Re-Driver Output Circuit for High-Voltage Surge Mitigation
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Solution Overview
Problem
Designing an inexpensive re-driver circuit that meets voltage specifications for low voltage host and sink devices in high-speed applications like USB and DisplayPort is challenging due to voltage surges during supply ramp-up and ramp-down, which can damage devices and complicate automatic cable connection detection.
Innovation Solution
A charge pump circuit with a comparator and NMOS transistor is used to provide a higher voltage during supply ramp-up and transition to the supply voltage during ramp-down, mitigating common mode voltage surges by activating and deactivating the NMOS transistor to isolate output pads and prevent voltage spikes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high voltage transistors are used at host and sink inputs to protect from voltage surges, then reliability is improved, but cost and power consumption increase
Solution Approach 1:
The patent introduces a protection circuit as an intermediary component between the re-driver output and the host/sink inputs. This circuit includes a switch connected between a USB port pin and a middle node, and a detection circuit that compares the middle node voltage with a reference voltage. The protection circuit clamps voltage surges to a desired level, protecting low-voltage transistors at the host and sink from damage while allowing the use of cheaper, lower-power transistors.
Solution Approach 2:
The protection circuit segments the voltage surge protection function from the main signal path. By separating the protection function into a distinct circuit with its own switch and detection components, the patent allows the host and sink to use low-voltage transistors for normal operation while still providing surge protection through the dedicated protection circuitry.
2Reliability
If a protection circuit with switch and detection circuit is used to clamp voltage during surges, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent merges the protection circuit functionality into the existing re-driver structure. The switch in the protection circuit is integrated with the re-driver output stage, and the detection circuit utilizes the same signal paths and power supply as the main driver circuitry. This integration reduces overall complexity compared to having completely separate protection and driver circuits.
Solution Approach 2:
The protection circuit components serve multiple functions: the switch is used both for normal signal transmission and for clamping during surges, while the detection circuit serves both cable connection detection and surge protection functions. This multi-functionality reduces the total number of components needed in the system.
3Reliability
If protection circuit is used to clamp voltage during surges, then reliability is improved, but automatic cable connection detection becomes more difficult
Solution Approach 1:
The protection circuit uses a dynamic switching mechanism that adapts its behavior based on operating conditions. The switch transitions between different states (connected/disconnected) based on the output of the detection circuit, which monitors voltage levels to determine both cable presence and surge conditions. This dynamic operation allows the same circuit to perform both cable detection and surge protection without interference.
Solution Approach 2:
The detection circuit provides feedback about the voltage level at the middle node to control the switch state. This feedback mechanism allows the circuit to automatically detect cable connections by monitoring voltage levels and to respond to surge conditions by clamping the voltage, thereby integrating both functions through a feedback-controlled switching mechanism.
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 reduces common mode voltage surges by almost 90%, meeting USB 3.1 and other standards, and allows for reliable high-speed signaling while maintaining low-cost and low-complexity re-driver circuit design.
Implementation Method 1
a charge pump circuit with a comparator and NMOS transistor is used to provide a higher voltage during supply ramp-up and transition to the supply voltage during ramp-down
Data Source
AI summary
A driver circuit includes an output terminal adapted for driving a data signal through a coupling capacitor to an external device. A first transistor is employed to drive the signal, and an N-type metal-oxide semiconductor (NMOS) transistor couples power to the first transistor. The NMOS transistor includes a first terminal connected to a positive terminal of a voltage supply, a second terminal coupled to an output terminal through a termination resistor, a gate terminal, and a bulk terminal connected to the negative terminal of the voltage supply. A charge pump circuit supplies a voltage to a gate terminal of the NMOS transistor, and is operable to provide a first voltage higher than that of the voltage supply to activate the NMOS device, and, responsive to detecting a ramp-down of the supply voltage, transition to providing the supply voltage to the NMOS device gate terminal.