ADL5506

Data Sheet

Rev. A | Page 20 of 23

Effect of Waveform Type on Intercept

Although specified for input levels in decibels relative to 1 mW

(dBm), the ADL5506 fundamentally responds to voltage and

not to power. A direct consequence of this characteristic is that

input signals of equal rms power but differing crest factors,

produce different results at the output of the log amplifier.

The effect of differing signal waveforms is to shift the effective

value of the intercept upwards or downwards. Graphically, this

looks like a vertical shift in the transfer function of the log

amplifier. The logarithmic slope, however, is not affected. For

example, consider the case of the ADL5506 being alternately fed

by an unmodulated sine wave and by a 64 QAM signal of the

same rms power. The output voltage of the ADL5506 differs by

the equivalent of 1.6 dB (31 mV) over the complete dynamic

range of the device (with the output for a 64 QAM input being

lower).

Figure 35 and Figure 38 shows the transfer function of the

ADL5506 when driven by both an unmodulated sine wave and

several different signal waveforms. For precision operation,

calibrate the ADL5506 for each signal type that is driving it. To

measure the rms power of a 64 QAM input, for example, add

the millivolt equivalent of the decibel value of the intercept shift

(18.5 mV/dB × 1.5 dB) to the output voltage of the ADL5506.

Temperature Drift at High Frequencies

Figure 23 and Figure 27 show the log slope and error over

temperature for a 3.5 GHz and 4.5 GHz input signal, respectively.

Error due to drift over temperature consistently remains within

±0.5 dB for a temperature range of 0°C to 85°C. Temperatures

below 0°C begin to exhibit error beyond 0.5 dB with error

becoming no worse than −3 dB typical at −40°C. For all

frequencies using a reduced temperature range, higher

measurement accuracy is achievable.

Operation Above 4.5 GHz

The ADL5506 works at high frequencies but exhibits slightly

higher output voltage temperature drift, especially at cold

temperatures as described in the Temperature Drift at High

over frequency from 30 MHz to 6 GHz. The ADL5506 exhibits

a significant intercept shift, high power ripple, and a continued

decrease of the slope, which all contribute to a decrease in

dynamic range. The changes in performance that occur as

frequency is increased is partly due to less energy transferring

into the device and partly to the bandwidth limitation of the

limiting amplifier stages.

10

0

–10

–20

–30

–40

–50

1.1

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

30MHz

50MHz

100MHz

450MHz

900MHz

1900MHz

2140MHz

2700MHz

3500MHz

4500MHz

10

0

–10

–20

–30

–40

–50

1.2

1.0

0.8

0.6

0.4

0

0.2

4.5GHz

5GHz

5.5GHz

6GHz