Impedance Matching Circuit With Shared Pull-Up and Pull-Down Calibration
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Solution Overview
Problem
Existing impedance matching circuits in semiconductor ICs face challenges with impedance mismatching due to external noise, power supply voltage changes, and manufacturing process variations, leading to distorted signals and operational issues like setup/hold failure and misjudgment, especially at high speeds.
Innovation Solution
An impedance matching circuit with a ZQ calibration system that includes a code generating unit, a calibration resistance unit with switching elements to control resistors, and identical termination pull-up and pull-down resistance units, which receive the same calibration code to minimize mismatches and enhance calibration efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate pull-up and pull-down calibration circuits are used, then calibration can be performed for both impedance directions, but the number of mismatches increases and circuit complexity increases
Solution Approach 1:
The patent merges the pull-up calibration circuit and pull-down calibration circuit into a single integrated calibration circuit. The same calibration code controls both the pull-up resistance unit and pull-down resistance unit, reducing the number of separate calibration circuits from two to one, while still achieving impedance matching for both directions.
Solution Approach 2:
The calibration circuit is designed with universal functionality to perform both pull-up and pull-down calibration using the same calibration code. The switching unit can configure the calibration resistance unit to function as either pull-up or pull-down resistance based on the calibration code, eliminating the need for separate dedicated circuits for each function.
2Reliability
If separate calibration codes are used for pull-up and pull-down, then each direction can be calibrated independently, but the calibration time increases
Solution Approach 1:
The patent combines the calibration process for pull-up and pull-down into a single unified calibration operation. By using one calibration code to control both the pull-up resistance unit and pull-down resistance unit simultaneously, the calibration time is reduced compared to performing separate calibration operations for each direction.
Solution Approach 2:
The calibration circuit performs preliminary configuration of both pull-up and pull-down resistance units using the same calibration code before actual signal transmission begins. This preliminary action ensures both impedance directions are pre-calibrated together, avoiding the need for sequential calibration operations.
Data Source
AI summary
An impedance matching circuit includes a code generating unit for generating a calibration code in response to a reference voltage and a voltage on a node, a calibration resistance unit for supplying a power supply voltage to the node, being calibrated to an external resistor, wherein the calibration resistance unit includes a switching unit for turning on/off a plurality of resistors connected in parallel in response to the calibration code, a termination pull-up resistance unit provided at an output node for receiving the calibration code, wherein the termination pull-up resistance unit has a switching unit which is identical to that of the calibration resistance unit, and a termination pull-down resistance unit at the output node, for receiving the calibration code, wherein the termination pull-down resistance unit has a switching unit which is identical to that of the calibration resistance unit.