Elantec EL4451 Wideband variable-gain amplifier, gain of 2 Datasheet

EL4451C
EL4451C
Wideband Variable-Gain Amplifier, Gain of 2
Features
General Description
# Complete variable-gain amplifier
with output amplifier, requires
no extra components
# Excellent linearity of 0.2%
# 70 MHz signal bandwidth
# Operates on g 5V to g 15V
supplies
# All inputs are differential
# 400V/ms slew rate
# l 70dB attenuation @ 4 MHz
The EL4451C is a complete variable gain circuit. It offers wide
bandwidth and excellent linearity while including a powerful
output voltage amplifier, drawing modest supply current.
Applications
The EL4451C is fabricated with Elantec’s proprietary complementary bipolar process which provides excellent signal symmetry and is free from latch up.
#
#
#
#
Leveling of varying inputs
Variable filters
Fading
Text insertion into video
The EL4451C operates on g 5V to g 15V supplies and has an
analog input range of g 2V, making it ideal for video signal
processing. AC characteristics do not change appreciably over
the g 5V to g 15V supply range.
The circuit has an operational temperature range of b 40§ C to
a 85§ C and is packaged in plastic 14-pin DIP and 14-lead SO.
Connection Diagram
Ordering Information
Part No.
Temp. Range
Package
Outline Ý
EL4451CN b 40§ C to a 85§ C 14-Pin P-DIP
MDP0031
EL4451CS b 40§ C to a 85§ C
MDP0027
14-Lead SO
4451-1
October 1994 Rev A
Note: All information contained in this data sheet has been carefully checked and is believed to be accurate as of the date of publication; however, this data sheet cannot be a ‘‘controlled document’’. Current revisions, if any, to these
specifications are maintained at the factory and are available upon your request. We recommend checking the revision level before finalization of your design documentation.
© 1994 Elantec, Inc.
EL4451C
Wideband Variable-Gain Amplifier, Gain of 2
Absolute Maximum Ratings (TA e 25§ C)
Va
VS
VIN
DVIN
IIN
Positive Supply Voltage
V a to Vb Supply Voltage
Voltage at any Input or Feedback
Difference between Pairs
of Inputs or Feedback
Current into any Input, or Feedback Pin
IOUT
PD
TA
TS
16.5V
33V
V a to Vb
Continuous Output Current
Maximum Power Dissipation
Operating Temperature Range
Storage Temperature Range
30mA
See Curves
b 40§ C to a 85§ C
b 60§ C to a 150§ C
6V
4mA
Important Note:
All parameters having Min/Max specifications are guaranteed. The Test Level column indicates the specific device testing actually
performed during production and Quality inspection. Elantec performs most electrical tests using modern high-speed automatic test
equipment, specifically the LTX77 Series system. Unless otherwise noted, all tests are pulsed tests, therefore TJ e TC e TA.
Test Level
I
II
III
IV
V
Test Procedure
100% production tested and QA sample tested per QA test plan QCX0002.
100% production tested at TA e 25§ C and QA sample tested at TA e 25§ C ,
TMAX and TMIN per QA test plan QCX0002.
QA sample tested per QA test plan QCX0002.
Parameter is guaranteed (but not tested) by Design and Characterization Data.
Parameter is typical value at TA e 25§ C for information purposes only.
