Frequency Offset Circuit for Radio Transmitter Receiver Calibration

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 due to high accuracy and cost requirements of crystals, and the need for factory calibration and memory storage for frequency trimming.

Innovation Solution

A frequency offset circuit that adjusts the operating frequency of the transmitter or receiver using a programmable constant added to the instantaneous frequency of the RF signal, allowing for alignment of frequencies through a series of coarse and fine adjustments based on bit error rate feedback, enabling the use of lower accuracy crystals without factory calibration or memory storage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If high accuracy crystals are used to maintain frequency alignment between transmitter and receiver, then frequency offset is reduced, but manufacturing cost and complexity increase due to trimming requirements

Engineering Contradiction:

Improvefrequency alignment accuracyVSAvoidmanufacturing complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces mechanical crystal trimming processes with a digital frequency calibration system. A calibration radio measures the actual frequency offset between transmitter and receiver, then a processor automatically calculates and applies correction values to adjust the local oscillators, eliminating the need for manual mechanical trimming of crystals.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The system performs self-calibration by automatically measuring its own frequency offset using a calibration radio and then adjusting its own oscillators based on the measured error. This self-correcting mechanism eliminates the need for external factory trimming operations.

Inventive Principle:

Principle #25Self-service

2Reliability

If high accuracy crystals are used to maintain frequency alignment, then receive sensitivity is improved, but initial cost increases

Engineering Contradiction:

Improvereceive sensitivityVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent changes the approach from using high-precision physical components (crystals) to using software-based frequency correction. By measuring the actual frequency parameters of the oscillators and applying digital corrections, the system achieves the same reliability outcome with lower-cost components.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces mechanical crystal trimming processes with a digital frequency calibration system. A calibration radio measures the actual frequency offset between transmitter and receiver, then a processor automatically calculates and applies correction values to adjust the local oscillators, eliminating the need for manual mechanical trimming of crystals.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If frequency trimming is implemented to compensate for oscillator inaccuracies, then frequency offset is reduced, but device complexity increases due to memory storage requirements

Engineering Contradiction:

Improvefrequency offset compensationVSAvoiddevice complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces mechanical crystal trimming processes with a digital frequency calibration system. A calibration radio measures the actual frequency offset between transmitter and receiver, then a processor automatically calculates and applies correction values to adjust the local oscillators, eliminating the need for manual mechanical trimming of crystals.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The system uses feedback from the calibration radio's frequency offset measurement to automatically adjust the transmitter and receiver oscillators. The measured offset is fed back to the frequency synthesizers, which automatically correct their frequencies, creating a closed-loop calibration system.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS7746922B2Apparatus and method for frequency calibration between two radios

Publication Date: 2010.06.29 INFINEON TECHNOLOGIES AMERICAS CORP

AI summary

Wireless devices transmit and receive radio signals based upon reference frequencies generated by crystal oscillators. If the reference frequencies of the transmitter and the receiver are different, the radio signals may not be received properly or may not be received at all. A measurement circuit measures the amount of error or signal corruption in the radio signals due to the reference frequency offset between the transmitter and the receiver. A frequency offset circuit generates an offset operating frequency in the transmitter or the receiver to align or calibrate the operating frequencies of the devices.