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Noise Figure Measurements

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Noise Figure Measurements Noise Figure Measurements Feb 24, 2009 Account Manager : Peter Caputo Presented by : Ernie Jackson Agenda • Overview of Noise Figure • Noise Figure Measurement Techniques • Accuracy Limitations • PNA-X’s Unique Approach Gain So/N o DUT Si/N i Noise Figure Basics Page 2 Noise Contributors Thermal Noise: (otherwise known as Johnson noise) is the kinetic energy of a body of particles as a result of its finite temperature Ptherm =kTB Shot Noise: caused by the quantized and random nature of current flow Flicker Noise: (or 1/f noise) is a low frequency phenomenon where the noise power follows a 1/f ααα characteristic Noise Figure Basics Page 3 Why do we measure Noise Figure? Example... Transmitter: ERP = ERP + 55 dBm +55 dBm Path Losses -200 dB Rx Ant. Gain 60 dB dB Power to Rx -85 dBm -200 ses: Los Receiver: Path Noise Floor@290K -174 dBm/Hz C/N= 4 dB Noise in 100 MHz BW +80 dB Receiver NF +5 dB Rx Sensitivity -89 dBm Choices to increase Margin by 3dB Receiver NF: 5dB 1. Double transmitter power Bandwidth: 100MHz Power to Antenna: +40dBm 2. Increase gain of antennas by 3dB Antenna Gain: +60dB Frequency: 12GHz 3. Lower the receiver noise figure by 3dB Antenna Gain: +15dB Noise Figure Basics Page 4 The Definition of Noise Factor or Noise Figure in Linear Terms • Noise Factor is a figure of merit that relates the Signal to Noise ratio of the output to the Signal to Noise ratio of the input. • Most basic definition was defined by Friis in the 1940’s. S S S N N in out N F = in S G , Na N out Reference: Harald Trap Friis: 1944: Proceedings of the IRE Noise Figure Basics Page 5 What is Noise Figure ? Noise Out Noise in Measurement bandwidth=25MHz a) C/N at amplifier input b) C/N at amplifier output Nin Nout Noise Figure Basics Page 6 Definition of Noise Figure S S Nout N in N out Noise N a Added G , Na GNin Sout f1 f2 Gain = G = Nout = Na + GNin Sin N + GN S Nout a in F = = Noise Factor N GNin GNin F = in S N + GN NF (dB) =10log a in N Noise Figure out GNin Noise Figure Basics Page 7 Noise Voltage Standard Equation for Noise Voltage produced by a Resistor e2 = 4kTBR k = Boltzman's Constant = .1 38×10−23 Joules/°K is T is absolute temperature ( °K) is B is bandwidth (Hz) e is rms voltage Reference: JB Johnson/Nyquist: 1928: Bell Labs Noise Figure Basics Page 8 Noise Power at Standard Temperature Thermal Load k = 1.38 x 10 -23 joule / k R - j X T = Temperature (K) R+jX L L B = Bandwidth (Hz) Available Noise Power Delivered to a Conjugate Load, Pav = kTB -21 At 290K P av = 4 x 10 W/Hz = -174dBm / Hz In deep space kT = -198dBm/Hz Noise Figure Basics Page 9 Noise Power is Linear with Temperature Nin Nout = Na + GNin = Na + GkTs B G , Na Z s @ Ts Nout Slope = kGB N2 N1 Na Output Noise Noise Output Power Ts T1 T2 Temperature of Source Impedance Noise Figure Basics Page 10 An Alternative Way to Describe Noise Figure: Effective Input Noise Temperature ( T e) N = N + GN ∑∑∑ out a in = GkTe B + GkTs B G , Na = 0 = GkB(Te +Ts ) Z s @ Ts Z s @ Te N out Slope = kGB T = (F −1)T e s N and a Output Noise Noise Output Power Ts Te +Ts TemperatureT of Source F = e Impedance Ts Noise Figure Basics Page 11 Te or NF: which should I use? ••UseUse