Programmable Pad Capacitance for Bidirectional Signaling
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Solution Overview
Problem
Unterminated endpoints in chip-to-chip interfaces of mobile devices cause signal reflections known as 'ringback' noise, leading to bit errors, especially at higher data rates, which existing techniques attempt to mitigate by redesigning transmission lines to reduce crosstalk but at the cost of increased manufacturing costs.
Innovation Solution
An unterminated endpoint with a pad coupled to ground through a capacitor and a switch, where a controller closes the switch during signal reception to load the input impedance with capacitance, reducing ringback noise, and opens it during transmission to prevent loading of output impedance, thereby selectively managing capacitance based on data rate thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If capacitance is added to the endpoint pad to reduce ringback noise, then signal reflection is reduced, but power dissipation increases due to continuous capacitor charging/discharging
Solution Approach 1:
The patent applies dynamics by making the capacitance connection dynamic rather than static. The switch is controlled to connect the capacitor to the pad only during specific periods (when data is transmitted from the first die to the second die), and disconnect it during other periods. This dynamic switching resolves the contradiction by providing ringback noise reduction only when needed, while avoiding continuous power dissipation from capacitor charging/discharging cycles.
Solution Approach 2:
The patent implements periodic action by enabling the capacitance connection only during specific time intervals corresponding to data transmission periods from the first die to the second die. The controller selectively activates the switch based on the transmission timing, creating a periodic pattern of capacitance connection that reduces ringback noise during critical periods while minimizing power consumption during idle periods.
2Reliability
If capacitance is continuously connected to reduce ringback, then bit error rate decreases, but device complexity increases due to continuous switching control
Solution Approach 1:
The patent applies self-service by making the switching control automatic and self-regulating based on the transmission state. The controller automatically determines when to connect or disconnect the capacitor based on whether data is being transmitted from the first die to the second die, without requiring external intervention or complex control logic. This reduces device complexity compared to continuously controlled switching systems.
3Object-affected harmful factors
If switch is closed during transmission, then ringback is reduced, but output impedance is adversely affected
Solution Approach 1:
The patent applies dynamics by implementing time-dependent switching control where the switch state changes based on the transmission direction. The switch is closed only when data is transmitted from the first die to the second die (when ringback reduction is needed), and opened when data is transmitted from the second die to the first die (to avoid affecting output impedance). This dynamic control resolves the contradiction by applying capacitance only when beneficial.
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 approach significantly reduces bit error rates by dampening signal reflections during reception while minimizing power dissipation and manufacturing costs by selectively adding capacitance only during reception, thus reducing ringback noise effectively.
Implementation Method 1
a pad (which may also be denoted as an endpoint terminal) coupled to ground through a capacitor and a switch
Implementation Method 2
the capacitor receives charge from the signal rising edges and discharges charge to the signal falling edges
Data Source
AI summary
A die is provided having an unterminated endpoint that capacitively loads its input impedance with a capacitance from capacitor while acting as a receiving endpoint and that isolates its output impedance from the capacitance while acting as a transmitting endpoint.