AC Coupling Level Shifter for Common-Mode and Signal Integrity
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Solution Overview
Problem
Conventional AC coupling mechanisms for high-speed interfaces using board level capacitors consume significant power and degrade signal quality due to voltage drops across interconnects, which are often compensated by active equalizers but at the cost of increased power consumption.
Innovation Solution
An AC coupling circuit comprising a level shifter circuit and a common mode voltage adjustment feedback circuit that adjusts the frequency response using adjustable RC networks to cancel out frequency responses introduced by interconnects, allowing for efficient common mode voltage regulation without additional power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If board level capacitors are used for AC coupling, then DC isolation is achieved, but signal quality degrades and power consumption increases
Solution Approach 1:
The patent extracts the AC coupling function from external board level capacitors and implements it directly on the chip using transistor-based circuits. This eliminates the need for external capacitors and their associated power consumption while maintaining DC isolation functionality through the level shifter circuit architecture.
Solution Approach 2:
The patent replaces the passive mechanical/electrical system of external capacitors with an active electronic system using transistors and RC networks integrated on the chip. This substitution enables AC coupling functionality without the power consumption and signal quality degradation associated with board level capacitors.
2Reliability
If active equalizers are used to compensate voltage drops, then signal quality is maintained, but power consumption increases significantly
Solution Approach 1:
The patent implements self-service by using the AC coupling circuit itself to provide frequency response compensation through its inherent RC network characteristics. The circuit automatically adjusts to compensate for interconnect voltage drops without requiring external active equalizers, thereby maintaining signal quality while avoiding the significant power consumption of traditional equalization approaches.
3Reliability
If board level capacitors are used for AC coupling, then DC isolation is achieved, but board area is consumed
Solution Approach 1:
The patent merges the AC coupling function with the chip's internal circuitry by integrating the level shifter and RC networks directly on the chip. This consolidation eliminates the need for separate external capacitors and their associated board area, while maintaining effective DC isolation through the integrated circuit architecture.
Solution Approach 2:
The patent nests the AC coupling functionality within the chip's existing circuit structure by embedding RC networks and level shifters inside the chip boundaries. This nesting approach eliminates external components and their board area requirements while preserving the DC isolation function through the nested circuit design.
Data Source
AI summary
An AC coupling circuit is provided that has a level shifter circuit having a p input voltage and an n input voltage and producing a p output voltage and a p output voltage. There is a common mode voltage adjustment feedback circuit configured to cause a common mode voltage output to tend towards a specified reference voltage, the common mode voltage output being an average of the p output and n output voltages of the level shifter circuit. In combination, the level shifter circuit and the feedback circuit allow the interconnection of a first circuit that operates at a first, unspecified, common mode voltage to be connected to a second circuit having a required common mode voltage. The level shifter may be formed of adjustable components such that the frequency response of the level shifter circuit can be adjusted to compensate for a frequency response of an interconnect between the first circuit and the second circuit.