Radio Receiver Frequency Trimming for Crystal Offset Compensation

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Solution Overview

Problem

Conventional short range data radios face challenges with frequency offset between transmitter and receiver crystal oscillators, leading to signal attenuation and reduced receive sensitivity, especially when using less expensive crystals with higher tolerance limits, which increases manufacturing costs.

Innovation Solution

A measurement circuit measures signal corruption due to frequency offset and a trimming circuit adjusts the reference frequency in the transmitter or receiver to minimize this offset, allowing for improved signal reception even with less accurate crystals.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high precision crystals are used to minimize frequency offset, then receive sensitivity is improved, but manufacturing cost increases

Engineering Contradiction:

Improvereceive sensitivityVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The system performs self-calibration by having the transmitter transmit a calibration signal and the receiver measure the actual frequency offset. The receiver then automatically adjusts its local oscillator frequency based on the measured offset, eliminating the need for manual calibration or extremely high precision crystals. This self-correcting mechanism allows the use of lower cost crystals while maintaining receive sensitivity.

Inventive Principle:

Principle #25Self-service

2Ease of manufacture

If crystal tolerance limits are increased to reduce cost, then manufacturing cost decreases, but frequency offset increases causing signal attenuation

Engineering Contradiction:

Improvemanufacturing costVSAvoidfrequency accuracy

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The system implements a feedback mechanism where the receiver measures the frequency offset of the received signal and uses this information to adjust its local oscillator frequency. This closed-loop feedback allows the system to compensate for crystal tolerance variations, maintaining accurate frequency alignment even when using lower precision, lower cost crystals with higher tolerance limits.

Inventive Principle:

Principle #23Feedback

3Manufacturing precision

If manual crystal trimming is performed during manufacturing to reduce offset, then frequency accuracy is improved, but manufacturing complexity increases

Engineering Contradiction:

Improvefrequency accuracyVSAvoidmanufacturing complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent replaces the mechanical/manual crystal trimming process with an electronic/software-based frequency adjustment mechanism. The receiver measures the frequency offset electronically and adjusts its local oscillator through digital or electronic control, eliminating the need for physical crystal trimming operations during manufacturing. This substitution reduces manufacturing complexity while maintaining frequency accuracy.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS7787829B1Method and apparatus for tuning a radio receiver with a radio transmitter

Publication Date: 2010.08.31 INFINEON TECHNOLOGIES AMERICAS CORP

AI summary

Wireless devices transmit and receive radio signals based upon reference frequencies that are generated by reference frequency circuits. If the reference frequency in the transmitter is different from the reference frequency in the receiver, the radio signals may not be received properly or may not be capable of being received at all. A measurement circuit measures the amount of error or signal corruption in radio signals due to the reference frequency offset. A trimming circuit then tunes the reference frequency in the transmitter or receiver to reduce the reference frequency offset.