Memory Controller Output Driver Using NMOS Pull-Up

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Solution Overview

Problem

Conventional output signal driving circuits in memory controllers face challenges in efficiently managing voltage levels for different memory standards, leading to insufficient operation voltage for PMOS transistors when using high-voltage devices, which results in increased transistor size and pad area.

Innovation Solution

The use of N-type transistors as both voltage pull-up and pull-down devices, along with a pre-driver operating at a specific voltage, allows for stable voltage level maintenance on the I/O pad, utilizing the source follower effect to achieve desired voltage levels without increasing transistor size or pad area.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If PMOS transistors are used as voltage pull-up devices in high-voltage I/O circuitry, then the voltage pull-up capability is improved, but the transistor size and pad area significantly increase when operating at lower voltages (1.5V-2.5V)

Engineering Contradiction:

Improvevoltage pull-up capabilityVSAvoidpad area

Core Design Contradiction:

PowerVSArea of stationary object

Solution Approach 1:

The patent changes the type of transistor used for voltage pull-up from PMOS to NMOS, fundamentally altering the device parameter. NMOS transistors are used with their source connected to the pad and gate controlled by a pre-driver, enabling effective voltage pull-up at lower operating voltages (1.5V-2.5V) without requiring increased device width or pad area

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces a pre-driver circuit as an intermediary component that controls the gate of the NMOS voltage pull-up device. The pre-driver operates at a higher voltage (3.3V) to provide sufficient gate drive voltage to the NMOS transistor, enabling the NMOS to effectively pull up the pad voltage to the required level despite the lower operating voltage

Inventive Principle:

Principle #24Intermediary (Mediator)

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 solution enables efficient operation of memory controllers across various standards like DDR, DDR II, and DDR III without increasing the area of the I/O pad, maintaining suitable current draining ability and voltage levels.

Implementation Method 1

Methodology Applied

Scientific EffectSource follower effect:

Data Source

PatentUS7701787B2Memory controller and output signal driving circuit thereof

Publication Date: 2010.04.20 REALTEK SEMICON CORP

AI summary

A memory controller for controlling a memory, where the memory controller includes: a pad, coupled to the memory, for generating an output signal to the memory according to a signal value of the memory controller; a voltage pull-up device, coupled to the pad, comprising a first N type transistor and for pulling up a voltage level on the pad according to the signal value; and a voltage pull-down device, coupled to the pad, comprising a second N type transistor and for pulling down the voltage level on the pad according to the signal value.