EL4452 Просмотр технического описания (PDF) - Intersil

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EL4452

Wideband Variable-Gain Amplifier with Gain of 10

Intersil 

EL4452

FIGURE 3.

Elantec application note). Fortunately, the detector will see a

constant amplitude of signal if the AGC is operating correctly.

A better-calibrated method is to use a four-quadrant

multiplier as a square-law detector. Here is a circuit

employing the EL4450 (Figure 3).

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 multiplier inputs adds to the -Reference

input and are passed to the output amplifier, which through

CF behaves as a pseudo-integrator. The “integrator” gain

does not pass through zero at high frequencies but has a

zero at 1/(2πCF × 1kΩ). This zero is cancelled by the pole

caused by the second capacitor of value CF connected at

the EL4452 -VGAIN input. The -Reference can be exchanged

for a positive reference by connecting it to the ground return

of the 1kΩ resistor at the FB terminal and grounding REF.

As a general consideration, the input signal applied to an

EL4452 should be kept below about 250mV peak for good

linearity. If the AGC were designed to produce a 1V peak

output, the input range would be 100mV–250mV 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 40mV–250mV 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 output 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

confusing the level detector during AGC control line

variations.

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