Crystal Oscillator Start-Up Circuit Using Zero-Crossing H-Bridge Pulses
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Solution Overview
Problem
Existing crystal oscillator start-up methods are limited by long start-up times and high energy consumption due to reliance on noise amplification, which is not well-defined and dependent on initial noise values, making it challenging to achieve short start-up times in low-power wireless systems like IoT and BLE devices.
Innovation Solution
A crystal oscillator start-up circuit utilizing an H-bridge circuit with a comparator and switch control generator to apply voltage pulses in a controlled manner, synchronizing with zero-crossing events of the motional current, optimizing the start-up time by alternating polarity and resistance configurations to enhance motional current amplitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If noise amplification is used to start-up the crystal oscillator, then the circuit is simple, but the start-up time is long and energy consumption is high
Solution Approach 1:
The patent applies preliminary action by providing an initial kick or pulse to the crystal oscillator at start-up to define the initial motional current. This preliminary energy injection prepares the oscillator for faster start-up by establishing a defined initial state rather than relying on random noise amplification.
Solution Approach 2:
The patent implements periodic action by periodically injecting energy pulses into the crystal oscillator in a well-defined manner. This periodic energy injection continuously increases the motional current up to the final value, optimizing the start-up time to the minimum possible value when the frequency and phase of injected energy match the motional current.
2Measurement precision
If maximum kick amplitude is applied to the crystal, then the initial motional current is well defined, but the amplitude is limited by supply voltage
Solution Approach 1:
The patent uses periodic energy injection to overcome the supply voltage limitation. By applying multiple periodic pulses rather than a single maximum amplitude kick, the motional current is gradually increased to the desired level, achieving well-defined initial current while managing energy consumption through controlled periodic excitation.
Solution Approach 2:
The patent applies dynamics by making the switch control generator dynamically adjust the switching patterns and energy injection timing. The system adapts the kick amplitude and frequency based on the oscillator's state, allowing optimal energy transfer while respecting supply voltage constraints and minimizing overall energy consumption.
3Productivity
If periodic pulses are applied in well-defined manner, then the motional current increases constantly, but the synchronization precision is critical
Solution Approach 1:
The patent implements feedback by using a comparator to detect zero-crossing events of the motional current and generate switch control signals based on these detections. This feedback mechanism ensures that periodic energy pulses are injected at the correct phase and frequency, automatically synchronizing with the oscillator's natural behavior and eliminating the need for external synchronization references.
Solution Approach 2:
The patent applies self-service by making the crystal oscillator's own motional current serve as the reference for synchronization. The zero-crossing detection of the motional current itself provides the timing reference for energy injection, allowing the system to self-synchronize without external clocks or complex phase-locked loops, thus achieving high precision synchronization inherently.
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
This approach significantly reduces start-up time and energy consumption by ensuring precise synchronization and increased motional current amplitude, enabling faster and more efficient start-up of crystal oscillators in low-power devices without the need for external clocks.
Implementation Method 1
a comparator having a first comparator input configured to be switchably coupled to a terminal of the crystal resonator, a second comparator input configured to be coupled to a supply node, a comparator clock input, and a comparator output configured to transition between a first state and a second state in response to a zero-crossing event of the motional current in the crystal resonator
Implementation Method 2
an H-bridge circuit comprising a plurality of switches configured to be coupled to a crystal resonator... the plurality of switches being configurable to apply a voltage source to the crystal resonator terminals in a first polarity during a first switch control phase and a second opposite polarity during a second switch control phase
Implementation Method 3
the initial motional current in the Crystal (Xtal) is well defined... the frequency and phase of the injected energy is exactly the same as the motional current in Crystal
Data Source
AI summary
A circuit and method for starting-up a crystal oscillator is described. A crystal resonator is configured to be coupled to a start-up circuit including an H-bridge circuit having a number of switches. A plurality of switch control signals are generated in response to detecting a zero-crossing event of the motional current in the crystal resonator. The switches of the H-bridge circuit are controlled by the switch control signals to apply a voltage to the terminals of the crystal resonator in a first polarity during a first switch control phase and a second opposite polarity during a second switch control phase. During a respective first subphase of the respective switch control phase, the plurality of switches are configured in a first configuration to couple the supply node to a respective crystal resonator terminal. During a respective second subphase of the respective switch control phase the plurality of switches are configured in a second configuration to couple the supply node to the respective crystal resonator terminal. The resistance between the supply node and the respective crystal resonator terminal is larger in the second configuration than the first configuration. A zero-crossing is detected during each respective second sub-phase.