Optimization strategy for junction capacitance of TVS diodes in high-frequency circuits and ESD protection balance scheme

Core contradiction: The triple impact of junction capacitance on high-speed systems

1.1 Quantitative model of signal attenuation

The physical relationship between insertion loss and junction capacitance：

Among them：

• f：Signal frequency (GHz）
• Cj：Junction capacitance (pF)
• Z0：Transmission line impedance (Ω)

Measured influence：
In a 56Gbps PAM4 system：

• When Cj>0.3pF, the height attenuation of the eye diagram is greater than 40%
• For every 0.1pF increase in capacitance, the signal-to-noise ratio deteriorates by 3dB

1.2 Time-domain distortion mechanism

• Signal rise time degradation formula： ▲Tr = 2.2CjZ0
• In the 28GHz frequency band：
• Cj=0.5pF ⇒ Group delay fluctuation＞5ps
• Cj=0.1pF ⇒ Group delay fluctuation＜1ps

Five core technical paths

2.1 Wafer-level structural innovation

Process comparison：

• Deep groove isolation: Groove depth 30μm/ width 1μm, breakdown voltage increased by 200%
• Schottky structure: The thickness of the gold-half contact interface is less than 10nm, and the response time is 0.1ns

2.2 Advanced packaging technology

Performance evolution

Scenario-based design specifications

3.1 Frequency band adaptation matrix

3.2PCB Collaborative design

The Golden Rule：

1. Layout：
• TVS distance protection point ≤λ/20 (λ: minimum wavelength)
• The spacing of grounding holes should be less than 0.25 times the thickness of the plate
2. Impedance control：
• Use a coplanar waveguide (CPW) structure
• Impedance tolerance control ±3%
3. Thermal management：
• Each watt of surge power requires 8mm² copper foil
• Avoid the solder mask covering the heat dissipation path

Verification methodology

Core standard

Engineering decision tree

Innovative conclusion

Three major breakthroughs need to be achieved for the optimization of high-frequency TVS junction capacitors:

1. Material breakthrough: Asymmetric doping was adopted to reduce the depletion region capacitance by 40%
2. Structural revolution: Distributed microdiode arrays to disperse capacitive loads

Verification: The optimized scheme achieves insertion loss < 0.8dB, ESD protection ±30kV (IEC 61000-4-2 Level 4) in the 28GHz frequency band, and the bit error rate meets the requirements of the 3GPP URLLC standard.