Disk Drive with Preamplifier for Multiple Readers in a Slider with a Common Return Signal
Disk drive embodiments with common lead connections in the slider, suspension, and preamplifier are described. The arm electronics IC includes a preamplifier with single-ended input from the set of signal traces that include a common signal return lead for the plurality of read transducers (readers) in the slider. Two embodiments of the preamps are described that include a single-ended design and a pseudo-single-ended design. Each embodiment supplies the required bias to each read transducer using an operational transconductance amplifier (OTA) that drives a variable current source connected to the transducer. The positive input to the OTA is a DC voltage with the AC signal from the transducer imposed on it. The negative input is a DC reference voltage. Various embodiments of the signal trace configuration on the suspension are described including a single and double layer embodiments.
This application is related to provisional application 61/879,544, which was filed on Sep. 18, 2013 and the benefit of which is hereby claimed for the present application. A related application is titled INTEGRATED LEAD SUSPENSION (ILS) FOR TWO-DIMENSIONAL MAGNETIC RECORDING (TDMR) DISK DRIVE filed Jul. 25, 2014, bearing Ser. No. 14/340,690.FIELD OF THE INVENTION
The present invention relates to the field of magnetic disk drive design and more particularly to the design and interconnection of sliders, suspensions for sliders and signal amplifiers and more particularly to the design and interconnection of such components in a system having a plurality of read heads (readers) in a slider.BACKGROUND
A disk drive system includes at least one magnetic disk, read/write heads, and a suspension which supports a slider with the magnetic read/write heads and provides electrical connections to the system electronics.
The flex cable 24 provides electrical connections between the actuators and the system electronics on a circuit board (not shown). The flex cable 24 is rigidly attached by stationary bracket 23 at one end, which connects to the system electronics. The other end of the flex cable is attached to the set of actuators 14 which move in unison in response to the VCM.
A plurality of electrical paths (not shown) extend from the flex cable along the actuators to the arm electronics chip 21. The arm electronics chip is in turn connected by a plurality of electrical paths that extend through the suspension 20 and connect to the slider 22 as further illustrated in
Typically the stainless steel spring metal layer in the suspension has been used as a ground plane for the traces. Because of the spatial constraints imposed on the suspension a multi-layer or stacked trace configurations have been used. Klaassen et al. in U.S. Pat. No. 6,608,736 disclose stacked read line traces arranged on top of each other and separated from each other by a dielectric layer and separated from the stainless steel base layer by another dielectric layer.
U.S. Pat. No. 8,094,413 to Hentges, et al. (Jan. 10, 2012) describes a disk drive head/slider suspension flexure with stacked traces having differing configurations on the gimbal and beam regions. A head suspension is described that includes integrated lead suspension flexure having stacked traces that run along one side of the spring metal layer and multi-layer traces that run along the other side. The traces come together in the tail region of the suspension where the set termination pads provide electrical connection to the system. The head suspension component includes stacked traces having first and second traces in the first and second conductor layers, respectively. The stacked traces are used for the writer in an embodiment and the multilayer traces are used for the reader and fly height traces and include a ground layer.
U.S. Pat. No. 8,233,240 to Contreras, et al. Jul. 31, 2012 describes an integrated lead suspension (ILS) in a magnetic recording disk drive has the transmission line portion of the ILS between the flex cable termination pads at the tail and the gimbal area formed of multiple interconnected segments, each with its own characteristic impedance. At the interface between any two segments there is a change in the widths and in impedance of the electrically conductive traces of the transmission line. The number of segments and their characteristic impedance values are selected to produce the largest frequency bandwidth with a substantially flat group delay from the write driver to the write head.
As areal densities continue to increase, recording schemes using more than one read head in each slider are being explored since having multiple readers allows higher density recording.
For Multiple Input Multiple Output (MIMO), also called Two Dimensional Magnetic Recording (TDMR), there are two or more TMR read transducers. Problem areas in front-end system design for multiple-reader architectures include: 1) slider design; 2) suspension interconnection, and 3) multiple reader preamplifier design. Each TMR transducer normally requires two electrical paths (traces or wires) from the slider to the preamplifier. There is limited room for these electrical paths between the slider and the preamplifier. Each trace path has a cost associated with it.
For the present disclosure, a three-reader (3R) architecture configuration and an independent differential amplifier (IDA) is assumed as the current state of the art. A 3R slider design using IDAs requires six connection pads (R1, −R1, R2, −R2, R3, & −R3) on the surface of the slider, which will consume much of the available external area on the slider.
