max2016etit Maxim Integrated Products, Inc., max2016etit Datasheet - Page 12

• Manufacturer Part Number: max2016etit
• Description: Max2016 Lf-to-2.5ghz Dual Logarithmic Detector/controller For Power, Gain, And Vswr Measurements
• Manufacturer: Maxim Integrated Products, Inc.

LF-to-2.5GHz Dual Logarithmic Detector/
Controller for Power, Gain, and VSWR Measurements
impedance results, leading to an increase in reflected
power and subsequent change in the transmission
line’s VSWR. This increase in reflected power is mani-
fested by an increase in the voltage at OUTD. An alarm
condition can be set by using the low comparator out-
put (COUTL) as shown in Figure 1. The comparator
automatically senses the change in VSWR, yielding a
logic 0 as it compares OUTD to a low DC voltage at
CSETL. CSETL, in turn, is set by using the internal refer-
ence voltage and an external resistor-divider network.
For accurate measurement of signals carrying signifi-
cant amplitude modulation, limit the bandwidth of the
difference amplifier to be less than the lowest modula-
tion frequency. This will minimize the ripple in the
OUTD waveform. This is particularly appropriate if the
system-level time delay between the two sense points
is significant with respect to the period of modulation.
Figure 1 illustrates a simple level detector. For window-
detector implementation, see the Comparator/Window
Detector section.
Figure 2. Measuring Return Loss and VSWR of a Given Load
12
______________________________________________________________________________________
IN
4-PORT DIRECTIONAL
COUPLER
RFINA
RFINB
LOGARITHMIC
LOGARITHMIC
DETECTOR
DETECTOR
MAX2016
LOAD
20kΩ
In Figure 2, the two logarithmic amplifiers measure the
incident and the reflected power levels to produce two
proportional output voltages at OUTA and OUTB. Since
OUTD is a DC voltage proportional to the difference of
OUTA and OUTB, return loss (RL) and VSWR can be
easily calculated within a microprocessor using the
following relationships:
where return loss (RL) is expressed in decibels,
V
P
-25mV/dB (for R3 = 0Ω).
VSWR can similarly be calculated through the following
relationship:
CENTER
RFINA
RL P
=
= P
OUTD
SETD
GND
is the output voltage (typically 1V) when
RFINA
RFINB
Measuring VSWR and Return Loss
VSWR
−
, and SLOPE is typically equal to
P
RFINB
ADC
=
1 10
1 10
+
−
=
(
V
−
−
OUTD
⎛
⎝
⎛
⎝
RL
20
RL
20
⎞
⎠
⎞
⎠
SLOPE
−
μP
V
CENTER
)