Bimodal Output Driver Biasing for QPI and CML Interfaces

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Solution Overview

Problem

Existing output drivers for integrated circuits struggle to support both QuickPath Interconnect (QPI) and Current Mode Logic (CML) interface protocols without using p-type transistors, which poses a challenge in achieving efficient and versatile data transmission.

Innovation Solution

The implementation of a bias control circuit that provides different voltage levels for operating modes, allowing the output driver to switch between supply-referenced and ground-referenced operations, utilizing only n-type transistors to drive data signals, thus supporting both QPI and CML protocols without PMOS transistors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If p-type transistors are used in the output driver to support both QPI and CML protocols, then protocol versatility is improved, but device complexity and manufacturing difficulty increase

Engineering Contradiction:

Improveprotocol support capabilityVSAvoidtransistor type diversity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The output driver is designed with a single n-type transistor configuration that can operate in multiple modes (QPI and CML protocols) by changing bias conditions and control signals, eliminating the need for separate p-type transistor circuits for each protocol

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The invention changes operational parameters (bias voltages, control signal levels) of the n-type transistor to switch between QPI and CML modes, allowing protocol versatility without adding p-type transistors

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If p-type transistors are used in the output driver, then protocol versatility is improved, but manufacturing precision requirements worsen

Engineering Contradiction:

Improveprotocol support capabilityVSAvoidtransistor fabrication tolerance

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

By changing bias parameters and control signal characteristics rather than transistor type, the invention reduces manufacturing precision requirements as n-type transistors have more relaxed fabrication tolerances compared to p-type transistors

Inventive Principle:

Principle #35Parameter changes

3Speed

If the output driver is designed for high-speed operation above gigabit rates, then transmission speed is improved, but susceptibility to inadvertent grounding increases

Engineering Contradiction:

Improvedata transmission rateVSAvoidgrounding stability

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

Instead of using the conventional approach where p-type transistors source current to the output node, the invention inverts the approach by using n-type transistors that sink current to ground, which are less susceptible to inadvertent grounding at high speeds

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The invention changes the biasing parameters and switching characteristics of the n-type transistor to optimize for high-speed operation while maintaining grounding stability through controlled current sinking behavior

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS8217682B1Output driver and operation thereof

Publication Date: 2012.07.10 XILINX INC

AI summary

Embodiments of an integrated circuit driver, a method for operating integrated circuit driver, and predrivers are described. In one embodiment of the integrated circuit driver, a bias control circuit provides a bias signal for a first mode and a second mode. The bias signal has a first voltage level associated with operation in the first mode and a second voltage level associated with operation in the second mode. An output driver circuit receives the bias signal. In the first mode, the output driver circuit operates as a supply referenced driver, and in the second mode, the output driver circuit operates as a ground referenced driver.