Common Types of Noise

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Buck Tyler
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2 Common Types of Noise Name Example Description Impulse Ignition, TVI Not Random, Cure by Shielding, Quantizing, Decoding, etc. BER Digital Systems, DAC's & ADC's. Often Bit Resolution and/or Bit Fidelity Shot Transistors Corpuscular Current Flow, Lots of Impulses Thermal Resistors, Atmosphere Thermal Agitation of Electrons Act Like Signal Flicker (1/f) Recombination Low frequency, FET s H

3 Noise Voltage

4 ktb----thenoise Floor R - j X R+jX L L k = 1.38 x 10 joule / k T = Temperature (K) B = Bandwidth (Hz) Available Noise Power, P av = ktb (Power Delivered to a Conjugate Load), (i.e. R = R, X = X) At Standard Temperature T (=290K) : kt= 4 x W/Hz = 174dBm / Hz Across 50 Ohms

5 Noise Power is a Function of Bandwidth Noise power = 10 log (BW 2 /BW 1 ) Bandwidth Noise power change Noise power 1 MHz 60 db -114 dbm 1 khz 30 db -144 dbm 10 Hz 10 db -164 dbm 2 Hz 3 db dbm 1 Hz 0 db -174 dbm

6 What is Noise Figure?. (Original Definition) (S/N) in (S/N) out F(dB) = 10 log (S/N) in (S/N) out Ts = 290K The linear ratio is known as Noise Factor

7 What is Noise Figure? Small Signal Imperfect Amplifier Signal larger But Noisier Thermal Agitation of Electrons adds noise to the signal Page 7

8 What is Noise Figure? Noise added by Amplifier Na Noise Added (Na) Noise (in) Noise (in) x Gain [N in G] Gain 20dB NF 10dB T o= 290K Nin at 290K N a Imperfect Amplifier Degrades Signal to Noise Ratio Np = Na + Nin G Page 8

9 What s the noise figure of an attenuator? Does an attenuator ADD noise? Does an attenuator attenuate noise? How does loss impact the noise figure of my receiver system?

10 Why do we measure Noise Figure? Example... Transmitter: ERP Path Losses Rcvr. Ant. Gain Power to Receiver + 55 dbm -200 db 60 db -85 dbm Power to Antenna: +40 dbm Frequency: 12 GHz Antenna Gain: +15 db Receiver: Noise 290K Noise in 100 MHz BW Receiver N.F. Receiver Sensitivity -174 dbm/hz + 80 db +5 db -89 dbm Link Margin: 4 db ERP = +55 dbm Path Losses: -200 db Choices to increase Margin by 3dB 1. Double transmitter power 2. Increase gain of antennas by 3dB 3. Lower the receiver noise figure by 3dB Receiver NF: 5 db Bandwidth: 100 MHz Antenna Gain: 60 db Page 10

11 Effect of 2nd Stage Contribution The Friis equation F12 = F1 + F2-1 G1 R Input Noise kt B o BG 1, Na1 BG, N 2 a2 1st Stage 2nd Stage Na1 Na2 N a1 G2 Total Noise Added Total Noise Power Output kt B o N a= (F-1)kT o B G K T obg1 k T o B G 1 G2 Noise Input x System Gain F = F total 1 + F F n- 1 G1 G 1 G2... Gn-1 F 12 = F 1 + F 2-1 G 1 Page 11

12 Friis Equation cascade or second stage noise contribution F12 = F1 + F2-1 G1 GAIN X 6dB (4) 12 db (16) 20 db (100) A B C N Factor Y F ABC = (2.0-1) + (4.0-1) 4 4 x 16 = = (3 db) F ACB = (4.0-1) + (2.0-1) 4 4 x 100 = = (4 db)

13 How Do We Get Low Noise Amps? Select or construct low-noise Transistors High electron mobility materials- Gaas low feedback and output resistance Low base current/small signal= low temp Find optimum balance between match, gain and noise output

14 Transistor Noise Parameters Finding the best balance between gain, match and noise

15 Noise Circles Gamma Optimum = Transistor match for minimum noise output

16 NF Measurement Techniques Signal Generator Method Y-factor Method (Calibrated noise source) Y-factor without a calibrated noise source

