ADL5519ACPZ-R2 datasheet(27/39 Pages) AD

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Data Sheet

ADL5519

Rev. C | Page 27 of 39

OUTPUT FILTERING

Accurate power detection for signals with RF bursts is achieved

when the ADL5519 is able to respond quickly to the change in

RF power. For applications in which maximum video bandwidth

and, consequently, fast rise time are desired, it is essential that

the CLPA, CLPB pins have very little capacitance on them (some

capacitance reduces the ringing).

The nominal output video bandwidth of 10 MHz can be reduced

by connecting a ground-referenced capacitor (CFLT) to the CLPA,

CLPB pins, as shown in Figure 65. This is generally done to

reduce output ripple (at twice the input frequency for a

symmetric input waveform, such as a sinusoidal signal).

ILOGA,

ILOGB

CFLT

1.5kΩ

OUTA, OUTB

CLPA, CLPB

3.5pF

ADL5519

Figure 65. Lowering the Post Demodulation Bandwidth

CFLT is selected using the following equation:















Bandwidth

Video

FLT

(12)

The video bandwidth should typically be set to a frequency less

than or equal to approximately 1/10 the minimum input

frequency. There are no problems with putting large capacitor

values on the CLPA, CLPB pins. These large capacitor values

ensure that the output ripple of the demodulated log output,

which is at twice the input frequency, is well filtered. Signals

with modulation may need additional filtering (a larger CFLT

capacitance) to remove modulation bleedthrough.

PACKAGE CONSIDERATIONS

The ADL5519 uses a compact, 32-lead LFCSP. A large exposed

paddle on the bottom of the device provides both a thermal

benefit and a low inductance path to ground for the circuit.

To make proper use of this packaging feature, the PCB RF/dc

common-ground reference needs to make contact with the paddle

with as many vias as possible to lower inductance and thermal

impedance.

OPERATION ABOVE 8 GHz

The ADL5519 is specified for operation up to 8 GHz, but it

provides useful measurement accuracy over a reduced dynamic

range of up to 10 GHz. Figure 66 shows the performance of the

ADL5519 over temperature for a input frequency of 10 GHz.

This high frequency performance is achieved using the configu-

ration shown in Figure 53. The dynamic range shown is reduced

from the typical device performance, but the ADL5519 can provide

30 dB of measurement range with less than 3 dB of linearity error.

Implementing an impedance match for frequencies greater

than 8 GHz can improve the sensitivity of the ADL5519 and its

measurement range.

2.00

1.75

1.50

1.25

1.00

0.75

0.50

0.25

4.0

3.0

2.0

1.0

–1.0

–2.0

–3.0

–4.0

–40

–35

–30

–25

–20

–15

–10

–5

PIN (dBm)

Figure 66. VOUT and Log Conformance vs. Input Amplitude at 10 GHz,

Over Temperature, ADJA, ADJB = 1.8 V, 1.8 V

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