Parameter
Description
VDIFF
Signal input differential input voltage - Clipping
0.2% nonlinearity
VCM
Common-mode range of VIN; VDIFF e 0, Vs e g 5V
Vs e g 15V
Test
Level
Units
2.0
1.3
I
V
V
V
g 2.8
I
V
V
V
Min
Typ
1.8
g 2.0
Max
g 12.8
VOS
Input offset voltage
7
25
I
mV
VOS, FB
Output offset voltage
8
25
I
mV
VG, 100%
Extrapolated voltage for 100% gain
VG, 0%
Extrapolated voltage for 0% gain
VG, 1V
1.9
2.1
2.2
I
V
b 0.16
b 0.06
0.06
I
V
Gain at VGAIN e 1V
0.95
1.05
1.15
I
V/V
IB
Input bias current (all inputs)
b 20
b9
0
I
mA
IOS
Input offset current between VIN a and VINb,
Gain a and Gainb, FB and Ref
0.2
4
I
mA
NL
Nonlinearity, VIN between b1V and a 1V, VG e 1V
Ft
Signal feedthrough, VG e b1V
RIN, VIN
Input resistance, VIN
100
RIN, FB
Input resistance, FB
200
RIN, RGAIN
Input resistance, gain input
50
2
0.2
0.5
I
%
b 100
b 70
I
dB
230
I
KX
460
V
KX
100
I
KX
TD is 3.3in
Open-Loop DC Electrical Characteristics Power Supplies at g 5V, TA e 25§ C, RL e 500X.
TD is 1.8in
EL4451C
Wideband Variable-Gain Amplifier, Gain of 2
Open-Loop DC Electrical Characteristics Ð Contd.
Power Supplies at g 5V, TA e 25§ C, RL e 500X.
Parameter
Description
CMRR
Common-mode rejection ratio of VIN
PSRR
Power supply rejection ratio of VOS, FB, VS e g 5V to g 15V
VO
Output voltage swing VS e g 5V
(VIN e 0, VREF varied) VS e g 15V
ISC
Output short-circuit current
IS
Supply current, VS e g 15V
Test
Level
Units
90
I
dB
I
dB
I
V
Min
Typ
70
50
60
g 2.5
g 2.8
g 12.5
g 12.8
40
Max
85
15.5
I
mA
I
mA
Test
Level
Units
V
MHz
MHz
18
Closed-Loop AC Electrical Characteristics
Parameter
Description
Min
Typ
70
Max
BW, b3dB
b 3dB small-signal bandwidth, signal input
BW, g 0.1dB
0.1dB flatness bandwidth, signal input
10
V
Peaking
Frequency response peaking
0.6
V
dB
BW, gain
b 3dB small-signal bandwidth, gain input
70
V
MHz
SR
Slew rate, VOUT between b2V and a 2V, RF e RG e 500X
400
V
V/ms
VN
Input referred noise voltage density
110
V
nV/ SHz
dG
Differential gain error, Voffset between b0.7V and a 0.7V
0.9
V
%
di
Differential phase error, Voffset between b0.7V and a 0.7V
0. 2
V
§
Test Circuit
4451 – 3
Note: For typical performance curves, RF e 0, RG e % , VGAIN e 1V, RL e 500X, and CL e 15 pF unless otherwise noted.
3
TD is 1.8in
Power supplies at g 12V, TA e 25§ C. RL e 500X, CL e 15pF, VG e 1V
EL4451C
Wideband Variable-Gain Amplifier, Gain of 2
Typical Performance Curves
Frequency Response
for Various Feedback
Divider Ratios
Frequency Response
for Various RL, CL
VS e g 5V
4451 – 4
Gain, b 3 dB Bandwidth,
and Peaking
vs Load Resistance
Frequency Response
for Various RL, CL
VS e g 15V
4451 – 5
b 3 dB Bandwidth and Peaking
vs Supply Voltage
b 3 dB Bandwidth and Peaking
vs Die Temperature
4451 – 8
4451 – 7
Frequency Response for
Various Gain Settings
4451 – 6
Slew Rate
vs Supply Voltage
Slew Rate
vs Die Temperature
4451 – 11
4451 – 10
4
4451 – 9
4451 – 12
EL4451C
Wideband Variable-Gain Amplifier, Gain of 2
Typical Performance Curves Ð Contd.
