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A Level     Signal     ADC Flash     ADC Ramp     DAC Summing     Distortion     Problems     Regenerator     Sample and Hold     Sampling     Serial and Parallel     >signal to noise ratio<    

Signal signal to noise ratio


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The Decibel Scale

The decibel (dB)  scale is logarithmic. Log scales have the advantage of representing a huge range of values with quite a small range of numbers.

Power Gain

The gain could be a loss called attenuation.

Gdb = 10 log10 ( POUT / PIN )

Combined Gain of Several Stages

Decibel Gains Add but Voltage or Power Gains Multiply

Signal to Noise Ratio

The signal is wanted. The unwanted electrical noise comes from external sources like lightning strikes, industrial machinery power switching, or warm components in sensitive electronics.

For Power        SNRdb = 10 log10 ( PS / PN )

For Voltage      SNRdb = 20 log10 ( VS / VN )

Conversions between Power Gain and dB

Ratio dB
POUT/PIN     10 log10(POUT/PIN)    
10 000 000 000  100 
1 000 000 000  90 
100 000 000  80 
10 000 000  70 
1 000 000  60 
100 000  50 
10 000  40 
1 000  30 
100  20 
10  10 
0.5  −3 
0.25  −6 
0.1  −10 
0.01  −20 
0.001  −30 
0.0001  −40 
0.00001  −50 
0.000001  −60 
0.0000001  −70 
0.00000001  −80 
0.000000001  −90 
0.0000000001  −100 

Conversions between Voltage or Current Gain and dB

Ratio dB
    Vout / Vin    
Iout / Iin
    20 log10 ( Vout / Vin )    
20 log10 ( Iout / Iin )
100 000  100 
10 000  80 
1 000  60 
100  40
10  20
1.414 
0.707  −3 
0.5  −6 
0.1  −20 
0.01  −40 
0.001  −60 
0.0001  −80 
0.00001  −100 

The Universe with a Log Scale

Log Scale Universe from XKCDThanks xkcd

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