Buck Converter Offset Compensation for Ripple-Induced Voltage Error
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Solution Overview
Problem
Conventional buck switching regulators experience accuracy issues due to ripple-induced offset in the output voltage, which affects the regulation of the output signal, especially when using fixed on-time control and capacitors with high equivalent series resistance (ESR).
Innovation Solution
Incorporating an offset compensation circuit that generates an offset compensation signal to adjust the comparator's input offset in the feedback control loop, using an operational transconductance amplifier (OTA) to sense the reference and feedback signals, and injecting a ripple signal into the feedback loop to regulate the output voltage, thereby minimizing ripple-induced offsets and maintaining fast transient response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ripple signal is injected into the feedback loop for regulation, then output voltage regulation is improved, but ripple-induced offset in the output voltage increases
Solution Approach 1:
The patent converts the harmful ripple-induced offset into a beneficial signal by intentionally injecting a ripple signal into the feedback loop. The offset compensation circuit then uses this injected ripple to generate a compensating signal that cancels the harmful offset, thereby improving output voltage regulation accuracy while maintaining the necessary ripple for control.
Solution Approach 2:
The offset compensation circuit acts as an intermediary between the feedback loop and the control circuit. It processes the feedback signal, extracts the ripple component, generates a compensating signal, and injects it back into the appropriate location to cancel the harmful offset without disrupting the main regulation function.
2Device complexity
If fixed on-time control is used, then circuit complexity is reduced, but output voltage accuracy deteriorates due to ripple-induced offset
Solution Approach 1:
The patent extracts the ripple signal from the feedback voltage and processes it separately through the offset compensation circuit. This allows the main fixed on-time control to remain simple while the extracted ripple component is used to generate compensation that improves accuracy without adding significant complexity to the core control logic.
3Power
If capacitors with high ESR are used, then ripple signal generation is enhanced, but output voltage accuracy deteriorates due to increased ripple-induced offset
Solution Approach 1:
The patent converts the harmful effect of high ESR capacitors (which generate large ripple-induced offsets) into a benefit by using the injected ripple signal to create a compensating signal. The offset compensation circuit generates a signal that specifically counteracts the offset caused by high ESR, allowing the use of such capacitors without sacrificing accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The offset compensation circuit effectively cancels out ripple-induced offsets, improving the accuracy of the output voltage regulation and maintaining fast transient response by adjusting the comparator's input offset, resulting in a substantially constant output voltage with reduced ripple effects.
Implementation Method 1
an operational transconductance amplifier (OTA) to sense a reference voltage and a feedback signal indicative of the regulator output voltage and to generate the offset compensation signal
Implementation Method 2
The switch node is coupled to an LC filter circuit including an output inductor and an output capacitor to generate an output voltage having substantially constant magnitude
Implementation Method 3
an LC filter circuit including an output inductor and an output capacitor
Implementation Method 4
the voltage across the inductor reverses and the current through the inductor reduces during this period. As a result, the inductor current ripples above and below the nominal output current. A relatively constant output voltage is maintained by the output capacitor
Data Source
AI summary
A buck switching regulator includes a feedback control circuit including a first gain circuit generating a first feedback signal indicative of the regulated output voltage; a ripple generation circuit generating a ripple signal that is injected to the first feedback signal; and a comparator receiving a first reference signal and the first feedback signal to generate a comparator output signal. The switching regulator further includes an offset compensation circuit including a second gain circuit generating a second feedback signal indicative of the regulated output voltage; and an operational transconductance amplifier (OTA) configured to receive the second feedback signal and the first reference signal and to generate an output signal. The output signal of the OTA is coupled to the comparator to adjust an offset to the comparator so as to cancel the offset at the regulated output voltage due to the injected ripple signal.