Class B Crystal Oscillator With Positive Feedback for Low-Power Clocks
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Solution Overview
Problem
Conventional crystal oscillator circuits in low power modes suffer from high power consumption due to static current sources, bias generator power usage, and inability to maintain oscillation in quartz crystals with high Equivalent Series Resistance, making them unsuitable for mobile applications.
Innovation Solution
A low-power crystal oscillator circuit operating in Class B with positive feedback and a step-down voltage regulator, utilizing a switched-capacitor voltage divider, PMOS and NMOS transistors, and capacitors to achieve rail-to-rail voltage swing and reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional crystal oscillator circuits use static current sources and bias generators in low power mode, then the circuit can maintain oscillation, but power consumption increases significantly
Solution Approach 1:
The patent implements Class B operation where the push-pull amplifier stage operates with periodic switching of transistors instead of continuous conduction. The circuit uses periodic charging and discharging of capacitors through the quartz crystal, eliminating the need for continuous static current flow while maintaining oscillation stability through the periodic action of the amplifier stage.
Solution Approach 2:
The patent removes the static current source and bias generator circuits from the low power mode implementation. By extracting these high power-consuming components and replacing them with a Class B amplifier stage that operates without continuous bias current, the design achieves significant power reduction while maintaining oscillation functionality through the inherent feedback mechanism of the push-pull configuration.
2Use of energy by moving object
If conventional crystal oscillator circuits reduce bias currents for low power consumption, then power is saved, but quartz crystals with high Equivalent Series Resistance cannot oscillate
Solution Approach 1:
The patent employs a push-pull amplifier stage with inherent positive feedback through the quartz crystal and associated capacitors. This feedback mechanism amplifies the oscillation signal and compensates for energy losses in high ESR crystals without requiring high bias currents. The feedback loop ensures that sufficient current is delivered to overcome crystal losses only when needed during oscillation cycles, rather than continuously.
Solution Approach 2:
The patent changes the operating parameters of the amplifier stage to Class B operation, where transistors switch between cutoff and saturation regions. This parameter change allows the circuit to deliver high peak currents to drive high ESR crystals during oscillation while maintaining low average power consumption, as the transistors are not continuously conducting current.
3Use of energy by moving object
If conventional crystal oscillator circuits use reduced voltage swing in deep sleep mode, then power consumption decreases, but noise level exceeds RF frequency generation requirements
Solution Approach 1:
The Class B push-pull amplifier stage operates with periodic full-rail voltage swings during oscillation cycles, ensuring that the output signal maintains sufficient amplitude margin even in low power mode. This periodic full-swing operation provides clean, high-amplitude clock edges that meet RF frequency generation noise requirements while the circuit remains in a low power state between oscillation cycles.
4Measurement precision
If conventional crystal oscillator circuits continue full power clock generation in low power mode, then accurate clock signal is maintained, but power consumption is not optimized
Solution Approach 1:
The patent implements a dynamic operating mode where the Class B amplifier stage adapts its operation based on the oscillation requirements. The circuit dynamically switches between active oscillation periods and low-power standby periods, adjusting the duty cycle and amplitude of the output signal. This dynamic operation maintains accurate clock signal characteristics during active periods while minimizing power consumption during transitions and standby states.
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 provides an accurate, low-power clock reference that is robust against high equivalent series resistance and noise, suitable for mobile devices, with significant power savings and compact integration.
Implementation Method 1
A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a precise frequency
Implementation Method 2
A low-power crystal oscillator circuit operating in Class B with positive feedback and a step-down voltage regulator
Implementation Method 3
A low-power crystal oscillator circuit operating in Class B with positive feedback
Data Source
AI summary
A low-power crystal oscillator circuit operating in Class B includes a PMOS transistor, an NMOS transistor, a step-down voltage regulator, and a bias voltage generator. A feedback mechanism includes an inverter whose input is connected to the drains of the PMOS and NMOS transistors and whose output is capacitively coupled to the gate of the PMOS transistor to provide positive feedback.