Datasheet
MAX2235
+3.6V, 1W Autoramping Power
Amplifier for 900MHz Applications
6 _______________________________________________________________________________________
Detailed Description
The MAX2235 power amplifier (PA) operates over a
wide frequency range of 800MHz to 1000MHz. The sig-
nal path consists of three stages: the input stage, the
driver stage, and the power stage. There are matching
circuits between the first and second stages, and
between the second and third stages. The bias circuits
process external commands to control the device’s
power-up/down and the gain of the PA.
Input Stage
The first stage is a variable-gain amplifier with 37dB
gain-control range. The input transistor acts as a
transconductor with constant bias current. Gain control
is achieved by steering the signal current from the input
transistor to the first output matching network (to drive
the second stage) or to a separate supply pin. This
stage operates in class A and remains on in standby
mode to ensure that the VSWR at the input does not
vary more than 1.5:1 compared with normal operation.
The input stage typically requires an external inductor
to achieve an optimum input VSWR.
Second Stage (Driver)
The driver produces a signal large enough to drive the
power stage into saturation. The driver stage operates
in Class C and is off during standby.
Second- and Third-Stage Matching
The interstage matching networks provide optimal load-
ing and power transfer. The circuits are on-chip to save
board space. The bandwidths of the matching net-
works allow the PA to operate over a wide frequency
range.
Typical Operating Circuit
20
19
18
17
8
7
6
5
4
3
2
1
16
15
14
13
9
10
11
12
GND
V
CC
V
CC
V
CC
GND
GND
V
CC
V
CC
GND
RFIN
SHDN
GND
GND
RFOUT
RFOUT
GND
GND
REF
RAMP
GC
0.068µF
470pF
470pF
1500pF
47pF
1000pF
1000pF
11pF
MAX2235
68pF
V
CC
V
CC
V
CC
V
CC
V
CC
J2
JU2
JU1
SMA
SMA
J3
J4
8.2nH
*
100pF
100pF
1000pF
1000pF
22pF
100pF
100pF
0.01µF1µF
J1
1
2
3
* VALUE OF OUTPUT INDUCTOR DEPENDS ON APPLICATION.