Low noise amplifier circuit for a thermal varying resistance

An amplifying circuit arrangement, comprising:

• a synthesizing circuit configured to synthesize a resistor having a resistance value having a variation in time equivalent to a resistance variation of a sensor resistor applied with a resistance bias voltage and a resistance current bias, wherein the synthesizing circuit comprises:
• an amplifier comprising an input transistor;
• a bias current generator comprising a control node coupled to an output of the input transistor, wherein the bias current generator is configured to generate a bias current flowing in the input transistor;
• and
• a further current generator configured to generate a current at least proportional to the resistance bias current and coupled to the output of the input transistor, wherein the resistance bias voltage is applied to an input of the amplifier, and wherein a transconductance of the input transistor is at least proportional to the resistance of the sensor resistor;
• a first amplifier stage configured to amplify a signal formed on the sensor resistor;
• a gain recovery stage comprising a second amplifying stage comprising at least one transistor having an input electrode coupled to an output of the first amplifier stage, wherein a load electrode of the at least one transistor is connected to a respective load circuit, the respective load circuit comprising:
• a NMOS transistor having scaled dimensions by a given scaling factor with respect to dimensions of at least one amplifying transistor of the first amplifier stage and biased with a scaled current, the scaled current being scaled by the scaling factor with respect to a bias current of the at least one amplifying transistor of the first amplifier stage;
• a circuit module comprising a resistance synthesizing transistor having same dimensions as the input transistor, wherein the circuit module is configured to sink a calibrated current to determine a transconductance value proportional to an inverse of a resistance of the sensor resistor, the calibrated current corresponding to a bias current flowing in the input transistor of the synthesizing circuit, and wherein other electrodes of the at least one transistor of the gain recovery stage are connected to a reference resistor.

A hard disk drive arrangement comprising:

• a thermal resistor configured to perform sensing and control of fly height of a tip in the hard disk drive;
• and
• a circuit configured to synthesize a resistor having a resistance value having a variation in time equivalent to a resistance variation of the thermal resistor applied with a resistance bias voltage and a resistance current bias, wherein the circuit comprises:
• an amplifier comprising an input transistor;
• a bias current generator comprising a control node coupled to an output of the input transistor, wherein the bias current generator is configured to generate a bias current flowing in the input transistor;
• and
• a further current generator configured to generate a current at least proportional to the resistance bias current and coupled to the output of the input transistor, wherein the resistance bias voltage is applied to an input of the amplifier, and wherein a transconductance of the input transistor is at least proportional to the resistance of the thermal resistor.