adl5387 Analog Devices, Inc., adl5387 Datasheet - Page 19

• Manufacturer Part Number: adl5387
• Description: 50 Mhz To 2 Ghz Quadrature Demodulator
• Manufacturer: Analog Devices, Inc.

As an example, a second-order, Butterworth, low-pass filter
design is shown in Figure 56 where the differential load impedance
is 500 Ω, and the source impedance of the ADL5387 is 50 Ω.
The normalized series inductor value for the 10-to-1, load-to-
source impedance ratio is 0.074 H, and the normalized shunt
capacitor is 14.814 F. For a 10.9 MHz cutoff frequency, the
single-ended equivalent circuit consists of a 0.54 μH series
inductor followed by a 433 pF shunt capacitor.
The balanced configuration is realized as the 0.54 μH inductor
is split in half to realize the network shown in Figure 56.
A complete design example is shown in Figure 59. A sixth-order
Butterworth differential filter having a 1.9 MHz corner frequency
interfaces the output of the ADL5387 to that of an ADC input.
The 500 Ω load resistor defines the input impedance of the
ADC. The filter adheres to typical direct conversion WCDMA
applications, where 1.92 MHz away from the carrier IF frequency,
1 dB of rejection is desired and 2.7 MHz away 10 dB of rejection
is desired.
V
V
V
Figure 56. Second-Order, Butterworth, Low-Pass Filter Design Example
S
S
S
R
R
S
L
= 0.1
R
R
R
R
S
2
2
S
S
S
= 50Ω
= 50Ω
= 25Ω
= 25Ω
CONFIGURATION
CONFIGURATION
DENORMALIZED
SINGLE-ENDED
SINGLE-ENDED
NORMALIZED
EQUIVALENT
L
BALANCED
N
0.54µH
0.27µH
0.27µH
= 0.074H
C
N
14.814F
433pF
433pF
f
f
C
R
C
R
R
R
2
2
= 10.9MHz
L
L
L
= 1Hz
L
= 500Ω
= 500Ω
= 250Ω
= 250Ω
Rev. 0 | Page 19 of 28
Figure 57 and Figure 58 show the measured frequency response
and group delay of the filter.
–10
–15
–20
900
800
700
600
500
400
300
200
100
10
–5
5
0
0
0
0.2
0.5
Figure 58. Baseband Filter Group Delay
Figure 57. Baseband Filter Response
0.4
1.0
0.6
FREQUENCY (MHz)
FREQUENCY (MHz)
0.8
1.5
1.0
2.0
1.2
2.5
1.4
1.6
3.0
ADL5387
1.8
3
.5