Crystal-Less LO Calibration Using RX Tone Feedback
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Solution Overview
Problem
Wireless system chips require accurate frequency calibration to comply with ETSI and FCC spectrum emission regulations, but existing solutions rely on off-chip crystal oscillators, which increase BOM costs and PCB area, and have stability and accuracy issues with on-chip active oscillators.
Innovation Solution
A crystal-less wireless system design using an on-chip active oscillator with a frequency synthesizer and calibration scheme that adjusts the LO signal by detecting a calibration tone in the down-converted RX signal to ensure accurate frequency setting, reducing reliance on external oscillators and enabling cost-effective frequency calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an off-chip crystal oscillator is used to provide reference clock, then frequency stability and accuracy are improved, but BOM cost and PCB area increase
Solution Approach 1:
The patent extracts the oscillator function from the external crystal component and integrates it into the wireless system chip itself. The active oscillator circuit is implemented on-chip using standard CMOS processes, eliminating the need for external crystal oscillators and reducing PCB area while maintaining frequency generation capability.
Solution Approach 2:
The patent combines the oscillator function with the wireless system chip by integrating the active oscillator circuit directly on the chip. This merging of functions allows the chip to generate its own reference clock without requiring separate external oscillator components, thereby reducing component count and PCB area.
2Reliability
If an off-chip crystal oscillator is used to provide reference clock, then frequency stability and accuracy are improved, but BOM cost increases
Solution Approach 1:
The patent removes the external crystal oscillator component from the bill of materials by integrating the oscillator function on-chip. This extraction eliminates the need to purchase and assemble external crystal components, directly reducing BOM cost while providing frequency generation capability through the integrated active oscillator.
Solution Approach 2:
The patent uses standard CMOS process components to create the active oscillator, replacing expensive external crystal oscillators with inexpensive on-chip circuit elements. The use of standard process components significantly reduces material costs while achieving the required frequency generation function.
3Area of stationary object
If an on-chip active oscillator is used to generate reference clock, then BOM cost and PCB area are reduced, but frequency accuracy and stability deteriorate
Solution Approach 1:
The patent implements a feedback-based frequency calibration system that measures the actual frequency output of the active oscillator and adjusts control parameters to compensate for frequency deviations. This closed-loop calibration process corrects accuracy errors inherent in on-chip oscillators, enabling frequency accuracy comparable to external crystal oscillators while maintaining the area benefits of integration.
Solution Approach 2:
The patent adjusts operational parameters of the active oscillator through calibration, including control voltage, current, and circuit configuration parameters. By dynamically changing these parameters based on measured frequency output, the system compensates for manufacturing variations and environmental effects, improving frequency accuracy without requiring external components.
4Reliability
If frequency calibration is implemented using external reference, then frequency accuracy is improved, but device complexity increases
Solution Approach 1:
The patent implements a self-calibration mechanism where the wireless system chip calibrates its own active oscillator using internal measurement and adjustment circuits. The calibration system uses the chip's own receiver and signal processing capabilities to measure frequency accuracy and adjust the oscillator parameters, eliminating the need for external calibration equipment and reducing overall system complexity.
Solution Approach 2:
The patent uses the wireless system chip's existing receiver and signal processing circuits for dual purposes: normal signal reception and frequency calibration measurement. By making these circuits multi-functional, the patent avoids adding dedicated calibration hardware, thereby improving frequency calibration accuracy without significantly increasing device complexity.
Data Source
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AI summary
A wireless system includes a local oscillator (LO) signal generation circuit, a receiver (RX) circuit, and a calibration circuit. The LO signal generation circuit generates an LO signal according to a reference clock. The LO signal generation circuit includes an active oscillator. The active oscillator generates the reference clock, wherein the active oscillator includes at least one active component, and does not include an electromechanical resonator. The RX circuit generates a down-converted RX signal by performing down-conversion upon an RX input signal according to the LO signal. The calibration circuit generates a frequency calibration control output according to a signal characteristic of the down-converted RX signal, and outputs the frequency calibration control output to the LO signal generation circuit. The LO signal generation circuit adjusts an LO frequency of the LO signal in response to the frequency calibration control output.