Traceability and Modulated-Signal Measurements

Transcription

1 Traceability and Modulated-Signal Measurements Kate A. Remley 1, Dylan F. Williams 1, Paul D. Hale 2 and Dominique Schreurs 3 1. NIST Electromagnetics Division 2. NIST Optoelectronics Division 3. K.U. Leuven Contact: remley@boulder.nist.gov

2 Agenda Traceable Measurements of Modulated Signals Measuring Modulated Signals Instrumentation for Traceable Measurements NPL peak power meter calibration NIST oscilloscope Calibration Signals for Modulated-Signal Measurements Conclusion

3 Fundamental Measurement Traceability Calibrations tending toward fundamental traceability to SI units or calculable physical phenomena Vector Network Analyzers: Dimension of an air-dielectric transmission line Power Meters, Noise Sources: Temperature AC Voltage: Josephson junction arrays Electro-optic Sampling Systems: Calculable electro-optic effect in materials LiTaO 3 E + -

4 Derived Measurement Traceability Calibrations that use a series of transfer standards: Oscilloscope Calibrations Digital sampling oscilloscope Transfer standard: Photodiode Source Calibrations Vector signal generator, pulsed source, comb generator Transfer standard: Oscilloscope Receiver Calibrations LSNA, peak-power meters, VSA, antennas Transfer standard: Calibrated source

5 Derived Measurement Traceability Commonly used for modulated signal traceability Issues: + Can provide traceability to many types of instruments Same methods can be applied across instruments: Almost a black-box approach - Higher uncertainties Sometimes difficult to combine uncertainties Instrument-specific issues: timebase distortion (oscilloscope) IF calibration (LSNA)

6 Measuring Modulated Signals Modulated signal: A signal containing multiple frequency components frequency Key for traceable uncertainty analysis: Instruments with traceability to fundamental physical units National Metrology Institutes certify traceability Uncertainty statement provides limits on expected range of measured values

7 Measuring Modulated Signals Scalar: Accurate power in all measured frequency components 0 LSNA: No Phase Correction Scope: With Correction Magnitude (dbm) Frequency (GHz) Measurement of square wave: Frequency-domain representation

8 Measuring Modulated Signals Vector: Accurate relative phase of all measured components Amplitude (volt) LSNA: No Phase Correction -0.6 LSNA: Phase Correction Scope: With Correction Time (ns) Enables time-domain representation Figure from [1]

9 Relative Phase For vector measurements, relative phase relationships must be maintained 2.0 At t = t M : 1.5 θ 1 = 115 o θ 2 = 345 o t P t P 1.0 θ 3 = 280 o Amplitude t ref t M ms Time Measured phases may appear random unless time aligned [2]

10 Instruments for Traceable Scalar Modulated-Signal Measurements Peak Power Meter RF source under test RF Detector Dynamic bias and digitization Display and interface Block diagram of peak power meter, after [3] + Relatively inexpensive and straightforward to use _ Traceability derived from complex scope cal Diode detector: linearity issues

11 Calibration of Instruments for Scalar Modulated-Signal Measurements Peak power meter [3] Step 1: Characterize the reference source Step 2: Use reference source as transfer standard to calibrate peak-power meter Reference source (modulated signal) Reference source (modulated signal) calibrated oscilloscope peak-power meter Goal is to separate response of signal generator from response of peak-power sensor + power meter

12 Calibration of Peak-Power Meter Thermoelectric power sensor provides traceability for oscilloscope measurements. Reference source (single frequency) Reference source (single frequency) calibrated thermoelectric power sensor calibrated oscilloscope Important Corrections: Power sensor response Reference source level Impedance mismatch Oscilloscope Impulse response (magnitude only) Impedance mismatch Time-base distortion Jitter Output is impulse response of peak-power sensor + meter.

13 Instruments for Traceable Vector Modulated-Signal Measurements Digital Sampling Oscilloscope: Good for periodic Trigger and trigger delay waveform measurements External Source + Broadband acquisition: relative phase maintained DUT _ Broadband acquisition: low dynamic range Calibration complicated Single (or two) channel

14 Calibration of Instruments for Vector Modulated-Signal Measurements From [4]: Step 1: Characterize a reference source in magnitude and phase Step 2: Use reference source as transfer standard to calibrate digital sampling oscilloscope Reference source (photodiode) Reference source (photodiode) electro-optic sampling system sampling oscilloscope Complete vector response of sampling oscilloscope must be determined.

15 NIST Electro-Optic Sampling System Physics-based measurement Intrinsic speed ~10 fs 200 GHz measurements (currently) Virtually jitter free Uncertainty discussed in [5] Pulsed Laser Variable optical delay LiTaO 3 + E - Photoreceiver Wafer Probe Voltage waveform measured here LiTaO 3 wafer Optical Polarization-state Analyzer

16 Mismatch Correction in the NIST Electro-Optic Sampling System Pulsed Laser Variable optical delay Photoreceiver Wafer Probe LiTaO 3 wafer -Y 12 Optical Polarization-state Analyzer I N Y s Source (photoreceiver) Y 11 +Y 12 Y 22 +Y 12 Transition (probe head) V Y L Load (CPW resistor) From [6].

