D844 datasheet(18/20 Pages) AD

18 / 20 page

AD844

Rev. F | Page 18 of 20

Figure 45 shows the small signal response for a 50 dB gain control

range (VX = 10 mV to 3.16 V). At small values of VX, capacitive

feedthrough on the PC board becomes troublesome and very

careful layout techniques are needed to minimize this problem.

A ground strip between the pins of the AD539 is helpful in this

regard. Figure 46 shows the response to a 2 V pulse on VY for

VX = 1 V, 2 V, and 3 V. For these results, a load resistor of 500 Ω

was used and the supplies were ±9 V. The multiplier operates

from supplies between ±4.5 V and ±16.5 V.

Disconnecting Pin 9 and Pin 16 on the AD539 alters the

denominator in Equation 1 to 1 V, and the bandwidth is

approximately 10 MHz, with a maximum gain of 10 dB.

Using only Pin 9 or Pin 16 results in a denominator of 0.5 V,

a bandwidth of 5 MHz, and a maximum gain of 16 dB.

FREQUENCY (Hz)

–6

–56

60M

100k

10M

–26

–36

–46

–16

VX = 3.15V

VX = 1.0V

VX = 0.316V

VX = 0.10V

VX = 0.032V

Figure 45. VGA AC Response

50ns

100

Figure 46. VGA Transient Response with VX = 1 V, 2 V, and 3 V

D844 Datasheet(PDF) 18 Page - Analog Devices