LT5521 datasheet(13/16 Pages) LINER

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LT5521

5521f

APPLICATIO S I FOR ATIO

Table 6. Matching Values Using M/A-COM ETC1.6-4-2-3

Output Transformer

fOUT

L1, L2

C12

∆f (10dB RL)

2.4GHz

0nH

82pF

450MHz

2.2GHz

1nH

82pF

430MHz

2.0GHz

2.7nH

82pF

400MHz

1.7GHz

4.7nH

82pF

400MHz

1.3GHz

10nH

82pF

400MHz

1.0GHz

10nH

3.9pF

1nF

500MHz

For applications with LO and output frequencies below

1GHz, the M/A-COM MABAES0054 is recommended for

the output component T2. This transformer maintains

better low frequency output symmetry. Table 7 lists com-

ponents necessary for a 750MHz output match using the

M/A-COM MABAES0054.

Table 7. Matching Values Using M/A-COM MABAES0054

Output Transformer

fOUT

L1, L2

C12

∆f (10dB RL)

750MHz

33nH

82pF

1nF

500MHz

Hybrid baluns provide a low cost alternative for differen-

tial to single-ended conversion. The critical performance

parameters of conversion gain, IIP3, noise figure and LO

suppression are largely unaffected by these transform-

ers. However, their limited bandwidth and reduced sym-

metry outside the frequency of operation degrades the

suppression of higher order LO harmonics, particularly

2xLO. Murata LBD21 series hybrid balun transformers,

for example, can be used for output frequencies as low as

840MHz and as high as 2.4GHz.

Figure 10. Output Return Loss vs Frequency

FREQUENCY (GHz)

0.7

–10

–5

1GHz

2.2

5521 F10

–15

–20

1.2

1.7

–25

–30

2GHz

Johanson Technology supplies the 3700BL15B100S hy-

brid balun for use between 3.4GHz and 4GHz. With addi-

tional matching, this transformer can be used for

applications between 3.3GHz and 3.7GHz. Example LT5521

performance is shown in Figure 11.

FREQUENCY (GHz)

3.2

–2

–4

IIP3

3.5

3.7

5521 F11

3.3

3.4

3.6

3.8

TA = 25°C

fIF = 300MHz

Figure 11. LT5521 Performance for an Application Tuned to

3.5GHz with Low Side (LS) and High Side (HS) LO Injection

LO Interface

The LO input pin is internally matched to 50

Ω. It has an

internal DC bias of 960mV. External AC coupling is re-

quired. Figure 12 shows a simplified schematic of the LO

input. Overdriving the LO input will dramatically reduce

the performance of the mixer. The LO input power should

not exceed +1dBm for normal operation. Select C1 (Figure

12) only large enough to achieve the desired LO input

return loss. This reduces external low frequency signal

amplification through the LO buffer.

For applications with LO frequency in the range of 2.1GHz

to 2.4GHz, the LT5521 achieves improved distortion and

Figure 12. Simplified LO Input Circuit

VCC

Ω

5521 F12

Ω

LT5521

LOIN

Ω

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