Crystal Oscillator Bias Control for Receiver Spur Sensitivity
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Solution Overview
Problem
Conventional communication systems face challenges in minimizing spurs in crystal oscillators, which are often addressed through floor-planning or spatial separation from other circuits, but these methods are not always effective.
Innovation Solution
A circuit and method that dynamically adjust the biasing conditions of a crystal oscillator based on the received signal strength, using a received signal strength indicator (RSSI) to apply different current levels and a control loop to supply a reference clock signal, thereby controlling the oscillating signal's amplitude and reducing sensitivity to spurs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the crystal oscillator is spaced away from other circuits or careful floor-planning is used, then spur sensitivity is reduced, but device complexity and layout constraints increase
Solution Approach 1:
The patent changes the electrical parameters of the crystal oscillator by dynamically adjusting its biasing conditions based on received signal strength. When the incoming signal is weak, the oscillator receives a first biasing condition (lower current) to reduce spur sensitivity. When the signal is strong, a second biasing condition (higher current) is applied to improve signal-to-noise ratio. This parameter adjustment resolves the contradiction by controlling spur sensitivity through electrical biasing rather than physical layout constraints.
2Reliability
If the crystal oscillator uses higher current biasing, then signal-to-noise ratio improves, but spur sensitivity increases
Solution Approach 1:
The patent implements dynamic biasing control where the crystal oscillator's current is adjusted in real-time based on the received signal strength indicator (RSSI). The system transitions from a static biasing approach to a dynamic one, switching between first and second biasing conditions according to signal strength. This resolves the contradiction by applying higher current only when necessary (strong signals) and using lower current when spurs are more problematic (weak signals).
Solution Approach 2:
The system uses feedback from the received signal strength indicator to control the biasing condition of the crystal oscillator. The RSSI monitors the strength of incoming signals and provides feedback that triggers appropriate biasing adjustments. This closed-loop control ensures that the oscillator operates at optimal current levels, improving signal-to-noise ratio when needed while reducing spur sensitivity when signal strength is low.
Data Source
AI summary
A circuit includes, in part, a receiver, a received signal strength indicator (RSSI), and an oscillator. The receiver receives an incoming signal and an oscillating signal. The RSSI is responsive to the receiver and generates an output signal representative of the strength of the incoming signal. The oscillator receives different biasing conditions in response to different outputs of the RSSI. The oscillator generates the oscillating signal received by the receiver. The oscillator receives a first biasing condition when the incoming signal is detected as having a strength lower than or equal to a predetermined threshold value and a second biasing condition when the incoming signal is detected as having a strength higher than the predetermined threshold value. The first biasing condition may be defined by a first current, and the second biasing condition may be defined by a sum of the first current and a second current.