# ADC in Digital Temperature Sensor DS18B20

According to the datasheet of DS18B20 temperature sensor, it is clear that the sensor is digital so the output is in digital form.

The resolution of the temperature sensor is 9, 10, 11, or 12 bits, corresponding to increments of 0.5°C, 0.25°C, 0.125°C, and 0.0625°C, respectively, and by default it is 12-bits. Which means, for 12-bits, a change of 0.0625°C in temperature causes an increment of 1-bit.

But there is no information given on how much change in voltage will result from a change in Temperature (i.e. scale factor). For example, there is an analog temperature sensor in which a change of 10mV in the output voltage is equal to a change of 1°C of temperature.

Is there any way to calculate the scale factor of the digital temperature sensor like the way we do for analog?

• I'm not sure what are interested in the analog voltage that corresponds to this change, you don't have access to it anyway, you can only read the sensor digitally. Commented Dec 24, 2013 at 11:11
• the sensor performs conversion from A-to-D itself, when master issues Convert T [44h] command, I'd want to know the scale factor at which the conversion is perform. there must be some scale factor. Commented Dec 24, 2013 at 11:13
• @alexan_e I'm wondering if the OP means the change in supply voltage to the device? The scale Factor is hard-defined - the bytes read directly related to temperature. Commented Dec 24, 2013 at 11:13

All you really need to know is contained here: -

Internally the device may have a sensor that produces 10uA per degree or 10mV per degree or it may be like a thermistor or RTD and vary its resistance to indictate temperature. This is Maxim IP and we are not allowed to know what method they use unless they tell us. If it's not in the data sheet then we cannot know - but you could assume it is one of the four methods I've mentioned and give details in your presentation of all ideas.

If you want to know the types of constant voltage or current sensors that could be used try looking up the AD590 (constant current at 10uA per degC) or the TMP36 (10mV per degC). I'm not aware of a particular name that describes the technology.

• I have already gone through this and have performed manual calculation to calculate the above data, for example, if the room temperature is 22C then, 22C/0.0625C = 352D = 0000 0001 0110 0000b = 0160H (if resolution is 12-bit). what i really need to know is the scale factor in terms of voltage. Commented Dec 24, 2013 at 11:33
• @Xufyan what voltage do you refer to? Internally the device may have a sensor that produces 10uA per degree or 10mV per degree or it may be like a thermistor or RTD and vary its resistance to indictate temperature. This is Maxim IP and we are not allowed to know what method they use unless they tell us. If it's not in the data sheet then we cannot know - but you could assume it is one of the four methods I've mentioned and give details in your presentation of all ideas. Commented Dec 24, 2013 at 11:36
• This is exactly the answer i was looking for, is there any particular name for such sensors that produces o/p in form of current/voltage ? Commented Dec 24, 2013 at 11:55
• and please add your above comment in the answer so i could mark it as correct. Commented Dec 24, 2013 at 11:56
• @Xufyan OK done!! Commented Dec 24, 2013 at 12:51

No, there is not. Either the datasheet will provide this information, or it will not.

But it is of no value to have this information regardless, since you cannot do anything with it.

• I have a presentation to be given on ADCs, and this sensor is in use, shouldn't there be some way of calculating the scale factor. because there is definitely something the sensor is doing to perform A-to-D conversion inside. Commented Dec 24, 2013 at 11:14
• Sure. But as the end-user, you don't need to care about it. Commented Dec 24, 2013 at 11:15

You can build a circuit that produces a current or voltage output in response to a temperature change by using temperature sensitive elements, like thermocouples, thermistors, Resistive temperature devices (RTDs), or the like. In fact, any semiconductor with a pn junction will serve. You would need to build an amplifier appropriate for your choice.

Your device has something like this inside, and skips the need for such extra design and processing.