Datasheet

AD844
Rev. F | Page 18 of 20
Figure 45 shows the small signal response for a 50 dB gain control
range (V
X
= 10 mV to 3.16 V). At small values of V
X
, 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 V
Y
for
V
X
= 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)
GAIN (dB)
4
–6
–56
60M1M100k 10M
–26
–36
–46
–16
V
X
= 3.15V
V
X
= 1.0V
V
X
= 0.316V
V
X
= 0.10V
V
X
= 0.032V
00897-045
Figure 45. VGA AC Response
00897-046
1V 1V 50ns
10
100
0
90
Figure 46. VGA Transient Response with V
X
= 1 V, 2 V, and 3 V