Circuit Note

CN-0187

Rev. 0| Page 5 of 7

INPUT (V rms)

VRMS OF

UNKNOWN WAVEFORM

(RESULT INDEPENDENT

OF WAVEFORM)

PEAK OF

CW, CF = 0dB

PEAK OF

UNKNOWN WAVEFORM

0

1

2

3

Figure 10. Procedure for Crest Factor Calculation

incoming waveform was a CW signal).

(5)

the CF can be calculated as

(6)

as shown in Figure 11 with the CW signal (taken from the

ADL5502 data sheet). 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

0

1

2

3

4

5

6

7

8

9

10

INPUT (dBm)

–25

–20

–15

–10

–5

0

5

10

15

8-TONE WAVEFORM, 9dB CF

4-TONE WAVEFORM, 6dB CF

2-TONE WAVEFORM, 3dB CF

CW, 0dB CF

Figure 11. Reported Crest Factor of Various Waveforms

–1.0

–0.5

0

0.5

1.0

1.5

2.0

2.5

3.0

–25

–15

–5

5

15

INPUT (dBm)

450MHz

900MHz

1900MHz

2350MHz

2600MHz

Figure 12. Measured Crest Factor of CW Signals vs. Input Level, 450 MHz,

900 MHz, 1900 MHz, 2350 MHz, 2600 MHz, Supply +3.3 V

The performance of this or any high speed circuit is highly

dependent on proper PCB layout. This includes, but is not

limited to, power supply bypassing, controlled impedance lines

(where required), component placement, signal routing, and

power and ground planes. (See MT-031 Tutorial, MT-101 Tutorial,

and article, A Practical Guide to High-Speed Printed-Circuit-

Board Layout, for more detailed information regarding PCB

layout.)

A complete design support package for this circuit note can be

found at http://www.analog.com/CN0187-DesignSupport.

COMMON VARIATIONS

For applications that require less RF detection range, the

AD8363 rms detector can be used. The AD8363 has a detection

range of 50 dB and operates at frequencies up to 6 GHz. For

non-rms detection applications, the AD8317/AD8318/AD8319

or ADL5513 can be used. These devices offer varying detection

ranges and have varying input frequency ranges up to 10 GHz

(see CN-0150 for more details).

CIRCUIT EVALUATION AND TEST

This circuit uses the EVAL-CN0187-SDPZ circuit board and the

EVAL-SDP-CB1Z System Demonstration Platform (SDP)

evaluation board. The two boards have 120-pin mating

connectors, allowing for the quick setup and evaluation of the

circuit’s performance. The EVAL-CN0187-SDPZ board contains

the circuit to be evaluated, as described in this note, and the

SDP evaluation board is used with the CN0187 evaluation

software to capture the data from the EVAL-CN0187-SDPZ

circuit board.