EL2020C View Datasheet(PDF) - Elantec -> Intersil
Part Name
Description
MFG CO.
'EL2020C' PDF : 20 Pages View PDF
EL2020C
50 MHz Current Feedback Amplifier
Application Information Contd
Offset Adjust
To calculate the amplifier system offset voltage
from input to output we use the equation
Output Offset Voltage e VOS (RF RGa1) g
IBIAS (RF)
The EL2020 output offset can be nulled by using
a 10 kX potentiometer from pins 1 to 5 with the
slider tied to pin 7 (aVCC) This adjusts both the
offset voltage and the inverting input bias cur-
rent The typical adjustment range is g80 mV at
the output
Compensation
The EL2020 is internally compensated to work
with external feedback resistors for optimum
bandwidth over a wide range of closed loop gain
The part is designed for a nominal 1 kX of feed-
back resistance although it is possible to get
more bandwidth by decreasing the feedback re-
sistance
The EL2020 becomes less stable by adding ca-
pacitance in parallel with the feedback resistor
so feedback capacitance is not recommended
The EL2020 is also sensitive to stray capacitance
from the inverting input to ground so the board
should be laid out to keep the physical size of this
node small with ground plane kept away from
this node
Active Filters
The EL2020’s low phase lag at high frequencies
makes it an excellent choice for high performance
active filters The filter response more closely ap-
proaches the theoritical response than with con-
ventional op amps due to the EL2020’s smaller
propagation delay Because the internal compen-
sation of the EL2020 depends on resistive feed-
back the EL2020 should be set up as a gain
block
Driving Cables
The EL2020 was designed with driving coaxial
cables in mind With 30 mA of output drive and
low output impedance driving one to three 75X
double terminated coax cables with one EL2020
is practical Since it is easy to set up a gain of
a2 the double matched method is the best way
to drive coax cables because the impedance
match on both ends of the cable will suppress
reflections For a discussion on some of the other
ways to drive cables see the section on driving
cables in the EL2003 data sheet
Video Performance Characteristics
The EL2020 makes an excellent gain block for
video systems both RS-170 (NTSC) and faster
It is capable of driving 3 double terminated 75X
cables with distortion levels acceptable to broad-
casters A common video application is to drive a
75X double terminated coax with a gain of 2
To measure the video performance of the EL2020
in the non-inverting gain of 2 configuration 5
identical gain-of-two circuits were cascaded (with
a divide by two 75X attenuator between each
stage) to increase the errors
The results shown in the photos indicate the en-
tire system of 5 gain-of-two stages has a differen-
tial gain of 0 5% and a differential phase of 0 5
This implies each device has a differential
gain phase of 0 1% and 0 1 but these are too
small to measure on single devices
Differential Phase
of 5 Cascaded
Gain-Of-Two Stages
Differential Gain
of 5 Cascaded
Gain-Of-Two Stages
2020 – 14
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