Datasheet

+
-
AMPLIFIER UNDER
TEST
+6.5V
-6.5V
R
LOAD
1k:
50:
2V
0
0
-2V
OR
HP 8082
PULSE
GENERATOR
TEK 7633
STORAGE SCOPE
+
TEK 7S14
SAMPLING INPUT
V
OUT
t
V
F
0
T
SR
T
SET
T
PD
LM6588
SNOSA77D –MAY 2003–REVISED MARCH 2013 www.ti.com
Figure 34. Large Signal Transient Response of an Operational Amplifier
Figure 34 illustrates how an op amp responds to a large-signal transient. When such a transient occurs at t = 0,
the output does not start changing until T
PD
, which is the op amp’s propagation delay time (typically 20ns for the
LM6588). The output then changes at the op amp’s slew rate from t = T
PD
to T
SR
. From t = T
SR
to T
SE
T, the
output settles to its final value (V
F
) at a speed determined by the op amp’s small-signal frequency response.
Although propagation delay and slew limited response time (t = 0 to T
SR
) can be calculated from data sheet
specifications, the small signal settling time (T
SR
to T
SET
) cannot. This is because an op amp’s gain vs. frequency
has multiple poles, and as a result, small-signal settling time can not be calculated as a simple function of the op
amp’s gain bandwidth. Therefore, the only accurate method for determining op amp settling time is to measure it
directly.
Figure 35. Gamma Buffer Settling Time Test Circuit
The test circuit in Figure 35 was used to measure LM6588 settling time for a 2V pulse and 1kΩ load, which
represents the maximum transient amplitude and output load for a gamma buffer. With this test system, the
LM6588 settled to within ±30mV of 2V pulse in approximately 170ns. Settling time for a 0 to –2V pulse was
slightly less, 150ns. These values are much smaller than the desired response time of 1μs, so the LM6588 has
sufficient bandwidth and slew rate for regulating gamma line transients.
PANEL REPAIR BUFFER
It is not uncommon for a TFT panel to be manufactured with an open in one or two of its column or row lines. In
order to repair these opens, TFT panels have uncommitted repair lines that run along their periphery. When an
open line is identified during a panel’s final assembly, a repair line re-routes its signal past the open. Figure 36
illustrates how a column is repaired. The column driver’s output is sent to the other end of an open column via a
repair line, and the repair line is driven by a panel repair buffer. When a column or row line is repaired, the
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