17 Traceability Path for Calibrated Scope Measurements Electro-optic sampling Calibrated photodiode Calibrated scope Adapter DUT Important corrections Impulse response Impedance mismatch Time-base distortion Jitter + VNA calibrations

18 In-Phase/Quadrature Reference Error in oscilloscope time Signals Create New Time Base From [7]. Oscilloscope time reference 90 hybrid 0 90 CH1 CH2 scope SIGNAL SOURCE modulator modulated signal CH3 Trigger

19 New Time Base Reduces Distortion 100 Amplitude (mv) Time (ns) Amplitude (mv) Time (ns) db dynamic range under good conditions with GHz of bandwidth amplitude (dbm) amplitude (dbm) frequency (GHz) frequency (GHz)

20 NIST Traceability for Modulated Signals Current capability: FD to 110 GHz TD to 15 ps EOS calibration VNA calibrations Scope calibration Source calibrations 60 db dynamic range Receiver calibrations Antenna calibrations Fundamental calibrations Derived calibrations

21 Example: Wideband Phase Response Traceable, error-corrected, measurement of multisine phase error over 1 GHz modulation bandwidth. EOS calibration Scope calibration Modulated-source calibration Measured Spectrum Phase and Phase Error

22 Pulse- and Phase-Standard Calibrations Calibrated step, impulse, and comb generators. Z s V s 50 Ω b Γ Full generator models

23 Other Instruments for Traceable, Vector, Modulated-Signal Measurements VNA-based instruments for higher dynamic range [8] On-board comb generator Vector network analyzer LO Demonstrated 85 db dynamic range with wide-bandwidth Power meter (magnitude cal) Comb-generator (phase cal) Impedance stds (mismatch) Signal generator (DUT) October 2006 A-to-I program review

24 Calibration Signals Well-established known pulse scope calibration [9]: Differences between known and measured = calibration coefficients known pulse source digital sampling oscilloscope Many NMIs have pulse calibration services Pulses have energy over broad bandwidth: For wireless, we may want a signal whose bandwidth better matches instrumentation

25 Calibration Signals Known Spectrum Multisine Calibration multisine signal generator frequency vector signal analyzer time 0 dbm 0 magnitude phase Used by manufacturers to calibrate vector receivers, also see [10]

26 Multisine Calibration Example A multisine is used for the IF Cal of the LSNA: RF (multisine) 4 MHz Downconverter (sampler) IF (multisine) 4 MHz ~0.2 dbm 2 GHz MHz LO sweep (single tone) Known spectrum : 2000-component Schroeder multisine, VSG-generated, VSA-measured (VSA previously calibrated) Measure same multisine on LSNA Differences between VSA-measured and LSNA-measured are correction coefficients

27 Multisine Calibration Example Known Spectrum : 2000-component Schroeder multisine measured on a VSA Center frequency is 2 GHz, 4 MHz modulation bandwidth Repeatability is ~0.11dB, LSNA resolution is ~0.2 db

28 Multisine Calibration Example Typical IF Cal Results: RF IF RF IF Magnitude Phase ~0.2 db magnitude variation, ~110 phase variation over 4 MHz Negligible variation with LO sweep Measured by Don DeGroot and Jan Verspecht at NIST It is obvious that the downconverter does need calibration!

29 Summary: Traceable Modulated Signal Measurements Similarities to uncertainties for single frequencies: Repeatability, reproducability found in same way as for CW signals Differences unique to modulated signals: Multistage derived traceability path Difficulty separating source response from receiver response (absolute calibrations often required) Baseband effects can occur when nonlinear detectors and receivers are used Future trends Vector calibrations, traceability Calibration signals whose statistics match excitation Methods for frequency-, modulation-agile systems

30 References [1] K.A. Remley, P.D. Hale, and D.F. Williams, Absolute magnitude and phase calibrations, from RF and Microwave Handbook, 2 nd ed., Mike Golio, editor, to be published in Oct [2] K.A. Remley, D.F. Williams, D. Schreurs, G. Loglio, and A. Cidronali, "Phase detrending for measured multisine signals," 61st ARFTG Conf. Dig., June 2003, pp [3] D.A. Humphreys and J. Miall, Traceable RF peak power measurements for mobile communications, IEEE Trans. Inst. and Meas., vol. 54, no. 2, Apr. 2005, pp [4] T.S. Clement, P.D. Hale, D.F. Williams, D.M. Wang, A. Dienstfrey, D.A. Keenan, Calibration of sampling oscilloscopes with high-speed photodiodes, IEEE Trans. Microw. Theory Tech., vol. 54, no. 8, Aug. 2006, pp [5] D. F. Williams, A. Lewandowski, T. S. Clement, C. M. Wang, P. D. Hale, J. M. Morgan, D. Keenan, and A. Dienstfrey, Covariance-Based Uncertainty Analysis of the NIST Electro-optic Sampling System, IEEE Trans. Microw. Theory Tech., vol. 54, no. 1, pp , Jan [6] D.F. Williams, P.D. Hale, T.S. Clement, C.M. Wang, "Uncertainty of the NIST electrooptic sampling system," NIST Tech. Note 1535, Dec

31 References [7] P. D. Hale, C. M. Wang, D. F. Williams, K. A. Remley, and J. Wepman, Compensation of random and systematic timing errors in sampling oscilloscopes, IEEE Trans. Instrum. Meas., vol. 55, no. 6, pp , Dec [8] P. Blockley, D. Gunyan, J.B. Scott, Mixer-based, vector-corrected, vector signal/network analyzer offering 300kHz-20GHz bandwidth and traceable phase response, IEEE MTT-S Int. Microwave Symp. Dig., pp , June [9] W. L. Gans, Dynamic calibration of waveform recorders and oscilloscopes using pulse standards, IEEE Trans. Instrum. and Measurement, vol. 39, pp , Dec [10] W. Van Moer and Y. Rolain, A multisine calibration procedure for broadband measurements, IEEE Inst. and Meas. Tech. Conf. Dig., pp. 1-6, May 2007.