Dynamic magnetic information storage or retrieval – General recording or reproducing – Specifics of the amplifier
Reexamination Certificate
1999-08-30
2001-07-03
Faber, Alan T. (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Specifics of the amplifier
C360S053000
Reexamination Certificate
active
06256161
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a disk drive read circuit, and more particularly to an echo cancellation system employed in the disk drive read circuit to improve the quality of a signal detected by a transducing read head from a data track of a disk.
In the current state of technology, large amounts of data may be stored on data tracks of a rotatable disk as encoded magnetic transitions representing logical binary 0's and 1's. These magnetic transitions are detected, or read, by a sensor, or transducing head, suspended over the surface of the disk as it rotates. The sensor provides an input signal based on the detected magnetic transitions on the disk to preamplifier circuitry located at a distance from the sensor, with an electrical interconnect being provided between the sensor and the preamplifier circuitry.
FIG. 1
is a simplified illustration of the underside of a typical disk drive configuration, including support structure
12
carrying slider
14
including transducing head
16
over the surface of a rotating disk. Sensor
16
is electrically connected to preamplifier circuit
20
by interconnect
18
.
One problem with disk drive systems such as the one shown in
FIG. 1
is that the input signal provided by head
16
is reflected by preamplifier circuit
20
due to an impedance mismatch between interconnect
18
and preamplifier circuit
20
, and then reflected again by head
16
due to an impedance mismatch between interconnect
18
and head
16
. As a result, the composite signal received by preamplifier circuit
20
includes both the true input signal and a delayed, distorted version of the input signal, which degrades the accuracy of the disk drive system in detecting magnetic transitions from the rotating disk.
FIG. 2
illustrates the signal generated by head
16
as it travels and is reflected between head
16
and preamplifier circuit
20
along interconnect
18
. The original input signal
22
is generated by head
16
, and after one propagation delay (T) is received as signal
23
at preamplifier circuit
20
. Signal
23
is the desired, undistorted signal that accurately represents the data transitions encoded on the magnetic disk. However, because interconnect
18
is not impedance matched to preamplifier circuit
20
, the incoming signal is partially reflected back along interconnect
18
to head
16
. Reflected signal
24
is received by head
16
after another propagation delay (T), and is attenuated and distorted based on the reflection coefficient of the preamplifier/interconnect interface (K
PA
). Reflected signal
24
is again reflected due to the impedance mismatch between head
16
and interconnect
18
, resulting in re-reflected signal
25
being received at preamplifier circuit
20
one more propagation delay (T) later. Re-reflected signal
25
is further attenuated and distorted according to the reflection coefficient of the head/interconnect interface (K
MR
). The reflection process continues until the attenuation of the signal reaches negligible levels, and composite signal
26
received by preamplifier circuit
20
therefore includes undesirable reflected components that degrade the circuit's ability to accurately detect data transitions encoded on the disk.
One potential solution to the reflection problem is to impedance match either the preamplifier/interconnect interface or the head/interconnect interface. However, impedance matching the preamplifier/interconnect interface inherently introduces additional noise into the system, and because of the low signal levels utilized in disk drive technology, such impedance matching would reduce the signal-to-noise ratio of the system to an unacceptable level. Impedance matching the head/interconnect interface is not practical because the impedance of the head is not a tightly controlled parameter in manufacturing. Therefore, there is a need in the art for a solution that eliminates undesired reflected signals at the disk drive preamplifier while maintaining an acceptable signal-to-noise ratio to accurately detect the data transition signals encoded on the disk.
BRIEF SUMMARY OF THE INVENTION
The present invention is an echo cancellation circuit and technique for use in a disk drive circuit having a transducing head connected to a preamplifier circuit by an electrical interconnect with a first time delay, a first interface between the preamplifier and the electrical interconnect having a first reflection coefficient and a second interface between the transducing head and the electrical interconnect having a second reflection coefficient. The echo cancellation circuit delays a preamplifier output signal with a second time delay, the second time delay being double the first time delay. The preamplifier output signal is also filtered so as to simulate the effects of the first and second reflection coefficients. The delayed and filtered signal is then subtracted from the preamplifier output signal, thereby removing echo content from the signal.
REFERENCES:
patent: 4914398 (1990-04-01), Jove et al.
patent: 5852521 (1998-12-01), Umeyama et al.
patent: 6046876 (2000-04-01), Osafune et al.
Doherty Sally A.
Leighton John D.
Agere Systems Guardian Corp.
Faber Alan T.
Kinney & Lange , P.A.
LandOfFree
Echo cancellation for disk drive read circuit does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Echo cancellation for disk drive read circuit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Echo cancellation for disk drive read circuit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2519960