How to Measure TVS Diode Dynamic Resistance Using TDR

Overview of Technical Issues:

The measurement structure insufficiently resolves the TVS diode's fast transient breakdown behavior when the TDR's rise time approaches the diode's sub-nanosecond response time, while parasitic inductance and capacitance in the test fixture create harmful impedance contributions that mask the true dynamic resistance; the goal is to accurately characterize the diode's dynamic resistance during voltage clamping for reliable circuit protection design.

Solution directions generated for this problem

Problem Direction 1 :

ImproveSignal bandwidth
VS
ConstraintMeasurement noise level

Inspiration 1 : Cross-domain reference

Application Principle: #22 Blessing in disguise
Cross-domain applicability Assess applicability
Reducing reflection at termination of optical fiber in a small volume
Innovative Solution Refine solution

Noise-referenced differential calibration for wideband TVS characterization

Characterize system noise as calibration reference
How to solve :
  • Capture noise spectrum baseline from 350MHz to 5GHz without DUT using identical TDR pulse conditions, store as reference signature with 1MHz resolution bins
  • Perform TVS diode measurement at >5GHz bandwidth, then apply frequency-domain noise subtraction using coherent deconvolution: S_true(f) = S_measured(f) - α·N_reference(f), where α=0.85-0.95 accounts for correlated noise
  • Implement adaptive noise floor tracking every 50 acquisitions to compensate thermal drift, updating reference with exponential moving average (β=0.1) to maintain <3dB calibration accuracy over 2-hour sessions
Expected Effect : SNR improvement 8-12dB; <200ps resolution; noise contribution <3%
Risk Control :
  • temperature-dependent noise drift
  • non-stationary noise components
  • calibration interval optimization

Problem Direction 2 :

ImproveFixture parasitic impedance suppression
VS
ConstraintFixture manufacturing precision

Inspiration 1 : Cross-domain reference

Application Principle: #1 Segmentation
Cross-domain applicability Assess applicability
Display panel and display device
Innovative Solution Refine solution

Modular precision-zone test fixture with relaxed-tolerance support frame

Split fixture into precision and standard zones
How to solve :
  • Divide fixture into precision microwave landing zone (≤10mm² area, <50μm trace tolerance) directly interfacing TVS diode, and standard-tolerance support frame (±100μm tolerance) for mechanical mounting and connectors
  • Fabricate precision zone using laser direct imaging photolithography on Rogers 4350B substrate (εr=3.48±0.05) with 25μm copper, achieving 50Ω±2Ω impedance in critical 8mm signal path
  • Attach precision zone to support frame via spring-loaded pogo pins (gold-plated, 1.0mm pitch) ensuring <0.3nH contact inductance while allowing tool-free device access
Expected Effect : Parasitic inductance <0.8nH, fabrication cost reduced 60%, <5% measurement error
Risk Control :
  • precision-zone alignment to support frame ±25μm
  • pogo pin contact resistance variation 10-20mΩ
  • thermal expansion mismatch between zones

Problem Direction 3 :

ImproveMeasurement temporal resolution
VS
ConstraintMeasurement noise level

Inspiration 1 : Cross-domain reference

Application Principle: #22 Blessing in disguise
Cross-domain applicability Assess applicability
Reducing reflection at termination of optical fiber in a small volume
Innovative Solution Refine solution

Noise spectrum signature calibration for sub-nanosecond TVS characterization

Characterize noise as calibration reference
How to solve :
  • Capture baseline noise spectrum from 350MHz to 5GHz with TDR system using open-circuit fixture, store as frequency-domain reference signature with 50MHz resolution bins
  • During TVS diode measurement, acquire raw waveform at >5GHz bandwidth (<200ps rise time), perform FFT decomposition to separate signal bands (DC-3GHz) from systematic noise bands (3-5GHz)
  • Apply spectral subtraction algorithm: subtract stored noise signature from measurement spectrum with 0.85 weighting factor, inverse FFT to reconstruct time-domain waveform with 12dB noise reduction while preserving transient edges
Expected Effect : Temporal resolution <200ps; SNR improved 12dB; measurement error <5%
Risk Control :
  • noise spectrum drift over temperature
  • FFT window function selection affects edge fidelity
  • weighting factor requires per-system tuning

Problem Direction 4 :

ImproveFixture parasitic impedance suppression
VS
ConstraintFixture manufacturing precision

Inspiration 1 : Cross-domain reference

Application Principle: #1 Segmentation
Cross-domain applicability Assess applicability
Display panel and display device
Innovative Solution Refine solution

Modular dual-zone fixture with precision insert and relaxed frame

Divide fixture into precision insert and standard frame
How to solve :
  • Design a removable precision microwave insert (8×8mm) with <50μm trace tolerance and <10μm dielectric control for TVS diode landing zone, embedded in a standard-tolerance outer frame (±150μm) providing mechanical support and connectors—insert fabricated via laser direct imaging on Rogers 4350B, frame via conventional PCB process
  • Implement spring-loaded pogo pins at insert-frame interface to ensure <0.2Ω contact resistance and ±0.1mm vertical compliance, enabling tool-free device access from top while maintaining RF continuity to 6GHz
  • Fabricate 5 interchangeable inserts for different TVS package footprints (SOD-323, SOT-23, 0402), each calibrated with SOLT standards and stored S-parameter correction files—user swaps insert in <30 seconds without fixture disassembly, preserving <5% measurement accuracy across device types
Expected Effect : Parasitic inductance <0.3nH, capacitance <0.15pF; fixture cost reduced 65% vs full-precision design; device swap time <30s; measurement error <4.2%
Risk Control :
  • pogo pin contact degradation over 500 cycles
  • insert-frame impedance mismatch at interface
  • thermal expansion mismatch between Rogers laminate and FR-4 frame
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