Cold Spare SerDes Circuit ESD Protection
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Solution Overview
Problem
Unpowered Serializer/Deserializer (SerDes) systems in space communication applications are vulnerable to large current inputs, leading to device failure due to electrostatic discharge (ESD) when connected to powered systems, as the common mode voltage can exceed the ESD diode threshold, causing significant current flow through ESD diodes.
Innovation Solution
A cold spare SerDes system is implemented, utilizing a receiver input termination circuit with a termination resistor and an N-type MOSFET connected to ground, and a cold spare circuit with two MOSFETs that discharge built-up common mode voltage to less than 200 mV or 0 V, preventing excessive current flow through ESD diodes during power-off states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the unpowered SerDes is connected to a powered SerDes, then data transmission can be enabled, but large current flows through the ESD diodes causing device failure
Solution Approach 1:
The patent applies preliminary action by discharging the common mode voltage at the input of the unpowered SerDes receiver before connecting it to the powered transmitter. The discharge circuit actively removes accumulated charge from the input capacitance, ensuring the voltage remains below the ESD diode threshold. This preventive measure is taken in advance (before normal operation) to avoid the harmful effect of large current flow when the cold spare is activated.
Solution Approach 2:
The discharge circuit acts as an intermediary between the unpowered SerDes input and the external signal source. It mediates the voltage level at the input by providing a controlled discharge path through resistors and switches, preventing the direct connection of a high-impedance floating input to a powered transmitter that would otherwise cause excessive current through the ESD protection diodes.
2Reliability
If the common mode voltage is allowed to build up, then the unpowered SerDes can maintain standby state, but voltage exceeds ESD diode threshold causing enormous current
Solution Approach 1:
The system performs preliminary discharge of the common mode voltage periodically or upon detection of impending threshold violation, preventing the voltage from reaching levels that would trigger enormous current through the ESD diodes. This proactive energy management maintains reliability while avoiding excessive current consumption.
Solution Approach 2:
The discharge circuit operates with feedback control, monitoring the common mode voltage level and activating the discharge path only when necessary to maintain voltage below the ESD diode threshold. This feedback mechanism ensures reliability by preventing over-voltage conditions while minimizing energy consumption by keeping the discharge circuit inactive during normal standby conditions.
3Object-affected harmful factors
If ESD diodes are installed for protection, then device can withstand static discharge, but large current still flows through diodes over time leading to failure
Solution Approach 1:
The patent applies preliminary anti-action by implementing a discharge circuit that actively counteracts the buildup of common mode voltage before it can cause harmful current flow through the ESD diodes. Instead of relying solely on the ESD diodes to clamp voltage spikes, the discharge circuit preemptively removes accumulated charge, preventing the condition that would lead to diode failure over time.
Solution Approach 2:
The discharge circuit serves as an intermediary protection layer between the input signal and the ESD diodes. It provides an alternative low-impedance path for charge discharge, reducing the burden on the ESD diodes and preventing them from conducting excessive current that would lead to thermal runaway and failure over time.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively prevents device failure by maintaining the voltage below the ESD diode threshold, ensuring the system remains tolerant to significant current inputs and avoiding damage during standby conditions without affecting normal operation.
Implementation Method 1
a circuit discharges any built up common mode voltage of the inputs at the unpowered SerDes receiver of a Metal Oxide semiconductor Field Effect Transistor (MOSFET) normally to less than 200 mV for 45 nm technology, or even to 0 V
Data Source
AI summary
A system for limiting or diminishing current to unpowered Serializer/Deserializer (SerDes) circuitry is provided. The system comprises receiver input termination circuitry and a cold spare circuitry. The receiver input circuitry comprises a termination resistor and an N-type metal oxide silicon field effect transistor (MOSFET). The cold spare circuitry comprises a first MOSFET and a second MOSFET. When the system is powered on, an input current flows to the receiver input termination circuit to be discharged by the N-type MOSFET which is electrically connected to a ground. When the system is powered off, the input current flows to the cold spare circuitry to discharge the input current. Discharging electrons between the first MOSFET and the second MOSFET depends on the polarity of an accumulated voltage.