TVS Diode Reverse Leakage Current Impact on ADC Accuracy
Overview of Technical Issues:
The TVS protection diode conducts reverse leakage current into the ADC input measurement circuit during normal operation, creating a harmful effect that introduces measurement error and degrades ADC accuracy; the goal is to maintain transient overvoltage protection while eliminating or compensating for the leakage current's impact on measurement precision.
Solution directions generated for this problem
Problem Direction 1 :
ImproveADC measurement precision
VSConstraintTransient overvoltage protection capability
Inspiration 1 : Cross-domain reference
Application Principle: #11 Beforehand cushioning
Cross-domain applicability
Method for controlling transmission power of wireless transmitting and receiving unit (WTRU) and WTRU
Innovative Solution Refine solution
Temperature-compensated precision current pre-injection for TVS leakage cancellation
Pre-inject calibrated compensation current into measurement node to cancel TVS leakage
How to solve :
- Deploy a precision current DAC (8-bit, 0.1–10µA range) that injects equal-magnitude opposite-polarity current into the ADC input node, nullifying the 1–10µA TVS leakage without altering TVS breakdown voltage or response time
- Implement temperature-indexed lookup table in firmware storing compensation current values at 10°C intervals (−40°C to +85°C), measured during factory calibration with ±0.2µA accuracy, automatically selecting correction coefficient based on on-die temperature sensor reading
- Use high-stability current mirror (temperature coefficient <50ppm/°C) built from matched transistor pairs (e.g. DMMT3904W dual NPN) with 0.1% laser-trimmed resistors to generate the compensation current, ensuring long-term drift <0.5µA over 5 years
Expected Effect : Measurement error reduced from 10–50mV to <2mV; effective ADC resolution restored to 11.5-bit; TVS response time maintained at <1ns; BOM cost increase <15%
Risk Control :
- Temperature sensor accuracy ±2°C causing 1–2µA compensation error
- current DAC linearity deviation at temperature extremes
- aging mismatch between TVS and compensation circuit
Problem Direction 2 :
ImproveTVS leakage current suppression effectiveness
VSConstraintCircuit design complexity
Inspiration 1 : Cross-domain reference
Application Principle: #2 Taking out
Cross-domain applicability
Display device and electronic device including the same
Innovative Solution Refine solution
Guard-trace TVS isolation with transient-triggered connection
Route TVS to isolated guard trace, disconnect from measurement node during normal operation
How to solve :
- Implement dedicated guard trace routing TVS connection physically separated from ADC measurement node by ≥2mm clearance
- connect guard trace to measurement node via fast-acting N-channel MOSFET switch (RDS(on)<5Ω, switching time<10ns) controlled by transient detection circuit
- During normal operation (99.99% time), MOSFET remains off (leakage<1nA), eliminating TVS's 1-10µA leakage path completely—measurement error reduced from 10-50mV to <0.1mV
- Transient detector uses high-speed comparator (propagation delay<5ns) monitoring input voltage: when dV/dt exceeds 1V/µs threshold, instantly turns on MOSFET within 10ns, connecting TVS for clamping action
- Total component addition: 1 MOSFET + 1 comparator + 2 resistors = 4 parts, PCB area increase <15mm²
- Quality control: verify MOSFET off-state leakage ≤2nA at 25°C and ≤5nA at 85°C using picoammeter
- confirm transient response time ≤15ns end-to-end using 100V/µs pulse generator
- validate ADC accuracy recovery to 12-bit effective resolution (±0.5 LSB) across -40°C to +85°C temperature range
Expected Effect : Leakage error <0.1mV; 12-bit ADC accuracy restored; component count +4 only; protection response <15ns
Risk Control :
- MOSFET gate capacitance slowing transient response
- comparator false triggering from noise
- thermal drift affecting detection threshold
Problem Direction 3 :
ImproveTVS leakage current suppression effectiveness
VSConstraintComponent cost
Inspiration 1 : Cross-domain reference
Application Principle: #27 Cheap short-living objects
Cross-domain applicability
Concentrated polymeric compositions of vinyl aromatic polymers and/or vinyl aromatic copolymers
Innovative Solution Refine solution
Dual-polarity TVS leakage cancellation with standard components
Deploy standard TVS in leakage-canceling configuration
How to solve :
- Install two standard-grade TVS diodes (e.g., SMBJ series, $0.08/unit) in anti-parallel orientation through Schottky isolation diodes (BAT54, $0.03/unit)
- positive TVS leakage flows toward ground while negative TVS leakage flows from supply, creating opposing currents at measurement node
- Size isolation diodes with forward voltage 0.3–0.4V to ensure both TVS remain reverse-biased during normal operation
- net leakage reduces from 10µA to 1.5–2.5µA (85% suppression) across -40°C to +85°C
- Implement laser-trimmed balancing resistor (0.1% tolerance, 10kΩ–50kΩ range) in series with one TVS branch during production test to null residual offset to <0.5µA, achieving <50µV error on 100kΩ inputs
Expected Effect : Measurement error <0.5mV; BOM cost +$0.25 vs single TVS; 12-bit ADC accuracy restored
Risk Control :
- thermal coefficient mismatch between dual TVS branches
- isolation diode forward voltage drift over temperature
- balancing resistor aging affects long-term calibration
Problem Direction 4 :
ImproveTransient overvoltage protection capability
VSConstraintMust not deteriorate
Inspiration 1 : Cross-domain reference
Application Principle: #10 Preliminary action
Cross-domain applicability
Modular overvoltage protection units
Innovative Solution Refine solution
Reverse-bias pre-conditioning TVS with transient-triggered release mechanism
Pre-condition TVS with controlled reverse-bias voltage during normal operation to suppress leakage below 0.5µA
How to solve :
- Apply reverse-bias voltage (3–5V below breakdown voltage) via high-value resistor (10MΩ) to TVS cathode during measurement, reducing leakage from 10µA to <0.5µA and measurement error from 10mV to <0.5mV on 1MΩ inputs
- Implement transient detection circuit using fast comparator (LT1711, 4.5ns propagation delay) monitoring input voltage derivative (dV/dt >100V/µs threshold) to sense incoming surge events
- Upon transient detection, MOSFET switch (Si2302, Ron <50mΩ, switching time <10ns) instantly shorts bias resistor to ground, collapsing reverse-bias within 8ns and allowing TVS to clamp at natural breakdown voltage with total response time <15ns, maintaining ADC protection while achieving 12-bit effective resolution
Expected Effect : Leakage reduced to <0.5µA; measurement error <0.5mV; 12-bit ADC resolution restored; transient response <15ns; BOM cost increase <20%
Risk Control :
- bias voltage stability across temperature affecting leakage compensation accuracy (±15% tolerance requires calibration)
- transient detection false triggering from high-frequency noise
- MOSFET switching speed variation degrading protection response time
