Signal to noise ratio is an important concept to learn while handling various analytical instruements.

1. Signal To Noise Ratio
Name: Shriya Mhatre
Roll No: P21006
MSc Part 2
Paper 1

2. What is signal
Signal carries the information of analyte of interest
Noise is the unwanted information that degrades accuracy and precision
Unit is Decibels (dB)
SNR should be high so that signal can be detected from noise
 S/N = Mean
Standard deviation

4. Continued…
Positive SNR Signal power > Noise power
Negative SNR Signal power < Noise power
Zero SNR Signal power = Noise power
SNR should be high as much as possible
SNR of 100 dB is better than SNR of 70 dB

5. SOURCES OF NOISE
Chemical Noise Instrumental Noise
-Uncontrollable variables
- Thomson Noise
- Shot Noise
- Flicker Noise
- Environmental Noise

6. Thermal Noise (Johnson Noise)
Arises due to excitation of electrons in resistors, capacitors etc
Excitation of electrons is random and creates inhomogeneity
 Voltage fluctuations appear on read out device as noise
Reduced by cooling the detector or decreasing the frequency bandwidth of signal

7. Shot Noise (White Noise)
Electrons crosses the junction randomly
In electronic circuits, electrons crosses pn- junction randomly
In photocells and vacuum tubes the junction is the empty space between anode and cathode.
Reduced by cooling the detector or by decreasing frequency bandwidth of signal

8. Flicker And Environmental Noise
Flicker noise
Magnitude is inversely proportional to frequency of signal
Significant at frequencies lower than 100 Hz
Reduced by wire wound or metallic film resistor
Environmental noise
Combination of different form of noise arising from surroundings
Conductors can pick up electromagnetic radiation
Sources are power lines, radio, TV station, ignition system, gasoline etc

9. Signal To Noise Ratio Enhancement
Hardware Methods Software Methods
- Grounding and shielding
- Analog filtering
- Modulation
- Lock in amplifiers
- Difference and instrumentation amplifier
-Ensemble Averaging
-Boxcar Averaging
-Digital filtering

10. Hardware Methods
 GROUNDING AND SHIELDING
Reduces electromagnetic radiation
Circuit is surrounded by conducting
material(shield) attached to the ground
EMR is absorbed by shield
 ANALOG FILTER
High pass filter:
-Allows high frequency signal
-Removes low frequency signal
Low pass filter:
-Allows low frequency signal.
-Removes high frequency signal

11. Modulation
Direct amplification of low frequency signal is difficult when instrument exhibits flicker
Flicker noise is larger than noise present at higher frequencies
Thus we follow the process called Modulation
Low frequency signal is superimposed on carrier wave (High frequency signal)

12. Modulated signal
Amplified
Amplifier noise is removed by passing the signal through high pass filter
Synchronous Demodulator
Demodulated signal
Low pass filter
dc signal

13. Software Methods
 ENSEMBLE AVERAGING
Successive sets of data is stored in memory as
array
Summed point by point (Co-addition)
Average is taken
 BOXCAR AVERAGING
Adjacent points are summed and average is
taken
2 to 50 points are averaged to generate a final
point

14. References….
What Is Signal-to-Noise Ratio and Why Does It Matter? (lifewire.com)
Signal to noise ratio formula statistics | Measure signal to noise ratio (byjus.com)
Signal-to-Noise (S/N) Ratio: Definition & Formula - Video & Lesson Transcript | Study.com
signal to noise ratio Ref Book - Google Docs

15. THANK YOU