AD8364-EVAL-500 Analog Devices, AD8364-EVAL-500 Datasheet - Page 23

• Manufacturer Part Number: AD8364-EVAL-500
• Description: LF to 2.7GHz, Dual 60dB TruPwr™ Detector; Package: EVALUATION BOARDS; No of Pins: -; Temperature Range: Commercial
• Manufacturer: Analog Devices

RF MEASUREMENT MODE BASIC CONNECTIONS
The AD8364 requires a single supply of nominally 5 V. The
supply is connected to the three supply pins, VPSA, VPSB, and
VPSR. Each pin should be decoupled using the two capacitors
with values equal or similar to those shown in Figure 60. These
capacitors must provide a low impedance over the full
frequency range of the input, and they should be placed as close
as possible to the VPOS pins. Two different capacitors are used
in parallel to provide a broadband ac short to ground.
The input signals are applied to the input differentially. The RF
inputs of the AD8364 have a differential input impedance of
200 Ω. When the AD8364 RF inputs are driven from a 50 Ω
source, a 4:1 balun transformer is recommended to provide the
necessary impedance transformation. The inputs can be driven
single-ended, however, this reduces the measurement range of
the rms detectors (see the Single-Ended Input Operation
section).
Table 4. Baluns Used to Characterize the AD8364
Frequency
450 MHz
880 MHz
1880 MHz
2140 MHz
2500 MHz
Balun
MIA-COM ETK4-2T
Mini-Circuits JTX-4-10T
Murata LDB181G8820C-110
Murata LDB212G1020C-001
Murata LDB182G4520C-110
Rev. 0 | Page 23 of 48
The device is placed in measurement mode by connecting OUTA
and/or OUTB to VSTA and/or VSTB, respectively. This closes the
AGC loop within the device with OUT[A, B] representing the
VGA control voltage, which is required to present the correct
rms voltage at the input of the internal square law detector.
As the input signal to Channel A and Channel B are swept over
their nominal input dynamic range of +10 dBm to −50 dBm,
the output swings from 0 V to 3.5 V. The voltages OUTA and
OUTB are also internally applied to a difference amplifier with
a gain of two. So as the dB difference between INA and INB
ranges from approximately −30 dB to +30 dB, the difference
voltage on OUTP and OUTN swings from −3.5 V to +3.5 V.
Input differences larger than ±30 dB can be measured as long as
the absolute input level at INA and INB are within their nominal
ranges of +10 dBm to −50 dBm. However, measurement of large
differences between INA and INB are affected by on-chip signal
leakage (see the Channel Isolation section). The common-mode
level of OUTP and OUTN is set by the voltage applied to VLVL.
These output can be easily biased up to a common-mode
voltage of 2.5 V by connecting VREF to VLVL. As the gain range
is swept, OUTP swings from approximately 1 V to 4.5 V and
OUTN swings from 4.5 V to 1 V.
AD8364