17 Signal Generator Method Signal Generator DUT Spectrum Analyzer/ Power Meter/ Receiver-Detector Load Steps 1. Measure SG Level output 2. Measure DUT output 3. Compute Gain 4. Terminate/Load Dut(KTB) 5. Measure Noise output of DUT 6. NFig= Noise Output -Gain dbm/hz

18 Signal Generator Method Can t see the DUT noise? >Add a preamp Signal Generator DUT Preamp Spectrum Analyzer/ Power Meter/ Receiver-Detector Load NF = Noise output - Gain(Dut) - Gain(Pre)+ 174 dbm/hz

19 . Noise Power is Linear with Temperature N IN Ts Na, G N = N +Gk(T )B out a { Added Noise Input Noise, N IN {s out Noise Output Power N 2 N 1 N a SLOPE kgb F = N IN OUT N G H 0 T 1 T 2 T s

20 Definition of Effective Input Noise Temperature, T e. Ts Na N = N + kgbts out a Zs@ Ts Zs@ Te Na=0 N out = kgb(t e + T s ) N out Noise Output Power Na T e T s H

21 Measurement of Noise. Z T c, T h N (T ) a e { N N 2 1 N 2 N p N kgb(t + T ) Y = 2 = h e N kgb(t + T ) 1 c e Noise Power Output N 1 N a T o= 290K Tc Th Ts T e = F = T h -YT T + T c F = e o Y-1 T o ( T T h T Y T c - 1) o o Y - 1 Temperature of Source Impedance

22 Where Do T H and T C Come From? Noise Sources.. Gas Discharge Tubes Load/Termination Sun Noise (stars and galaxies, cold sky, cold load) Diode Noise sources Commercial and home-built

23 Avalanche Diode Noise Source ENR table Matching Pad Bias Input 28 VDC Noise Output

24 Excess Noise Ratio ENR (db) = 10 log ( Th 290 ) 290 Model Frequency Range ENR HP HP 346A 10 MHz - 18 GHz 6 db HP 346B 10 MHz - 18 GHz 15 db HP 346C 10 MHz GHz 15 db HP 346C/K01 HP 346B/H GHz GHz 20 to 7 db 5 db

25 Noise Figure Meter. Low Pass Filter f (2 GHz) IF

26 Making a Measurement. Calibration (Measurement System) DUT Measurement (DUT & System) N p N 2 N 2 ' N 1 ' N a ' N a N 1 kg G B kg B N a Y = N2 / N1 T c ' T ' h T s T c T h slope = kg 2 B = N 2 N 1 slope = kg G B = N 2 N T h T c T h T c G DUT = N 2 - N 1 T h T c N2 ' - N1 ' T h ' -T c ' F = F + Meas DUT F sys 1 G DUT

27 Simpler Yet.. +28V Measurement System N P (on) On Noise Source Off Noise Sourc e DUT Low Pass Filter N P (off) SECOND STAGE NF = ENR - 10 log ( Y-1) Y = N Pon / N Poff Page 27

28 ERRORS! Adapter and path losses Noise Source Cable C1 G 1 Coax/WG adapter G 2 DUT Coax/WG adapter Cable C2 Measurement system Page 28

29 ERRORS! Mismatch Uncertainty Noise Source Calibration ρ 3 ρ 1 ρ 2 ρ 4 DUT Measuring System Measurement ρ = reflection coefficient at a reference plane Page 29

30 Y-factor without a calibrated noise source Differentiating

31 Y-factor without a calibrated noise source Step Attenuator

32 Y-factor without a calibrated noise source 2 NF = 1 Y/ ENR

33 Conclusions ktb is THE noise floor at -174 dbm/hz Noise figure = Signal input /Noise input vs. Signal output /Noise output Noise figure is noise added by an amplifier or receiver Optimize noise figure by placing lowest noise/loss elements near antenna Second stage contribution is typically low There are several methods to measure noise figure The uncalibrated noise method could be very popular with hams

34 Noise Algebra N2 N1 No Tc Th - N2 kgb(te+th) Y = --- = N1 kgb(te+tc) --- Th-YTc Te = Y-1 (Solve for Te) Using T e = ( F -1 ) x To F Th Tc Y To To = Y F Th Tc Y Tc Tc = Y Page 34

Noise Figure Definitions and Measurements What is this all about?...

Noise Figure Definitions and Measurements What is this all about?... Bertrand Zauhar, ve2zaz@rac.ca November 2011 1 Today's Program on Noise Figure What is RF noise, how to quantify it, What is Noise Factor