ADRF6518ACPZ-R7 datasheet(32/39 Pages) AD

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ADRF6518

Data Sheet

Rev. A | Page 32 of 39

INSTABILITY AT LOW FILTER CORNERS AND LOW

POWER MODE

The ADRF6518 has a tendency to oscillate when the filter

corner is 8 MHz or less and when in low power mode. This

oscillation is primarily out of band, occurring at approximately

1.2 GHz. The oscillation worsens at cold temperatures. It is

recommended that high power mode be used when in filter

mode to lessen the inherent instability of the device. A low-pass

filter can be added between the output of the ADRF6518 and

the following stage to attenuate the out of band oscillation.

PEAK DETECTOR BANDWIDTH AND SLEW RATE

The VPK pin on the ADRF6518 has an attack bandwidth of

100 MHz, where the VPK pin is responding to a rise in signal

level, and a droop slew rate, where VPK is responding to a fall

in signal level; this can be seen in Figure 47, where very large

values of the off-chip RAVG were used. RAVG controls the slew rate

of the peak detector. This resistor must be connected from the

VPK pin to the VPS pin.

Figure 86. Peak Detector Droop time over RAVG

Figure 87. Peak Detector Droop time over RAVG, zoomed

Figure 86 and Figure 87 show the slew rate for three different

values of RAVG: 100 kΩ, 10 kΩ, and 1 kΩ, with slew rates of

5 mV/μs, 50 mV/μs, 500 mV/μs, respectively. Note that these

slew rates start to decrease as the peak detector nears its

minimum value. This is a result of the nonlinearities of the

output stage of the peak detector.

LINEAR OPERATION OF THE ADRF6518

The ADRF6518 has multiple stages per channel. Each stage can

independently be driven into compression depending on the

gain settings and input signal level. There is only access to the

input stages (INP1/INM1, INP2/INM2) and the output stages

(OPP1/OPM2, OPP2/OPM2); therefore, the user must infer the

signal level at the input and output of each stage from the device

under test (DUT) input signal level and the gain settings, both

analog and digital. The maximum recommended signal levels

are shown in Figure 90. All signal levels are in V p-p differential.

Figure 88. Maximum Signal Levels; Single Channel Shown

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

100

120

140

160

180

TIME (µs)

100kΩ

10kΩ

1kΩ

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

TIME (µs)

100kΩ

10kΩ

1kΩ

OPP1/OPP2

OPM1/OPM2

VGN3

INP1/INP2

INM1/INM2

VGN1

VGN2

5.0V p-p

2.2V p-p

2.6V p-p

2.6V p-p 5.0V p-p

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