Driver Circuit Limits Wave Front Voltage to Prevent Receiver Damage

Solution Overview

Problem

The reduction in rise and fall times of signals on interconnects has changed their behavior from lumped capacitive loads to transmission lines, leading to impedance discontinuities and reflected wave fronts that can damage receivers and drivers, as they cannot handle the increased voltage.

Innovation Solution

A driver circuit that includes p-channel and n-channel transistors, a trip point circuit, and control circuits to match the impedance of the driver with the transmission line, limiting the initial wave front voltage to approximately 0.5 VDD, preventing damage from reflected waves by ensuring the driver and receiver voltages are within safe limits.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the rise and fall times are reduced to increase data transmission speed, then the productivity is improved, but the interconnects respond as transmission lines causing impedance discontinuities and reflected wave fronts that can damage receivers and drivers

Engineering Contradiction:

Improvedata transmission speedVSAvoidreflected wave front voltage

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The driver circuit proactively shapes the output voltage waveform to create a controlled initial wave front with limited voltage magnitude before the signal enters the transmission line. By预先 limiting the wave front voltage to approximately 0.5*VDD through the voltage divider configuration (Z0/(Z0+Zs)), the circuit prevents harmful reflections from occurring in the first place, rather than trying to mitigate them after they occur

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention changes the voltage parameter of the initial wave front by controlling the driver's output impedance Zs relative to the transmission line impedance Z0. By designing the driver with specific impedance characteristics, the voltage magnitude of the launched wave front is transformed to be approximately 0.5*VDD, which is a controlled parameter change that prevents receiver damage while maintaining signal integrity

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the driver outputs a high voltage signal to ensure full logic high levels, then the reliability of logic high representation is improved, but the reflected wave front can double the voltage to 2*Vi which exceeds receiver handling capability

Engineering Contradiction:

Improvelogic high representationVSAvoidvoltage at receiver input

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The driver circuit proactively shapes the output voltage waveform to create a controlled initial wave front with limited voltage magnitude before the signal enters the transmission line. By预先 limiting the wave front voltage to approximately 0.5*VDD through the voltage divider configuration (Z0/(Z0+Zs)), the circuit prevents harmful reflections from occurring in the first place, rather than trying to mitigate them after they occur

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention changes the voltage parameter of the initial wave front by controlling the driver's output impedance Zs relative to the transmission line impedance Z0. By designing the driver with specific impedance characteristics, the voltage magnitude of the launched wave front is transformed to be approximately 0.5*VDD, which is a controlled parameter change that prevents receiver damage while maintaining signal integrity

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS7388404B1Driver circuit that limits the voltage of a wave front launched onto a transmission line

Publication Date: 2008.06.17 NAT SEMICON CORP

AI summary

A driver circuit limits the magnitude of the initial wave front launched onto a transmission line to a voltage that is approximately one-half of the supply voltage. Thus, immediately after the initial wave front is reflected from an open circuit receiver, a voltage at the receiver is approximately equal to the supply voltage when a rising voltage is launched, and ground when a falling voltage is launched.