Low-Power Local Oscillator Circuit With Multi-Phase Harmonic Recombination
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Solution Overview
Problem
Local oscillator (LO) generation in wireless communication systems experiences signal degradation and interference due to power amplifier coupling, leading to frequency pulling and performance degradation, which traditional fractional divider/multipliers and resistor-capacitor circuits fail to adequately address without introducing phase noise and performance degradation.
Innovation Solution
A transmitter circuit with a multi-phase divider and an I/Q generator using a ring oscillator circuit, which eliminates the need for duty-cycle correction and reduces phase noise by generating phase-shifted clock signals and using active bandpass filters to suppress unwanted harmonics, thereby stabilizing the voltage-controlled oscillator and improving frequency conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional fractional divider/multipliers are used in the LO path to mitigate PA-to-OSC pulling, then frequency pulling is reduced, but duty cycle correction causes phase noise and performance degradation
Solution Approach 1:
The patent divides the LO generation into separate functional blocks: a VCO for frequency generation, a multi-phase divider for frequency division and phase generation, and an I/Q generator for signal modulation. This segmentation allows each block to be optimized independently, avoiding the duty cycle correction issue while maintaining frequency stability.
Solution Approach 2:
The patent extracts the duty cycle correction function from the LO path by using a ring oscillator-based I/Q generator that naturally produces clean square waves without requiring duty cycle correction, thereby eliminating the source of phase noise while maintaining frequency pulling mitigation.
2Adaptability or versatility
If RCCR circuit implementation is used for I/Q signal generation, then baseband processing is enabled, but RC attenuation and input impedance issues cause performance degradation
Solution Approach 1:
The patent replaces the passive RCCR circuit implementation with an active ring oscillator-based I/Q generator. This substitution eliminates the RC attenuation and input impedance problems by using active devices (transistors) to generate the I/Q signals directly, maintaining signal quality while enabling baseband processing.
3Power
If power amplifier coupling is present in the LO path, then signal amplification is achieved, but frequency pulling and signal degradation occur
Solution Approach 1:
The patent extracts the power amplification function from the LO path by placing the power amplifier only in the final RF output stage, not in the LO generation path. The LO path uses a VCO followed by dividers and I/Q generators, isolating the frequency-sensitive LO signals from the high-power amplification that causes pulling.
Data Source
AI summary
A circuit for providing a fractional divider/multiplier using harmonic recombination may include a power amplifier, an oscillator coupled to the power amplifier, and a divider coupled to the oscillator. In one or more implementations, the divider is configured to generate one or more phases of a harmonic from the oscillator to reduce signal interference from the power amplifier. In one or more implementations, the divider includes a divide-by-M divider, where M is a positive integer, and an array of transconductance cells coupled to the output of the divide-by-M divider. In one or more implementations, the divider includes an inductor or a filter coupled to the output of the array of transconductance cells. In one or more implementations, the oscillator includes a logical gate and a resistor-capacitor circuit coupled in series feedback with a multi-stage ring oscillator. The oscillator may include a divider coupled to the multi-stage ring oscillator.