High-impedance architecture for mode-hop detection in hard disk drives

Abstract

This provides a high-impedance (Hi-Z) mode-hop detection circuit that achieves good immunity to sensor GND noise without false mode-hop detection. [Solution] The Hi-Z mode-hop detection circuit 100 includes a first laser sensor Rsense 102 that senses radiant heat from the laser source 110 of the storage device 112, a second laser sensor Rref 104 that is isolated from the laser source and provides a reference for the temperature of the storage device, a bias circuit 114 that provides a constant voltage or constant current to bias the voltage difference between the first sensing pad P106 and the second sensing pad N108, and gain amplifiers (front-end gain amplifiers 118, 120, back-end gain amplifiers 124, 126) that amplify the biased voltage difference between the first sensing pad and the second sensing pad for detection of the mode-hop state of the laser source.

Description

Background Art

[0001] [Related Application] This application is a non-provisional application and claims the benefit and priority of Provisional Application No. 63 / 725,500, filed on November 26, 2024, which is hereby incorporated by reference in its entirety.

[0002] A hard disk drive (HDD) magnetically stores data on a platter, where smaller bits are required for higher areal density. Heat Assisted Magnetic Recording (HAMR) technology utilizes a laser as auxiliary energy to increase the areal density, where the medium heated by the laser will have lower coercivity characteristics, making it easier to reverse data at a specific small laser spot. Thus, the laser enables the HDD to have smaller bits and denser tracks without increasing the write energy. However, the laser can have an abnormality called mode hopping, which is a sudden change in the laser wavelength that can cause power variations and phase changes. The power variation can cause erasure in adjacent tracks, and the phase change can increase the Bit Error Rate (BER).

[0003] Therefore, HAMR HDD technology requires a mode-hop detection circuit to perform both real-time mode-hop detection (in AC mode) and power adjustment (in DC mode) in parallel. Furthermore, the mode-hop detection circuit must have good immunity to sensor ground (GND) noise, where the sensor is used to detect the mode-hop state in real time. Conventional solutions use a low-impedance mode-hop detection circuit, which shares the sensor GND with other blocks in the preamplifier, potentially causing large current spikes (e.g., approximately 50mA) during switching, leading to sensor GND jumps (e.g., approximately 100mV) and disturbances in the mode-hop detection circuit. Moreover, the low-impedance mode-hop circuit shares the bias and front-end (FE) gain circuits for both AC and DC modes. However, turning on both AC and DC modes simultaneously can create uncertainty because both drivers adjust their offsets differently at the same time. As a result, mode-hop detection and power adjustment are not performed in parallel in the low-impedance mode-hop circuit.

[0004] The above-mentioned examples and related limitations relating to the relevant technical fields are intended to be illustrative, not exclusive. Other limitations relating to the relevant technical fields will become apparent upon reading this specification and examining the drawings. [Brief explanation of the drawing]

[0005] The aspects of this disclosure will be best understood from the detailed description below, when read in conjunction with the attached figures. Note that, in accordance with standard industrial practice, various features are not depicted to scale. In practice, the dimensions of various features may be arbitrarily increased or decreased for the sake of clarity in the discussion.

[0006] [Figure 1] This is a schematic diagram of an example of a high-impedance (Hi-Z) mode hop detection circuit according to one aspect of this embodiment.

[0007] [Figure 2A] This is a schematic diagram of an example of a bias circuit implemented in voltage mode according to one aspect of this embodiment. [Figure 2B] This is a schematic diagram of an example of a bias circuit implemented in current mode according to one aspect of this embodiment.

[0008] [Figure 3] This is a schematic diagram of an example of a front-end gain amplifier that includes both an AC-mode gain amplifier and a DC-mode gain amplifier, according to one aspect of this embodiment.

[0009] [Figure 4] This is a schematic diagram of a simplified equivalent impedance of a Hi-Z mode hop detection circuit according to one aspect of this embodiment.

[0010] [Figure 5] This is a schematic diagram of a simplified equivalent impedance of a Hi-Z mode hop detection circuit according to one aspect of this embodiment, where a signal is injected into the center of two sensors connected in series to a sensing pad. [Modes for carrying out the invention]

[0011] The following disclosure provides numerous different embodiments or examples to implement different features of the subject matter. Specific examples of components and arrangements are described below for the sake of brevity of the disclosure. These are, of course, merely examples and are not intended to be limiting. Furthermore, the disclosure may repeat reference numerals and / or letters in various examples. This repetition is for the sake of brevity and clarity and does not in itself define relationships between the various embodiments and / or configurations discussed.

