As a general consideration, the input signal ap-
plied to an EL4452 should be kept below about
250 mV peak for good linearity. If the AGC were
designed to produce a 1V peak output, the input
range would be 100 mV–250 mV peak when the
EL4452 has a feedback network that establishes a
maximum gain of 10. This is an input range of
only 2.5:1 for precise output regulation. Raising
the maximum gain to 25 allows a 40 mV–250 mV
input range with the output still regulated, better
than 6:1. Unfortunately, the bandwidth will be
reduced. Bandwidth can be maintained by adding
a high frequency op-amp cascaded with the out-
put to make up gain beyond the 10 of the
EL4452, current feedback devices being the most
flexible. The op-amp’s input should be capacitor
coupled to prevent gained-up offsets from confus-
ing the level detector during AGC control line
variations.
Applications Information Ð Contd.
In this circuit, the EL4450 not only calculates the
square of the input, but also provides the offset
integrator function. The product of the two mul-
b
tiplier inputs adds to the Reference input and
are passed to the output amplifier, which
through C behaves as a pseudo-integrator. The
F
‘‘integrator’’ gain does not pass through zero at
c
high frequencies but has a zero at 1/(2qC
1
F
kX). This zero is cancelled by the pole caused by
the second capacitor of value C connected at the
F
b
b
V input. The Reference can be
GAIN
EL4452
exchanged for a positive reference by connecting
it to the ground return of the 1 kX resistor at the
FB terminal and grounding REF.
General Disclaimer
Specifications contained in this data sheet are in effect as of the publication date shown. Elantec, Inc. reserves the right to make changes
in the circuitry or specifications contained herein at any time without notice. Elantec, Inc. assumes no responsibility for the use of any
circuits described herein and makes no representations that they are free from patent infringement.
WARNING Ð Life Support Policy
Elantec, Inc. products are not authorized for and should not be
used within Life Support Systems without the specific written
consent of Elantec, Inc. Life Support systems are equipment in-
tended to support or sustain life and whose failure to perform
Elantec, Inc.
1996 Tarob Court
when properly used in accordance with instructions provided can
be reasonably expected to result in significant personal injury or
death. Users contemplating application of Elantec, Inc. products
Milpitas, CA 95035
in Life Support Systems are requested to contact Elantec, Inc.
Telephone: (408) 945-1323
(800) 333-6314
factory headquarters to establish suitable terms & conditions for
these applications. Elantec, Inc.’s warranty is limited to replace-
ment of defective components and does not cover injury to per-
Fax: (408) 945-9305
European Office: 44-71-482-4596
sons or property or other consequential damages.
12
Printed in U.S.A.
ELANTEC [ ELANTEC SEMICONDUCTOR ]
