Capacitive Structures for DIMM Crosstalk Reduction
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Solution Overview
Problem
In computing systems, the proximity of DIMM connector pins leads to far end crosstalk, limiting data rates and requiring increased pin separation or footprint, which increases the cost and reduces the number of memory modules that can be accommodated on a system PCB.
Innovation Solution
Incorporating capacitive structures to increase mutual capacitance between DDR memory channels at or near the DIMM connector, which mitigates mutual inductance and reduces far end crosstalk, allowing for higher data rates and reduced footprint without increasing the number of ground pins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If DIMM connector pins are positioned relatively close together to reduce surface area and maximize pin count, then the footprint is reduced and pin density is increased, but far end crosstalk is produced between adjacent signal pins
Solution Approach 1:
A capacitive structure is introduced as an intermediary element between adjacent signal pins to provide mutual capacitance. This capacitive structure acts as a mediator that counteracts the harmful inductive coupling (crosstalk) by introducing a beneficial capacitive coupling path, thereby reducing far end crosstalk while allowing pins to remain closely spaced
Solution Approach 2:
The electrical parameters of the signal path are modified by adding the capacitive structure, which changes the impedance characteristics and signal coupling between adjacent pins. By adjusting the capacitance value through the structure's geometry and material properties, the harmful inductive effects are compensated, enabling reduced pin separation without increasing crosstalk
2Object-generated harmful factors
If pin separation is increased to reduce far end crosstalk, then crosstalk is reduced, but the footprint of the DIMM connector increases
Solution Approach 1:
The capacitive structure serves as an intermediary that enables close pin spacing by actively compensating for the crosstalk that would normally require increased separation. The structure's capacitance provides a counteracting effect that allows maintaining small pitch while achieving acceptable crosstalk levels
3Object-generated harmful factors
If ground pins are added between adjacent signal pins to reduce crosstalk, then far end crosstalk is reduced, but the footprint and device complexity increase
Solution Approach 1:
The solution extracts the crosstalk mitigation function from the traditional ground pin approach and implements it through a dedicated capacitive structure. This separates the signal coupling function from the reference/ground function, allowing crosstalk reduction without adding ground pins or increasing connector complexity
Solution Approach 2:
The capacitive structure performs multiple functions: it provides mutual capacitance for crosstalk reduction, maintains signal integrity, and allows for compact pin spacing. By consolidating these functions into a single structure rather than requiring additional ground pins, device complexity is reduced while achieving the same or better performance
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 capacitive structures effectively reduce far end crosstalk, enabling higher DDR data rates and decreasing the DIMM connector footprint, while maintaining or increasing the number of signal pins and memory capacity on the system PCB.
Implementation Method 1
capacitive structures for crosstalk reduction... Incorporating capacitive structures to increase mutual capacitance between DDR memory channels... The provided mutual capacitance is configured to mitigate DIMM connector pin mutual inductance and, thus, to reduce far end crosstalk
Data Source
AI summary
One embodiment provides an apparatus. The apparatus includes a dual in-line memory module (DIMM). The DIMM includes at least one memory module integrated circuit (IC); a DIMM printed circuit board (PCB); a plurality of DIMM PCB contacts; and a capacitive structure. Each DIMM PCB contact is to couple the memory module IC to a respective DIMM connector pin. The capacitive structure is to provide a mutual capacitance between a first DIMM connector signal pin and a second DIMM connector signal pin.