8

LT5525

5525f

APPLICATIO S I FOR ATIO

As shown in Figure 3, the RF input return loss with no

external matching is greater than 12dB from 1.3GHz to

2.3GHz. The RF input match can be shifted down to

800MHz by adding a series 3.9pF capacitor at the RF input.

A series 1.2nH inductor can be added to shift the match up

to 2.5GHz. Measured return losses with these external

components are also shown in Figure 3.

2

OPTIONAL SERIES

REACTANCE FOR

LOW BAND OR

HIGH BAND

MATCHING

LT5525

5525 F02

3

Figure 2. RF Input Schematic

RF FREQUENCY (MHz)

500

–30

–25

–20

–15

–10

–5

0

1000

1500

2000

2500

5525 F03

3000

NO RF

MATCHING

SERIES 1.2nH

SERIES 3.9pF

Figure 3. RF Input Return Loss Without and

with External Matching Components

Figure 4 illustrates the typical conversion gain, IIP3 and NF

performance of the LT5525 when the RF input match is

shifted lower in frequency using an external series 3.9pF

capacitor on the RF input.

RF input impedance and reflection coefficient (S11) ver-

sus frequency are shown in Table 1. The listed data is

external matching). This information can be used to simu-

late board-level interfacing to an input filter, or to design

a broadband input matching network.

Table 1. RF Port Input Impedance vs Frequency

FREQUENCY

INPUT

REFLECTION COEFFICIENT

(MHz)

IMPEDANCE

MAG

ANGLE

50

10.4 + j2.63

0.675

174

500

18.1 + j23.7

0.551

124

700

25.8 + j30.7

0.478

106

900

36.5 + j34.5

0.398

90

1100

48.4 + j33.3

0.321

74

1300

59.5 + j25.7

0.244

57

1500

65.9 + j13.1

0.177

33

1700

65.0 – j1.0

0.131

–3

1900

59.0 – j12.2

0.138

–47

2100

50.2 – j19.0

0.187

–79

2300

41.8 – j22.1

0.250

–97

2500

34.9 – j22.7

0.311

–109

2700

29.1 – j21.9

0.369

–118

3000

23.2 – j19.1

0.435

–130

RF FREQUENCY (MHz)

800

–5

0

5

10

15

900

1000

1100

1200

5525 F04

IIP3

25

20

850

950

1050

1150

LOW SIDE LO

HIGH SIDE LO

SSB NF

GAIN

Figure 4. Typical Gain, IIP3 and NF with

Series 3.9pF Matching Capacitor

A broadband RF input match can be easily realized by

using both the series capacitor and series inductor as

shown in Figure 5. This network provides good return loss

at both lower and higher frequencies simultaneously,

while maintaining good mid-band return loss. The broad-

band return loss is plotted in Figure 6. The return loss is

better than 12dB from 700MHz to 2.6GHz using the

element values of Figure 5.

LO Input Port

The LO buffer amplifier consists of high speed limiting

differential amplifiers designed to drive the mixer core for