LC Frequency Reference Generator With LUT Temperature Compensation
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Solution Overview
Problem
Existing on-chip LC-based frequency references face significant process spread and temperature/lifetime dependency issues, making it challenging to achieve absolute frequency accuracy without extensive trimming and compensation.
Innovation Solution
A frequency reference generator design that incorporates a non-trimmable LC tank and temperature sensor to generate a differential oscillator signal, with frequency-adjustment circuitry that uses a look-up table to compensate for process and temperature variations, ensuring stability over the operating range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If passive and active on-chip components are used in the processing front-end, then integration is improved, but process spread and temperature/lifetime dependency increase
Solution Approach 1:
The patent applies preliminary action by performing factory trimming of the LC tank components (inductor or capacitor) to pre-compensate for process variations before the device is deployed. This preliminary calibration stores correction data that is later used during operation to maintain frequency accuracy despite process spread and temperature variations, thereby resolving the contradiction between integration and reliability.
2Measurement precision
If temperature trimming and re-trimming are employed, then frequency accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent eliminates the need for complex temperature trimming and re-trimming operations by performing all necessary frequency calibration during factory trimming. The LC tank components are pre-adjusted to compensate for process variations, and the trimmed values are stored for use during operation. This preliminary action approach achieves high frequency accuracy without requiring complex runtime trimming mechanisms.
Solution Approach 2:
The patent uses a lookup table that stores pre-calibrated frequency correction data obtained during factory trimming. Instead of performing complex real-time trimming operations, the system copies and applies pre-computed correction values from the lookup table based on measured process parameters, thereby achieving frequency accuracy with minimal device complexity.
3Measurement precision
If a trimmable LC tank is used, then frequency accuracy is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent performs all frequency calibration operations during the factory trimming process, before the device is shipped to the customer. The LC tank components are trimmed to the correct frequency values, and the trimmed parameters are stored in memory. This preliminary action eliminates the need for complex trimmable structures and runtime adjustment mechanisms, thereby achieving frequency accuracy while simplifying manufacturing.
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
The solution significantly reduces frequency temperature coefficient variations, achieving better than ±0.1% accuracy over a wide temperature range, reducing the need for extensive trimming and calibration, and providing a competitive alternative to quartz crystal oscillators.
Implementation Method 1
an LC tank that includes an inductor leg in parallel with a capacitor leg
Implementation Method 2
temperature sensor 110, a frequency source 120
Data Source
AI summary
An LC oscillator has a tank driver connected to cause a matched-resistance LC tank to oscillate. The LC tank has an inductor leg in parallel with a capacitor leg. The inductor leg has an explicit inductor having an implicit resistance level RL. The capacitor leg has an explicit capacitor having an implicit resistance level RC connected in series with an explicit resistor having an explicit resistance level RR, where RM=(RC+RR) is substantially equal to RL. The LC oscillator may have a non-trimmable LC tank and be part of a temperature-compensated frequency reference generator having standalone frequency adjustment circuitry that offers better than ±0.1% frequency accuracy (after single trim and batch calibration) over process, voltage, and temperature variations, and lifetime, which can serve as a low-cost replacement for a crystal oscillator for many applications.