EL4450 Datasheet

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January 1996, Rev B
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8
1-88
EL4450
FN7168
Wideband Four-Quadrant Multiplier
Features
The EL4450 is a complete fourquadrant multiplier circuit. It offers
wide bandwidth and good linearity
while including a powerful output voltage amplifier, drawing
modest supply current.
• Complete four-quadrant multiplier with output amp—
requires no extra components
The EL4450 operates on ±5V supplies and has an analog
input range of ±2V, making it ideal for video signal
processing. AC characteristics do not vary over the ±5V to
±15V supply range.
• Operates on ±5V to ±15V supplies
The multiplier has an operational temperature range of
-40°C to +85°C and are packaged in plastic 14-pin PDIP and
SO.
Applications
• Good linearity of 0.3%
• 90MHz bandwidth for both X and Y inputs
• All inputs are differential
• 400V/µs slew rate
• Modulation/Demodulation
• RMS computation
Pinout
• Real-time power computation
• Nonlinearity correction/generation
EL4450
(14-PIN PDIP, SO)
TOP VIEW
Ordering Information
PART
NUMBER
1
TEMP. RANGE
PACKAGE
PKG. NO.
EL4450CN
-40°C to +85°C
14-Pin PDIP
MDP0031
EL4450CM
-40°C to +85°C
14-Pin SO
MDP0027
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
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All other trademarks mentioned are the property of their respective owners.
EL4450
Absolute Maximum Ratings (TA = 25°C)
V+
VS
VIN
VIN
IIN
Positive Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . 16.5V
V+ to V- Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . .33V
Voltage at any Input or Feedback . . . . . . . . . . . . . . . V+ to VDifference between Pairs of Inputs or Feedback. . . . . . . . .6V
Current into any Input or Feedback Pin. . . . . . . . . . . . . . 4mA
IOUT
PD
TA
TS
Output Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30mA
Maximum Power Dissipation . . . . . . . . . . . . . . . . See Curves
Operating Temperature Range . . . . . . . . . . . .-40°C to +85°C
Storage Temperature Range. . . . . . . . . . . . .-60°C to +150°C
CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the
device at these or any other conditions above those indicated in the operational sections of this specification is not implied.
IMPORTANT NOTE: All parameters having Min/Max specifications are guaranteed. Typical values are for information purposes only. Unless otherwise noted, all tests
are at the specified temperature and are pulsed tests, therefore: TJ = TC = TA
Open-Loop DC Electrical Specifications
PARAMETER
VDIFF
Power Supplies at ±5V, TA = 25°C, VFB = VOUT.
DESCRIPTION
Differential Input Voltage—Clipping
MIN
TYP
1.8
2.0
V
1.0
V
0.2% nonlinearity
VCM
MAX
UNITS
Common-Mode Range of VDIFF = 0, VS = ±5V
±2.5
±2.8
V
VS = ±15V
±12.5
±12.8
V
VOS
Input Offset Voltage
8
35
mV
IB
Input Bias Current
9
20
µA
IOS
Input Offset Current between XIN+ and XIN-, YIN+ and YIN-, REF and FB
0.5
4
µA
Gain
Gain Factor of VOUT = Gain × XIN+ × YIN
0.5
0.55
V/V2
NLx
Nonlinearity of X Input; XIN between -1V and +1V
0.3
0.7
%
NLy
Nonlinearity of Y Input; YIN between -1V and +1V
0.2
0.35
%
RIN
Input resistance
XIN+ to XIN-, YIN+ to YIN-
230
REF to FB
90
0.45
kΩ
CMRR
Common-Mode Rejection Ratio, XIN and YIN
70
90
dB
PSRR
Power-Supply Rejection Ratio, FB
60
72
dB
VO
Output Voltage Swing
(VIN = 0, VREF Varied)
VS = ±5V
±2.5
±2.8
V
VS = ±15V
±12.5
±12.8
40
85
ISC
Output Short-Circuit Current
IS
Supply Current, VS = ±15V
2
15.4
mA
18
mA
EL4450
Closed-Loop AC Electrical Specifications
PARAMETER
Power Supplies at ±12V, TA = 25°C, RL = 500Ω, CL = 15pF.
DESCRIPTION
MIN
TYP
MAX
UNITS
BW, -3dB
-3dB Small-Signal Bandwidth, X or Y
90
MHz
BW, ±0.1dB
0.1dB Flatness Bandwidth
10
MHz
Peaking
Frequency Response Peaking
1.0
dB
SR
Slew Rate, VOUT between -2V and +2V
400
V/µs
VN
Input-Referred Noise Voltage Density
100
nV/Hz
300
Test Circuit
Note: For typical performance curves, RF = 0, RG = ∞, VS = ±5V, RL = 500Ω, and CL = 15pF unless otherwise noted.