[0012] Before various embodiments are described in more detail, it should be understood that the embodiments are not limiting, as the elements in such embodiments may differ. It should also be understood that certain embodiments described and / or illustrated herein may be easily separable from a particular embodiment and, optionally, may be combined with any of several other embodiments, or may have elements that can be used in place of elements in any of several other embodiments described herein. It should also be understood that the terms used herein are for illustrative purposes only and are not intended to be limiting. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as those commonly understood in the art to which the embodiments belong.

[0013] A novel high-impedance (Hi-Z) mode-hop detection circuit is proposed, comprising a first laser sensor positioned in close proximity to a laser source used by a storage device and configured to sense radiant heat from the laser source. The Hi-Z mode-hop detection circuit further comprises a second laser sensor isolated from the laser source and configured to provide a reference for the temperature of the storage device. The Hi-Z mode-hop detection circuit further comprises a bias circuit configured to bias the detected voltage or current difference between the first sensing pad and the second sensing pad by providing a constant voltage or constant current, and a gain amplifier configured to amplify the biased voltage difference between the first sensing pad and the second sensing pad for detection of the mode-hop state of the laser source.

[0014] The proposed high-impedance mode-hop detection circuit allows for simultaneous and parallel operation in both AC and DC modes. Compared to low-impedance mode-hop detection circuits, the proposed high-impedance mode-hop detection circuit achieves good immunity to sensor GND noise without false mode-hop detection because the amount of GND noise spikes at both sensing pads is very similar and can cancel each other out. Furthermore, the proposed high-impedance mode-hop detection circuit helps the firmware in the application achieve load-independent gain without requiring calibration when the load resistance changes.

[0015] Figure 1 depicts a schematic diagram of an example of a Hi-Z mode hop detection circuit 100 according to one embodiment of the present disclosure. As shown in Figure 1, the Hi-Z mode hop detection circuit 100 includes a pair of laser sensors Rsense 102 and Rref 104, where, in a non-limiting example, the pair of laser sensors may be modeled as resistors having resistors Rsense and Rref, respectively (using laser diodes, in a non-limiting example). In some embodiments, the laser sensor Rsense 102 is coupled between a sensing pad / pin / terminal P106 and ground / GND, while the laser sensor Rref 104 is coupled between a sensing pad / pin / terminal N108 and GND. In some embodiments, the laser sensor Rsense 102 is positioned in close proximity to a laser source / channel 110 used by a storage device 112, which may be an HDD device 112, and is configured to sense radiant heat, while the laser sensor Rref 104 is isolated from the laser source 110 and is configured to function as / provide a reference for the temperature of the HDD device 112. In some embodiments, a pair of laser sensors / resistors Rsense102 and Rref104 are configured to detect the mode-hop state of the laser source 110 by detecting power changes in the laser source 110 in terms of voltage difference or current difference / delta between the sensing pads P106 and N108 of the two sensors 102 and 104.

[0016] In some embodiments, the Hi-Z mode-hop detection circuit 100 is configured to bias and amplify with gain the voltage difference between the sensing pads P106 and N108 of two sensors Rsense102 and Rref104 to obtain better resolution for detecting mode-hop states. As shown in the example in Figure 1, the Hi-Z mode-hop detection circuit 100 further includes a front-end (FE) stage 116 which is a common-source gain amplifier including a bias circuit 114, a front-end AC mode gain amplifier 118 and a front-end DC mode gain amplifier 120, and a back-end (BE) stage 122 which includes a back-end AC stage 124 and a back-end DC stage 126. In some embodiments, the backend AC stage 124 includes one or more of a high-gain amplifier, a high-pass filter, a low-pass filter, and a comparator for AC mode operation, while the backend DC stage 126 includes one or more of a high-gain amplifier, a low-pass filter, and an analog-to-digital converter (ADC) for performing DC offset calibration for DC mode operation. Under this architecture, the Hi-Z mode hop detection circuit 100 isolates the bias from the FE gain, where the independent bias circuit 114 is shared (but not interfered with) between two independent gain paths that correspond in parallel to both AC mode (e.g., frontend AC mode gain amplifier 118 and backend AC stage 124) and DC mode (e.g., frontend DC mode gain amplifier 120 and backend DC stage 126), respectively.

