ADL5502ACBZ-P2 datasheet(21/28 Pages) AD

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ADL5502

Rev. A | Page 21 of 28

A three-stage process must be taken to measure and calculate

the crest factor of any waveform. First, the unknown signal

must be applied to the RF input and the corresponding VRMS

level is measured. This level is indicated in Figure 57 as

VVRMS-UNKNOWN

. The RF input, VIN, is calculated using

VVRMS-UNKNOWN

and Equation 5.

INPUT (V rms)

VRMS OF

UNKNOWN WAVEFORM

(RESULT INDEPENDENT

OF WAVEFORM)

PEAK OF

CW, CF = 0dB

PEAK OF

UNKNOWN WAVEFORM

VIN

VVRMS-UNKNOWN

VPEAK-CW

VPEAK-UNKNOWN

Figure 57. Procedure for Crest Factor Calculation

Next, the CW reference level of PEAK, VPEAK-CW, is calculated

using VIN (that is, the output voltage that would be seen if the

incoming waveform was a CW signal).

VPEAK-CW

= (VIN GainPEAK) + InterceptPEAK

(7)

Finally, the actual level of PEAK, VPEAK-UNKNOWN, is measured and

the CF can be calculated as

= 20·log10 (VPEAK-UNKNOWN/VPEAK-CW)

(8)

where VPEAK-CW, is used as a reference point to compare

VPEAK-UNKNOWN

,. If both VPEAK values are equal, then the CF is 0 dB,

as shown in Figure 58 with the CW signal. Across the dynamic

range, the calculated CF hovers about the 0 dB line. Likewise, for

complex waveforms of 3 dB, 6 dB, and 9 dB CFs, the calculations

accurately hover about the corresponding CF levels.

–1

INPUT (dBm)

–25

–20

–15

–10

–5

8-TONE WAVEFORM, 9dB CF

4-TONE WAVEFORM, 6dB CF

2-TONE WAVEFORM, 3dB CF

CW, 0dB CF

Figure 58. Reported Crest Factor of Various Waveforms

DRIFT OVER A REDUCED TEMPERATURE RANGE

Figure 59 and Figure 60 shows the error over temperature for a

1.9 GHz input signal. RMS error due to drift over temperature

consistently remains within ±0.25 dB and only begins to exceed

this limit when the ambient temperature rises above +65°C and

drops below −30°C. For all frequencies using a reduced

temperature range, higher measurement accuracy is achievable.

–1.00

–0.75

–0.50

–0.25

0.25

0.50

0.75

1.00

–25

–20

–15

–10

–5

INPUT (dBm)

–30°C

0°C

+35°C

+65°C

–40°C

–10°C

+15°C

+55°C

+85°C

+25°C

–20°C

+5°C

+45°C

+75°C

Figure 59. VRMS Typical Drift at 1.9 GHz for Various Temperatures

–1.00

–0.75

–0.50

–0.25

0.25

0.50

0.75

1.00

–25

–20

–15

–10

–5

INPUT (dBm)

–30°C

0°C

+35°C

+65°C

–40°C

–10°C

+15°C

+55°C

+85°C

+25°C

–20°C

+5°C

+45°C

+75°C

Figure 60. PEAK Typical Drift at 1.9 GHz for Various Temperatures

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