Reference-Less Clock Circuit With On-Chip Temperature Compensation
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Solution Overview
Problem
Existing clock chips rely on crystal oscillators, which are costly due to hermetic packaging and provide higher frequency stability than necessary for many applications, necessitating a solution that eliminates the need for a reference source and reduces manufacturing expenses.
Innovation Solution
A programmable reference-less oscillator circuit using a voltage-controlled oscillator (VCO) in an open loop configuration, coupled with a programmable divider and non-volatile storage for calibration, allowing for temperature compensation and programmable output frequencies without the need for crystals or hermetic packaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If crystal oscillators are used, then frequency stability is improved (±10 ppm), but manufacturing cost increases due to hermetic packaging
Solution Approach 1:
The patent extracts and eliminates the crystal oscillator component from the clock circuit, replacing it with a reference-less oscillator that uses an on-chip temperature sensor and calibration mechanism. This removal of the crystal and hermetic packaging directly reduces manufacturing cost while maintaining acceptable frequency stability through the alternative temperature compensation approach.
Solution Approach 2:
The patent replaces the expensive, durable crystal oscillator with a cheaper integrated circuit-based oscillator that achieves sufficient frequency stability through software calibration and temperature compensation. The calibration data stored in non-volatile memory enables the cheaper circuit to achieve comparable performance for the target application range.
2Measurement precision
If crystal oscillators are used, then frequency accuracy is improved, but device complexity increases due to hermetic packaging requirements
Solution Approach 1:
The patent merges the temperature sensing, calibration storage, and oscillator functions into a single integrated circuit package. The temperature sensor, non-volatile memory for calibration data, and reference-less oscillator are combined on one chip, eliminating the need for separate crystal components and hermetic packaging while achieving sufficient frequency accuracy through integrated temperature compensation.
Solution Approach 2:
The oscillator circuit performs self-calibration by using its own integrated temperature sensor to detect temperature variations and automatically adjusting the oscillation frequency based on calibration data stored in on-chip non-volatile memory. This self-service mechanism eliminates the need for external reference components and complex packaging.
3Ease of manufacture
If reference-less oscillators are used, then manufacturing cost is reduced, but frequency stability deteriorates compared to crystal oscillators
Solution Approach 1:
The patent performs preliminary calibration during manufacturing by measuring the actual oscillation frequency at different temperatures and storing correction factors in non-volatile memory. This preliminary action enables the reference-less oscillator to compensate for process variations and temperature drift, achieving frequency stability sufficient for the target application range without requiring expensive crystal components.
Solution Approach 2:
The oscillator incorporates a feedback mechanism where the temperature sensor continuously monitors temperature variations and the control logic adjusts the oscillation frequency based on pre-stored calibration data. This feedback loop compensates for temperature-induced frequency drift, maintaining acceptable frequency stability despite the absence of a crystal oscillator.
4Adaptability or versatility
If programmable dividers are used, then frequency range is expanded, but device complexity increases
Solution Approach 1:
The patent implements a programmable divider that can be configured through I2C interface to provide multiple division ratios, enabling a single oscillator circuit to generate a wide range of output frequencies. This multi-functional approach allows the same hardware to serve multiple frequency requirements, expanding adaptability while keeping the base oscillator circuit simple and reference-less.
Data Source
AI summary
A programmable reference-less oscillator provides a wide range of programmable output frequencies. The programmable reference-less oscillator is implemented on an integrated circuit that includes a free running controllable oscillator circuit such as a voltage controlled oscillator (VCO), a programmable divider circuit coupled to divide an output of the controllable oscillator circuit according to a programmable divide value. A non-volatile storage stores the programmed divide value and a control word that controls the output of the controllable oscillator circuit. The control word provides a calibration capability to achieve a desired output frequency in conjunction with the programmable divider circuit. Open loop temperature compensation is achieved by adjusting the control word according to a temperature detected by a temperature sensor on the integrated circuit. Additional clock accuracy may be achieved by adjusting the control word for process as well as temperature.