Polar Modulation Circuit Using Normalized Delay to Cut Spurious RF
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Solution Overview
Problem
Existing RF communication technologies face challenges with polar modulation, including spurious frequencies generated due to large phase shifts and errors such as Error Vector Magnitude (EVM) in Cartesian modulation, particularly when phase symbols exceed certain limits.
Innovation Solution
A polar phase or frequency modulator is developed, comprising a normalized delay circuit and calculator that processes phase and frequency samples to generate digital delay control values, allowing for precise modulation of carrier signals without exceeding phase shift limits, thereby reducing spurious emissions and EVM.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If polar modulation is used to directly modulate the phase of the carrier frequency, then amplitude and phase can be processed separately leading to low cost implementation, but spurious frequencies are generated particularly when phase shift exceeds 360 degrees
Solution Approach 1:
The patent implements dynamic phase unwrapping that continuously tracks and adjusts phase values to maintain them within the -180 to +180 degree range. The system dynamically detects when phase transitions would exceed this range and applies corrective unwrapping operations, transforming the static phase modulation approach into a dynamic one that adapts to prevent spurious frequency generation while preserving the simplicity of polar modulation.
Solution Approach 2:
The patent changes the parameter representation by introducing unwrapped phase values that are constrained to a specific range (-180 to +180 degrees). Instead of allowing phase to freely exceed 360 degrees, the system transforms phase parameters through unwrapping operations, changing the mathematical representation to eliminate discontinuities that cause spurious frequencies while maintaining the underlying modulation integrity.
2Adaptability or versatility
If Cartesian modulation is used with multiple phase symbols, then modulation capacity is increased, but Error Vector Magnitude (EVM) errors occur when the number of phase symbols exceeds a certain limit
Solution Approach 1:
The patent implements a feedback mechanism where the system continuously monitors phase transitions and applies unwrapping corrections based on detected phase exceedances. This feedback loop ensures that phase symbols remain within the optimal range for accurate representation, preventing EVM errors that would otherwise occur with excessive phase symbols in Cartesian modulation by actively correcting phase values in real-time.
Solution Approach 2:
The patent applies preliminary phase unwrapping processing before the phase symbols are used for modulation. By pre-processing the phase values to ensure they fall within the -180 to +180 degree range, the system prevents EVM errors from occurring in the first place, rather than correcting them after they manifest. This preliminary action ensures reliable modulation capacity expansion.
Data Source
AI summary
The present disclosure relates to a polar phase or frequency modulator comprising: a normalized delay circuit (602) configured to delay edges of an input carrier signal (CLK_IN) based on normalized delay control values (φi) to generate a modulated output signal (RF_OUT); and a normalized delay calculator (604) configured to receive the modulated output signal (RF_OUT) and to generate the normalized delay control values (φi).