Common-Mode
Rejection Ratio
vs Frequency
Input Voltage Noise
vs Frequency
4451 – 13
Nonlinearity vs
Input Signal
4451 – 14
4451 – 15
Differential Gain Error
vs Input Offset Voltage
VS e g 5V or g 12V
Differential Phase Error
vs Input Offset Voltage
VS e g 5V
4451 – 16
Differential Phase Error
vs Input Offset Voltage
VS e g 12V
4451 – 17
Differential Gain
and Phase Errors
vs Gain Setting
4451 – 18
Differential Gain
and Phase Errors
vs Load Resistance
4451 – 19
4451 – 20
5
EL4451C
Wideband Variable-Gain Amplifier, Gain of 2
Typical Performance Curves Ð Contd.
Change in
VG, 100% and VG, 0%
vs Die Temperature
Gain vs VGAIN
Common Mode
Input Range
vs Supply Voltage
Bias Current
vs Die Temperature
4451 – 24
Supply Current
vs Die Temperature
4451 – 23
4451 – 22
4451 – 21
Offset Voltage
vs Die Temperature
VG, 0% and VG, 100%
vs Supply Voltage
4451 – 25
Supply Current
vs Supply Voltage
4451 – 27
4451 – 28
6
4451 – 26
14-Pin Package
Power Dissipation vs
Ambient Temperature
4451 – 29
EL4451C
Wideband Variable-Gain Amplifier, Gain of 2
360X or less. Alternatively, a small capacitor
across RF can be used to 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.
Applications Information
The EL4451 is a complete two-quadrant multiplier/gain control with 70 MHz bandwidth. It has
three sets of inputs; a differential signal input
VIN, a differential gain-controlling input VGAIN,
and another differential input which is used to
complete a feedback loop with the output. Here is
a typical connection:
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 VGAIN in the above equations is
bounded as 0 s VGAIN s 2, even though the externally applied voltages 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%-VGAIN voltage nor above the
100%-VGAIN level. An overdrive of 0.3V must be
applied to VGAIN to obtain truly 0% or 100%.
Because the 0%- or 100%- VGAIN levels cannot
be precisely determined, they are extrapolated
from two points measured inside the slope of the
gain transfer curve. Generally, an applied VGAIN
range of b 0.5V to a 2.5V will assure the full numerical span of 0 s VGAIN s 2.
4451-2
The gain of the feedback divider is
He
RG
.
RG a RF
The transfer function of the part is
VOUT e AO c (((VIN a ) b (VIN b )) c ((VGAIN a ) b (VGAIN b )) a
(VREF b VFB)).
VFB is connected to VOUT through a feedback
network, so VFB e H c VOUT. AO is the openloop gain of the amplifier, and is approximately
600. The large value of AO drives
((VIN a ) b (VIN b )) c ((VGAIN a ) b (VGAIN b )) a (VREF b VFB)
x 0.
The gain control has a small-signal bandwidth
equal to the VIN channel bandwidth, and overload recovery resolves in about 20 nsec.
Rearranging and substituting for VFB
VOUT e (((VIN a ) b (VIN b )) c ((VGAIN a ) b (VGAIN)) a VREF)/H,
or
Input Connections
VOUT e (VIN c VGAIN a VREF)/H
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 500 MHz. 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 51X to
de-Q the inputs.
Thus the output is equal to the difference of the
VIN’s times the difference of VGAIN’S and offset
by VREF, all gained up by the feedback divider
ratio. The EL4451 is stable for a direct connection between VOUT and FB, and the divider may
be used for higher output gain, although with the
traditional loss of bandwidth.
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 150 MHz; typical strays
of 3 pF thus require a feedback impedance of
7
EL4451C
Wideband Variable-Gain Amplifier, Gain of 2
For instance, the EL4451 draws a maximum of
% and the
18mA. With light loading, RPAR
dissipation with g 5V supplies is 180 mW. The
maximum supply voltage that the device can run
on for a given PD and other parameters is
Applications Information Ð Contd.
x
Signal Amplitudes
Signal input common-mode voltage must be between (V b ) a 3V and (V a ) b 3V to ensure linearity. Additionally, the differential voltage on any
input stage must be limited to g 6V to prevent
damage. The differential signal range is g 2V in
the EL4451. The input range is substantially constant with temperature.