[0017] In the example in Figure 1, the shared bias circuit 114 is coupled to sensing pads P106 and N108 and configured to bias the sensing pads P106 and N108 of the two sensors Rsense102 and Rref104 by providing a constant voltage or constant current. Figure 2A depicts a schematic diagram of an example of a bias circuit 200 implemented in voltage mode (V-mode). Under the V-mode implementation shown in Figure 2A, the bias circuit 114 is configured to generate / bias a constant voltage at the sensing pads P106 and N108 with a bias voltage value. In some embodiments, the two amplifiers 202 and 204 of the bias circuit 114 are configured to accept two reference voltages Vrefp and Vrefn as their respective inputs and to force the voltage at the sensing pads P106 and N108 to be equal to the bias voltage value by providing two currents Isense and Iref flowing through the sensors Rsense102 and Rref104 via a pair of transistors 206 and 208, respectively. Next, any voltage difference across sensors Rsense102 and Rref104 resulting from the laser heat sensed in Rsense is amplified by the front-end gain amplifier 116 and the back-end gain amplifier 122. As shown in Figure 2A, the V-mode implementation of the bias circuit 114 is a closed-loop amplifier that places a dominant pole on either sensing pad P106 or N108 to achieve stability between the interacting sensing pads P106 and N108.

[0018] Figure 2B shows a schematic diagram of an example of a bias circuit 250 implemented in current mode (I-mode). Under the I-mode implementation shown in Figure 2B, the bias circuit 114 is configured to program constant current sources flowing through the sensing pads P106 and N108 to the sensors Rsense 102 and Rref 104, respectively, by current mirroring Ibias as bias current sources 252 and 254. The voltage difference between the sensing pads P106 and N108 as detected by the sensors Rsense 102 and Rref 104 is then amplified by the front-end gain amplifier 116 and the back-end gain amplifier 122. It should be understood that the I-mode implementation is an open-loop implementation that does not contain loops.

[0019] Referring again to the example in Figure 1, the front-end gain amplifier 116 is configured to amplify the biased voltage difference between the sensing pads P106 and N108 of the two sensors Rsense 102 and Rref 104. Figure 3 is a schematic diagram of an example of the front-end gain amplifier 116, which includes both a front-end AC-mode gain amplifier 118 and a front-end DC-mode gain amplifier 120. In some embodiments, the front-end gain amplifier 116 is configured to support parallel gain amplification for both real-time detection of the mode-hop state of the laser source 110 in AC mode and power adjustment of the laser source 110 in DC mode, respectively, via the front-end AC-mode gain amplifier 118 and the front-end DC-mode gain amplifier 120.

[0020] As shown in the example in Figure 3, the front-end AC mode gain amplifier 118 includes a pair of transistors 302 and 304, whose gates are capacitively coupled to sensing pads P106 and N108 via a pair of coupling capacitors 306 and 308, respectively. The front-end AC mode gain amplifier 118 further includes a current source 310 that biases the sources of the pair of transistors 302 and 304. During operation, the open-loop front-end AC mode gain amplifier 118 performs signal amplification in response to rapid changes in the biased current difference and / or voltage difference between sensing pads P106 and N108 to flag mode hop conditions in real time when they occur. The front-end DC mode gain amplifier 120 also includes a pair of transistors 312 and 314 that are directly coupled to sensing pads P106 and N108 without coupling capacitors, with a resistor 316 coupled between the sources of the pair of transistors 312 and 314 to form a feedback loop. The front-end DC mode gain amplifier 120 further includes a pair of current sources 318 and 320 that bias the sources of the pair of transistors 312 and 314. During operation, the front-end DC mode gain amplifier 120 outputs the differential voltage between sensing pads P106 and N108 and the voltage offset between Vsp and Vsn at the sources of the pair of transistors 312 and 314 to the firmware / software in order to adjust the laser power (for example, by reducing or increasing the laser power of the laser source 110 to correct mode-hop conditions). There is no interference or conflict between the front-end AC-mode gain amplifier 118 and the front-end DC-mode gain amplifier 120 in controlling the bias circuit 114, because the front-end AC-mode gain amplifier 118 amplifies its signal through its own path, while the front-end DC-mode gain amplifier 120 performs its own DC autocalibration, for example using an analog-to-digital converter (ADC) 128, to produce a Vsp-Vsn difference / delta similar to that of sensing pads P106 and N108, thereby realizing a balanced amplifier.

