Benefits Of Digital Receivers And Fiber Optics To Reduce Uncertainty

Transcript

Benefits of Digital Receivers and Fiber Optics to reduce uncertainty Focusing on Emission Testing CISPR 16-4-2 Standard clearly defines Uncertainty topics for Emission Tests, whose most relevant contributions come from: - EMI/EMC Receivers - Test Set-Up (layout, cables, adapters, site attenuation,…) - LISNs and AMNs in general (ISNs, CDNs, Voltage Probes,…) - Absorbing Clamps - Antennas - Coupling between above components Compliance Assessment by CISPR 16-4-2 The Expanded Measurement Instrumentation Uncertainty Ulab for a test laboratory shall be calculated using: A graphical example Receiver Uncertainty Contribution In Radiated & Conducted Emission measurements the receiver is the most complex equipment due to: Sophisticated measuring functions Large number of active & passive components Effect of aging on calibration Effect of environmental factors on calibration Complexity = more uncertainty? Not necessarily! But certainly… More complexity = more components More components = more adjustments/calibrations More components = lower MTBF The costs of Complexity Service Time Calibration Reliability Can these all be improved ? Price Task: move complexity to a different dimension OBJECTIVES: a) reducing uncertainty sources b) reducing calibration time & cost c) reducing service time & cost a) reducing uncertainty sources Design options: Using less components Using different technologies Using different measuring methods A look to the past: old PMM models ’80s technology ’90s technology PMM 9000 Block Diagram PMM 9010: The improvement Receiver functions have been moved from Hardware to Firmware (not Software!) Block Diagram 10 Hz-30 MHz ADC specifications must provide Full Compliance to CISPR-16-1-1 & MIL-STD-461F PMM 9010: maths on duty Real RF PK, QPK, AVG, RMS Detection Imag. ADC Numeric Oscillator CLOCK DSP RSP Analog to Digital Receivers Uncertainty Budget Comparison PMM 9010 Item (Receiver Specification) 10 Hz - 30 MHz CISPR Specified Uncertainty (dB) Digital Receiver Uncertainty (dB) Receiver Reading ± 0,1 ± 0,1 Receiver Correction: Sine wave voltage Pulse absolute calibration Pulse repetition rate @1Hz ± 1,0 ± 1,5 ±2 ± 0,15 ± 0,2 ± 0,2 Moving over 30 MHz Today’s ADC do not allow for full CISPR – MIL compliance at higher sampling rates (dynamic range, linearity etc.) Higher frequency bands are: 3, 6, 18… GHz Conventional (heterodyne) method must be used for But it can be implemented too… PMM 9030 & 9060: the innovation in 3 & 6 GHz bands DESIGN PRINCIPLES: Combining 9010’s ADC-based structure with heterodyne Minimizing the number of down-conversions Applying ADC to an IF signal as wide as possible Allowing direct installation on antenna Block Diagram 30 MHz – 3/6 GHz 36 MHz IF, BW = 3 MHz Analog to Digital Receivers Uncertainty Budget Comparison PMM 9030 Item (Receiver Specification) 30 MHz – 3 GHz CISPR Specified Uncertainty (dB) Digital Receiver Uncertainty (dB) Receiver Reading ± 0,1 ± 0,1 Receiver Correction: Sine wave voltage Pulse absolute calibration Pulse repetition rate @ 20 Hz Pulse repetition rate @ 1Hz ± 1,0 ± 1,5 ±1 ±2 ± 0,3 ± 0,5 ± 0,2 ± 1,3 Digital Architecture benefits No calibrations/adjustments required after ADC CISPR/MIL RBW filters as well as Detectors (QP, Pk, Avg, RMS, C-Avg, RMS Avg) are all mathematical operations not affected by variations during time Intrinsically reliable Example of CISPR RBW filter shaping 9030/9060 direct antenna matching via Fiber Optic An innovative way to reduce uncertainty: bringing the receiver to the antenna! Digital signal from ADC A simple test: coax cable vs. f/o 1) Simulation of an antenna connected to the receiver by coaxial cable Chamber 3 GHz EMI Receiver PMM 9010 + 9030 full CISPR 16-1-1 compliance 3 GHz RF Generator PMM 3030 10 + 10 m Coax cable RG213U N – N transition Fiber Optic Digital Link A simple test: coax cable vs. f/o 2) Simulation of: direct connection antenna – receiver remote unit receiver main unit connected by fiber optic Chamber 3 GHz RF Generator 3 GHz EMI Receiver PMM 9010 + 9030 full CISPR 16-1-1 compliance PMM 3030 Fiber Optic Digital Link A simple test: coax cable vs. f/o 1) Simulation of an antenna connected to the receiver by coaxial cable Gen Pulsed 1 Hz -> Cable -> RX 60 55 dBuV 50 PK QP 45 C-AVG 40 35 30 30 200 600 1000 1400 1800 2200 2600 3000 A simple test: coax cable vs. f/o Loss of dynamic range 20 15 dB PK QP 10 C-AVG 5 0 30 200 600 1000 1400 1800 2200 2600 3000 Additional loss: antenna factors A simple test: coax cable vs. f/o 2) Simulation of: direct connection antenna – receiver remote unit receiver main unit connected by fiber optic Gen Pulsed -> RX 65 60 dBuV 55 PK 50 QP C-AVG 45 40 35 30 200 600 1000 1400 1800 2200 2600 3000 Conclusion Coax cable reduces sensitivity. Lower sensitivity could lead to incorrect weighting Thus, usually a preamplifier close to antenna is used BUT Account for mismatch uncertainty twice First: Antenna/Preamp Second: Preamp/Receiver EN 55014-1 Testing: Another Opportunity Traditional RF Cable EN 55014-1 Testing • Short RF Cable PMM 9030 Receiver from Clamp to Receiver • Fiber Optic Cable from PMM 9030 to Main Unit 9010 EN 55014-1 Testing • Measurements of disturbance power using an absorbing clamp are sensitive to the surrounding environment, including the nature and proximity of room surfaces. • CISPR 16-1-3 specifies a validation method that allows deviations of up to +/- 2,5 dB from the reference test site. ANALOGUE TO DIGITAL UNCERTAINTY COMPARISON Input Quantity Receiver reading Aging Attenuation: Antenna-receiver Cables Connections Receiver correction: Sine wave voltage Pulse amplitude response Pulse repetition rate response Mismatch: antenna-receiver antenna-cable cable-cable Cable-Antenna (or other transducer, e.g. E.M. clamp) balance Cables coupling to ground Analogue uncertainty contribution (typical) in dB ±0,1 TBD, but present ±0,1 TBD, but present TBD, but present ±1,0 ±1,5 ±1,5 +0,9/-1,0 TBD, but present TBD, but present ±0,9 TBD, but present PMM 9010 uncertainty contribution Equal or better Absent Equal Absent Absent Better Better Better Equal Absent Absent Better (w/ 9030-9060) Absent with 9030 or 9060 Splitted Architecture benefits No expensive coaxial cables No cable loss No cable/antenna coupling No cable scattering No connectors loss Antenna decoupling not needed Higher flexibility of Optical cable Longer connection distance (100 m) Thank you !