H-Bridge Bidirectional Current Sensing Circuit with Auto-Zero Amplifiers
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Solution Overview
Problem
Conventional bidirectional current sensing circuits for H-bridge circuits suffer from low signal-to-noise ratio due to significant common mode noise, making it difficult to process bidirectional load current measurements effectively.
Innovation Solution
A bidirectional current sensing circuit utilizing a sensing resistor, voltage polarity indicating circuit, and auto-zero amplifiers configured to operate in output and zeroing modes based on voltage polarity, with an output transistor providing a current sensing signal, effectively reducing common mode noise and improving signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a differential amplifier is used to amplify voltage across the sensing resistor, then the bidirectional load current can be sensed, but significant common mode noise is introduced resulting in low signal-to-noise ratio
Solution Approach 1:
The patent divides the sensing function into two separate single-ended sensing paths instead of using one differential amplifier. Each path senses current in one direction through separate sensing resistors (RSENSE1 and RSENSE2), avoiding the introduction of common mode noise while maintaining bidirectional sensing capability
Solution Approach 2:
The patent extracts and removes the differential amplifier component that causes common mode noise. By eliminating this component and replacing it with two independent single-ended sensing paths, the harmful common mode noise is completely avoided while the useful bidirectional current sensing function is preserved
2Measurement precision
If a sensing resistor is connected in series with the load for current sensing, then the load current can be measured, but the voltage across the sensing resistor becomes discontinuous AC pulses for bidirectional current making processing difficult
Solution Approach 1:
The patent segments the bidirectional current measurement into two separate unidirectional measurement paths. Each path uses a sensing resistor configured to measure current in one direction only, producing continuous unipolar voltage signals that are much easier to process than discontinuous bipolar signals
Solution Approach 2:
The patent extracts the problematic discontinuous AC pulse signal generation and replaces it with two separate continuous unipolar signal paths. This eliminates the need for complex signal processing to handle discontinuous bipolar signals while maintaining accurate bidirectional current measurement capability
Data Source
AI summary
A bidirectional current sensing circuit includes: a sensing resistor coupled between a load and a reference ground, a first and second auto-zero amplifiers coupled to the sensing resistor to sense the voltage across the sensing resistor, and an output transistor. One of the first and second auto-zero amplifiers operates in an output mode and the other of the first and second auto-zero amplifiers operates in a zeroing mode according to a polarity of a voltage across the sensing resistor. The output transistor has a first terminal providing a current sensing signal indicating a load current, a second terminal electrically connected to an inverting terminal of the one of the first and second auto-zero amplifiers operating in the output mode, and a control terminal electrically connected to an output terminal of the one of the first and second auto-zero amplifiers operating in the output mode.