MAX2240 Maxim, MAX2240 Datasheet - Page 6

• Manufacturer Part Number: MAX2240
• Description: 2.5GHz / +20dBm Power Amplifier IC in UCSP Package
• Manufacturer: Maxim

four levels (magnitudes) of precisely controlled currents
to the VGA, depending on power control digital inputs
D0 and D1. Each current level presents a different
power level to the final amplifier stage, therefore con-
trolling the output power.
The digital power control circuit of the PA greatly sim-
plifies control of the output power. The two digital bits
D0 and D1 control the output power in four steps with
approximately a 6dB/step. The PA is optimized to pro-
vide power control steps within a 2dB/step to 8.6dB/
step over the full temperature range and V
input power variations. Table 1 shows the D0 and D1
digital control states, the corresponding nominal output
power, and the typical current consumption of the IC.
The bias circuit provides separate bias voltages and
currents to the amplifier stages. An internal lowpass RC
filter isolates the bias circuit from being corrupted by
the RF signals. The bias circuit is optimized to minimize
output power variations due to the variations in temper-
ature, V
also ensures the stability of the PA when connected to
high VSWR loads over all power levels. A digital low at
the SHDN port turns the amplifier down with a current
consumption of less than 1µA.
The MAX2240 integrates all the RF matching compo-
nents on-chip, except for the output stage match. The
internal input match enables the RF input with 50Ω
impedance to be directly connected to the RFIN port
through a 50Ω transmission line.
The MAX2240 PA requires an external match at the
RFOUT port to optimize the amplifier for output power
and efficiency. For an optimum match at 2.45GHz, the
load impedance at the RFOUT port is approximately
15Ω + j18Ω (Figure 1). There are numerous ways of
transforming 50Ω to the optimum impedance. The out-
put matching in the typical operating circuit is imple-
mented using a series transmission line of 75Ω and
electrical length of 26°, and an open-ended shunt stub
2.5GHz, +20dBm Power Amplifier IC
in UCSP Package
Table 1. Control Inputs
6
_______________________________________________________________________________________
SHDN
0
1
1
1
1
CC
DIGITAL CONTROL INPUTS
, and RF power input. The bias circuit design
D1
0
0
0
1
1
D0
0
0
1
0
1
CC
and RF
POWER LEVEL
PA OFF-
P1
P2
P3
P4
OUTPUT POWER AND SUPPLY CURRENT
of 65Ω and 41° in length. The shunt stub also reduces
the second harmonic at the output.
The MAX2240 power amplifier requires a relatively
small number of external components. These compo-
nents are small, low-cost surface-mount passive ele-
ments. The capacitors are all 0402 multilayer ceramic
chip capacitors. These capacitors possess excellent
high-frequency properties and are cost effective. The
Typical Application Circuit is shown on page 1.
The inductor is a Q (>25) 0603 chip inductor. All trans-
mission lines are simple microstrip structures printed
on the PC board.
The MAX2240 is designed to operate from a single, posi-
tive supply voltage (V
ply voltage: BIAS, V
voltage connection requires a separate RF bypass
capacitor for proper operation. Use a 0.1µF bypass
capacitor to filter the supply at the common V
(see Typical Application Circuit).
BIAS requires a 220pF capacitor to ground. Locate one
end of the capacitor as close as possible to BIAS and
the other end of the capacitor near GND1 with several
vias to the ground plane.
V
inductor in series with V
tor is needed for optimal output power and efficiency.
An 18pF bypass capacitor to ground is required at the
supply end of the 1.2nH inductor.
RFOUT is connected to the power supply through a
choke inductor (through transmission line section T1).
Select a choke with a self-resonant frequency at or
slightly below 2.4GHz. A 220pF bypass capacitor is
needed at the supply voltage end of the inductor.
CC
powers the amplifier 1st stage output. A 1.2nH
(dBm)
P
3
3
3
3
3
IN
Applications Information
Power-Supply Considerations
CC
CC
CC
). Three pins are fed by the sup-
(dBm)
P
, and RFOUT. Each supply
-22
OUT
12
19
3
8
and the V
CC
bypass capaci-
I
CC
<1µA
105
65
68
75
(mA)
CC
node