isl55211 Intersil Corporation, isl55211 Datasheet - Page 16

• Manufacturer Part Number: isl55211
• Description: Wideband, Low Noise, Low Distortion, Fixed Gain, Differential Amplifier
• Manufacturer: Intersil Corporation

2. AC-coupled, higher frequency range interstage filter design.
FIGURE 36. AC- COUPLED BROADBAND RLC INTERSTAGE FILTER
FIGURE 37. AC-COUPLED, HIGHER FREQUENCY RLC INTERSTAGE
IS L 55211
V
ISL55211
V
This design replaces the R
valued inductors and implements the filter just using shunt
resistors at the end of the RLC filter. In this case, the ADC V
can be tied to the centerpoint of the bias path inductors (very
much like a Bias-T) to provide the common mode voltage and
current to the ADC inputs. These bias inductors do limit the
low frequency end of the operation where, with 1µH values,
operation from 10MHz to 200MHz is supported using the
approach of Figure 37.
C M 1
C M 1
+ 3.3V
1.2V
+3.3V
1.2V
DESIGN
FILTER DESIGN
R
R
S
S
R
R
S
S
C
C
B
B
V
R >
C
b
C
t
B
B
−
L
I
R
p
cm
16
s
>>
T
L
×
S
L
L
V
resistors in Figure 35 with large
L
S
R
L
S
B
S
R
s
t
T
=
V
cm
2
R
R
I
C M
L
L
T
T
P
P
I
I
I
C M
C M
C M
C
C
T
T
C
C
T
T
IN +
IN -
IN -
A D C
IN +
A D C
V
R
IN
CM2
R
V
IN
CM2
ISL55211
C
IN
C
CM
IN
3. AC-coupled with output side transformer. This design includes
4. DC-coupled with ADC V
FIGURE 39. DC-COUPLED WITH A V
IS L 55211
V
FIGURE 38. AC-COUPLED WITH OUTPUT SIDE TRANSFORMER
ISL55211
an output side transformer, very similar to ADC
characterization circuits. This approach allows a slightly lower
amplifier output swing (if N>1 is used) and very easy 2nd or
3rd order low pass responses to be implemented. It also
provides the I
transformer centertap. This approach would be attractive for
higher ADC input swing targets and more aggressive noise
power bandwidth control needs. Figure 1 on page 1 is an
example showing this approach.
amplifier. Here, DC to very high frequency interstage low pass
filter can be provided. Again, the R
reduce the IR drop from the V
shows up on the output of the ISL55211, to the ADC input
pins.
C M 1
+ 3.3V
1.2V
+3.3V
V
CM
CM
R
R
S
S
and V
R
R
S
S
R
C
C
R
s
B
B
T
≤30
< 30
CM
CM
1:N
Ω
L
bias to the ADC through the
S
and I
L
S
CM
CM
CM
of the converter, which now
R
R
R
T
S
T
provided from the
T
VOLTAGE FROM THE ADC
2I
element must be low to
C M
I
I
I
I
CM
CM
C M
C M
C
C
T
T
C
C
T
T
IN+
IN-
ADC
IN +
IN -
A D C
June 21, 2011
V
V
R
CM2
R
IN
CM2
IN
FN7868.0
C
C
IN
IN