AD8038(RevB) 查看數據表（PDF） - Analog Devices
零件编号
产品描述 (功能)
生产厂家
AD8038 Datasheet PDF : 12 Pages
| |||
AD8038/AD8039
The AD9203 works best when the common-mode voltage at the
input is at the midsupply or 2.5 V. The output stage design of
the AD8039 makes it ideal for driving these types of ADCs.
In this circuit, one of the op amps is configured in the inverting
mode, while the other is in the noninverting mode. However, to
provide better bandwidth matching, each op amp is configured
for a noise gain of +2. The inverting op amp is configured for a
gain of –1, while the noninverting op amp is configured for a
gain of +2. Each has a very similar ac response. The input signal
to the noninverting op amp is divided by 2 to normalize its
voltage level and make it equal to the inverting output.
The outputs of the op amps are centered at 2.5 V, which is the
midsupply level of the ADC. This is accomplished by first taking
the 2.5 V reference output of the ADC and dividing it by 2 with a
pair of 1 kΩ resistors. The resulting 1.25 V is applied to each op
amp’s positive input. This voltage is then multiplied by the gain of
the op amps to provide a 2.5 V level at each output.
Low Power Active Video Filter
Some composite video signals derived from a digital source
contain clock feedthrough that can limit picture quality. Active
filters made from op amps can be used in this application, but
they will consume 25 mW to 30 mW for each channel. In
power-sensitive applications, this can be too much, requiring the
use of passive filters that can create impedance matching prob-
lems when driving any significant load.
The AD8038 can be used to make an effective low-pass active
filter that consumes one-fifth of the power consumed by an
active filter made from an op amp. Figure 4 shows a circuit that
uses an AD8038 to create a single ± 2.5 V supply, three-pole
Sallen-Key filter. This circuit uses a single RC pole in front
of a standard two-pole active section.
680pF
+2.5V
RF
1k⍀
0.1F 10F
R1
200k⍀
R2
R3
499k⍀ 49.9k⍀
AD8038
VIN
R4
C1
C3
49.9k⍀ 100pF
33pF
0.1F
–2.5V
10F
VOUT
R5
49.9k⍀
Figure 4. Low-Pass Filter for Video
Figure 5 shows the frequency response of this filter. The response
is down 3 dB at 6 MHz, so it passes the video band with little
attenuation. The rejection at 27 MHz is 45 dB, which provides
more than a factor of 100 in suppression of the clock components
at this frequency.
10
0
–10
–20
–30
–40
–50
–60
0.1
1
10
100
FREQUENCY – MHz
Figure 5. Video Filter Response
–10–
REV. B
Share Link: 