Tandberg Data
Introduction to the Drive
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Tandberg SLR Reference Manual
2-7
Read Channel SLR50
The read channel consists of the three ASICs: Preamplifier, READ
(Read Equalizer And
Detector)
and Dataseparator. The low-noise preamplifier ASIC features individually
programmable gain and MR-head sense current.
The READ circuit is a mixed digital/analog ASIC that performs signal conditioning and
detection. The circuit features fully programmable electronic filtering for high flexibility. This
enables coverage of a wide range of tape formats and speeds, and a very good and
consistent drive-to-drive read performance.
The Dataseparator circuit is a mixed digital/analog ASIC that performs the clock recovery of
the detected read signal. Most of the circuitry is digital and based upon oversampling the
detected read signal. The digital implementation secures high accuracy of the implemented
delays and pulse-widths, thereby keeping the timing window margins very good.
A special feature of the Write/Read Channel is a
“Write/Read Test Loop”
. This loop is used to
perform a selftest of the Write and Read Channels during Drive selftest
Read Channel SLR7/60/75/100/140
A PRML (Partial Response Maximum Likelihood) Read Channel has been implemented
which brings higher density and performance compared to the ”peak detection” mechanism
implemented on the SLR24/50. The read back signal coming from the head is amplified and
shaped by the Preamplifier and READ ASICs. The analog signals are then received by the
Overland’s VR
2
ASIC and converted to the digital signals. The Viterbi detection algorithms
then look for the best match (maximum likelihood) of least error with incoming data.
Erase Circuit (Tandberg SLR50 only)
The Erase circuit/head provides full-width tape erasure for writing of backwards compatible
tape formats.
“Double fault protection/single fault detection”
is also an Erase circuit feature.
Head Servo System (Not for Tandberg SLR7)
To achieve the required positioning accuracy, the SLR servo system comprises two
positioning components.
In addition to a normal
stepper motor
for coarse head positioning to, or in close vicinity to the
track, a so-called
voice coil
with a linear operating range of ±0.075 mm (±3 mil) is used to
fine position the head with respect to the track center-line.
The Voice Coil Motor is part of a
head positioning feed-back loop
which includes a servo-
controller ASIC containing an
Analog Front End Signal Processor
and a
Digital Signal Proc-
essor (DSP).
The
Analog Front End Signal Processing
demodulates the signals from the
servo track, converting them to a position error signal which is passed on to the DSP. Based
on a position control algorithm, the DSP will control the Voice Coil Motor in such a way that
the position error is minimized.