VS, max e (PD a VO2/RPAR) / (2IS a VO/RPAR)
The maximum dissipation a package can offer is
PD, max e (TJ, max b TA, max) / iJA
Where
The Ground Pin
The ground pin draws only 6mA maximum DC
current, and may be biased anywhere between
(V b ) a 2.5V and (V a ) b 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.
TJ, max is the maximum die temperature, 150§ C for reliability, less to retain optimum electrical performance
TA, max is the ambient temperature,
70§ C for commercial and 85§ C for industrial range
iJA is the thermal resistance of the
mounted package, obtained from
data sheet dissipation curves
The more difficult case is the SO-14 package.
With a maximum die temperature of 150§ C and a
maximum ambient temperature of 85§ C, the 65§ C
temperature rise and package thermal resistance
of 120§ C/W gives a dissipation of 542 mW at
85§ C. This allows the full maximum operating
supply voltage unloaded, but reduced if loaded.
Power Supplies
The EL4451 works with any supplies from g 3V
to g 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. 4.7mF tantalum capacitors
are very good, and no smaller bypasses need be
placed in parallel. Capacitors as small as 0.01mF
can be used if small load currents flow.
Output Loading
Single-polarity supplies, such as a 12V with
a 5V can be used, where the ground pin is connected to a 5V and V b to ground. The inputs
and outputs will have to have their levels shifted
above ground to accommodate the lack of negative supply.
The output stage of the EL4451 is very powerful.
It typically can source 80mA and sink 120mA. Of
course, this is too much current to sustain and
the part will eventually be destroyed by excessive
dissipation or by metal traces on the die opening.
The metal traces are completely reliable while delivering the 30mA continuous output given in the
Absolute Maximum Ratings table in this data
sheet, or higher purely transient currents.
The power dissipation of the EL4451 increases
with power supply voltage, and this must be
compatible with the package chosen. This is a
close estimate for the dissipation of a circuit:
Gain changes only 0.2% from no load to 100X
load. Heavy resistive loading will degrade frequency response and video distortion for loads
k 100X.
PD e 2 c VS c IS, max a (VS b VO) c VO/RPAR
Capacitive loads will cause peaking in the frequency response. If capacitive loads must be driven, a small-valued series resistor can be used to
isolate it. 12X to 51X should suffice. A 22X series
resistor will limit peaking to 2.5 dB with even a
220pF load.
where IS, max is the maximum supply current
VS is the g supply voltage (assumed
equal)
VO is the output voltage
RPAR is the parallel of all resistors loading
the output
8
EL4451C
Wideband Variable-Gain Amplifier, Gain of 2
EL4451 Leveler Circuit
Attenuation Ratio e 1.5
Applications Information Ð Contd.
Leveling Circuits
Often a variable-gain control is used to normalize
an input signal to a standard amplitude from a
modest range of possible input amplitude. A good
example is in video systems, where an unterminated cable will yield a twice-sized standard video amplitude, and an erroneously twice-terminated cable gives a 2/3-sized input.
Here is a g 6 dB range preamplifier:
Linearized Leveling Amplifier
4451 – 31
EL4451 Leveler Circuit
Attenuation Ratio e 2
4451 – 30
In this arrangement, the EL4451 outputs a mixture of the signal routed through the multiplier
and the REF terminal. The multiplier port produces the most distortion and needs to handle a
fraction of an oversized video input, whereas the
REF port is just like an op-amp input summing
into the output. Thus, for oversized inputs the
gain will be decreased and the majority of the
signal is routed through the linear REF terminal.
For undersized inputs, the gain is increased and
the multiplier’s contribution added to the output.
