Data storage device shaping read thermal sensor bias signal to balance write thermal sensor signal during laser operation
A data storage device comprises a disk and a recording head. The recording head comprises a write thermal sensor, a read thermal sensor, and a laser configured for heat assisted magnetic recording (HAMR). Control circuitry shapes a bias signal applied to the read thermal sensor to mirror a thermal response of the write thermal sensor during laser operation, generates a differential signal based on a difference between the write thermal sensor response and the read thermal sensor response, and monitors the differential signal to detect laser mode hopping.
1 . A data storage device comprising:
a disk;
a recording head comprising a write thermal sensor configured in or adjacent to a write element, a read thermal sensor configured in or adjacent to a read element, and a laser configured for heat assisted magnetic recording (HAMR); and
one or more processing devices or components, configured, alone or in combination, to shape a bias signal applied to the read thermal sensor to mirror a transient thermal response of the write thermal sensor during activation of the laser.
2 . The data storage device of claim 1 , wherein the one or more processing devices or components are further configured, alone or in combination, to generate a differential signal based on a difference between the transient thermal response of the write thermal sensor and a thermal response of the read thermal sensor.
3 . The data storage device of claim 2 , wherein the one or more processing devices or components are further configured, alone or in combination, to monitor the differential signal to detect mode hopping of the laser.
4 . The data storage device of claim 2 , wherein the one or more processing devices or components are further configured, alone or in combination, to detect mode hopping of the laser by detecting spikes in the differential signal.
5 . The data storage device of claim 1 , wherein the read thermal sensor is an embedded contact sensor (ECS) and the write thermal sensor is a near field temperature sensor (NTS).
6 . The data storage device of claim 5 , wherein during an initial sector write, the one or more processing devices or components are further configured, alone or in combination, to shape the bias signal applied to the read thermal sensor as ECS(t)=ECS Bias +ECS OS *exp(-t/ECS Tau ), where ECS(t) is the bias signal, ECS Bias is a programmable baseline level for the bias signal, ECS OS is a programmable offset that counteracts a temperature spike in the transient thermal response of the write thermal sensor from laser activation, and ECS Tau is a programmable time constant that controls a rate of exponential decay of the bias signal.
7 . The data storage device of claim 6 , wherein during a servo identification data (ID) read, the one or more processing devices or components are further configured, alone or in combination, to shape the bias signal applied to the read thermal sensor as ECS(t2)=ECS(t1)+ (ECS Bias +ECS OS −L(t1))*(1−exp((t1-t2)/ECS GapTau )), where t1 is a beginning of the servo ID read, t2 is an end of the servo ID read, and ECS GapTau is a time constant that controls a rate of exponential ramp up of the bias signal.
8 . The data storage device of claim 7 , wherein during a sector write following the servo ID read, the one or more processing devices or components are further configured, alone or in combination, to shape the bias signal applied to the read thermal sensor as ECS(t)=ECS Bias + (ECS (t2)−ECS Bias )*exp((t2-t)/ECS Tau ).
9 . A method for detecting laser mode hopping in a data storage device, the method comprising:
shaping a bias signal applied to a read thermal sensor configured in a recording head of the data storage device to mirror a thermal response of a write thermal sensor configured in the recording head during operation of a laser configured for heat assisted magnetic recording (HAMR);
generating a differential signal based on a difference between the thermal response of the write thermal sensor and a thermal response of the read thermal sensor; and
monitoring the differential signal to detect laser mode hopping.
10 . The method of claim 9 , further comprising detecting spikes in the differential signal to detect laser mode hopping.
11 . The method of claim 9 , further comprising shaping the bias signal applied to the read thermal sensor during an initial sector write as ECS(t)=ECS Bias +ECS OS *exp(-t/ECS Tau ), where ECS(t) is the bias signal, ECS Bias is a programmable baseline level for the bias signal, ECS OS is a programmable offset that counteracts a temperature spike in the thermal response of the write thermal sensor from laser activation, and ECS Tau is a programmable time constant that controls a rate of exponential decay of the bias signal.
12 . The method of claim 11 , further comprising shaping the bias signal applied to the read thermal sensor during a servo ID read as ECS (t2)=ECS(t1)+ (ECS Bias +ECS OS −L(t1))*(1−exp((t1-t2)/ECS GapTau )), where t1 is a beginning of the servo ID read, t2 is an end of the servo ID read, and ECS GapTau is a time constant that controls a rate of exponential ramp up of the bias signal.
13 . The method of claim 12 , further comprising shaping the bias signal applied to the read thermal sensor during a sector write following the servo ID read as ECS(t)=ECS Bias + (ECS(t2)−ECS Bias )*exp((t2-t)/ECS Tau ).
14 . Control circuitry for controlling a recording head of a data storage device, the recording head comprising a write thermal sensor configured in a write element, a read thermal sensor configured in a read element, and a laser configured for heat assisted magnetic recording (HAMR),
the control circuitry being configured to shape a bias signal applied to the read thermal sensor to mirror a transient thermal response of the write thermal sensor during activation of the laser.
15 . The control circuitry of claim 14 , wherein the control circuitry is further configured to generate a differential signal based on a difference between the transient thermal response of the write thermal sensor and a thermal response of the read thermal sensor.
16 . The control circuitry of claim 15 , wherein the control circuitry is further configured to monitor the differential signal to detect mode hopping of the laser.
17 . The control circuitry of claim 15 , wherein the control circuitry is further configured to detect mode hopping of the laser by detecting spikes in the differential signal.
18 . The data storage device of claim 5 , wherein during an initial sector write, the one or more processing devices or components are further configured, alone or in combination, to shape the bias signal applied to the read thermal sensor based on one or more of a programmable baseline level for the bias signal, a programmable offset that counteracts a temperature spike in the transient thermal response of the write thermal sensor from laser activation, and a programmable time constant that controls a rate of exponential decay of the bias signal.
19 . The data storage device of claim 18 , wherein during a servo identification data (ID) read, the one or more processing devices or components are further configured, alone or in combination, to shape the bias signal applied to the read thermal sensor based on the programmable baseline level for the bias signal, the programmable offset that counteracts the temperature spike in the transient thermal response of the write thermal sensor from laser activation, and a programmable time constant that controls a rate of exponential ramp up of the bias signal.
20 . The data storage device of claim 19 , wherein during a sector write following the servo ID read, the one or more processing devices or components are further configured, alone or in combination, to shape the bias signal applied to the read thermal sensor based on the programmable baseline level for the bias signal and the programmable time constant that controls the rate of exponential decay of the bias signal.