MAX9933 Maxim, MAX9933 Datasheet - Page 12

• Manufacturer Part Number: MAX9933
• Description: The MAX9930–MAX9933 low-cost, low-power logarithmic amplifiers are designed to control RF power amplifiers (PA) and transimpedance amplifiers (TIA), and to detect RF power levels
• Manufacturer: Maxim

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
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
2MHz to 1.6GHz 45dB RF-Detecting
Controllers and RF Detector
Figure 3. Control Mode Application Circuit Block
12
50Ω
ANTENNA
______________________________________________________________________________________
XX
C
C
C
DAC
CLPF
Applications Information
(MAX9930/MAX9931/MAX9932)
RFIN
SHDN
SET
CLPF
MAX9930
MAX9931
MAX9932
CC
to decouple the supply.
GND
OUT
N.C.
V
CC
POWER AMPLIFIER
Controller Mode
0.1µF
RF INPUT
V
CC
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
sourcing capabilities and output swing of OUT.
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
operation.
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
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
MAX9930
MAX9931
MAX9932
MAX9933
PART
-58 to -13
-58 to -13
CC
-43 to +2
-48 to -3
dBV
By Load Current graph that shows the
RMS
INPUT POWER RANGE
CC
dBm IN A 50Ω
NETWORK
-35 to +10
-30 to +15
together for continuous on
-45 to 0
-45 to 0
sine wave, yields a less
SHDN and Power-On
Power Convention
-31.75 to +13.25
-36.75 to +8.25
dBm IN A 75Ω
-46.75 to -1.75
-46.75 to -1.75
NETWORK