Two-Point Modulator Gain Calibration for Fast Channel Switching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional two-point modulators face challenges in accurately calibrating gain mismatch between modulation paths, particularly due to process, voltage, and temperature (PVT) dependencies, which can lead to erroneous modulation and require lengthy calibration processes that are not suitable for fast channel switching operations.
Innovation Solution
A calibration circuit with a phase detector and gain control circuit is implemented to compare reference and feedback frequency signals, generating a phase detect signal that adjusts the gain of the modulation path to match the gains of both paths, ensuring accurate modulation by using a bang-bang phase detector, sign detector, and correlator circuit to generate a gain control signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional calibration procedures are used to match gains of modulation paths, then gain accuracy is improved, but calibration time becomes excessively long and unsuitable for fast channel switching
Solution Approach 1:
The patent replaces conventional lengthy calibration procedures with a streamlined calibration sequence that uses a bang-bang phase detector and correlator circuit to rapidly determine gain mismatch. The calibration is performed by injecting test signals and measuring phase detector output during specific time intervals, reducing calibration time from potentially seconds to mere microseconds while maintaining accuracy through digital signal processing.
Solution Approach 2:
The patent changes the calibration approach by using digital domain processing instead of analog adjustment methods. The gain control signal is generated through digital correlation of phase detector outputs with known test signal patterns, allowing rapid computation of gain mismatch and immediate digital adjustment without mechanical or analog calibration steps.
2Reliability
If gain calibration is performed to address PVT dependencies, then modulation accuracy is improved, but circuit complexity and power consumption increase
Solution Approach 1:
The patent substitutes complex analog gain adjustment circuits with digital signal processing elements. The bang-bang phase detector, sign detector, and correlator circuit work in the digital domain to measure and compensate for gain mismatch, eliminating the need for complex analog variable gain amplifiers or multiple calibration components while maintaining compensation for PVT dependencies.
Solution Approach 2:
The calibration circuit uses the existing phase detector and signal paths within the PLL to perform self-calibration. The same phase detector used for frequency locking also detects gain mismatch when test signals are injected, and the correlator circuit processes this information to generate appropriate gain control signals, making the system self-calibrating without requiring external calibration equipment or additional complex circuitry.
3Measurement precision
If conventional calibration methods are used, then gain matching can be achieved, but the process is sensitive to PVT variations requiring repeated calibration
Solution Approach 1:
The patent implements continuous or periodic calibration by keeping the calibration circuit active and ready to perform measurements. The system can rapidly re-calibrate when channel switching occurs or when PVT conditions change, using the same fast calibration sequence that measures gain mismatch through phase detector output correlation with test signals, ensuring continuous adaptation to changing conditions.
Solution Approach 2:
The calibration system uses feedback from the phase detector to continuously monitor gain mismatch conditions. The correlator circuit processes the phase detector output in real-time, and the resulting gain control signal is fed back to the modulation path to correct gain imbalance, creating a closed-loop system that automatically adapts to PVT variations without requiring manual re-calibration.
Data Source
AI summary
A modulation circuit includes a locked loop circuit with two-point modulation control and a phase-frequency detector configured to compare a reference frequency signal with a feedback frequency signal. A two-point modulation control circuit includes a first modulation path having a controllable gain and coupled to one of the first and second modulation control points and a second modulation path coupled to another of the first and second modulation control points. Gain matching of the first and second modulation paths is accomplished through the operation of a calibration circuit. The calibration circuit includes a phase detector circuit configured to compare the reference frequency signal with the feedback frequency signal to generate a phase detect signal, and a gain control circuit configured to adjust the controllable gain of the first modulation path as a function a correlation of the phase detect signal with signs of the modulation data.