Signal-to-Noise Ratio

Introduction to Signal-to-Noise Ratio

In this video, the concept of signal-to-noise ratio is introduced. The importance of signal-to-noise ratio is discussed, and how it can be defined.

Definition of Signal-to-Noise Ratio

• A signal is a function that changes over time.

• Noise can interfere with the signal and make it difficult to measure or understand.

• Noise is one of the limiting factors in communication systems.

• Signal-to-noise ratio (SNR) characterizes the relative strength of the signal and noise.

• SNR can be expressed as power or voltage ratios.

Power and Voltage Ratios

Power Signal-to-Noise Ratio

• Power SNR is given by average signal power divided by average noise power.

• Power SNR can be expressed in terms of voltage SNR using a square relationship.

Voltage Signal-to-Noise Ratio

• Voltage SNR is given by RMS signal voltage divided by RMS noise voltage.

• Average signal power and average noise power can be computed from RMS values.

Decibels

• Decibels (dB) are a logarithmic scale used to express SNR.

• dB can be calculated from power or voltage ratios.

Manipulating Signal-to-Noise Ratios

Example 1 - Low SNR

• An SNR of 1 means that noise power equals signal power, which is not ideal.

Example 2 - High SNR

• An SNR of 100 means that signal power is much greater than noise power, which is desirable.

Signal-to-Noise Ratios

This section explains how to calculate signal-to-noise ratios and express them in decibels (dB).

Calculating Signal-to-Noise Ratios

• A power signal-to-noise ratio of 100 is equivalent to a voltage signal-to-noise ratio of 10.

• The dB expression for a voltage or power signal-to-noise ratio is the same: 20 log to the base 10 of the ratio.

• For example, a power signal-to-noise ratio of 100 is equal to 20 dB.

• The log base 10 of a number can be multiplied by 10 to get its dB value.

Using Signal-to-Noise Ratios

• A gain or attenuation expressed in dB corresponds to a ratio that is either twice or half the value of something else, respectively.

• For example, a gain of 3 dB corresponds to a ratio that is twice the value of something else, while an attenuation of -3 dB means that something is half the value of something else.

• Filters are often discussed in terms of their bandwidth at frequencies where they have attenuated signals by three DB or by a factor of two.

Overall, this section provides an introduction to calculating and using signal-to-noise ratios and expressing them in decibels.