Parallel Bus Split-Level Signaling With Third-Supply Noise Balancing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing SDRAM output driver circuitry experiences significant switching noise due to the decoupling of power supply domains, which affects data integrity and adds complexity, as the Vddq/Vssq domain is more susceptible to noise from high-current switching.
Innovation Solution
Implementing a three-power-supply system with high and low common mode signaling, where odd and even transmitter stages use Vddq, Vssq, and an intermediate voltage Vx, respectively, to ensure that no more than half of the transmitter stages source or sink current from any power supply at a given time, reducing power supply loading and minimizing switching noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dual power supply domains (Vdd/Vss and Vddq/Vssq) are used to power different circuit blocks, then power supply isolation is achieved, but switching noise increases due to decoupling effects
Solution Approach 1:
The data bus is divided into two separate sub-buses: an odd-numbered data sub-bus (DQ1, DQ3, DQ5, DQ7) and an even-numbered data sub-bus (DQ0, DQ2, DQ4, DQ6). Each sub-bus is driven by dedicated output driver circuitry powered by different power supply domains. This segmentation allows noise from one power domain to affect only half of the total data signals, rather than all signals simultaneously.
Solution Approach 2:
Different power supply domains are assigned to different subsets of output drivers based on their connection to specific sub-buses. The odd sub-bus drivers are powered by one power domain while even sub-bus drivers use another domain. This local differentiation ensures that power supply noise is localized to specific signal groups, improving overall signal integrity despite the presence of multiple power domains.
2Adaptability or versatility
If power supply domains are decoupled for isolation, then circuit block independence is improved, but data integrity deteriorates due to increased susceptibility to noise
Solution Approach 1:
The data bus is segmented into odd and even sub-buses, each with dedicated drivers powered by different power domains. This segmentation ensures that when one power domain experiences switching noise, only the corresponding sub-bus is affected, while the other sub-bus maintains integrity. This approach preserves circuit block independence while mitigating the impact of noise on data integrity.
3Power
If all transmitter stages source or sink current simultaneously, then output driving capability is improved, but power supply loading increases causing more noise
Solution Approach 1:
The output driver array is segmented into two independent groups: odd-numbered drivers and even-numbered drivers. Each group is powered by a separate power supply domain and drives a separate sub-bus. This segmentation ensures that when all drivers operate simultaneously, the current loading is distributed across two independent power domains rather than concentrated on a single domain, reducing the noise impact on each individual power supply.
Data Source
AI summary
Disclosed herein are circuitry and methods for transmitting data across a parallel bus using both high common mode and low common mode signaling. The transmitter stages are configured to work with two of three possible power supply voltages: a high Vddq voltage, a low Vssq voltage, and an intermediate Vx voltage. In one embodiment, the odd numbered transmitter stages, that drive the odd numbered outputs to the bus, use the Vddq and Vx supplies, such that the odd numbered outputs comprise high common mode signals. The even numbered transmitter stages, that drive the even numbered outputs to the bus, use the Vx and Vssq supplies, such that the even numbered outputs comprise low common mode signals. With the transmitter and power supplies so configured, no one of the three power supplies must source or sink current to or from more than half of the transmitters at any given time, which reduces power supply loading and minimizes switching noise. As a result, use of the technique may dispense with the need to provide power supply isolation at the transmitters.