LT5521 datasheet(12/16 Pages) LINER

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LT5521

5521f

APPLICATIO S I FOR ATIO

The user can tailor the biasing of the LT5521 to meet

individual system requirements. It is recommended to

choose a source resistance as large as possible to mini-

mize sensitivity to power supply variation.

Output Interface

A DC connection to VCC must be provided on the PCB to the

output pins. These pins will draw approximately 20mA

each from the power supply. On-chip, there is a nominal

300

Ω differential resistance between the output pins.

Figure 9 shows a typical matching circuit using an external

balun to provide differential to single-ended conversion.

LO suppression and 2xLO suppression are influenced by

the symmetry of the external output matching circuitry.

PCB design must maintain the trace layout symmetry of

the output pins as much as possible to minimize these

signals.

The M/A-COM ETC1.6-4-2-3 4:1 transformer (T2, Fig-

ure 9) is suitable for applications with output frequencies

between 500MHz and 2700MHz. Output matching at vari-

ous frequencies is achieved by adding inductors in series

with the output (L1, L2) and DC blocking capacitor C3, as

shown in Figure 9. Table 6 specifies center frequency and

bandwidth of the output match for different matching

configurations. Figure 10 shows the typical output return

loss vs frequency for 1GHz and 2GHz applications. Capaci-

tor C12 provides a solid AC ground at the RF output

frequency.

Figure 7. IIP3, GC and Noise Figure vs Core Current,

Constant Supply Voltage

Figure 6. IIP3, GC and Noise Figure vs External Resistance,

Constant Core Current (Variable Supply Voltage)

R1 AND R7 (

Ω)

1.5

2.5

IIP3

3.5

100

5521 F06

0.5

–0.5

120

140

–1.5

–2.5

TA = 25°C

fIF = 250MHz

fLO = 1.7GHz

fRF = 1.95GHz

CORE CURRENT (mA)

5521 F07

IIP3

–1.8

–1.2

–0.6

0.6

1.8

1.2

TA = 25°C

fIF = 250MHz

fLO = 1.7GHz

fRF = 1.95GHz

VCC = 4V

CORE CURRENT (mA)

–3

–1

5521 F08

IIP3

RFC

TA = 25°C

fIF = 250MHz

fLO = 1.7GHz

fRF = 1.95GHz

VCC = 3.3V

Figure 8. Comparison of 3.3V Performance With

and Without Input RF Choke

Figure 9. Simplified Output Circuit

with External Matching Components

VCC

LT5521

300

Ω

5521 F09

4:1

VCC

OUT+

OUT–

OUT

C12

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