LT1227 데이터 시트보기 (PDF) - Linear Technology
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LT1227 Datasheet PDF : 12 Pages
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SI PLIFIED SCHE ATIC
14k
CURRENT
SOURCE
BIAS
8
S/D
+IN 3
NULL 1
NULL 5
2 –IN
LT1227
7 V+
6 VOUT
4 V–
1227 SS
APPLICATI S I FOR ATIO
The LT1227 is a very fast current feedback amplifier.
Because it is a current feedback amplifier, the bandwidth
is maintained over a wide range of voltage gains. The
amplifier is designed to drive low impedance loads such as
cables with excellent linearity at high frequencies.
Feedback Resistor Selection
The small-signal bandwidth of the LT1227 is set by the
external feedback resistors and the internal junction ca-
pacitors. As a result, the bandwidth is a function of the
supply voltage, the value of the feedback resistor, the
closed-loop gain and load resistor. The characteristic
curves of Bandwidth vs Supply Voltage show the effect of
a heavy load (100Ω) and a light load (1k). These curves
use a solid line when the response has less than 0.5dB of
peaking and a dashed line when the response has 0.5dB to
5dB of peaking. The curves stop where the response has
more than 5dB of peaking.
At a gain of two, on ±15V supplies with a 1k feedback
resistor, the bandwidth into a light load is over 140MHz,
but into a heavy load the bandwidth reduces to 120MHz.
The loading has this effect because there is a mild reso-
nance in the output stage that enhances the bandwidth at
light loads but has its Q reduced by the heavy load. This
enhancement is only useful at low gain settlings; at a gain
of ten it does not boost the bandwidth. At unity gain, the
enhancement is so effective the value of the feedback
resistor has very little effect. At very high closed-loop
gains, the bandwidth is limited by the gain bandwidth
product of about 1GHz. The curves show that the band-
width at a closed-loop gain of 100 is 12MHz, only one tenth
what it is at a gain of two.
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