rftools login` saved

result = client.calculate("mosfet-operating-point", {
    "vgs": 5,
    "vth": 2,
    "kn": 100,
    "vds": 10,
    "vdd": 12,
    "rdLoad": 1,
    "biasMode": 0,
})
print(result.values)
print(result.warnings, result.provenance.formula_ref)

const response = await fetch("https://rftools.io/api/py/v1/calculate", {
  method: "POST",
  headers: {
    "X-API-Key": process.env.RFTOOLS_API_KEY,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    "slug": "mosfet-operating-point",
    "inputs": {
      "vgs": 5,
      "vth": 2,
      "kn": 100,
      "vds": 10,
      "vdd": 12,
      "rdLoad": 1,
      "biasMode": 0
    }
  }),
});
console.log(response.status, await response.json());

package main

import (
	"bytes"
	"fmt"
	"io"
	"net/http"
	"os"
)

func main() {
	body := []byte(`{
	  "slug": "mosfet-operating-point",
	  "inputs": {
	    "vgs": 5,
	    "vth": 2,
	    "kn": 100,
	    "vds": 10,
	    "vdd": 12,
	    "rdLoad": 1,
	    "biasMode": 0
	  }
	}`)
	req, err := http.NewRequest("POST", "https://rftools.io/api/py/v1/calculate", bytes.NewReader(body))
	if err != nil {
		panic(err)
	}
	req.Header.Set("X-API-Key", os.Getenv("RFTOOLS_API_KEY"))
	req.Header.Set("Content-Type", "application/json")
	res, err := http.DefaultClient.Do(req)
	if err != nil {
		panic(err)
	}
	defer res.Body.Close()
	out, _ := io.ReadAll(res.Body)
	fmt.Println(res.Status, string(out))
}

application/json

{
  "slug": "mosfet-operating-point",
  "values": {
    "id": 11.959865316811522,
    "vdsSat": 3,
    "powerDissipation": 0.4800054054671004,
    "gm": 4.013468318847833,
    "region": 1,
    "vdsOperating": 0.04013468318847833
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:mosfet-operating-point",
    "version": "api@3f2c1a9b04de",
    "formulaRef": "Sedra & Smith, Microelectronic Circuits, 7th ed. (Oxford, 2015), §5.3, Example 5.5 and Exercise 5.11",
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "vgs": {
          "min": 0,
          "max": null,
          "unit": "V"
        },
        "vth": {
          "min": 0.1,
          "max": null,
          "unit": "V"
        },
        "kn": {
          "min": 0.001,
          "max": null,
          "unit": "mA/V²"
        },
        "vds": {
          "min": 0,
          "max": null,
          "unit": "V"
        },
        "vdd": {
          "min": 0.1,
          "max": null,
          "unit": "V"
        },
        "rdLoad": {
          "min": 0.001,
          "max": null,
          "unit": "kΩ"
        },
        "biasMode": {
          "min": 0,
          "max": 1,
          "unit": ""
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "vgs": 5,
      "vth": 2,
      "kn": 100,
      "vds": 10,
      "vdd": 12,
      "rdLoad": 1,
      "biasMode": 0
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "vgs"
      ],
      "msg": "Input should be a valid number, unable to parse string as a number",
      "input": "abc"
    }
  ]
}

An input sent as text. Nothing was counted.

{
  "detail": "More than 120 requests in 60 seconds from this address.",
  "errorKind": "rate_limited",
  "limit": 120,
  "windowSeconds": 60,
  "upgradeUrl": "https://rftools.io/pricing/"
}

Too many requests in a minute, with Retry-After.

Same inputs on the calculator pageMOSFET Operating Point Calculator, at these values