4451 – 32
With the higher attenuation ratio, the multiplier
sees a smaller input amplitude and distorts less,
however the higher output gain reduces circuit
bandwidth. As seen in the next curves, the peak
differential gain error is 0.47% for the attenuation ratio of 1.5, but only 0.27% with the gain of
2 constants. To maintain bandwidth, an external
op amp can be used instead of the RF - RG divider to boost the EL4451’s output by the attenuation ratio.
Here are some component values for two designs:
Sinewave Oscillators
Attenuation
Ratio
Generating a stable, low distortion sinewave has
long been a difficult task. Because a linear oscillator’s output tends to grow or diminish continuously, either a clipping circuit or automatic gain
control (AGC) is needed. Clipping circuits generate severe distortion which needs subsequent filtering, and AGC’s can be complicated.
RF
RG
R1
R2
R3
b 3 dB
Bandwidth
1.5
200X 400X 300X 100X 200X
47 MHz
2
400X 400X 500X 100X 200X
28 MHz
9
EL4451C
Wideband Variable-Gain Amplifier, Gain of 2
Applications Information Ð Contd.
Here is the EL4451 used as an oscillator with simple AGC:
Low-Distortion Sinewave Oscillator
4451 – 33
The oscillation frequency is set by the resonance
of a series-tuned circuit, which may be an L-C
combination or a crystal. At resonance, the series
impedance of the tuned circuit drops and its
phase lag is 0§ , so the EL4451 needs a gain just
over unity to sustain oscillation. The VGAIN b
terminal is initially at b 0.7V and the VGAIN a
terminal at about a 2.1V, setting the maximum
gain in the EL4451. At such high gain, the loop
oscillates and output amplitude grows until D1
rectifies more positive voltage at VGAIN b , ultimately reducing gain until a stable 0.5Vrms output is produced.
Filters
The EL4451 can be connected to act as a voltagevariable integrator as shown:
EL4451 Connected As Variable Integrator
Using a 2 MHz crystal, output distortion was
b 53 dBc, or 0.22%. Sideband modulation was
only 14 Hz wide at b 90 dBc, limited by the filter
of the spectrum analyzer used.
4451 – 34
The input RC cancels a zero produced by the output op-amp feedback connection at 0 e 1/RC.
With the input RC connected VOUT/VIN e
1/sRC; without it VOUT/VIN e (1 a sRC)/sRC.
This variable integrator may be used in networks
such as the Bi-quad. In some applications the input RC may be omitted. If a negative gain is required, the VIN a and VIN b terminals can be
exchanged.
The circuit works up to 30 MHz. A parallel-tuned
circuit can replace the 510X resistor and the 510X
resistor moved in place of the series-tuned element to allow grounding of the tuned components.
10
EL4451C
Wideband Variable-Gain Amplifier, Gain of 2
The main signal path is via the REF pin. This
ensures maximum signal linearity, while the multiplier input is used to allow a variable amount of
frequency-shaped input from R1, R2, and C. For
optimum linearity, the multiplier input is attenuated by R1 and R2. This may not be necessary,
depending on input signal amplitude, and R1
might be set to 0. R1and R2 should be set to provide sufficient peaking, depending on cable highfrequency losses, at maximum gain. RF and RG
are chosen to provide the desired circuit gain, including backmatch resistor loss.
Applications Information Ð Contd.
A voltage-controlled equalizer and cable driver
can be constructed so:
Equalization and Line Driver Amplifier
4451 – 35
11
EL4451C
EL4451C
Wideband Variable-Gain Amplifier, Gain of 2
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.
October 1994 Rev A
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 intended to support or sustain life and whose failure to perform
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
in Life Support Systems are requested to contact Elantec, Inc.
factory headquarters to establish suitable terms & conditions for
these applications. Elantec, Inc.’s warranty is limited to replacement of defective components and does not cover injury to persons or property or other consequential damages.
Elantec, Inc.
1996 Tarob Court
Milpitas, CA 95035
Telephone: (408) 945-1323
(800) 333-6314
Fax: (408) 945-9305
European Office: 44-71-482-4596
12
Printed in U.S.A.
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