Closed-Loop Biasing Circuit for Low-Noise Resistive Sensors
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Solution Overview
Problem
Conventional biasing circuits for resistive sensors in hard disk drives require calibration, leading to increased costs and inaccuracies, especially for low-resistance sensors, and struggle to accurately measure fly height due to noise interference.
Innovation Solution
A closed-loop biasing circuit with a high-impedance structure and noise-canceling techniques that separate and amplify high-frequency and low-frequency components of the sensing signal, reducing noise by more than 25 dB in the low-frequency band without impacting higher frequencies, and eliminating the need for calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional biasing circuits are used for resistive sensors, then the circuit can operate, but calibration is required which increases cost and reduces accuracy
Solution Approach 1:
The biasing circuit automatically adjusts its operating point by sensing the actual resistance of the resistive sensor and self-calibrating without external intervention. This eliminates the need for manual calibration procedures while maintaining measurement accuracy across process variations.
Solution Approach 2:
The circuit incorporates a feedback mechanism that continuously monitors the sensor resistance and adjusts the bias voltage accordingly. This closed-loop approach compensates for resistance variations and maintains optimal operating conditions without requiring external calibration.
2Measurement precision
If conventional biasing circuits are used, then the circuit structure is simple, but noise interference prevents accurate fly height measurement
Solution Approach 1:
The biasing circuit is divided into multiple functional blocks: a high-frequency path for signal extraction, a low-frequency path for noise filtering, and a feedback path for bias adjustment. This segmentation allows each block to optimize its function while collectively achieving noise-rejected measurements.
Solution Approach 2:
An intermediary filtering stage is introduced between the sensor and the measurement circuitry. This intermediate stage selectively passes high-frequency sensor signals while blocking low-frequency noise, enabling accurate measurements without direct coupling that would transmit noise.
3Measurement precision
If low-resistance sensors are used, then the sensor can detect fly height, but conventional circuits struggle to measure accurately due to noise
Solution Approach 1:
The circuit dynamically adjusts its input impedance and filtering parameters based on the sensor resistance value. For low-resistance sensors, the circuit modifies its operating parameters to maximize signal-to-noise ratio, ensuring reliable measurements across different sensor types and resistance values.
4Measurement precision
If calibration is performed to improve accuracy, then measurement precision improves, but cost and complexity increase
Solution Approach 1:
The circuit performs self-calibration during normal operation using built-in sensing and adjustment mechanisms. This eliminates the need for external calibration equipment and manual adjustment procedures, reducing manufacturing costs while maintaining high measurement accuracy.
Data Source
AI summary
According to an embodiment, a circuit includes a biasing and a low-frequency recovery circuit. The biasing circuit includes a voltage digital to analog converter (V-DAC), a differential difference amplifier coupled to the V-DAC, a common-mode feedback (CMFB) amplifier coupled to the differential difference amplifier, and a first pair of transistors arranged as a high-impedance structure and coupled to the differential difference amplifier and the CMFB amplifier. The low-frequency recovery circuit includes a current digital to analog converter (C-DAC), a second pair of transistors arranged as a high-impedance structure and coupled to the first pair of transistors, a pair of resistors having a resistance value equal to half a resistance of the resistive sensor, the pair of resistors arranged between the second pair of transistors and coupled to the C-DAC, and a gain circuit coupled to shared nodes between the second pair of transistors and the pair of resistors.