Differential Input Circuit With Low-Frequency Restoration
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Solution Overview
Problem
Computer systems often require differential input circuits that can support both AC and DC coupling modes to accommodate various interconnect standards like PCIe and QPI, which currently necessitate separate designs, increasing complexity and resource usage.
Innovation Solution
A unified input circuit design that selectively switches between AC and DC coupling modes using a high-pass filter and a low-frequency restoration feedback unit, allowing the same differential inputs to operate in either mode based on a coupling control signal, thereby supporting multiple standards with reduced complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate input circuit designs are used for AC coupling (PCIe) and DC coupling (QPI) modes, then each mode can be optimized for its specific coupling requirements, but the overall device complexity increases and engineering resources are duplicated
Solution Approach 1:
The input circuit is designed to perform multiple functions by supporting both AC and DC coupling modes through a unified architecture. The circuit uses coupling capacitors that can operate in either AC coupling configuration or be bypassed for DC coupling, allowing the same hardware to serve multiple interconnect standards (PCIe and QPI) without requiring separate dedicated circuits for each mode.
Solution Approach 2:
The input circuit incorporates dynamic switching capability through control signals that can reconfigure the coupling capacitors and associated switching elements. This allows the circuit to transition between AC and DC coupling modes as needed, adapting its configuration based on the operating requirements of different interconnect standards while maintaining a single unified design.
2Device complexity
If a unified input circuit design is used for both AC and DC coupling modes, then device complexity is reduced and engineering resources are conserved, but the circuit must accommodate both coupling types which may compromise optimization for either specific mode
Solution Approach 1:
The unified input circuit is segmented into functional modules that can be independently configured. The coupling capacitors are divided into first and second coupling capacitors that can be selectively connected or disconnected based on the operating mode. This segmentation allows each module to be optimized for its specific function while contributing to the overall unified architecture.
Solution Approach 2:
Switching elements and control logic act as intermediaries between the unified circuit architecture and the specific coupling mode requirements. These intermediary components enable the circuit to adapt its behavior to match the optimal configuration for either AC or DC coupling, preserving mode-specific optimization benefits within the unified design framework.
3Measurement precision
If AC coupling with high-pass filter is used for PCIe, then high-frequency components are preserved and low-frequency noise is filtered, but low-frequency signal components are lost requiring separate DC coupling design for QPI
Solution Approach 1:
The input circuit is designed to universally support both PCIe and QPI interconnect standards through a single unified architecture. By incorporating coupling capacitors that can be selectively engaged or bypassed, the circuit provides AC coupling for PCIe applications while being capable of DC coupling for QPI applications, eliminating the need for separate dedicated circuits for each standard.
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
This solution allows for a common design that conserves engineering resources, simplifies routing and verification, and provides flexibility in configuring data lanes for different roles, enabling the same IC to support both PCIe and QPI interconnects, thus reducing design complexity and increasing configuration options.
Implementation Method 1
removing low frequency components from an input signal to form a high-pass input signal
Implementation Method 2
detecting transitions in the high-pass input signal at an input of a receiver
Implementation Method 3
the low frequency components are restored by latching the transitions when in the DC coupling mode
Implementation Method 4
an output signal is provided by summing the high-pass input signal with the restored low frequency components
Data Source
AI summary
Low frequency components are removed from an input signal, and transitions in the input signal are detected at a receiver input. A feedback loop restores the low frequency components at the input of the receiver.