either either - - they they are are completely completely interchangeable interchangeable ••TypicallyTypically NF NF for for terrestrial terrestrial and and Te Te for for space space ••NFNF referenced referenced to to 290K 290K - - not not appropriate appropriate in in space space ••IfIf Te Te used used in in terrestrial terrestrial systems, systems, the the temperatures temperatures cancan be be large large (10dB=2610K) (10dB=2610K) ••TeTe is is easier easier to to characterize characterize graphically graphically Noise Figure Basics Page 12 Friis or Cascade Equation • Here we see what contribution a second amplifier has on the overall noise factor. N = N + G N + G G N Nin out a2 1 a1 1 2 in G = G1G2 G , N G , N 1 a1 2 a2 Nin = kTs B Z s @ Ts Na1 = kTe1B = (F1 −1)kTs B Na2 Na2 = kTe2 B = (F2 −1)kTs B N F = out Na1G2 GNin Na1 kT B kT BG kT BG G F2 −1 Nin = s s 1 s 1 2 F12 = F1 + G1 Noise Figure Basics Page 13 Effects of Multiple Stages on Noise Factor • The cascade equation can be generalized for multiple stages Nin G1 , Na1 G2 , Na2 GN , N N 2 Z s @ Ts F −1 F −1 F = F + 2 +L+ N total 1 K G1 G1G2 GN −1 N F −1 F = F + i total 1 ∑ N i=2 G ∏ j−1 j=i Noise Figure Basics Page 14 Demo of Cascade Equation F2 −1 F = F1 + G1 ABC Gain (dB) 6.0 12.0 20.0 Gain 4.0 16.0 100.0 Noise Figure(dB) 2.3 3.0 6.0 Noise Factor 1.7 2.0 4.0 0.2 −1 0.4 −1 F = 7.1 + + = .1 70 + .0 25 + .0 047 = .1 997 ABC 4.0 4.0×16.0 NFABC =10log( .1 997) = .3 00 dB 0.4 −1 0.2 −1 F = 7.1 + + = .1 70 + .0 75 + .0 025 = .2 475 ACB 4.0 4.0×100.0 NFACB =10log( .2 475) = .3 93 dB Noise Figure Basics Page 15 Agenda • Overview of Noise Figure • Noise Figure Measurement Techniques • Accuracy Limitations • PNA-X’s Unique Approach Gain So/N o DUT Si/N i Noise Figure Basics Page 16 Measuring Noise Figure Na + Nin .Ga F = Nin . Ga Nin Nout = Na + kTB Ga Rs Ga , Na r e w Slope=kBGa o P t u tic p ris t te u c To solve for Na: ara To solve for Na: O h C 1) establish 2 points on curve ee 1) establish 2 points on curve Fr ise oror No 2)2) establish establish 1 1 point point and and gradient gradient Na -Te Te Source Temperature (K) Noise Figure Basics Page 17 Hot/Cold Technique Nin = kB(Th or Tc) Nout = Nh or Nc Rs r e w o Nh P t u Slope=kBGa p t u O •Physically•Physically hot/ hot/ cold cold source source Nc •avalanche•avalanche diode diode Na -Te TcSource Temp (K) Th Noise Figure Basics Page 18 ) o N ( No = kGB • Ts + Na r e Measured w o Nh P Slope=kGB Nh t Y = u p Nc t u O Nc Na Source Temp (Ts) -Te Tc Th Input (Th − To ) ENR = To Calculated ENR Na Na = kBGTo −1 Te = Y −1 kGB Na + kGBTo ENR Te + To F = = = Te = To(F −1) kGBTo Y −1 To Noise Figure Basics Page 19 Noise Source - the Avalanche Diode Matching Pad Bias Noise Input Output Excess Noise Ratio, ENR (dB) = 10 Log ( T - 290) 10 h Frequency ENR dB 290 XXX AAA YYY BBB ZZZ CCC . Noise Figure Basics Page 20 Noise Figure Analyzer Nout_cold Nh Nin_cold Source variable DUT impedance attenuator Nout_hot Nc Nin_hot Nh kGB(Te + Th) Th - Y Tc Y= ___ = ___________ Te = _______ (solve for Te) Nc kGB(Te + Tc) Y - 1 Te + To F = _______ To Noise Figure Basics Page 21 Calibrating out System NF Source variable DUT impedance attenuator F1, Ga1 F2 F12 F2-1 F1 = F 12 - Ga1 F2-1 if F 12 ≈≈≈ then uncertainty increases, so beware if F 1 and G 1 are low Ga1 Noise Figure Basics Page 22 How does the