AD8364ACPZ-R2 datasheet(23/44 Pages) AD

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Data Sheet

AD8364

Rev. C | Page 23 of 44

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 must 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 must 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

Balun

450 MHz

MIA-COM ETK4-2T

880 MHz

Mini-Circuits JTX-4-10T

1880 MHz

Murata LDB181G8820C-110

2140 MHz

Murata LDB212G1020C-001

2500 MHz

Murata LDB182G4520C-110

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.

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