Crystal Oscillator Bias Circuit Using Current Mirrors at Low Current
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Solution Overview
Problem
Existing crystal oscillators driven by AC coupled driver circuits with high value resistors or class-A/class-C amplifiers are inefficient and costly, necessitating a low current bias solution that eliminates the need for high value resistors.
Innovation Solution
A bias circuit utilizing current mirrors and cascode devices to generate bias currents for crystal oscillators, providing efficient operation at low current levels without requiring high value resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If high value resistors are used to drive crystal oscillators at low current levels, then the crystal oscillator can operate at low current, but the device size and cost increase
Solution Approach 1:
The patent introduces a bias circuit as an intermediary component between the crystal oscillator and the driver circuit. This bias circuit generates precise bias currents that enable the oscillator to operate at low current levels without requiring high value resistors, thus resolving the contradiction between low current operation and device simplicity
Solution Approach 2:
The patent changes the operating parameters by implementing a bias circuit that dynamically manages current levels. The bias circuit uses current mirrors and cascode devices to precisely control bias currents, allowing the system to achieve low current operation while maintaining device compactness and reducing cost
2Reliability
If class-A or class-C amplifiers are used to drive crystal oscillators, then the oscillators can be driven effectively, but current efficiency is poor and excessive current is wasted
Solution Approach 1:
The patent implements a dynamic bias circuit that adjusts current distribution in real-time based on operating conditions. The circuit uses cascode devices and current mirrors to dynamically optimize the bias currents supplied to the crystal oscillator, achieving effective driving while minimizing current waste compared to static class-A or class-C amplifier approaches
Solution Approach 2:
The bias circuit dynamically changes operating parameters by adjusting bias currents through controlled current mirrors. This allows the system to maintain effective oscillator driving while operating at higher current efficiency, resolving the contradiction between driving effectiveness and energy loss
3Ease of operation
If traditional bias circuits are used, then crystal oscillators can operate, but they require high value resistors that increase cost and size
Solution Approach 1:
The patent merges multiple functions into the bias circuit by combining current generation, current mirroring, and biasing functions in a single integrated circuit block. This eliminates the need for separate high value resistors and other discrete components, reducing device size and cost while maintaining full operational capability
Solution Approach 2:
The bias circuit serves as an intermediary that replaces traditional high value resistor-based biasing networks. By introducing this active circuit with current mirrors and cascode devices, the patent achieves the same biasing function without requiring large passive components, thus reducing device complexity
Data Source
AI summary
A bias circuit may generate a one or more bias outputs for a crystal oscillator. The bias circuit may include a first current mirror, a second current mirror and a third current mirror. A capacitor may be coupled between the second current mirror and the third current mirror. In operation, a first bias output may be generated by the third current mirror, and a second bias output may be generated by the second current mirror. The first bias output and second bias output may be coupled to a crystal oscillator.