The Measurement of (1/f) AM noise of Oscillators Enrico Rubiola - PowerPoint PPT Presentation

The Measurement of (1/f) AM noise of Oscillators Enrico Rubiola FEMTO-ST Institute, Besançon, France (CNRS and Université de Franche Comté) Outline Introduction Power detectors Experimental method Results Perspectives and conclusions http://rubiola.org

introduction 1 2 Motivations for AM noise metrology • Emerging need, after the progress of • oscillators and sources • phase noise metrology (bridge/interferometric) method • Impacts on • frequency synthesis ⇄ AM/PM conversion • oscillators ⇄ power effects on the resonator • microwave photonic systems ⇄ laser RIN • ........ • Measurement the AM noise of a source relies on instruments

introduction 2 3 AM noise v ( t ) = V 0 [1 + α ( t )] cos [ ω 0 t + ϕ ( t )] polar coordinates v ( t ) = V 0 cos ω 0 t + n c ( t ) cos ω 0 t − n s ( t ) sin ω 0 t Cartesian coordinates α ( t ) = n c ( t ) ϕ ( t ) = n s ( t ) and In low noise conditions V 0 V 0 α ( t ) = 1 δ P Relates to power fluctuations 2 P 0 α ( t ) ⇔ y ( t ) Same formulae as for frequency noise 0 h –2 / f 2 random walk � h i f i Power-law S α ( f ) = h –1 / f flicker h 0 white i = − 2 2 τ + 2 ln(2) h − 1 + 4 π 2 α ( τ ) = h 0 σ 2 Allan variance h − 2 τ 6 white flicker random walk

detectors 1 4 The diode power detector same form as in optical law: v = k d P quantum detectors di ff erential resistance R d = V T V T = kT/q ≃ 25 mV thermal voltage I 0 rf in video out rf in video out external external ~60 50 Ω to ~60 50 Ω to 10−200 10−200 Ω 100 k Ω Ω 100 k Ω pF pF 1000 two-diode detector 500 200 output voltage, mV 100 100 k Ω linear region 50 (envelope detector) 100 Ω 20 10 1 k Ω 5 linear region 2 (power detector) 1 − 30 − 20 − 10 0 10 input power, dBm

detectors 2 5 Tunnel and Schottky power detectors parameter Schottky tunnel The “tunnel” diode is actually a backward input bandwidth up to 4 decades 1–3 octaves diode. The negative 10 MHz to 20 GHz up to 40 GHz resistance region is vsvr max. 1.5:1 3.5:1 absent. max. input power (spec.) − 15 dBm − 15 dBm absolute max. input power 20 dBm or more 20 dBm output resistance 1–10 k Ω 50–200 Ω output capacitance 20–200 pF 10–50 pF gain 300 V/W 1000 V/W cryogenic temperature no yes electrically fragile no yes 0 Herotek DZR124AA s.no. 227489 Herotek DT8012 s.no. 232028 Measured -20 Schottky Tunnel detector gain, A − 1 -20 -40 output voltage, dBV output voltage, dBV load resistance, Ω DZR124AA DT8012 10 k Ω -40 (Schottky) (tunnel) 3.2 k Ω 10 k Ω -60 1 × 10 2 35 292 1 k Ω -60 3.2 k Ω 3 . 2 × 10 2 98 505 320 Ω 1 × 10 3 217 652 -80 100 Ω -80 1 k Ω 3 . 2 × 10 3 374 724 320 Ω 1 × 10 4 494 750 -100 -100 100 Ω conditions: power − 50 to − 20 dBm ampli dc offset ampli dc offset -120 -60 -50 -40 -30 -20 -10 0 10 -60 -50 -40 -30 -20 -10 0 10 input power, dBm input power, dBm

detectors 3 6 Noise mechanisms Rothe-Dahlke model of the amplifier Shot noise S I ( f ) = 2 qI 0 detector noise−free amplifier rf in video out v n in out external i n ~60 50 Ω to 10−200 Ω 100 k Ω pF Flicker (1/ f ) noise is also present Thermal noise Never say that it ’ s not fundamental , S V ( f ) = 4 k B T 0 R unless you know how to remove it In practice the amplifier white noise turns out to be higher than the detector noise and the amplifier flicker noise is even higher

method 1 7 Cross-spectrum method v a ( t ) = 2 k a P a α ( t ) + noise P a v a v b ( t ) = 2 k a P b α ( t ) + noise FFT analyzer dual channel The cross spectrum S ba ( f ) rejects P b v b the single-channel noise because source under test the two channels are independent. monitor 1 S ba ( f ) = S α ( f ) power meter 4 k a k b P a P b S α (f) log/log scale • Averaging on m spectra, the single- channel noise is rejected by √ 1/2m single channel • A cross-spectrum higher than the 1 averaging limit validates the measure 2m cross spectrum • The knowledge of the single-channel meas. limit noise is not necessary f

