Datasheet

MAX9930–MAX9933
2MHz to 1.6GHz 45dB RF-Detecting
Controllers and RF Detector
12 ______________________________________________________________________________________
Applications Information
Controller Mode
(MAX9930/MAX9931/MAX9932)
Figure 3 provides a circuit example of the MAX9930/
MAX9931/MAX9932 configured as a controller. The
MAX9930/MAX9931/MAX9932 require a 2.7V to 5.25V
supply voltage. Place a 0.1µF low-ESR, surface-mount
ceramic capacitor close to V
CC
to decouple the supply.
Electrically isolate the RF input from other pins (espe-
cially SET) to maximize performance at high frequen-
cies (especially at the high-power levels of the
MAX9932). The MAX9930/MAX9931/MAX9932 require
external AC-coupling. Achieve 50Ω input matching by
connecting a 50Ω resistor between the AC-coupling
capacitor of RFIN and ground.
The MAX9930/MAX9931/MAX9932 logarithmic ampli-
fiers function as both the detector and controller in
power-control loops. Use a directional coupler to couple
a portion of the PA’s output power to the log amp’s RF
input. For applications requiring dual-mode operation
and where there are two PAs and two directional cou-
plers, passively combine the outputs of the directional
couplers before applying to the log amp. Apply a set-
point voltage to SET from a controlling source (usually a
DAC). OUT, which drives the automatic gain-control
input of the PA, corrects any inequality between the RF
input level and the corresponding set-point level. This is
valid assuming the gain control of the variable gain ele-
ment is positive, such that increasing OUT voltage
increases gain. The OUT voltage can range from 150mV
to within 250mV of the positive supply rail while sourcing
10mA. Use a suitable load resistor between OUT and
GND for PA control inputs that source current. The
Typical Operating Characteristics has the Maximum Out
Voltage vs. V
CC
By Load Current graph that shows the
sourcing capabilities and output swing of OUT.
SHDN and Power-On
The MAX9930–MAX9933 can be placed in shutdown by
pulling SHDN to ground. Shutdown reduces supply cur-
rent to typically 13µA. A graph of SHDN Response Time
is included in the Typical Operating Characteristics .
Connect SHDN and V
CC
together for continuous on
operation.
Power Convention
Expressing power in dBm, decibels above 1mW, is the
most common convention in RF systems. Log amp
input levels specified in terms of power are a result of
the following common convention. Note that input
power does not refer to power, but rather to input volt-
age relative to a 50Ω impedance. Use of dBV, decibels
with respect to a 1V
RMS
sine wave, yields a less
ambiguous result. The dBV convention has its own pit-
falls in that log amp response is also dependent on
waveform. A complex input, such as CDMA, does not
have the exact same output response as the sinusoidal
signal. The MAX9930–MAX9933 performance specifi-
cations are in both dBV and dBm, with equivalent dBm
levels for a 50Ω environment. To convert dBV values
into dBm in a 50Ω network, add 13dB. For CATV appli-
cations, to convert dBV values to dBm in a 75Ω net-
work, add 11.25dB. Table 1 shows the different input
power ranges in different conventions for the
MAX9930–MAX9933.
Table 1. Power Ranges of the MAX9930–
MAX9933
INPUT POWER RANGE
PART
dBV
dBm IN A 50Ω
NETWORK
dBm IN A 75Ω
NETWORK
MAX9930 -58 to -13 -45 to 0 -46.75 to -1.75
MAX9931 -48 to -3 -35 to +10 -36.75 to +8.25
MAX9932 -43 to +2 -30 to +15 -31.75 to +13.25
MAX9933 -58 to -13 -45 to 0 -46.75 to -1.75
V
CC
OUT
N.C.
GND
C
CLPF
DAC
50Ω
RFIN
SHDN
CLPF
SET
0.1µF
RF INPUT
V
CC
C
C
XX
ANTENNA
POWER AMPLIFIER
MAX9930
MAX9931
MAX9932
Figure 3. Control Mode Application Circuit Block