LT5526EUF Ver la hoja de datos (PDF) - Linear Technology

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componentes Descripción

Fabricante

LT5526EUF

High Linearity, Low Power Downconverting Mixer

Linear Technology 

LT5526

APPLICATIO S I FOR ATIO

The external inductance is split in half (1.4nH), with each

half connected between the pin and C1 as shown in

Figure 4. The inductance may be realized with short, high

impedance printed transmission lines, as in Figure 3,

which provides a compact board layout and reduced

component count. A 1:1 transformer (T1 in Figure 3)

converts the 50Ω differential impedance to a 50Ω single-

ended input.

1/2 XEXT

RF+ 1/2 XRF

2

LT5526

RS

50Ω

C1

1/2 XEXT

RF– 1/2 XRF

RRF

3

5526 F04

Figure 4. RF Input Impedance Matching Topology

Table 1. RF Input Differential Impedance

FREQUENCY

(MHz)

INPUT

IMPEDANCE

REFLECTION COEFFICIENT

MAG

ANGLE

70

28.0 + j1.34

0.282

176

140

28.2 + j2.46

0.280

172

240

28.4 + j3.30

0.278

169

360

28.4 + j4.75

0.282

164

450

28.6 + j5.42

0.280

162

750

29.9 + j7.39

0.268

155

900

31.3 + j8.41

0.251

150

1500

38.3 + j17.9

0.237

112

1900

42.5 + j24.6

0.269

92.2

An alternative method of driving the RF input is to use a

lumped-element balun configuration, as shown in Fig-

ure 5. This type of network may provide a more cost-

effective solution for narrow band applications (fractional

bandwidths < 30%). The actual balun is composed of

components C7, C9, L1 and L4, and their values may be

estimated as follows:

RFIN

50Ω

C7

L1

LT5526

RF+ 1/2 XRF

2

L5

L4

RF– 1/2 XRF

RRF

3

C9

5526 F05

Figure 5. Schematic of Lumped Element Input Balun

L1= L4 = RS • RRF

ω

C7 = C9 =

1

ω RS • RRF

Where RS is the source resistance (50Ω) and RRF is the

mixer input resistance from Table 1.

The computed values are only approximate, as they don’t

factor in the effects of XRF or the parasitics of the external

components. Actual component values for several fre-

quencies are listed in Table 2, and measured return loss

vs. frequency is plotted for each example in Figure 6.

0

–5

–10

–15

–20

–25

100 300 500 700 900 1100 1300

FREQUENCY (MHz)

5526 F06

Figure 6. Input Return Loss with Lumped Element Baluns

Using Values from Table 2

5526f

10

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