Zero-IF Transceiver LO Division Chain for Reduced VCO Pulling
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Solution Overview
Problem
Modern radio transmitters using zero-IF architecture face significant challenges with VCO pulling, particularly at high harmonic orders, which require complex conversion circuits and are not adequately addressed by existing designs.
Innovation Solution
A radio transmitter circuit comprising a controlled oscillator, divide-by-1.5 circuits, a divide-by-2 circuit, a modulator, and a controller, where the controlled oscillator outputs an oscillation signal that is divided down to achieve a high-order harmonic relation between the local oscillator and oscillation signals, reducing VCO pulling while maintaining design simplicity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-order harmonic relation is used between LO and VCO signals to reduce VCO pulling, then VCO pulling severity is reduced, but circuit complexity increases
Solution Approach 1:
The patent segments the frequency division function into multiple stages: a first divide-by-1.5 circuit, a second divide-by-1.5 circuit, and a divide-by-2 circuit. This segmentation achieves the high-order harmonic relation (divide-by-4.5) while distributing the complexity across simpler, modular stages rather than requiring a single complex conversion circuit.
Solution Approach 2:
The patent combines multiple frequency division operations (1.5x, 1.5x, and 2x division) into an integrated frequency synthesis path. By merging these division stages with the phase-locked loop architecture, the system achieves high-order harmonic relation without requiring a separate complex conversion circuit, thus reducing overall system complexity.
2Device complexity
If traditional frequency division is used to generate LO signal, then circuit design is simple, but VCO pulling is severe
Solution Approach 1:
The patent changes the frequency division ratio parameter from traditional integer division (divide-by-2, divide-by-3) to fractional division (divide-by-1.5). This parameter change enables a higher effective harmonic relation between the VCO and LO signals, reducing VCO pulling while maintaining a relatively simple circuit architecture through the use of standard divide-by-1.5 circuit blocks.
Data Source
AI summary
A method uses a controlled oscillator to output an oscillation signal in accordance with a control signal. The method operates by using a first divide-by-1.5 circuit to convert the oscillation signal into a first divided-down signal, using a second divide-by-1.5 circuit to convert the first divided-down signal into a second divided-down signal, using a divide-by-2 circuit to convert the second divided-down signal into a LO (local oscillator) signal, using a modulator to modulate the LO signal into a RF (radio frequency) signal in accordance with a baseband signal, and using a controller to establish the control signal in accordance with a relative timing between a reference signal and the oscillation signal.