Thermal Noise Floor

In the absence of any broadband noise sources 1 f noise or brownian noise the minimum noise level you can hope to measure in an electronic system is the thermal noise floor.

Thermal noise floor.

A common way to lower the noise floor in electronics systems is to cool the system to reduce thermal noise when this is the major noise source. In acoustics this may be background noise or in electronics there are often things like thermal noise radiated noise or any other interfering signals. Following equation or formula is used for thermal noise power and voltage calculator. What determines the thermal noise floor.

When we say noise floor we are referring to the same idea as a general noise floor. Thermal noise is a noise that is a result of the thermal agitation of electrons. Dbm is the power level expressed in decibels relative to one milliwatt. Thermal noise increases with temperature.

Thermal noise spectrum is gaussian in shape. It is then easy to relate this to other bandwidths. It is measured in noise power units of dbm or watt or noise voltage. If we look at the normalized b 1 hz bandwidth noise floor equation we have.

The thermal noise power depends of the bandwidth and temperature of the surroundings. Thermal noise in a 50 ω system at room temperature is 174 dbm hz. Because the power level is proportional to the bandwidth twice the bandwidth level gives twice the power level 3db and ten times the bandwidth gives ten times the power level 10db. Let s calculate the thermal noise floor of the 200 khz channel bandwidth used by gsm.

The noise resulting from thermal agitation of electrons is referred as thermal noise. Enter the temperature and bandwidth and click on calculate to get the thermal noise power. Nf is the noise figure. It is then possible to calculate the noise floor for the receiver at 20 c 290 k in a 1hz bandwidth.

Thermal noise is present in all electrical circuits and in sensitive electronic equipment such as radio receivers can drown out weak signals and can be the limiting factor on sensitivity of an electrical measuring instrument. To convert the noise power to db watts use 10 times the log of the noise power in watts. Noise floor 174 nf 10 log 10 bandwidth where. Ktb for gsm 200 khz 174 dbm hz 10 log 200 000 hz 121dbm the 121dbm is therefore the absolute lowest noise power we get in a 200 khz gsm channel.

Thermal noise floor k joules k t k b hz the resulting noise is in joules second or watts. When the temperature of the system is higher the thermal noise floor will be higher. The noise floor limits the smallest measurement that can be taken with certainty since any measured amplitude can on average be no less than the noise floor.