LTC5582

11

Rev. D

For more information www.analog.com

APPLICATIONS INFORMATION

The LTC5582 is a true RMS RF power detector, capable

of measuring an RF signal over the frequency range from

40MHz to 10GHz, independent of input waveforms with

different crest factors such as CW, CDMA2K, WCDMA,

LTE and WiMAX signals. Up to 60dB dynamic range is

achieved with a very stable output within the full tempera-

ture range from –40°C to 125°C. Its sensitivity can be as

low as –57dBm up to 2.7GHz even with single-ended 50Ω

input termination.

RF Inputs

The differential RF inputs are internally biased at 1.585V.

The differential impedance is 400Ω. These pins should be

DC blocked when connected to ground or other matching

components.

TheLTC5582canbedriveninasingle-endedconfiguration

asillustratedinFigure 3.Thesingle-endedinputimpedance

vs frequency is detailed in Table 1. The DEC Pin can be

either left floating or AC-coupled to ground via an external

capacitor. While the RF signal is applied to the IN+ (or IN–)

Pin, the other pin IN– (or IN+) should be AC-coupled to

ground. By simply terminating a 91Ω resistor between

the IN+ and IN– Pins and coupling the non-signal side

to ground using a 1nF capacitor, broadband 50Ω input

matching can be achieved with typical return loss better

than 10dB from 40MHz to 5.5GHz. At higher RF frequen-

cies, additional matching components may be needed.

Table 1. Single-Ended Input Impedance (DEC Floating)

FREQUENCY

(MHZ)

INPUT IMPEDANCE

(Ω)

S11

MAG

ANGLE (˚)

40

220.7-j63.0

0.655

–7.0

100

195.2-j47.3

0.611

–7.1

200

175.1-j37.6

0.571

–7.3

400

200.9-j42.2

0.618

–6.3

600

159.8-j52.9

0.563

–11.5

800

154.8-j52.4

0.554

–12.2

1000

158.6-j57.1

0.568

–12.4

1200

164.1-j81.1

0.612

–14.7

1400

138.1-j110.5

0.650

–21.0

1600

102.7-j113.3

0.659

–28.5

1800

80.1-j103.1

0.647

–35.3

2000

67.1-j92.0

0.628

–41.3

2200

58.4-j82.3

0.607

–46.7

2400

52.9-j74.5

0.586

–52.0

2600

48.5-j67.6

0.566

–57.0

2800

44.8-j61.5

0.546

–62.0

3000

41.8-j56.1

0.526

–66.9

3200

41.8-j56.3

0.508

–72.0

3400

37.3-j47.0

0.490

–77.1

3600

35.4-j42.9

0.473

–80.2

3800

33.9-j39.1

0.457

–87.7

4000

32.4-j35.5

0.445

–93.1

4200

31.1-j32.3

0.429

–98.8

4400

29.9-j29.1

0.416

–104.7

4600

28.9-j26.2

0.405

–110.7

4800

27.9-j23.3

0.395

–117.0

5000

27.0-j20.5

0.388

–123.5

5200

26.2-j17.8

0.382

–130.2

5400

25.4-j15.2

0.376

–136.9

5600

24.7-j12.6

0.376

–144.1

5800

24.0-j10.0

0.377

–151.3

6000

23.3-j7.5

0.377

–158.4

The LTC5582 differential inputs can also be driven from

a fully balanced source as shown in Figure 4. When the

signal source is a single-ended 50Ω, conversion to a dif-

ferential signal can be achieved using a 1:8 balun to match

the internal 400Ω input impedance to the 50Ω source.

This impedance transformation results in 9dB voltage

gain, thus 9dB improvement in sensitivity is obtained

Figure 3. Single-Ended Input Configuration

R4

91

J1

RF INPUT

C5

C8

OPTIONAL

C9

1nF

IN–

4

IN+

VCC

5582 F03

200

200

LTC5582

2

C4

1nF

DEC

3

50pF