MR Sensor Bias Calibration Circuit with Charging Path
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Solution Overview
Problem
As magnetic storage systems, such as hard disk drives, achieve higher areal densities, the strength of magnetic fields decreases, requiring precise electronic biasing for advanced read/write transducers like GMR and TuMR sensors, but existing biasing schemes introduce noise and errors due to feedback resistors, necessitating calibration to maintain accurate signal detection.
Innovation Solution
A preamplifier circuit with a charging circuit that generates and applies current to an MR sensor node, samples voltage, and adjusts bias voltage to match the sampled voltage, compensating for errors introduced by feedback paths, using feedback switches and digital-to-analog converters to ensure accurate calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If feedback resistors are used in the biasing circuit, then the circuit can provide stable bias voltage, but noise and errors are introduced that degrade measurement precision
Solution Approach 1:
The patent extracts the feedback resistor from the signal path by using a separate calibration path. During calibration, the feedback resistor is disconnected from the biasing circuit and placed in a dedicated calibration path, allowing the bias to be calibrated without the noise and errors introduced by the feedback resistor during normal operation.
Solution Approach 2:
The patent introduces an intermediary calibration path that includes a calibration resistor and calibration switches. This intermediary path allows the bias to be calibrated using a different resistor (calibration resistor) that does not introduce the same noise and errors as the feedback resistor, thereby improving measurement precision while maintaining bias stability.
2Measurement precision
If calibration is performed to compensate for feedback resistor errors, then measurement precision improves, but device complexity increases due to additional circuits
Solution Approach 1:
The patent designs the calibration circuit to serve multiple functions: it can calibrate both voltage bias and current bias using the same calibration path and switches. The calibration path includes components that can work with both voltage and current biasing schemes, reducing the need for separate calibration circuits for each biasing method.
Solution Approach 2:
The patent merges the calibration function with the existing feedback path by using the same operational amplifier and sharing certain circuit nodes. The calibration path is integrated into the existing circuit architecture rather than being a completely separate system, which reduces overall device complexity while still providing accurate calibration capability.
3Productivity
If fast calibration is implemented to reduce calibration time, then productivity increases, but calibration accuracy may be compromised
Solution Approach 1:
The patent performs preliminary actions by pre-charging calibration capacitors and pre-positioning calibration switches to their required states before the actual calibration measurement begins. This preliminary preparation ensures that when calibration is initiated, all components are ready to operate immediately, enabling fast calibration without sacrificing accuracy.
Solution Approach 2:
The patent uses periodic switching between calibration mode and normal operation mode, with calibration performed in periodic intervals. During calibration periods, the circuit quickly switches to calibration mode, performs the necessary measurements and adjustments, then returns to normal operation. This periodic action allows for sufficiently accurate calibration without requiring continuous calibration that would slow down productivity.
Data Source
AI summary
Circuits, systems, and methods for generating and calibrating bias for a magneto-resistive (MR) sensor. The circuit relates to a preamplifier circuit in a magnetic storage system, including an amplifier having an input coupled to a first MR sensor node, a first feedback path comprising a feedback resistor, the path configured to receive an amplifier output from the amplifier and to provide a feedback output to the first MR sensor node, a charging circuit configured to generate a current, apply the current to the first MR sensor node, and sample a voltage between the first MR sensor node and a second MR sensor node to produce a sampled voltage, the charging circuit operating when the feedback path is activated, and a bias circuit configured to apply a bias voltage across the first and second MR sensor nodes and to adjust the bias voltage to match the sampled voltage, the bias circuit operating when the feedback path is deactivated. The present invention advantageously provides for fast and accurate calibration of bias across an MR sensor that compensates for bias error introduced by the feedback path.