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参数资料
| 型号： | EL2120CS |
| 元件分类： | 运算放大器 |
| 英文描述： | 100 MHz Current Feedback Amplifier |
| 中文描述： | 100 MHz电流反馈放大器 |
| 文件页数： | 12/12页 |
| 文件大小： | 354K |
| 代理商： | EL2120CS |
EL2120C
100 MHz Current Feedback Amplifier
Applications Information
The EL2120C represents the third generation of
current-feedback amplifier design It is designed
to provide good high-frequency performance over
wide supply voltage load impedance gain tem-
perature and manufacturing lot variations It is
a well-behaved amplifier in spite of its 100 MHz
bandwidth but a few precautions should be tak-
en to obtain maximum performance
The power supply pins must be well bypassed
001
mF ceramic capacitors are adequate but lead
length should be kept below
and a ground
plane is recommended Bypassing with 47
mF
tantalum capacitors can improve settling charac-
teristics and smaller capacitors in parallel will
not be needed The lead length of sockets general-
ly deteriorates the amplifier’s frequency response
by exaggerating peaking and increasing ringing
in response to transients Short sockets cause lit-
tle degradation
Load capacitance also increases ringing and
peaking Capacitance greater than 35 pF should
be isolated with a series resistor Capacitance at
the VINb terminal has a similar effect and
should be kept below 5 pF Often the inductance
of the leads of a load capacitance will be self-reso-
nant at frequencies from 40 MHz to 200 MHz
and can cause oscillations A resonant load can be
de-Q’ed with a small series or parallel resistor A
‘‘snubber’’ can sometimes be used to reduce reso-
nances This is a resistor and capacitor in series
connected from output to ground Values of 68
X
and 33 pF are typical Increasing the feedback
resistor can also improve frequency flatness
The VINa pin can oscillate in the 200 MHz to
500 MHz realm if presented with a resonant or
inductive source impedance A series 27
X to 68X
resistor right on the VINa pin will suppress such
oscillations without affecting frequency response
b
3 dB bandwidth is inversely proportional to
the value of feedback resistor RF The EL2120C
will tolerate values as low as 180
X for a maxi-
mum bandwidth of about 140 MHz but peaking
will increase and tolerance to stray capacitance
will reduce At gains greater than 5 b3 dB band-
width begins to reduce and a smaller RF can be
used to maximize frequency response
The greatest frequency response flatness (to
01 dB for instance) occurs with RF e 300X to
330
X Even the moderate peaking caused by low-
er values of RF will cause the gain to peak out of
the 01 dB window and higher values of RF will
cause an overcompensated response where the
gain falls below the 01 dB level Parasitic capaci-
tances will generally degrade the frequency flat-
ness
The EL2120C should not output a continuous
current above 50 mA as stated in the ABSO-
LUTE MAXIMUM RATINGS table The out-
put current limit is set to 120 mA at a die temper-
ature of 25 C and reduces to 85 mA at a die tem-
perature of 150 C This large current is needed to
slew load capacitance and drive low impedance
loads with low distortion but cannot be support-
ed continuously Furthermore package dissipa-
tion capabilities cannot be met under short-cir-
cuit conditions Current limit should not occur
longer than a few seconds
The output disable function of the EL2120C is
optimized for video performance While in dis-
able mode the feedthrough of the circuit can be
modeled as a 02 pF capacitor from VINa to the
output No more than g5V can be placed be-
tween VINa and VINb in disable mode but this
is compatible with common video signal levels
In disabled state the output can withstand about
1000 V
ms slew rate signals impressed on it with-
out the output transistors turning on
The
Disable pin logic level is referred to Va
With g5V supplies a CMOS or TTL driver with
pull-up resistor will suffice g15V supplies re-
quire a a14 a11V drive span or a15 a10V
nominally
Open-collector TTL with a tapped
pull-up resistor can provide these spans The im-
pedance of the divider should be 1k or less for
optimum enabledisable speed
The EL2120C enables in 50 ns or less When VIN
e
0 only a small switching glitch occurs at the
output When VIN is some other value the out-
put overshoots by about 07V when settling
toward its new enabled value
9
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