Ground Reference Circuit Using Current Mirror for IR Drop Compensation
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Solution Overview
Problem
Power converters face issues with parasitic IR drops affecting the stability of the internal ground reference, leading to load regulation problems, especially during lower duty cycle operations, which impact the output voltage.
Innovation Solution
A ground reference system is integrated with the controller to dynamically shift the ground reference used by the bandgap voltage reference circuit, compensating for parasitic currents by amplifying a sample current using a current mirror and RC filters to provide a stable ground reference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional ground reference is used in the voltage reference circuit, then the circuit structure is simple, but parasitic IR drops cause ground reference instability and load regulation problems
Solution Approach 1:
The ground reference circuit is segmented into multiple functional blocks: a current mirror circuit that amplifies the sample current, an RC filter circuit that filters the amplified current, and a dedicated ground reference terminal. This segmentation allows each block to perform its specific function optimally, resolving the contradiction between stability and complexity by organizing the complex circuit into manageable, functionally-specific segments.
Solution Approach 2:
The patent introduces an intermediary ground reference terminal that is electrically isolated from the system ground terminal through the resistor and current mirror circuit. This intermediary terminal serves as a mediator between the voltage reference circuit and the system ground, blocking parasitic currents while allowing the ground reference to remain stable. The RC filter circuit acts as another intermediary that filters out noise and instability before the ground reference is established.
2Reliability
If the ground reference is shared with the system ground, then the circuit design is simplified, but parasitic currents from switching operations affect the reference voltage stability
Solution Approach 1:
The patent extracts the ground reference function from the system ground by creating a separate, dedicated ground reference terminal. The current mirror circuit extracts and amplifies the sample current from the switching node, and the RC filter extracts the stable DC component while filtering out switching noise. This extraction separates the sensitive voltage reference circuit from the noisy system ground, resolving the contradiction between reliability and complexity.
Solution Approach 2:
A resistor is introduced as an intermediary element between the ground reference terminal and the system ground terminal. This resistor acts as a barrier that blocks parasitic currents from the system ground from affecting the ground reference, while still allowing the ground reference to be established. The RC filter circuit serves as another intermediary that mediates between the amplified current and the ground reference terminal, filtering out high-frequency noise.
3Manufacturing precision
If parasitic IR drops are not compensated, then the circuit operation is straightforward, but load regulation performance deteriorates during lower duty cycle operations
Solution Approach 1:
The patent implements a feedback mechanism where a sample current is taken from the switching node and fed into the current mirror circuit. This sample current reflects the actual operating conditions including parasitic IR drops. The current mirror amplifies this feedback signal, and the RC filter processes it to generate a compensation voltage that is applied to the ground reference terminal. This feedback loop continuously compensates for parasitic effects, resolving the contradiction between output voltage precision and compensation complexity.
Solution Approach 2:
The ground reference circuit serves itself by using the sample current from its own switching node to generate the compensation voltage. The current mirror circuit uses the sampled parasitic current to create an equal and opposite compensation voltage at the ground reference terminal, effectively self-correcting for parasitic IR drops without requiring external intervention. This self-service approach achieves high output voltage precision while managing the complexity of parasitic compensation.
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 solution stabilizes the ground reference, reducing the impact of parasitic IR drops and maintaining consistent output voltage levels by using a dedicated ground reference that is less affected by system parasitics.
Implementation Method 1
amplifying a sample current using a current mirror to provide a stable ground reference
Implementation Method 2
amplifying a sample current using a current mirror and RC filters to provide a stable ground reference
Data Source
AI summary
A ground reference circuit to generate a ground reference for a voltage reference circuit includes a resistor coupled in series with a transistor via a current mirror. The resistor is coupled between a ground reference terminal of the voltage reference circuit and a ground terminal of a power converter. The transistor control terminal is configured to receive a pulse width modulation (PWM) control signal having a duty cycle similar to a switching element duty cycle of the power converter. The current mirror circuit is coupled between a current terminal of the transistor and the ground reference terminal. A controller configured to control the switching element duty cycle may include the ground reference circuit, along with the voltage reference circuit, and a PWM circuit configured to determine the switching element duty cycle based on a comparison between a reference voltage provided by the voltage reference circuit and the converter output voltage.