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參數(shù)資料
| 型號(hào)： | LM6588MAX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 運(yùn)算放大器 |
| 英文描述： | TFT-LCD Quad, 16V RRIO High Output Current Operational Amplifier |
| 中文描述： | QUAD OP-AMP, 4000 uV OFFSET-MAX, 15.3 MHz BAND WIDTH, PDSO14 |
| 封裝： | SOIC-14 |
| 文件頁(yè)數(shù)： | 13/16頁(yè) |
| 文件大小： | 603K |
| 代理商： | LM6588MAX |
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TFT Display Application
(Continued)
GAMMA BUFFER
Illumination in a TFT display, also referred to as grayscale, is
set by a series of discrete voltage levels that are applied to
each LCD pixel. These voltage levels are generated by
resistive DAC networks that reside inside each of the column
driver ICs. For example, a column driver with 64 Grayscale
levels has a two 6 bit resistive DACs. Typically, the two
DACs will have their 64 resistors grouped into four seg-
ments, as shown in
Figure 8
. Each of these segments is
connected to external voltage lines, VGMA1 to VGMA10,
which are the Gamma Levels. VGMA1 to VGMA5 set gray-
scale voltage levels that are positive with respect to V
(high polarity gamma levels). VGMA6 to VGMA10 set gray-
scale voltages negative with respect to V
COM
(low polarity
gamma levels).
Figure 9
shows how column drivers in a TFT display are
connected to the gamma levels. VGMA1, VGMA5, VGMA6,
and VGMA10 are driven by the Gamma Buffers. These
buffers serve as low impedance voltage sources that gener-
ate the display’s gamma levels. The Gamma Buffers’ outputs
are set by a simple resistive ladder, as shown in
Figure 9
.
Note that VGMA2 to VGMA4 and VGMA7 to VGMA9 are
usually connected to the column drivers even though they
are not driven by external buffers. Doing so, forces the
gamma levels in all the column drivers to be identical, mini-
mizing grayscale mismatch between column drivers. Refer-
ring again to
Figure 9
, the resistive load of a column driver
DAC (i.e. resistance between GMA1 to GMA5) is typically
10k
to 15k
. On a typical display such as XGA, there can
be up to 10 column drivers, so the total resistive load on a
Gamma Buffer output can be as low as 1k
. The voltage
between VGMA1 and VGMA5 can range from 3V to 6V,
depending on the type of TFT panel. Therefore, maximum
load current supplied by a Gamma Buffer is approximately
6V/1k
= 6mA, which is a relatively light load for most op
amps. In many displays, VGMA1 can be less than 500mV
below V
, and VGMA10 can be less than 500mV above
ground. Under these conditions, an op amp used for the
Gamma Buffer must have rail-to-rail inputs and outputs, like
the LM6588.
Another important specification for Gamma Buffers is small
signal bandwidth and slew rate. When column drivers select
which voltage levels are written to a row of pixels, their
internal DACs inject current spikes into the Gamma Lines.
This generates voltage transients at the Gamma Buffer out-
puts, and they should settle-out in less than 1μs to insure a
steady output voltage from the column drivers. Typically,
these transients have a maximum amplitude of 2V, so a
gamma buffer must have sufficient bandwidth and slew rate
to recover from a 2V transient in 1μs or less.
Figure 10
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
, 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
to T
SR
. From t = T
to T
T, the output settles
to its final value (V
) at a speed determined by the op amp’s
small-signal frequency response. Although propagation de-
20073433
FIGURE 8. Simplified Schematic of Column Driver IC
20073434
FIGURE 9. Basic Gamma Buffer Configuration
20073435
FIGURE 10. Large Signal Transient Response of an
Operational Amplifier
L
www.national.com
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM6588MAX/NOPB | 功能描述:運(yùn)算放大器 - 運(yùn)放 RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補(bǔ)償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LM6588MT | 功能描述:運(yùn)算放大器 - 運(yùn)放 RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補(bǔ)償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LM6588MT/NOPB | 功能描述:運(yùn)算放大器 - 運(yùn)放 Tft-Lcd 16V,Quad Op Amp,High RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補(bǔ)償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LM6588MT/NOPB | 制造商:Texas Instruments 功能描述:Operational Amplifier (Op-Amp) IC |
| LM6588MTX | 功能描述:運(yùn)算放大器 - 運(yùn)放 RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補(bǔ)償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
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