Crystal-Less LO Frequency Calibration Using an Active Oscillator
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Solution Overview
Problem
Current wireless system chips rely on off-chip crystal oscillators, which increase BOM costs and PCB area, and require accurate frequency calibration to comply with regulatory standards, but internal stability and accuracy of on-chip active oscillators are lower, necessitating innovative frequency calibration schemes.
Innovation Solution
A crystal-less wireless system design using an active oscillator without electromechanical resonators, integrated into the wireless system chip, which includes a local oscillator generation circuit, receiver circuit, and calibration circuit to generate and adjust the LO signal frequency based on signal characteristics of the down-converted RX signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an off-chip crystal oscillator is used to generate the reference clock, then the frequency accuracy and stability are improved, but the BOM cost and PCB area increase
Solution Approach 1:
The patent merges the oscillator function into the wireless system chip by integrating an active oscillator circuit, eliminating the need for a separate off-chip crystal oscillator. This consolidation reduces PCB area and BOM cost while maintaining frequency accuracy through on-chip integration and calibration mechanisms.
Solution Approach 2:
The patent extracts the electromechanical resonator (crystal) from the system and replaces it with an active oscillator circuit that uses only active components and passive components integrated on the chip. This extraction eliminates the need for external crystal components while preserving the essential oscillation function.
2Measurement precision
If an off-chip crystal oscillator is used to generate the reference clock, then the frequency accuracy and stability are improved, but the BOM cost increases
Solution Approach 1:
The patent merges the oscillator function into the wireless system chip by integrating an active oscillator circuit, eliminating the need for a separate off-chip crystal oscillator. This consolidation reduces PCB area and BOM cost while maintaining frequency accuracy through on-chip integration and calibration mechanisms.
Solution Approach 2:
The patent replaces the expensive off-chip crystal oscillator with a cost-effective active oscillator circuit implemented using standard CMOS or bipolar process components. This substitution significantly reduces BOM cost while achieving acceptable frequency accuracy through calibration.
3Area of stationary object
If an active oscillator without electromechanical resonator is used, then the BOM cost and PCB area are reduced, but the internal stability and accuracy deteriorate
Solution Approach 1:
The patent implements a feedback-based frequency calibration mechanism where the down-converted RX signal is analyzed to generate a frequency calibration control output. This feedback loop continuously adjusts the LO signal generation circuit to compensate for frequency drift and maintain stability despite using an active oscillator without electromechanical resonator.
Solution Approach 2:
The patent dynamically adjusts the LO frequency parameter based on the frequency calibration control output derived from the down-converted signal characteristics. This parameter adjustment compensates for the lower inherent stability of active oscillators, maintaining reliable operation.
4Area of stationary object
If an active oscillator without electromechanical resonator is used, then the BOM cost and PCB area are reduced, but the frequency calibration complexity increases
Solution Approach 1:
The patent implements a self-calibrating mechanism where the wireless system chip performs its own frequency calibration using its receiver circuit and LO signal generation circuit. The down-converted RX signal is directly used to generate calibration control outputs, eliminating the need for external calibration equipment or complex external circuits.
Solution Approach 2:
The patent makes the receiver circuit and LO signal generation circuit serve dual functions: normal signal reception and frequency calibration. This multi-functionality reduces the need for dedicated calibration hardware, simplifying the overall system despite the increased calibration requirements.
Data Source
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.