Datasheet

MAX2016
LF-to-2.5GHz Dual Logarithmic Detector/
Controller for Power, Gain, and VSWR Measurements
______________________________________________________________________________________ 15
Power-Controller Mode
The MAX2016 can also be used as a power detector/
controller within an AGC loop. Figure 7 depicts a sce-
nario where the MAX2016 is employed as the AGC cir-
cuit. As shown in the figure, the MAX2016 monitors the
output of the PA through a directional coupler. An inter-
nal differencing amplifier (Figure 5) compares the
detected signal with a reference voltage determined by
V
SET_
. The differencing amplifier increases or decreas-
es the voltage at OUT_, according to how closely the
detected signal level matches the V
SET_
reference. The
MAX2016 maintains the power of the PA to a level
determined by the voltage applied to SET_.
Since the logarithmic detector responds to any ampli-
tude modulation being carried by the carrier signal, it
may be necessary to insert an external lowpass filter
between the differencing amplifier output
(OUTA/OUTB) and the gain-control element to remove
this modulation signal.
OUTA and OUTB Slope Adjustment
The transfer slope function of OUTA and OUTB can be
increased from its nominal value by varying resistors
R1 and R2 (see the Typical Application Circuit). The
equation controlling the slope is:
OUTD Slope Adjustment
The transfer slope function of OUTD can be increased
from its nominal value by varying resistor R3 (see the
Typical Application Circuit). The equation controlling
the slope is:
Input Highpass Filters
The MAX2016 integrates a programmable highpass fil-
ter on each RF input. The lower cutoff frequency of the
MAX2016 can be decreased by increasing the external
capacitor value between FA1 and FA2 or FB1 and FB2.
By default, with no capacitor connecting FA1 and FA2
or FB1 and FB2, the lower cutoff frequency is 20MHz.
Using the following equation determines the lowest
operating frequency:
where R = 2Ω.
Differential Output Video Filter
The bandwidth and response time difference of the out-
put amplifier can be controlled with the external capaci-
tor, C
15
, connected between FV1 and FV2. With no
external capacitor, the bandwidth is greater than 20MHz.
The following equation determines the bandwidth of the
amplifier difference:
where R = 1.8kΩ.
Use a video bandwidth lower than the anticipated low-
est amplitude-modulation frequency range to yield the
greatest accuracy in tracking the average carrier
power for high peak-to-average ratio waveforms.
frequency
RC
=
1
2π
frequency
RC
=
1
2π
SLOPE OUTD
mV
dB
Rk
k
=−
⎛
⎝
⎜
⎞
⎠
⎟
+
⎛
⎝
⎜
⎞
⎠
⎟
25
320
20
SLOPE OUTA OR OUTB
mV
dB
RorR k
k
=
⎛
⎝
⎜
⎞
⎠
⎟
()
+
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥
9
1240
20
MAX2016
LOGARITHMIC
DETECTOR
TRANSMITTER
SET-POINT
DAC
OUTA/
OUTB
SETA/
SETB
COUPLER
RFINA/
RFINB
POWER AMPLIFIER
GAIN-CONTROL INPUT
LOWPASS
FILTER
20kΩ
20kΩ
Figure 7. In Power-Controller Mode, the DC Voltage at OUTA or
OUTB Controls the Gain of the PA, Leading to a Constant
Output Power Level (Note: Only one controller channel is
shown within the figure. Since the MAX2016 is a dual con-
troller/detector, the second channel can be easily implemented
by using the adjacent set of input and output connections.)