VCO Pulling Compensation Circuit for Baseband Signal Distortion
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Solution Overview
Problem
VCO pulling in mobile wireless communication devices causes signal distortion due to undesired coupling between components, leading to frequency shifts and distortion in the signal output by the voltage controlled oscillator (VCO), which results in transmit signal distortion.
Innovation Solution
A VCO pulling compensation circuit is integrated into the electronic device, comprising an exponential block, filter, and emulated transmitter gain block to compensate for transmit distortion by predistorting the baseband signal, using a receiver to sense the transmit signal and adjust the baseband signal to cancel out distortion caused by aggressing signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If components are integrated at package or chip level to reduce device size, then device integration is improved, but coupling between power amplifier harmonics and VCO increases causing signal distortion
Solution Approach 1:
A VCO pulling compensation circuit is introduced as an intermediary component between the power amplifier and VCO. This circuit receives the baseband signal and applies predistortion compensation based on sensed transmit signal characteristics, effectively mediating the harmful interaction by pre-correcting the signal to cancel out expected distortion from coupling.
Solution Approach 2:
The compensation circuit implements feedback by sensing the transmit signal and using this information to adjust the baseband signal. The circuit continuously monitors the transmit signal characteristics and dynamically modifies the baseband signal to compensate for VCO pulling effects, creating a closed-loop system that actively counteracts distortion.
2Object-affected harmful factors
If shielding cavities are added to reduce coupling between power amplifier and VCO, then signal distortion is reduced, but device complexity increases
Solution Approach 1:
The patent replaces the mechanical/physical shielding approach with an electronic signal processing solution. Instead of using physical barriers (shielding cavities) to prevent coupling, the invention uses electronic predistortion and feedback mechanisms to compensate for the coupling effects, substituting a complex mechanical structure with a more compact electronic circuit.
3Object-affected harmful factors
If predistortion compensation is applied to baseband signal, then transmit signal distortion is mitigated, but circuit complexity increases
Solution Approach 1:
The VCO pulling compensation circuit is merged with the existing baseband signal path and transmitter architecture. The compensation functions are integrated into the signal flow rather than being added as completely separate systems, combining multiple functions (signal sensing, predistortion, feedback processing) into a unified circuit block that works synergistically with existing components.
Data Source
AI summary
An electronic device includes a transmitter with a baseband input for a baseband signal, a mixer downstream from the baseband input, and a phase-locked loop (PLL) having a voltage controlled oscillator (VCO) and a phase detector coupled thereto, the VCO coupled to the mixer. A power amplifier is downstream from the mixer, and generates at least one aggressing signal that would otherwise generate an output pull of the VCO, causing transmit distortion on a transmit signal. A receiver is coupled to the power amplifier and has a sense input configured to receive the transmit signal. A VCO pulling compensation circuit is coupled to the baseband input and is configured to compensate the at least one baseband signal for the transmit distortion based upon the sensed transmit signal.