LT5519

9

5519f

Table 4. Input Capacitor Values vs Frequency

FREQUENCY

CAPACITANCE (C1, C2)

CAPACITANCE (C3)

(MHz)

(pF)

(pF)

44

2200

33

70

820

33

140

220

33

240

68

15

300

39

6.8

350

27

6.8

440

18

6.8

The performance was evaluated with the input tuned for

each of these frequencies and the results are summarized

in Figures 6-8. The same IF input balun transformer was

used for all measurements. In each case, the LO input

frequency was adjusted to maintain an RF output fre-

quency of 1000MHz.

Low Frequency Matching of the RF Output Port

Without any external components on the RF output, the

internal transformer of the LT5519 provides a good 50

Ω

impedance match for RF frequencies above approximately

850MHz. Below this frequency, the return loss drops

below 10dB and degrades the conversion gain. The addi-

tion of a single 10pF capacitor in series with the RF output

improves the match at lower RF frequencies, shifting the

10dB return loss point to about 700MHz, as demonstrated

in Figure 9. This change also results in an improvement of

the conversion gain.

RF OUTPUT FREQUENCY (MHz)

700

–3

–2

0

1000

1200

5519 F09

–4

–5

800

900

1100

1300 1400

–6

–7

–1

–15

–10

0

–20

–25

–30

–35

–5

GAIN

RETURN LOSS

Figure 9. Conversion Gain and Return Loss vs Output Frequency

APPLICATIO S I FOR ATIO

Figure 8. LO to RF Leakage vs Tuned IF Input Frequency

Figure 7. IIP3 and IIP2 vs Tuned IF Input Frequency

Figure 6. Conversion Gain and Single Sideband Noise Figure

vs Tuned IF Input Frequency

INPUT FREQUENCY (MHz)

0

2

4

6

400

5519 F06

0

–2

1

3

5

–1

–3

–4

12

16

20

8

4

10

14

18

6

2

0

100

200

300

500

HIGH SIDE LO

INPUT TUNED FOR EACH TEST FREQUENCY

HIGH SIDE LO

LOW SIDE

LOW SIDE

SSB NF

GAIN

INPUT FREQUENCY (MHz)

0

23

25

27

400

5519 F07

21

19

100

200

300

500

17

15

13

50

60

70

40

30

20

10

0

INPUT TUNED FOR EACH TEST FREQUENCY

LOW SIDE

LOW SIDE

IIP2

IIP3

HIGH SIDE

HIGH SIDE LO

INPUT FREQUENCY (MHz)

1

–60

–50

–40

–30

–20

–10

0

100

200

300

400

5519 F08

500

LOW SIDE LO

HIGH SIDE LO

INPUT TUNED FOR EACH TEST FREQUENCY