EL4451CS 데이터 시트보기 (PDF) - Elantec -> Intersil

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EL4451CS

Wideband Variable-Gain Amplifier, Gain of 2

Elantec -> Intersil 

EL4451C

Wideband Variable-Gain Amplifier Gain of 2

Applications Information Contd

Here is the EL4451 used as an oscillator with simple AGC

Low-Distortion Sinewave Oscillator

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 VGAINb

terminal is initially at b0 7V and the VGAINa

terminal at about a2 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 VGAINb ulti-

mately reducing gain until a stable 0 5Vrms out-

put is produced

Using a 2 MHz crystal output distortion was

b53 dBc or 0 22% Sideband modulation was

only 14 Hz wide at b90 dBc limited by the filter

of the spectrum analyzer used

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 ele-

ment to allow grounding of the tuned compo-

nents

4451 – 33

Filters

The EL4451 can be connected to act as a voltage-

variable integrator as shown

EL4451 Connected As Variable Integrator

4451 – 34

The input RC cancels a zero produced by the out-

put 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 asRC) sRC

This variable integrator may be used in networks

such as the Bi-quad In some applications the in-

put RC may be omitted If a negative gain is re-

quired the VINa and VINb terminals can be

exchanged

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