PWM Amplifier Feedback Controller Pulse Constraint Logic
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Solution Overview
Problem
PWM amplifiers with feedback control face challenges due to variations in power supply voltage, leading to high-frequency oscillations and audible distortion, particularly when the supply voltage fluctuates or has poor load regulation, which limits their performance and reliability.
Innovation Solution
The introduction of Pulse-constraint Logic ensures that for every input pulse, there is only one output pulse, implemented through a feedback controller with a pulse conditioner that modifies the switching control signal based on predetermined constraints, preventing unnecessary high-frequency activity and eliminating spurious low-frequency output components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If feedback control is applied to PWM amplifier to suppress modulation effects, then output amplitude accuracy is improved, but the system becomes sensitive to power supply voltage variations causing high-frequency oscillations and audible distortion
Solution Approach 1:
The patent introduces a pulse conditioner as an intermediary component between the feedback controller and the output stage. This pulse conditioner processes the feedback control signal to ensure it meets specific pulse width and timing constraints before being applied to the PWM amplifier, thereby preventing the propagation of control signals that could cause oscillations or distortion under power supply variations.
Solution Approach 2:
The pulse conditioner performs preliminary conditioning on the control signal by enforcing minimum and maximum pulse width constraints and ensuring proper pulse spacing before the signal reaches the amplifier. This preliminary action prevents the amplifier from receiving control signals that would cause harmful oscillations or distortion, especially under varying power supply conditions.
2Measurement precision
If pulse width is increased to compensate for supply voltage drop, then output signal amplitude is maintained, but adjacent pulses collide causing reduced pulse-repetition frequency and audible distortion
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the pulse width constraints based on the operating conditions. The pulse conditioner enforces minimum and maximum pulse width limits that prevent pulses from becoming too wide and colliding with adjacent pulses, even when supply voltage drops and compensation is needed. This maintains output amplitude while preventing the harmful effect of pulse collision and audible distortion.
3Adaptability or versatility
If feedback loop operates with poor load regulation power supply, then system can handle varying load conditions, but high-frequency oscillations occur disrupting the feedback loop and causing gross audible distortion
Solution Approach 1:
The pulse conditioner serves as a protective intermediary that filters and conditions the control signal before it reaches the PWM amplifier. By enforcing pulse width and timing constraints, it prevents the amplification of high-frequency noise and oscillations that can occur when the feedback loop interacts with a poorly regulated power supply, thus maintaining feedback loop stability while still handling varying load conditions.
Data Source
AI summary
A feedback controller in a PWM amplifier comprises a signal input for receiving a pulse width modulated (PWM) input signal (Vin) whose duty cycle represents a desired analogue output signal. A feedback loop filter 518 generates a filtered error signal (Vint) comprising a filtered representation of differences between the input signal (Vin) and a feedback signal (Vfb). A comparator (520) compares the filtered error signal with a reference to generate a provisional PWM switching control signal (C) for controlling the PWM amplifier (500). A pulse conditioner (532) receives both the provisional PWM switching control signal (C) and the PWM input signal (X=Vin) and outputs to the amplifier (500) a conditioned PWM switching control signal (Y), modified in accordance with predetermined constraints in relation to the PWM input signal. The pulse conditioner includes a single pulse function (534) whereby only a single pulse is permitted for every pulse in the input signal, thereby eliminating oscillations that can otherwise Occur under over-voltage supply conditions. Missing pulse and minimum pulse width functions (536, 538) can also be provided.