LTC5577 datasheet(13/20 Pages) LINER

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LTC5577

5577f

For more information www.linear.com/LTC5577

applicaTions inForMaTion

To optimize the LO input match for frequencies below

1GHz, the value of C5 is increased and shunt capacitor C6

is added. A summary of values for C5 and C6, versus LO

frequency range is listed in Table 2. Measured LO input

return losses are shown in Figure 6. Finally, LO input im-

pedance and input reflection coefficient, versus frequency

is shown in Table 3.

Table 2. LO Input Matching Values vs LO Frequency Range

FREQUENCY (MHz)

C5 (pF)

C6 (pF)

285 to 392

330

338 to 415

330

415 to 505

525 to 700

8.2

645 to 803

7.5

800 to 1150

6.8

2.7

930 to 4000

3.9

—

3500 to 6000

1.0

—

The LO buffers have been designed such that the LO input

impedance does not change significantly when the IC is

disabled. This feature only requires that supply voltage is

applied. The actual performance of this feature is shown

in Figure 7. As shown, the LO input return loss is better

than 10dB over the 1GHz to 4GHz frequency range when

the IC is enabled or disabled.

Figure 6. LO Input Return Loss

Figure 7. LO Input Return Loss—Mixer Enabled and Disabled

FREQUENCY (GHz)

0.2

–2

–4

–6

–8

–10

–12

–14

–16

–18

4.7

4.2

5577 F07

1.2

2.2

3.2 3.7

0.7

1.7

2.7

TC = 25°C

C5 = 3.9pF

DISABLED

ENABLED

Table 3. LO Input Impedance and S11 (at Pin 10, No External

Matching, Mixer Enabled)

FREQUENCY

(MHz)

INPUT

IMPEDANCE

S11

MAG

ANGLE

350

5.2 + j14.9

0.83

146.5

400

6.0 + j17.3

0.81

141.7

450

6.6 + j19.5

0.80

137.0

500

7.2 + j21.5

0.78

132.7

600

9.1 + j26.5

0.75

123.6

800

15.1 + j35.7

0.67

106.0

1000

24.9 + j43.6

0.58

89.5

1500

67.5 + j36.4

0.33

47.1

2000

61.7 – j4.2

0.11

–18.3

2500

40.3 – j7.1

0.13

–139.4

3000

31.7 + j1.8

0.23

173.1

3500

29.8 + j12.3

0.29

140.0

4000

31.5 + j22.9

0.35

113.2

4500

36.0 + j32.4

0.38

92.8

5000

59.0 + j40.6

0.36

57.1

5500

64.2 + j30.8

0.29

50.1

6000

57.4 + j19.7

0.19

59.0

FREQUENCY (GHz)

0.2

–10

–5

4.2

5577 F06

–15

–20

–25

1.2

2.2

3.2

5.2

0.7

4.7

1.7

2.7

3.7

5.7 6.2

C5 = 27pF, C6 = 8.2pF

C5 = 6.8pF, C6 = 2.7pF

C5 = 3.9pF

C5 = 1.0pF

TC = 25°C

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