[0021] As shown in Figure 3, the front-end gain amplifier 116 is a common-source amplifier, where the source of the transistors is a common reference, the gates of the transistors are controlled by biased input signals from sensing pads P106 and N108, and the drains of the transistors provide the output of the amplifier. Since the biased input signals are applied to the gates of transistors 302 / 304 and 312 / 314, and therefore there is no current flowing to the gates (except for a small leakage current), the front-end gain amplifier 116 provides a high input impedance. Since the input impedance is high in relation to both sensing pads P106 and N108, the sensor GND jump causes a relatively equal amount of noise spikes at both pads, canceling each other out and resulting in a nearly zero net delta. Figure 4 is a schematic diagram of the simplified equivalent impedance of the Hi-Z mode hop detection circuit 100 with Rsense = 250Ω and Rref = 240Ω. Since the input impedance Zin is close to infinity (∞), the differential voltage Delta (PN) between the two sensing pads P106 and N108, caused by a sensor GND jump (e.g., 100mV), can be calculated using the concept of resistive voltage division as follows:

[0022] Delta(PN) = (∞ / (∞+250) - ∞ / (∞+240)) *100mV ≒ 0 In other words, the sensor GND jump is not converted into a differential voltage between the output voltages at sensing pads P106 and N108, because both will follow the GND noise together when the input impedance is high.

[0023] In some embodiments, the Hi-Z mode hop detection circuit 100 achieves a gain independent of the load resistance. FIG. 5 is a schematic diagram of the simplified equivalent impedance of the Hi-Z mode hop detection circuit 100 with a signal injected as Vin' at the center of two sensors / loads Rsense102 and Rref104 connected in series to the sensing pads P106 and N108, respectively. The overall gain Gain of the Hi-Z mode hop detection circuit 500 depends on the resistance of Rsense or Rref and can be calculated as follows using the concept of resistor voltage division:

[0024] Gain = Vout / Vin' = (Zin / (Zin +Rsense or Rref)) * Vout / Vin = (∞ / (∞ +Rsense or Rref)) * Vout / Vin ≒ Vout / Vin That is, when the input impedance Zin is high, the gain of the Hi-Z mode hop detection circuit 100 is fixed and does not depend on the load resistances of the first and second laser sensors (i.e., Rsense102 and Rref104).

[0025] The foregoing description of the various embodiments of the subject matter according to the claims is provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the subject matter of the claims to the exact forms disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments have been chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others of ordinary skill in the relevant art to understand the subject matter of the claims, the various embodiments, and the various modifications suitable for the particular uses contemplated.

Claims

1. A first laser sensor coupled between a first sensing pad and ground, wherein the first laser sensor is positioned in close proximity to a laser source used by a storage device and is configured to sense radiant heat from the laser source; A second laser sensor coupled between the second sensing pad and the ground, wherein the second laser sensor is isolated from the laser source and configured to provide a reference for the temperature of the storage device; A bias circuit coupled to the first sensing pad and the second sensing pad, and configured to provide a constant voltage or constant current to bias the voltage difference between the first sensing pad and the second sensing pad; and A gain amplifier configured to amplify the biased voltage difference between the first sensing pad and the second sensing pad in order to detect the mode-hop state of the laser source. An electronic circuit configuration comprising the above.

2. The first and second laser sensors are modeled as pairs of resistors. The electronic circuit configuration according to claim 1.

3. The aforementioned storage device is a hard disk drive (HDD). The electronic circuit configuration according to claim 1.

4. The first and second laser sensors are configured to detect the mode-hop state of the laser source by detecting a power change in the laser source in terms of the voltage difference between the first and second sensing pads. The electronic circuit configuration according to claim 1.