In addition, having three separate independent readers requires additional space between read transducers inside the slider. Having additional distance between read transducers creates skew problems caused by physical distance between the transducers. The fly-height control between transducers also creates spacing control problems due to the additional distance between transducers. For the suspension interconnection, having six conductive traces creates area issues in the layout, where the suspension's tail width space is limited. For the preamplifier, having IDAs requires additional IC area and power, which are key design constraints for the electronic packaging (flex area and mechanical connection to actuator).
For the above three segments of the front-end system, a design solution is needed to minimize the overall required area and power requirement.SUMMARY OF THE INVENTION
Disk drive embodiments of the invention with common lead connections in the slider, suspension, and preamplifier creates the common lead system, which allows for a substantial reduction in layout area for the interconnects in the slider, for the suspension, and in the arm electronics IC. The arm electronics IC includes a preamplifier with input from the set of signal traces that include a common signal return lead for the plurality of read transducers (readers) in the slider. In embodiments with three readers, for example, four signal traces (wires) are used to connect the set of readers in the slider to the preamps. Two embodiments of the preamps are described that include a single-ended (SE) design and a pseudo-single-ended (PSE) design. Each embodiment supplies the required bias to each read transducer using an operational transconductance amplifier (OTA) that drives a variable current source connected to the transducer. The positive input to the OTA is a DC voltage with the AC signal from the transducer imposed on it. The negative input is a DC reference voltage, which floats with respect to signal ground in the PSE preamp and is generated with respect to signal ground in the SE preamp.
Various embodiments of the signal trace configuration on the suspension are described. In a single-layer embodiment, the common return lead is split into two traces on the suspension which are interleaved with the three dedicated signal traces. In a dual-layer embodiment, the three dedicated signal traces are placed in one layer and common return lead is placed in a second layer. In one embodiment a shielding network of traces acts like a shield in a coaxial cable.
The common lead connections of the slider, suspension, and preamplifier creates the common lead system, which allows for a substantial reduction in layout area for the interconnects in the slider, for the suspension, and in the arm IC. Utilizing a common-lead connection according to embodiments of the invention for the plurality of readers creates compact electrical connections between the amplifier and the readers. The suspension can then have a reduced or minimum number of signal traces. Therefore, a common-lead architecture readers (CLAR) system enables a compact system design of the TMR transducers, suspension, and amplifier. The CLAR solution reduces the electrical traces/wiring for the three segments of the front-end system: 1) heads and slider, 2) suspension, and 3) a multiple reader preamplifier. The CLAR system reduces the I/O count which helps reduce the layout area for a more compact design of all three front-end segments. A common-lead (CL) connection is used for the slider, which enables a compact design of the readers. In addition, this architecture allows for lower power consumption using single-ended preamplifier circuit designs with a single supply voltage.
For a three reader (3R) system, the minimum total number of connection pads is 4 (R1, R2, R3, & Rg), where Rg is the CL connection. For the suspension interconnection, using a CL design allows for a reduction of leads in a 3R system, from 6 to 4 leads. This suspension interconnect can be a dual layer configuration or a coplanar configuration with interstitial return lines, which then allows for the reduction of lines from 6 to 5 lines. With both the dual-layer and coplanar suspension interconnect, the CL connection allows for a reduction of I/Os and area savings in the layout.
Single-ended (SE) or pseudo single-ended (PSE) amplifier designs can be used in a system with the CL connection to achieve compact connection between the R/W IC and the plurality of readers.
In contrast in the SE embodiment the current source I0 is connected to the common lead, which is also the power supply return and, therefore, V-ref2 96 is directly referenced to common lead level. In the SE embodiment the common lead is the signal ground, so the signal return symbol in
The transistors Q1, Q2, Q3 are effectively DC current sources that pull current through their corresponding resistors connected to their collectors, which are connected to the corresponding positive input leads to the OTAs. The variable signal from the TMR transducers is a midband AC signal, for which the transistors Q1, Q2, Q3 act as a short circuit. Therefore, the AC signal from a transducer passes from the emitter lead through the corresponding transistor and is applied to the positive input of the corresponding OTA. The OTAs generate a signal that drives the variable current sources that supply the bias current to the transducers. The negative input of each OTA is a reference voltage, therefore, the OTAs act to control the bias current through the transducers so that the difference between the positive and negative inputs tends toward zero in the operational frequency band of the OTAs.
In the PSE embodiment the variable current sources are paired push-pull sources in which one source supplies the transducer and the other source provides a balancing return path for the current from the emitter of Q4, which is connected to current source I4. The base lead of Q4 is connected to the negative side of the floating voltage bias source V-bias. The positive side of V-bias is connected to each of the base leads of Q1-Q3. The emitters of Q1-Q3 are connected to corresponding current sources I1-I3. These current sources have a high impedance with respect to the transducer signal frequency and therefore, are effectively open circuits with respect to the transducer signal.
