On-Chip Current Sampling Circuit With Real-Time Resistance Calibration
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Solution Overview
Problem
Existing current sampling circuits in power management chips face challenges in achieving high precision, low power consumption, and cost-effectiveness, particularly in DC motor driving applications, due to high precision resistors requiring additional pins and causing power inefficiencies.
Innovation Solution
A current sampling circuit with on-chip real-time calibration that uses a first resistor, a second resistor, a voltage sampling circuit, and an on-state resistance calibration circuit to accurately measure on-state current of a driving transistor without external devices, protecting the chip from latch-up effects by adjusting resistance values and current sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high precision sampling resistor is used for current sampling, then measurement precision is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent merges the current sampling function with the existing driving transistor by using the transistor's on-state resistance as the sampling element. The driving transistor serves dual purposes: switching control and current sampling, eliminating the need for separate external sampling resistors and reducing chip pin requirements.
Solution Approach 2:
The driving transistor performs self-sampling by utilizing its own on-state resistance characteristics. The circuit uses the voltage drop across the driving transistor during its on-state to derive current information, allowing the component to serve both its primary switching function and the sampling function simultaneously.
2Measurement precision
If high precision sampling resistor is used for current sampling, then measurement precision is improved, but power consumption increases
Solution Approach 1:
The patent merges the current sampling function with the existing driving transistor by using the transistor's on-state resistance as the sampling element. The driving transistor serves dual purposes: switching control and current sampling, eliminating the need for separate external sampling resistors and reducing chip pin requirements.
Solution Approach 2:
The driving transistor performs self-sampling by utilizing its own on-state resistance characteristics. The circuit uses the voltage drop across the driving transistor during its on-state to derive current information, allowing the component to serve both its primary switching function and the sampling function simultaneously.
3Device complexity
If traditional current sampling methods are used, then circuit simplicity is maintained, but measurement accuracy and reliability are insufficient
Solution Approach 1:
The patent implements a feedback mechanism where the voltage sampling circuit continuously monitors the voltage drop across the driving transistor, and the operational amplifier adjusts the sampling signal based on this feedback. This closed-loop approach compensates for variations in transistor parameters and improves measurement accuracy while maintaining circuit simplicity.
Solution Approach 2:
The patent utilizes the dynamic parameter changes of the driving transistor during its switching operation. By sampling the voltage drop across the transistor during its on-state when parameters are stable and predictable, the circuit achieves accurate current measurement without requiring complex external components.
4Ease of manufacture
If DCR sampling method is used, then integration is improved, but time constant matching becomes difficult
Solution Approach 1:
The patent extracts the time constant matching problem by eliminating the RC branch entirely. Instead of using capacitor and resistor combinations that require precise time constant matching, the invention directly uses the driving transistor's on-state resistance with a simple operational amplifier circuit, achieving full integration without matching constraints.
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
This solution enables precise control of DC motor driving current, improves measurement accuracy, and reduces power consumption by integrating calibration within the chip, thus enhancing reliability and cost-effectiveness.
Implementation Method 1
The voltage sampling circuit is used for obtaining on-state voltage drop value of the driving transistor Vds
Implementation Method 2
On-state resistance value of the calibrating transistor is set to be K1 times of on-state resistance value of the driving transistor
Data Source
AI summary
A current sampling circuit with on-chip real-time calibration is used to detect the on-state current of a driving transistor. The current sampling circuit includes a first resistor, a second resistor, a voltage sampling circuit, a sampling voltage operational circuit and an on-state resistance calibration circuit. The voltage sampling circuit is used to obtain on-state voltage drop value of the driving transistor Vds. The on-state resistance calibration circuit includes a reference current source and a calibrating transistor. On-state resistance value of the calibrating transistor is set to be K1 times of on-state resistance value of the driving transistor. The on-state voltage drop value Vds obtained by the voltage sampling circuit and the on-voltage drop value of the calibrating transistor Vrsns are input to the sampling voltage operational circuit to obtain proportional relationship K2 between the on-state voltage drop value Vds and the on-state voltage drop value Vrsns.