5. The bias circuit is configured to generate a constant bias voltage value in the first and second sensing pads under voltage mode. The electronic circuit configuration according to claim 1.

6. The bias circuit is configured to force the voltages at the first and second sensing pads to be equal to the bias voltage value, respectively. The electronic circuit configuration according to claim 5.

7. The bias circuit is a closed-loop amplifier under voltage mode that places a dominant pole at its output to achieve stability between the first and second sensing pads. The electronic circuit configuration according to claim 5.

8. The bias circuit is configured to program the constant current flowing through the first and second sensors, respectively, via the first and second sensing pads, by current mirroring in current mode. The electronic circuit configuration according to claim 1.

9. The bias circuit is an open-loop implementation that does not include loops under the current mode. The electronic circuit configuration according to claim 8.

10. The gain amplifier is configured to handle parallel amplification of the biased voltage difference or current difference between the first sensing pad and the second sensing pad for both real-time detection of the mode-hop state of the laser source in AC mode and power adjustment of the laser source in DC mode. The electronic circuit configuration according to claim 1.

11. The bias circuit is shared by the separate AC mode and DC mode, but is not subject to interference. The electronic circuit configuration according to claim 10.

12. The aforementioned gain amplifier is a common-source amplifier with an input impedance close to infinite. The electronic circuit configuration according to claim 1.

13. The sensor GND jump has zero effect on the voltage difference between the first sensing pad and the second sensing pad. The electronic circuit configuration according to claim 12.

14. The gain of the aforementioned electronic circuit configuration does not depend on the load resistance of the first and second laser sensors. The electronic circuit configuration according to claim 12.

15. A step of sensing radiant heat from a laser source via a first laser sensor coupled between a first sensing pad and ground, and positioned in close proximity to the laser source used by a storage device; A step of providing a reference for the temperature of the storage device via a second laser sensor coupled between a second sensing pad and the ground, and isolated from the laser source; A step of biasing the voltage difference between the first sensing pad and the second sensing pad using a constant voltage or constant current; and A step of amplifying the biased voltage difference between the first sensing pad and the second sensing pad in order to detect the mode-hop state of the laser source. A method that includes [a certain feature].

16. A step of detecting the mode-hop state of the laser source by detecting a power change in the laser source in terms of the voltage difference or current difference between the first and second sensing pads. The method according to claim 15, further comprising:

17. Steps to generate constant bias voltage values ​​in the first and second sensing pads under voltage mode. The method according to claim 15, further comprising:

18. A step in which the voltages in the first and second sensing pads are forced to be the same as the bias voltage value. The method according to claim 17, further comprising:

19. To achieve stability between the first and second sensing pads, a step is taken to place a dominant pole at the output. The method according to claim 17, further comprising:

20. In current mode, the step of programming the constant current flowing through the first and second sensors, respectively, via the first and second sensing pads, by current mirroring. The method according to claim 15, further comprising:

21. A step corresponding to parallel amplification of the biased voltage difference between the first sensing pad and the second sensing pad for real-time detection of the mode-hop state of the laser source in AC mode and power adjustment of the laser source in DC mode. The method according to claim 15, further comprising:

22. The biasing stage is shared by the separate AC mode and DC mode, but is not subject to interference. The method according to claim 21.

23. This stage results in an input impedance that is close to infinite, acting as a common-source amplifier. The method according to claim 15, further comprising:

24. A step that brings zero influence to the voltage difference between the first sensing pad and the second sensing pad due to a sensor GND jump. The method according to claim 23, further comprising the above.

25. A step that enables the gain to be independent of the load resistance of the first and second laser sensors. The method according to claim 23, further comprising the above.

26. A first means coupled between a first sensing pad and ground, wherein the first means is positioned in close proximity to a laser source used by a storage device and is configured to sense radiant heat from the laser source; A second means coupled between the second sensing pad and the ground, wherein the second means is isolated from the laser source and is configured to provide a reference for the temperature of the storage device; A third means coupled to the first sensing pad and the second sensing pad, and configured to provide a constant voltage or constant current to bias the voltage difference between the first sensing pad and the second sensing pad; and A fourth means configured to amplify the biased voltage difference between the first sensing pad and the second sensing pad in order to detect the mode-hop state of the laser source. An electronic circuit configuration comprising the above.

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