AD5539

REV. B

–14–

Figure 43. A Simulated Ideal Test Circuit Error Signal

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

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

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,

+10 mV to +3.16 V; this is with a 75

Ω load on the output. The

Figure 45. AC Response of the VCA at Different Gains

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

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,

it provides a choice of either noninverting or inverting responses,

output of the op amp will equal:

V

()

2V

Figure 44. A Wide Bandwidth Voltage-Controlled Amplifier