Typical Performance Curves
Transfer Function of X Input for
Various Y Inputs
3
Transfer Function of Y Input for
Various X Inputs
EL4450
Typical Performance Curves
Frequency Response
for Various Feedback
Divider Ratios
X Input Frequency Response
for Various Y DC Inputs
Change in Bandwidth
and Peaking vs Temperature
4
(Continued)
Frequency Response
for Various RL, CL
VS = ±5V
Y Input Frequency Response
for Various X DC Inputs
Total Harmonic Distortion
of X Input vs Frequency
Frequency Response
for Various RL, CL
VS = ±15V
-3dB Bandwidth
and Peaking
vs Supply Voltage
Total Harmonic Distortion
of Y Input vs Frequency
EL4450
Typical Performance Curves
(Continued)
Slew Rate
vs Supply Voltage
Slew Rate
vs Die Temperature
Input Voltage Noise
vs Frequency
Nonlinearity of X Input
Bias Current
vs Die Temperature
Supply Current
vs Die Temperature
5
CMRR vs Frequency
Nonlinearity of Y Input
Common-Mode Input Range
vs Supply Voltage
Supply Current
vs Supply Voltage
14-Pin Package
Power Dissipation vs
Ambient Temperature
EL4450
Applications Information
The EL4450 is a complete four-quadrant multiplier with
90MHz bandwidth. It has three sets of inputs; a differential
multiplying X-input, a differential multiplying Y-input, and
another differential input which is used to complete a
feedback loop with the output. Here is a typical connection:
The gain of the feedback divider is H, and
H = RG/(RG + RF). The transfer function of the part is:
VOUT = AO × (1/2 × ((VINX+–VINX-) × (VINY+–VINY-)) +
(VREF–VFB)).
VFB is connected to VOUT through a feedback network, so
VFB = H*VOUT. AO is the open-loop gain of the amplifier, and
is about 600. The large value of AO drives:
(1/2 × ((VINX+–VINX-) × (VINY+–VINY-)) + (VREF–
VFB))→0.
Rearranging and substituting for VREF:
VOUT = (1/2 × ((VINX+–VINX-) × (VINY+–VINY-))
+VREF)/H, or VOUT = (XY/2 + VREF)/H
Thus the output is equal to one-half the product of X and Y
inputs and offset by VREF, all gained up by the feedback
divider ratio. The EL4450 is stable for a direct connection
between VOUT and FB, and the feedback 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 150MHz; typical strays of 3pF
thus require a feedback impedance of 360Ω 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 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 1 will dominate parasitic effects and allow
a higher divider resistance.
The REF pin can be used as the output’s ground reference,
or for DC offsetting of the output, or it can be used to sum in
another signal.
Input Connections
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 to 51Ω to de-Q the inputs.
Signal Amplitudes
Signal input common-mode voltage must be between (V-)
+2.5V and (V+) -2.5V to ensure linearity. Additionally, the
differential voltage on any input stage must be limited to ±6V
to prevent damage. The differential signal range is ±2V in the
EL4450. The input range is substantially constant with
temperature.
The Ground Pin
The ground pin draws only 6µA maximum DC current, and
may be biased anywhere between (V-) +2.5V and (V+)
-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 over
frequency, and if connected to a potential other than ground,
it must be bypassed.
Power Supplies
The EL4450 works well on supplies from ±3V to ±15V. The
supplies may be of different voltages as long as the
requirements of the GND pin are observed (see the Ground
Pin section for a discussion). The supplies should be
bypassed close to the device with short leads. 4.7µF
tantalum capacitors are very good, and no smaller bypasses
need be placed in parallel. Capacitors as low as 0.01µF can
be used if small load currents flow.
Single-polarity supplies, such as +12V with +5V can be
used, where the ground pin is connected to +5V and V- to
ground. The inputs and outputs will have to have their levels
shifted above ground to accommodate the lack of negative
supply.
The power dissipation of the EL4450 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:
PD =2*IS,max*VS + (VS–VO)*VO/RPAR
where
IS,max is the maximum supply current
VS is the ± supply voltage (assumed equal)
VO is the output voltage
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 about 6 of
unterminated input transmission line. The oscillation has a
characteristic frequency of 500MHz. Placing one’s finger (via
6
RPAR is the parallel of all resistors loading the output
For instance, the EL4450 draws a maximum of 18mA. With
light loading, RPAR→∞ and the dissipation with ±5V supplies
is 180mW. The maximum supply voltage that the device can
run on for a given PD and the other parameters is:
VS,max = (PD + VO2/RPAR)/(2IS + VO/RPAR)
EL4450
The maximum dissipation a package can offer is:
PD,max = (TJ,max–TA,max)/θJA
inputs between 200mVRMS and 1VRMS. The traditional use
of the EL4450 as an AGC detector and control loop would
be:
Where
TJ,max is the maximum junction 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
θJA 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 junction temperature of 150°C and a maximum
ambient temperature of 85°C, the 65°C temperature rise and
package thermal resistance of 120°/W gives a dissipation of
542mW at 85°C. This allows the full maximum operating
supply voltage unloaded, but reduced if loaded significantly.
