Datasheet

MAX2016
LF-to-2.5GHz Dual Logarithmic Detector/
Controller for Power, Gain, and VSWR Measurements
14 ______________________________________________________________________________________
Measuring Power (RSSI Detector Mode)
In detector mode, the MAX2016 acts like a receive-sig-
nal-strength indicator (RSSI), which provides an output
voltage proportional to the input power. This is accom-
plished by providing a feedback path from OUTA
(OUTB) to SETA (SETB) (R1/R2 = 0Ω; see Figure 5).
By connecting SET_ directly to OUT_, the op-amp gain
is set to 2V/V due to two internal 20kΩ feedback resis-
tors. This provides a detector slope of approximately
18mV/dB with a 0.5V to 1.8V output range.
Gain-Controller Mode
The MAX2016 can be used as a gain controller within
an automatic gain-control (AGC) loop. As shown in
Figure 6, RFINA and RFINB monitor the VGA’s input
and output power levels, respectively. The MAX2016
produces a DC voltage at OUTD that is proportional to
the difference in these two RF input power levels. An
internal op amp compares the DC voltage with a refer-
ence voltage at SETD. The op amp increases or
decreases the voltage at OUTD until OUTD equals
SETD. Thus, the MAX2016 adjusts the gain of the VGA
to a level determined by the voltage applied to SETD.
Place the nominal signal levels of RFINA and RFINB
near the middle of their respective dynamic ranges to
accommodate the largest range of gain compensation.
This is nominally -25dBm to -30dBm. If so selected, the
nominal voltage applied to SETD will be approximately
1.0V. Operate the SETD voltage within the range of
0.5V to 1.5V for the greatest accuracy of gain control.
MAX2016
RFIN+A
RFIN-A
OUTA
IN_
GND
R1/R2
20k
Ω
20k
Ω
DETECTORS
SETA
OUTA
RFIN+B
RFIN-B
OUTB
IN_
R1/R2
20k
Ω
20k
Ω
DETECTORS
SETB
OUTB
Figure 5. In Detector Mode (RSSI), OUTA/OUTB is a DC
Voltage Proportional to the Input Power
MAX2016
LOGARITHMIC
DETECTOR
LOGARITHMIC
DETECTOR
20k
Ω
VGA
GAIN CONTROL INPUT
RFINA
RFINB
OUTDSETD
VGA INPUT
VGA OUTPUT
SET-POINT
DAC
COUPLER
COUPLER
Figure 6. In Gain-Controller Mode, the OUTD Maintains the
Gain of the VGA