Differential PWM Modulator Circuit With Current Comparator Noise Rejection
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Solution Overview
Problem
High-frequency pulse-width modulation (PWM) modulators in class-D power amplifiers face increased disturbances and higher area/current consumption, reducing the effectiveness of in-phase modulation and increasing common mode harmonics, which are not effectively addressed by existing technologies.
Innovation Solution
A fully-differential PWM modulator circuit is introduced, utilizing current comparators instead of voltage comparators, which enhances robustness against disturbances, reduces component count, and eliminates common-mode feedback, thereby minimizing area and power consumption while maintaining immunity to common-mode noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If switching frequency is increased in class-D power amplifiers, then LC demodulation filter cost is reduced, but disturbances increase due to increased switching slopes
Solution Approach 1:
The patent divides the single-ended modulator into a fully differential architecture with separate positive and negative signal paths. This segmentation allows independent control of each path, reducing the impact of switching slopes and disturbances in one path on the overall signal quality.
Solution Approach 2:
The patent converts the harmful effect of high switching slopes into a benefit by using differential signaling. The common-mode disturbances generated by high-frequency switching are rejected by the differential output stage, which subtracts the common-mode components, thereby converting the harmful switching noise into a rejectable common-mode signal.
2Power
If switching frequency is increased, then LC filter cost is reduced, but in-phase modulation benefits are lost
Solution Approach 1:
The modulator is segmented into fully differential operation with separate in-phase and quadrature paths. This allows the preservation of in-phase modulation benefits at high frequencies by maintaining precise control over the differential signal paths and their respective timing.
Solution Approach 2:
The patent changes the modulation approach by implementing a fully differential architecture that maintains modulation effectiveness through differential signaling. The parameter change from single-ended to differential operation preserves the benefits of in-phase modulation even at high switching frequencies where traditional approaches fail.
3Ease of manufacture
If conventional PWM modulator is used, then implementation is simple, but area and current consumption are high
Solution Approach 1:
The patent merges the common-mode control function into the differential architecture itself, eliminating the need for separate common-mode feedback circuits. The differential pair inherently provides common-mode rejection, allowing the removal of additional control circuits that would otherwise be required, thereby reducing area and power consumption.
Solution Approach 2:
The patent extracts and removes the common-mode feedback circuitry from the conventional PWM modulator design. By using fully differential operation, the explicit common-mode control is taken out as it becomes inherently managed by the differential architecture, reducing component count and power consumption.
4Reliability
If common-mode feedback is included, then common-mode control is improved, but component count and power consumption increase
Solution Approach 1:
The differential amplifier circuit serves its own common-mode control needs through its inherent differential operation. The circuit automatically rejects common-mode signals through its symmetric structure and differential output, making external common-mode feedback circuits unnecessary. The system is self-sufficient in managing common-mode control.
Solution Approach 2:
The common-mode control function is merged into the core differential amplifier operation itself. Rather than being a separate control loop, common-mode rejection is an intrinsic property of the differential architecture, combining signal amplification and common-mode rejection into a single integrated function.
Data Source
AI summary
An embodiment pulse-width modulation (PWM) modulator circuit comprises a first half-bridge stage having a first output node and a second half-bridge stage having a second output node. The first output node and the second output node are configured to have an electrical load coupled therebetween to apply thereto a PWM-modulated output signal. The circuit comprises a differential stage having input nodes configured to receive an input signal applied between the input nodes and produce a differential control signal for the first half-bridge stage and the second half-bridge stage. A current comparator is arranged intermediate the differential stage and the first and second half-bridge stages. The current comparator is configured to produce a PWM-modulated drive signal to drive the half-bridge stages as a function of the input signal applied between the input nodes in the differential stage.