MAX4000EUA+ Maxim Integrated Products, MAX4000EUA+ Datasheet - Page 13

• Manufacturer Part Number: MAX4000EUA+
• Description: RF Detector IC CNTRLR RF-DETECT F-Detecting Controll
• Manufacturer: Maxim Integrated Products

Specifications of MAX4000EUA+

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The MAX4000/MAX4001/MAX4002 family of logarithmic
amplifiers (log amps) is comprised of four main amplifi-
er/limiter stages each with a small-signal gain of 10dB.
The output stage of each amplifier is applied to a full-
wave rectifier (detector). A detector stage also pre-
cedes the first gain stage. In total, five detectors each
separated by 10dB, comprise the log amp strip. Figure
1 shows the functional diagram of the log amps.
A portion of the PA output power is coupled to RFIN of
the log amp controller, and is applied to the log amp
strip. Each detector cell outputs a rectified current and
all cell currents are summed and form a logarithmic
output. The detected output is applied to a high-gain
g
OUT is applied to the gain-control pin of the PA to close
the control loop. The voltage applied to SET determines
the output power of the PA in the control loop. The volt-
age applied to SET relates to an input power level
determined by the log amp detector characteristics.
Extrapolating a straight-line fit of the graph of SET vs.
RFIN provides the logarithmic intercept. Logarithmic
slope, the amount SET changes for each dB change of
RF input, is generally independent of waveform or ter-
mination impedance. The MAX4000/MAX4001/
MAX4002 slope at low frequencies is about 25mV/dB.
Variance in temperature and supply voltage does not
alter the slope significantly as shown in the Typical
Operating Characteristics.
The MAX4000/MAX4001/MAX4002 are specifically des-
igned for use in PA control applications. In a control
loop, the output starts at approximately 2.9V (with sup-
ply voltage of 3V) for the minimum input signal and falls
to a value close to ground at the maximum input. With a
portion of the PA output power coupled to RFIN, apply
a voltage to SET and connect OUT to the gain-control
pin of the PA to control its output power. An external
Figure 1. Functional Diagram
(PADDLE)
SHDN
m
RFIN
GND
V
CC
stage, which is buffered and then applied to OUT.
DET
OFFSET
10dB
COMP
______________________________________________________________________________________
DET
Detailed Description
10dB
2.5GHz 45dB RF-Detecting Controllers
DET
10dB
DET
10dB
BANDGAP
OUTPUT
ENABLE
DELAY
NOISE
LOW-
DET
+
-
gm
MAX4000
X1
V-I
OUT
CLPF
SET
capacitor from the CLPF pin to ground sets the band-
width of the PA control loop.
Logarithmic slope and intercept determine the transfer
function of the MAX4000/MAX4001/MAX4002 family of
log amps. The change in SET voltage per dB change in
RF input defines the logarithmic slope. Therefore, a
250mV change at SET results in a 10dB change at
RFIN. The Log-Conformance plots (see Typical Oper-
ating Characteristics) show the dynamic range of the
log amp family. Dynamic range is the range for which
the error remains within a band of ±1dB.
The intercept is defined as the point where the linear
response, when extrapolated, intersects the y-axis of
the Log-Conformance plot. Using these parameters,
the input power can be calculated at any SET voltage
level within the specified input range with the following
equation:
where SET is the set-point voltage, SLOPE is the loga-
rithmic slope (V/dB), RFIN is in either dBm or dBV and
IP is the logarithmic intercept point utilizing the same
units as RFIN.
Figure 2 provides a circuit example of the MAX4000/
MAX4001/MAX4002 configured as a controller. The
MAX4000/MAX4001/MAX4002 require a 2.7V to 5.5V
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 frequencies
(especially at the high-power levels of the MAX4002).
The MAX4000 has an internal input-coupling capacitor
Figure 2. Controller Mode Application Circuit Block
V
ANTENNA
CC
50Ω
DAC
Applications Information
C
F
XX
RFIN
RFIN
SHDN
SET
CLPF
=
SLOPE
MAX4000
SET
CC
to decouple the supply.
POWER AMPLIFIER
Transfer Function
GND
OUT
N.C.
V
+
CC
IP
Controller Mode
0.1μF
V
RF INPUT
CC
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