method 2 8 Calibration • Set a reference ∆ P/P a (0.1 dB) P a v a with a by-step attenuator voltm. • Measure ∆ v a at the output atten v b ∆ v a P b k a P a = source 0.1 dB ∆ P/P a under test step • Repeat interchanging the power channels meter Note that only the kP product is needed because 1 S ba ( f ) = S α ( f ) 4 k a k b P a P b P a v a Alternate (and complex) calibration method. voltm. – It exploits the sensitivity and the accuracy ν 0 atten v b P b of a lock-in amplifier. source – As before, it requires a reference under test power-ratio power meter ν b = | ν 0 ν s − | ν s ref in input out atten lock − in Re amplifier reference Im

results 1 9 Example of AM noise spectrum Wenzel 501−04623E 100 MHz OCXO = −10.2 dBm P 0 −123.1 avg 2100 spectra −133.1 dB/Hz −143.1 ( f ) S α −153.1 Fourier frequency, Hz −163.1 10 2 10 3 10 4 10 5 10 h − 1 = 1 . 5 × 10 − 13 Hz − 1 ( − 128 . 2 dB) σ α = 4 . 6 × 10 − 7 flicker: ⇒ Single-arm 1/f noise is that of the dc amplifier (the amplifier is still not optimized)

results 2 10 AM noise of some sources source h − 1 (flicker) ( σ α ) floor 2 . 5 × 10 − 11 5 . 9 × 10 − 6 Anritsu MG3690A synthesizer (10 GHz) − 106 . 0 dB 1.1 × 10 − 12 1 . 2 × 10 − 6 Marconi synthesizer (5 GHz) − 119 . 6 dB 1.0 × 10 − 12 1 . 2 × 10 − 6 Macom PLX 32-18 0 . 1 → 9 . 9 GHz multipl. − 120 . 0 dB 8 . 1 × 10 − 11 1 . 1 × 10 − 5 Omega DRV9R192-105F 9.2 GHz DRO − 100 . 9 dB 2 . 9 × 10 − 11 6 . 3 × 10 − 6 Narda DBP-0812N733 amplifier (9.9 GHz) − 105 . 4 dB 6 . 8 × 10 − 13 9 . 7 × 10 − 7 HP 8662A no. 1 synthesizer (100 MHz) − 121 . 7 dB 1 . 3 × 10 − 12 1 . 4 × 10 − 6 HP 8662A no. 2 synthesizer (100 MHz) − 118 . 8 dB 1 . 5 × 10 − 12 1 . 5 × 10 − 6 Fluke 6160B synthesizer − 118 . 3 dB 8 . 4 × 10 − 12 3 . 4 × 10 − 6 Racal Dana 9087B synthesizer (100 MHz) − 110 . 8 dB 4 . 7 × 10 − 12 2 . 6 × 10 − 6 Wenzel 500-02789D 100 MHz OCXO − 113 . 3 dB 2.0 × 10 − 13 5 . 2 × 10 − 7 Wenzel 501-04623E no. 1 100 MHz OCXO − 127 . 1 dB 1 . 5 × 10 − 13 4 . 6 × 10 − 7 Wenzel 501-04623E no. 2 100 MHz OCXO − 128 . 2 dB worst best

persp. & concl. 1 11 Measurement of the detector noise adj. gain A v a In progress P a diff. ampli g(P c − P a ) R a low noise source C v c P c dual channel dual channel JFET input FFT analyzer FFT analyzer R c AM input monitor B power v b P b g(P c − P b ) meter diff. ampli R b adj. gain In all previous experiments, the amplifier noise was higher than osc. out osc. out input input the detector noise out out lock − in lock − in adjust the gain for the Re Re amplifier amplifier Re output to be zero Im Im Basic ideas • Remove the noise of the source by balancing C–A and C–B • Use a lock-in amplifier to get a sharp null measurement • Channels A and B are independent –> noise is averaged out • Two separate JFET amplifiers are needed in the C channel • JFETs have virtually no bias-current noise • Only the noise of the detector C remains

persp. & concl. 1 12 Conclusions Method for the measurement of AM noise in oscillators High sensitivity and accurate calibration Suitable to optics and to microwave photonics Measurement of some RF/microwave sources Single-channel sensitivity still limited by the dc amplifier Measurement of the detector noise in progress http://rubiola.org Free downloads (text and slides) http://arxiv.org/abs/physics/0512082 (text only)