AD5539 Ver la hoja de datos (PDF) - Analog Devices

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componentes Descripción

Fabricante

AD5539

Operational Amplifier Ultrahigh Frequency

Analog Devices 

AD5539

Figure 42 shows the oscilloscope response of the generator

alone, set up to simulate the ideal test circuit error signal

(Figure 43).

Figure 42. The Oscilloscope Response Alone Directly

Driven by the Test Generator. Vertical Scale: 5 ns/div.;

Horizontal Scale: 500 µV/div

Figure 43. A Simulated Ideal Test Circuit Error Signal

A 50 MHz VOLTAGE-CONTROLLED AMPLIFIER

Figure 44 is a circuit for a 50 MHz voltage-controlled amplifier

(VCA) suitable for use in high quality video-speed applications.

This circuit uses the AD5539 as an output amplifier for the

AD539, a high bandwidth multiplier. The outputs from the two

signal channels of the AD539 are applied to the op amp in a

subtracting configuration. This connection has two main advan-

tages: first, it results in better rejection of the control voltage,

particularly when over-driven (VX < 0 or VX > 3.3 V). Secondly,

it provides a choice of either noninverting or inverting responses,

using either input VY1 or VY2, respectively. In this circuit, the

output of the op amp will equal:

( ) V X VY1 – VY 2

VOUT =

2V

for VX > 0

Hence, the gain is unity at VX = +2 V. Since VX can overrange

to +3.3 V, the maximum gain in this configuration is about

4.3 dB. (Note: If Pin 9 of the AD539 is grounded, rather than

connected to the output of the 5539N, the maximum gain be-

comes 10 dB.)

The bandwidth of this circuit is over 50 MHz at full gain, and is

not substantially affected at lower gains. Of course, when VX is

zero (or slightly negative, to override the residual input offset)

there is still a small amount of capacitive feedthrough at high

frequencies; therefore, extreme care is needed in laying out the

PC board to minimize this effect. Also, for small values of VX,

the combination of this feedthrough with the multiplier output

can cause a dip in the response where they are out of phase.

Figure 45 shows the ac response from the noninverting input,

with the response from the inverting input, VY2, essentially iden-

tical. Test conditions: VY1 = 0.5 V rms for values of VX from

+10 mV to +3.16 V; this is with a 75 Ω load on the output. The

feedthrough at VX = –10 mV is also shown.

Figure 44. A Wide Bandwidth Voltage-Controlled Amplifier

Figure 45. AC Response of the VCA at Different Gains

VY = 0.5 V RMS

–14–

REV. B

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