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EL4451CN

更新时间: 2024-10-27 22:49:11
品牌 Logo 应用领域
英特矽尔 - INTERSIL 放大器光电二极管
页数 文件大小 规格书
10页 185K
描述
Wideband Variable-Gain Amplifier, Gain of 2

EL4451CN 数据手册

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EL4451  
The gain of the feedback divider is:  
H = R /(R + R )  
transfer curve. Generally, an applied V  
GAIN  
+2.5V will assure the full numerical span of 0 V  
range of -0.5V to  
2.  
GAIN  
G
G
F
The gain control has a small-signal bandwidth equal to the  
channel bandwidth, and overload recovery resolves in  
The transfer function of the part is:  
V
IN  
V
= A × (((V +) - (V -)) × ((V  
+) - (V  
-)) +  
about 20nsec.  
OUT  
O
IN IN GAIN  
GAIN  
(V  
- V ))  
FB  
REF  
Input Connections  
V
V
is connected to V through a feedback network, so  
OUT  
FB  
The input transistors can be driven from resistive and  
capacitive sources, but are capable of oscillation when  
presented with an inductive input. It takes about 80nH of  
series inductance to make the inputs actually oscillate,  
equivalent to four inches of unshielded wiring or 6 of  
unterminated input transmission line. The oscillation has a  
characteristic frequency of 500MHz. Often placing one’s  
finger (via a metal probe) or an oscilloscope probe on the  
input will kill the oscillation. Normal high-frequency  
construction obviates any such problems, where the input  
source is reasonably close to the input. If this is not possible,  
one can insert series resistors of around 51to de-Q the  
inputs.  
= H × V  
. A is the open-loop gain of the amplifier,  
FB  
OUT  
O
and is approximately 600. The large value of A drives:  
O
((V +)-(V -))×((V  
+)-(V  
-))+(V  
REF  
- V ) 0  
FB  
IN IN GAIN  
GAIN  
Rearranging and substituting for V  
FB:  
V
V
= (((V +) - (V -)) × ((V  
IN IN  
+) - (V )) +  
GAIN  
OUT  
)/H  
GAIN  
REF  
or  
V
= (V × V + V  
IN GAIN REF  
)/H  
OUT  
Thus the output is equal to the difference of the V ’s times  
IN  
the difference of V  
by the feedback divider ratio. The EL4451 is stable for a  
direct connection between V and FB, and the divider  
may be used for higher output gain, although with the  
traditional loss of bandwidth.  
and offset by V  
, all gained up  
GAIN’S  
REF  
Signal Amplitudes  
Signal input common-mode voltage must be between  
(V-)+3V and (V+)-3V to ensure linearity. Additionally, the  
differential voltage on any input stage must be limited to ±6V  
to prevent damage. The differential signal range is ±2V in the  
EL4451. The input range is substantially constant with  
temperature.  
OUT  
It is important to keep the feedback divider’s impedance at  
the FB terminal low so that stray capacitance does not  
diminish the loop’s phase margin. The pole caused by the  
parallel impedance of the feedback resistors and stray  
capacitance should be at least 150MHz; typical strays of 3pF  
thus require a feedback impedance of 360or less.  
The Ground Pin  
The ground pin draws only 6µA maximum DC current, and  
may be biased anywhere between(V-)+2.5V and (V+)-3.5V.  
The ground pin is connected to the IC’s substrate and  
frequency compensation components. It serves as a shield  
within the IC and enhances input stage CMRR and  
feedthrough over frequency, and if connected to a potential  
other than ground, it must be bypassed.  
Alternatively, a small capacitor across R can be used to  
F
create more of a frequency-compensated divider. The value  
of the capacitor should scale with the parasitic capacitance  
at the FB input. It is also practical to place small capacitors  
across both the feedback and the gain resistors (whose  
values maintain the desired gain) to swamp out parasitics.  
For instance, two 10pF capacitors across equal divider  
resistors for a maximum gain of 4 will dominate parasitic  
effects and allow a higher divider resistance.  
Power Supplies  
The EL4451 works with any supplies from ±3V to ±15V. The  
supplies may be of different voltages as long as the  
requirements of the ground pin are observed (see the  
Ground Pin section). The supplies should be bypassed close  
to the device with short leads. 4.7µF tantalum capacitors are  
very good, and no smaller bypasses need be placed in  
parallel. Capacitors as small as 0.01µF can be used if small  
load currents flow.  
The REF pin can be used as the output’s ground reference,  
for DC offsetting of the output, or it can be used to sum in  
another signal.  
Gain-Control Characteristics  
The quantity V  
0 V  
GAIN  
in the above equations is bounded as  
2, even though the externally applied voltages  
GAIN  
Single-polarity supplies, such as +12V with +5V can be  
used, where the ground pin is connected to +5V and V- to  
ground. The inputs and outputs will have to have their levels  
shifted above ground to accommodate the lack of negative  
supply.  
exceed this range. Actually, the gain transfer function around  
0 and 2V is “soft”, that is, the gain does not clip abruptly  
below the 0%-V  
level. An overdrive of 0.3V must be applied to V  
GAIN  
obtain truly 0% or 100%. Because the 0%- or 100%- V  
voltage nor above the 100%-V  
GAIN  
GAIN  
to  
GAIN  
The power dissipation of the EL4451 increases with power  
supply voltage, and this must be compatible with the  
levels cannot be precisely determined, they are extrapolated  
from two points measured inside the slope of the gain  
7

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