Output Loading
The output stage is very powerful. It typically can source
85mA 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.
Gain accuracy degrades only 0.2% from no load to 100Ω
load. Heavy resistive loading will degrade frequency
response and video distortion for loads < 100Ω.
Capacitive loads will cause peaking in the frequency
response. If a capacitive load must be driven, a small-valued
series resistor can be used to isolate it. 12Ω to 51Ω should
suffice. A 22Ω series resistor will limit peaking to 2.5dB with
even a 220pF load.
Mixer Applications
Because of its lower distortion levels, the Y input is the better
choice for a mixer’s signal port. The X input would receive
oscillator amplitudes of about 1V RMS maximum. Carrier
suppression is initially limited by the offset voltage of the Y
input, 20mV maximum, and is about 37dB worst-case. Better
suppression can be obtained by nulling the offset of the X
input. Similarly, nulling the offset of the Y input will improve
signal-port suppression. Driving an input differentially will
also maximize feedthrough suppression at frequencies
beyond 10MHz.
AC Level Detectors
Square-law converters are commonly used to convert AC
signals to DC voltages corresponding to the original
amplitude in subsystems like automatic gain controls (AGCs)
and amplitude-stabilized oscillators. Due to the controlled AC
amplitudes, the inputs of the multiplier will see a relatively
constant signal level. Best performance will be obtained for
7
FIGURE 1. TRADITIONAL AGC DETECTOR/DC
FEEDBACK CIRCUIT
The EL4450 simply provides an output equal to the square
of the input signal and an integrator filters out the AC
component, while comparing the DC component to an
amplitude reference. The integrator output is the DC control
voltage to the variable-gain sections of the AGC (not shown).
If a negative polarity of reference is required, one of the
multiplier input terminal pairs is reversed, inverting the
multiplier output. Input bias current will cause input voltage
offsets due to source impedances; putting a compensating
resistor in series with the grounded inputs of the EL4450 will
reduce this offset greatly.
This control system will attempt to force:
VIN,RMS2/4=VREF
EL4450
FIGURE 2. SIMPLIFIED AGC DETECTOR/DC FEEDBACK CIRCUIT
The extra op-amp can be eliminated by using this circuit
(Figure 2).
Here the internal op-amp of the EL4450 replaces the
external amplifier. The feedback capacitor CF does not
provide a perfect integration action; a zero occurs at a
frequency of 1/2πRCF. This is canceled by including another
RCF pair at the AGC control output. If the reference voltage
must be negative, the resistor at pin 11 is connected to
ground rather than the reference and pin 10 connected to the
reference.
An ECL comparator produces an output corresponding to
the sign of the input, which when multiplied by the input
produces an effective absolute-value function. The RC
product connected to the X inputs simply emulates the time
delay of the comparator to maintain circuit accuracy at
higher frequencies.
Nonlinear Function Generation
The REF pin of the EL4450 can be used to sum in various
quantities of polynomial function generators. For instance,
The amplitude reference will have to support some AC
currents flowing through R. If this is a problem, several
changes can be made to eliminate it. The reference is
connected to pin 10 and the resistor R connected to pin 11
reconnected to ground, and one of the multiplier input
connections are reversed.
Square-law detectors have a restricted input range, about
10:1, because the output rapidly disappears into the DC
errors as signal amplitudes reduce. This circuit gives a
multiplier output that is the absolute value of the input, thus
increasing range to 100:1(Figure 3).
FIGURE 3. ABSOLUTE-VALUE INPUT CIRCUITRY
8
EL4450
FIGURE 4. POLYNOMIAL FUNCTION GENERATOR
this sum of REF allows a linear signal path which can have
various amounts of squared signal added (Figure 4).
the bandwidth of the circuit will reduce for smaller input
signals (Figure 5).
The polarity of the squared signal can be reversed by
swapping one of the X or Y input pairs.
The REF and FB terminals can also be used to implement
division.
The REF and FB pins also simplify feedback schemes that
allow square-rooting.
The output frequency response reduces for smaller values of
VX, but is not affected by VREF(Figure 6).
The diode and IPULLDOWN assure that the output will always
produce the positive square-root of the input signal.
IPULLDOWN should be large enough to assure that the diode
be forward-biased for any load current. In this configuration,
FIGURE 5. SQUARE-ROOTER
FIGURE 6. DIVIDER CONNECTION
9
EL4450
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10
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