- 您現(xiàn)在的位置：買(mǎi)賣(mài)IC網(wǎng) > PDF目錄369797 > LM9820 PDF資料下載
參數(shù)資料
| 型號(hào)： | LM9820 |
| 文件頁(yè)數(shù)： | 17/20頁(yè) |
| 文件大?。?/td> | 245K |
| 代理商： | LM9820 |
第1頁(yè)第2頁(yè)第3頁(yè)第4頁(yè)第5頁(yè)第6頁(yè)第7頁(yè)第8頁(yè)第9頁(yè)第10頁(yè)第11頁(yè)第12頁(yè)第13頁(yè)第14頁(yè)第15頁(yè)第16頁(yè)當(dāng)前第17頁(yè)第18頁(yè)第19頁(yè)第20頁(yè)
Applications Information
(Continued)
LM9810/20 enters the Power Down mode. Recovery from
Power Down typically takes 50 μs (the time required for
the reference voltages to settle to 0.5 LSB accuracy).
2.0 CLAMPING
To perform a DC restore across the AC coupling capaci-
tors at the beginning of every line, the LM9810/20 imple-
ments a clamping function. When NewLine is high and
SampCLK is low, all three OS inputs will be connected to
either V
or V
, depending on B4 of the Sampling
and Color Mode register. If B4 is set to one (positive signal
polarity), then the OS inputs will be connected to V
. If
B4 is set to zero (negative signal polarity), then they will
be connected to V
REF+
.
2.1 Clamp Capacitor Selection
This section explains how to select appropriate clamp
capacitor values.
The output signal of many sensors rides on a DC offset
(greater than 5V for many CCDs) which is incompatible
with the LM9810/20’s 5V operation. To eliminate this off-
set without resorting to additional higher voltage compo-
nents, the output of the sensor is AC coupled to the
LM9810/20 through a DC blocking capacitor, C
. The
sensor’s DOS output, if available, is not used. The value
of this capacitor is determined by the leakage current of
the LM9810/20’s OS input and the output impedance of
the sensor. The leakage through the OS input determines
how quickly the capacitor value will drift from the clamp
value of ,V
or V
, which then determines how
many pixels can be processed before the droop causes
errors in the conversion (
±
0.1V is the recommended limit
for CDS operation). The output impedance of the sensor
determines how quickly the capacitor can be charged to
the clamp value during the black reference period at the
beginning of every line.
The minimum clamp capacitor value is determined by the
maximum droop the LM9810/20 can tolerate while con-
verting one sensor line. The minimum clamp capacitor
value is much smaller for CDS mode applications than it is
for CIS mode applications. The LM9810/20 input leakage
current is considerably less when the LM9810/20 is oper-
ating in CDS mode. In CDS mode, the LM9810/20 leak-
age current should be no more than 20 nA. With CDS
disabled, which will likely be the case when CIS sensors
are used, the LM9810/20 leakage current can be as high
as 25 μA at the maximum conversion rate.
2.1.1 CDS Mode Minimum Clamp Capacitor
Calculation
The following figure takes the maximum leakage current
into the OS input, the maximum allowable droop, the
number of pixels on the sensor, and the pixel conversion
rate, f
SampCLK
, and provides the minimum clamp capacitor
value:
(7)
For example, if the OS input leakage current is 20 nA
worst-case, the sensor has 2700 active pixels, the con-
version rate is 2 MHz (t
= 500 ns), and the max
droop desired is 0.1V, the minimum clamp capacitor value
is:
(8)
2.1.2 CIS Mode Minimum Clamp Capacitor
Calculation
If CDS is disabled, then the maximum LM9810/20 OS
input leakage current can be calculated from:
I
LEAKAGE
= V
SAT
f
SampCLK
C
SAMP
where V
is the peak pixel signal swing of the CIS OS
output and C
is the capacitance of the LM9810/20’s
internal sampling capacitor (2 pF). Inserting this into
Equation (7) results in:
(9)
(10)
with C
SAMP
equal to 2 pF and V
SAT
equal to 2V (the
LM19810/20’s maximum input signal), then Equation (10)
reduces to:
(11)
In CIS mode (CDS disabled), the max droop limit must be
much more carefully chosen, since any change in the
clamp capacitor’s DC value will affect the LM9810/20’s
conversion results. If a droop of one 10-bit LSB across a
line is considered acceptable, then the allowed droop
voltage is calculated as 2V/1024, or approximately 2 mV.
If there are 2700 active pixels on a line then:
(12)
2.1.3 Maximum Clamp Capacitor Calculation
The maximum size of the clamp capacitor is determined
by the amount of time available to charge it to the desired
value during the optical black portion of the sensor output.
The internal clamp is on when NewLine is high and Samp-
CLK is low. If the applied SampCLK is low for half its
cycle, then the available charge time per line can be
calculated using:
DS100943-82
FIGURE 10. OS Clamp Capacitor and Internal Clamp
L
www.national.com
17
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LM9822CCWM | Signal Conditioner |
| LM9822CCWMX | Signal Conditioner |
| LM9823 | |
| LMA110 | .5-6 GHz MESFET Amplifier |
| LMA110A | .5-6 GHz MESFET Amplifier |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM9820CCWM | 制造商:NSC 制造商全稱(chēng):National Semiconductor 功能描述:LM9810/20 10/12-Bit Image Sensor Processor Analog Front End |
| LM9820CCWMX | 制造商:NSC 制造商全稱(chēng):National Semiconductor 功能描述:LM9810/20 10/12-Bit Image Sensor Processor Analog Front End |
| LM9822 | 制造商:NSC 制造商全稱(chēng):National Semiconductor 功能描述:LM9822 3 Channel 42-Bit Color Scanner Analog Front End |
| LM9822CCWM | 制造商:Rochester Electronics LLC 功能描述: 制造商:Texas Instruments 功能描述: |
| LM9822CCWM/NOPB | 功能描述:ADC / DAC多通道 RoHS:否 制造商:Texas Instruments 轉(zhuǎn)換速率: 分辨率:8 bit 接口類(lèi)型:SPI 電壓參考: 電源電壓-最大:3.6 V 電源電壓-最小:2 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-40 |
發(fā)布緊急采購(gòu)，3分鐘左右您將得到回復(fù)。