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EL4450

Wideband Four-Quadrant Multiplier

Intersil 

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

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