DC-Coupled RF Modulator With Common-Mode Bias Control
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Solution Overview
Problem
Existing RF transmitters are sensitive to input common-mode voltages, which can degrade modulator performance, and rely on intermediate frequency amplifiers to manage these voltages, consuming power and increasing circuit area.
Innovation Solution
A modulator circuit that controls common-mode voltage without an intermediate frequency amplifier by generating a bias voltage as a sum of the desired common-mode voltage and the voltage drop across a load circuit, ensuring optimal common-mode voltage is applied to the modulator input.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If intermediate frequency amplifiers are used to manage common-mode voltages, then modulator performance is maintained, but power consumption increases and circuit area increases
Solution Approach 1:
The patent removes the intermediate frequency amplifier from the signal path between DAC and modulator. Instead, it extracts only the necessary common-mode voltage control function and implements it directly at the modulator input through a common-mode control circuit that generates appropriate bias voltages, eliminating the need for the power-consuming IF amplifier while maintaining modulator performance.
Solution Approach 2:
The modulator circuit incorporates its own common-mode voltage control capability through integrated bias voltage generation circuits. The common-mode control circuit within the modulator self-regulates the common-mode voltage at its input by generating appropriate bias voltages based on feedback, making the system self-sufficient without requiring external IF amplifiers.
2Reliability
If intermediate frequency amplifiers are used to manage common-mode voltages, then modulator performance is maintained, but circuit area increases
Solution Approach 1:
The patent removes the intermediate frequency amplifier from the signal path between DAC and modulator. Instead, it extracts only the necessary common-mode voltage control function and implements it directly at the modulator input through a common-mode control circuit that generates appropriate bias voltages, eliminating the need for the power-consuming IF amplifier while maintaining modulator performance.
Solution Approach 2:
The patent combines the common-mode voltage control function with the modulator circuit itself. The bias voltage generation circuits and common-mode control are integrated into the modulator block, merging previously separate functions (IF amplification and modulation) into a single integrated unit, thereby reducing total circuit area.
3Device complexity
If common-mode voltage is not controlled, then circuit complexity is reduced, but modulator performance degrades
Solution Approach 1:
The patent introduces a common-mode control circuit as an intermediary between the DAC output and the modulator input. This control circuit generates appropriate bias voltages that mediate the common-mode voltage level, ensuring the modulator receives the correct common-mode voltage without requiring complex external control systems or IF amplifiers.
Solution Approach 2:
The common-mode control circuit employs feedback mechanisms to monitor and regulate the common-mode voltage at the modulator input. By using feedback from the actual voltage conditions to adjust the bias voltage generation, the system maintains precise common-mode voltage control with relatively simple circuitry, avoiding the need for complex open-loop control systems.
Data Source
AI summary
A radio frequency transmitter includes a digital-to-analog converter (DAC), a load circuit, and a modulator circuit. The load circuit is coupled to an output of the DAC. The modulator circuit is coupled to the DAC and the load circuit. The modulator circuit includes a driver circuit configured to provide a bias voltage to the load circuit, and an amplifier configured to receive an output of the DAC biased by an output of the load circuit.