The intermediate output signals Va, Vb, Vc are further processed by subtracting the V-ref signal 95, i.e. the final output signal for each transducer is the difference between its intermediate output signal (Va, Vb, or Vc) and the V-ref signal 95. Differential amplifiers in the next stage as shown in
There are fewer active components in the SE embodiment than in the PSE embodiment. The variable current sources 97a-c in the PSE embodiment are push-pull current sources. The variable current sources 98a-c in the SE embodiment of
The PSE embodiment in
1. A disk drive comprising:
- a slider with a plurality of read transducers that are each connected to a common return signal lead;
- a suspension with a set of signal traces that include a first trace connected to the common return signal lead in the slider and a selected signal trace connected respectively to each of the plurality of read transducers; and
- a preamplifier connected to the set of signal traces on the suspension, the preamplifier having an input from each of the read transducers and being connected to the first trace as the common return signal lead, the preamplifier supplying a bias current for each read transducer through the selected signal trace connected to each read transducer.
2. The disk drive of claim 1 wherein the preamplifier further comprises a plurality of operational transconductance amplifiers (OTAs) with each OTA driving a variable current source that supplies the bias current for one of the read transducers.
3. The disk drive of claim 2 wherein each operational transconductance amplifier (OTA) has a DC reference voltage as a negative input and a positive input of DC voltage with an AC signal from one of the read transducers.
4. The disk drive of claim 2 wherein each wherein each operational transconductance amplifier (OTA) has a DC reference voltage as a negative input and a positive input signal that includes a DC voltage generated by a current flowing through a resistor and a transistor configured as a current source with an emitter of the transistor being connected to one of the read transducers; and wherein an AC signal from the read transducer passes through the transistor and is applied to the positive input signal of the OTA.
5. The disk drive of claim 4 wherein the transistor's base lead is connected to a positive output of a voltage bias source.
6. The disk drive of claim 1 wherein the set of signal traces on the suspension are arranged in a first layer with at least two selected traces being connected to the common return signal lead.
7. The disk drive of claim 1 wherein the two selected traces connected to the common return signal lead are arranged with one of the selected signal traces connected to the read transducers extending between the two selected traces.
8. The disk drive of claim 1 wherein the slider include at least three read transducers and the set of signal traces on the suspension includes first, second and third signal traces, and wherein the first, second and third signal traces are arranged in a first layer and the trace connected to the common return signal lead is positioned in a second layer under the first layer and wherein the trace connected to the common return signal lead is at least as wide as the first, second and third signal traces combined.
9. The disk drive of claim 1 wherein the slider include at least three read transducers and the set of signal traces on the suspension includes first, second and third signal traces, and wherein the first, second and third signal traces are arranged in a first layer and wherein first and second common lead traces connected to the common return signal lead are positioned in the first layer and wherein the first common lead trace is positioned between the first and second signal traces and the second common lead trace is positioned between the second and third signal traces.
10. The disk drive of claim 9 wherein the suspension includes a shielding network of conductive material in a second layer disposed above the first layer containing the first, second and third signal traces, and wherein the shielding network of conductive material in the second layer is connected to the first and second common lead traces through vias that are filled with electrically conductive material and extend through dielectric material separating the first and second layers.
11. The disk drive of claim 1 wherein the preamplifier has a single supply voltage and a voltage supply return line that is directly connected to the common return signal lead.
12. The disk drive of claim 1 wherein the preamplifier includes a plurality of differential amplifiers that each have an input signal from a selected read transducer and an input of a reference voltage.
13. The disk drive of claim 12 wherein the reference voltage is generated with respect to the common return signal lead.
14. The disk drive of claim 12 wherein the reference voltage is generated with respect to a supply voltage and floats with respect to the common return signal lead.
15. The disk drive of claim 1 wherein the preamplifier is a single-ended design in which a reference voltage that is used as a differential signal for subtraction from signals from the read transducers and the reference voltage is generated with respect to the common return signal lead.
16. The disk drive of claim 1 wherein the preamplifier is a pseudo-single-ended design in which a reference voltage that is used as a differential signal for subtraction from signals from the read transducers and the reference voltage floats with respect to the common return signal lead.
Filed: Sep 18, 2014
Publication Date: Mar 19, 2015
Inventors: John Contreras (Palo Alto, CA), Joey Martin Poss (Rochester, MN), Rehan Ahmed Zakai (San Ramon, CA)
Application Number: 14/489,477
International Classification: G11B 20/10 (20060101); G11B 5/48 (20060101);