NFA measure gain Nh_meas r e w o P t u Nh_cal p t u O Nc_meas Slope=kBG ent Nc_cal urem 1 G meas 2 DUT Slope=kBG Calibration measurement 2 Noise Figure Basics cTh Tc Source Temp (K) Page 23 Avoidable Measurement Errors: EM Susceptance Lights (Esp. Fluorescent) Noise Source FM TV * Double-shielded Cables for IF Computers (Ordinary Braid if porous) * Shielded HP-IB Cables * Enclose All Circuits * Jiggle Connectors (Esp. BNC) * Try snap-on ferrite cores on cables, dampen common-mode currents * LO Contributes Spurious and Noise Noise Figure Basics Page 24 Avoidable Measurement Errors: Choose the Appropriate Noise Source •15dB•15dB ENRENR noisenoise sourcesource toto measuremeasure NFNF ofof upup toto 30dB30dB (( egeg N4001A,N4001A, N4002A,N4002A, 346B/C)346B/C) •Use•Use 66 dBdB ENRENR forfor veryvery lowlow noisenoise figurefigure devicesdevices toto keepkeep noisenoise detectordetector linearitylinearity issuesissues toto aa minimumminimum (( egeg N4000A,N4000A, 346A).346A). •Use•Use aa NoiseNoise SourceSource withwith greatergreater internalinternal attenuationattenuation ifif thethe DUTDUT isis matchmatch sensitivesensitive (eg(eg N4000A,N4000A, 346A).346A). Noise Figure Basics Page 25 Avoidable Measurement Errors: Accurate Loss Compensation Cable C1 Noise Coax/WG adapter Source G 1 DUT Cable C2 G 2 Measurement system Coax/WG adapter Noise Figure Basics Page 26 Avoidable Measurement Errors: Loss Compensation and Calibration Noise Figure Basics Page 27 Noise Source - the Avalanche Diode Matching Pad Bias Noise Input Output Excess Noise Ratio, ENR (dB) = 10 Log ( T - 290) 10 h Frequency ENR dB 290 XXX AAA YYY BBB ZZZ CCC . Noise Figure Basics Page 28 AvoidableAvoidable Measurement Measurement Errors: Errors: TemperatureTemperature Considerations Considerations (Diode) (Diode) r e To=296.5 K w Th=10,000 or 1,500 o Nh P t u p t u O Nc Na -Te ToTc Th Th’ Source Temp (K) Report Ambient Temperature to Analyzer for Accurate ENR Interpre tations Noise Figure Basics Page 29 Noise Figure Basics Page 30 Avoidable Measurement Errors: Loss and Temperature Corrections • A temperature must be entered in Loss Compensation Setup for valid results NFA & PSA Default = 0 degrees K • The NFA and PSA accept S2P files from a Network Analyzer for the Loss Compensation table Noise Figure Basics Page 31 Avoidable Measurement Errors: Account for Frequency Conversion (DSB Measurement) Mixer Noise fMeasure f IF Noise Source Meter f NP NP LO fLO External LO f IF f IF f IF Freq Freq DSB is recommended when : • The application is DSB • The DUT is broadband • No SSB filter is available • The frequency range make SSB filters impossible/impractical Loss compensation of 3dB (under perfect conditions) needs to be entered to account for doubling of power during measurement Noise Figure Basics Page 32 Avoidable Measurement Errors: Account for Frequency Conversion (SSB Measurement) Mixer Noise SSB fMeasure f IF Noise Source Filter Meter fLO NP NP External LO fLO f IF f IF f IF Freq Freq SSB is recommended when : • The application is SSB • The DUT is narrowband If down conversion is part of the measurement system, filters should be included in calibration path and measurement path because the calibration and measurement are performed at the same frequencies.
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