Datasheet

MAX2016
LF-to-2.5GHz Dual Logarithmic Detector/
Controller for Power, Gain, and VSWR Measurements
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The differential RF inputs allow for the measurement of
broadband signals ranging from low frequency to
2.5GHz. For single-ended signals, RFINA- and RFINB-
are AC-coupled to ground. The RF inputs are internally
biased and need to be AC-coupled. Using 680pF
capacitors, as shown in the Typical Application Circuit,
results in a 10MHz highpass corner frequency. An
internal 50Ω resistor between RFINA+ and RFINA- (as
well as RFINB+ and RFINB-) produces a good low-fre-
quency to 3.0GHz match.
SETA, SETB, and SETD Inputs
The SET_ inputs are used for loop control when the
device is in controller mode. Likewise, these same
SET_ inputs are used to set the slope of the output sig-
nal (mV/dB) when the MAX2016 is in detector mode.
The center node of the internal resistor-divider is fed to
the negative input of the power detector’s internal out-
put op amp.
Reference
The MAX2016 has an on-chip 2V voltage reference.
The internal reference output is connected to REF. The
output can be used as a reference voltage source for
the comparators or other components and can source
up to 2mA.
OUTA and OUTB
Each OUT_ is a DC voltage proportional to the RF input
power level. The change of OUT_ with respect to the
power input is approximately 18mV/dB (R
1
= R
2
= 0Ω).
The input power level can be determined by the following
equation:
where P
INT
is the extrapolated intercept point of where
the output voltage intersects the horizontal axis.
OUTD
OUTD is a DC voltage proportional to the difference of
the input RF power levels. The change of the OUTD
with respect to the power difference is -25mV/dB (R3 =
0Ω). The difference of the input power levels (gain) can
be determined by the following equation:
where V
CENTER
is the output voltage, typically 1V, when
P
RFINA
= P
RFINB
.
Applications Information
Monitoring VSWR and Return Loss
The MAX2016 can be used to measure the VSWR of an
RF signal, which is useful for detecting the presence or
absence of a properly loaded termination, such as an
antenna (see Figure 1). The transmitted wave from the
power amplifier is coupled to RFINA and to the anten-
na. The reflected wave from the antenna is connected
to RFINB through a circulator. When the antenna is
missing or damaged, a mismatch in the nominal load
PP
VV
SLOPE
RFINA RFINB
OUTD CENTER
−
=
−()
P
V
SLOPE
P
RFIN
OUT
INT_
_
=+
MAX2016
CSETL
COUTL
V
REF
LOGARITHMIC
DETECTOR
LOGARITHMIC
DETECTOR
COUTL
OUTD
SETD
20kΩ
RFINB
RFINA
OUTD
TRANSMITTER
COUPLER
CIRCULATOR
ATTENUATOR
GND
Figure 1. VSWR Monitoring Configuation