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LTC5552

5552f

For more information www.linear.com/LTC5552

APPLICATIONS INFORMATION

The RF input impedance and input reflection coefficient

versusRFfrequencyislistedinTable1.Thereferenceplane

for this data is Pin 5 of the IC, with no external matching,

and the LO is driven at 12GHz.

Table 1. RF Port Impedance and S11

(at Pin 5, No External Matching, LO Input Driven at 12GHz)

FREQUENCY

(GHz)

RF INPUT

IMPEDANCE

S11

MAG

ANGLE

50.1 + j33.8

0.32

71.3

63.3 + j37.1

0.33

52.1

96.2 + j14.7

0.33

11.9

75.4 + j16.6

0.24

–25.6

54.9 + j18.5

0.18

–65.2

37.5 – j8.2

0.17

–141.2

39.7 – j3.0

0.12

161.7

44.7 – j4.1

0.07

–140.7

45.2 – j10.4

0.12

–108.4

38.9 – j16.5

0.22

–113.4

32.5 – j22.1

0.33

–113.3

28.1 – j24.3

0.40

–114.7

30.1 – j22.2

0.36

–116.4

27.6 – j13.1

0.33

–140.0

24.8 + j3.1

0.34

170.5

19.8 + j18.9

0.47

141.8

17.0 + j19.6

0.55

132.9

21.3 + j19.6

0.47

130.2

LO Input

The mixer’s LO input, shown in Figure 5, consists of a

single-ended to differential conversion and high speed

limiting differential amplifier. The LO amplifier is optimized

forthe1GHzto20GHzLOfrequencyrange.LOfrequencies

above or below this frequency range may be used with

degraded performance.

The DC voltage at the LO input is about 1.6V. A DC block-

ing capacitor (C1) is required.

Figure 5. Simplified LO Input Schematic

LTC5552

5552 F05

The LO is 50Ω matched from 1GHz to 20GHz. External

matching components may be needed for extended LO

operating frequency range. To ensure the best LO imped-

ance matching over the very wide bandwidth, no ESD

protection devices are used at the LO input. As a result, the

LO is the most sensitive pin to ESD stress for the mixer.

The measured LO input return loss is shown in Figure 6.

The nominal LO input level is 0dBm, although the limiting

amplifierswilldeliverexcellentperformanceovera±6dBm

input power range.

Figure 6. LO Input Return Loss

EN = HIGH

EN = LOW

LO FREQUENCY (GHz)

9 11 13 15 17 19 21

5552 F06

The LO input impedance and input reflection coefficient

versus frequency, is shown in Table 2.

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