Choke inductor, Layout considerations – Rainbow Electronics MAX2055 User Manual
Page 11
feedback topology. This amplifier is optimized for a fre-
quency range of operation from 30MHz to 300MHz with
a high-output third-order intercept point (OIP3). The
bias current is chosen to optimize the IP3 of the amplifi-
er. When R
1
is 1.13k
Ω (909Ω if using the circuit of
Figure 2), the current consumption is 240mA while
exhibiting a 40dBm typical output IP3 at 70MHz. The
common-mode inductor, L
2
, provides a high common-
mode rejection with excellent amplitude and phase bal-
ance at the output. L
2
must handle the supply current
and have DC resistance less than 0.2
Ω.
Choke Inductor
The single-ended amplifier input and differential output
ports require external choke inductors. At the input,
connect a 330nH bias inductor from AMP
IN
(pin 15) to
I
BIAS
(pin 12). Connect 680nH choke inductors from
RF_OUT+ (pin 11) and RF_OUT- (pin 10) to V
CC
. These
connections provide bias current to the amplifier.
Layout Considerations
A properly designed PC board is an essential part of
any RF/microwave circuit. Keep RF signal lines as short
as possible to reduce losses, radiation, and induc-
tance. For best performance, route the ground-pin
traces directly to the exposed pad underneath the
MAX2055
Digitally Controlled, Variable-Gain, Differential
ADC Driver/Amplifier
______________________________________________________________________________________
11
20
19
18
17
16
15
14
13
1
2
3
4
5
6
7
8
ATTN
OUT
I
SET
R
1
B4
1
RF_IN
V
CC
AMP
IN
C
BP
B0
B1
B2
B3
12
11
9
10
I
BIAS
RF_OUT+
RF_OUT
RF_OUT-
CONTROL
INPUTS
ATTENUATION
LOGIC
CONTROL
V
CC
MAX2055
C
12
C
11
T
2
C
10
V
CC
C
9
L
5
L
4
C
8
C
7
C
5
C
4
C
3
C
1
C
2
L
1
L
2
L
3
V
CC
RF_IN
GND
V
CC
R
7
GND
GND
C
C
L
E
Figure 2. Low-Cost Application Circuit