LT5521 datasheet(14/16 Pages) LINER

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LT5521

5521f

APPLICATIO S I FOR ATIO

noise performance with slightly reduced current through

the mixer core. Accordingly, in a 5V application operating

within this LO frequency range, the recommended source

resistor value (R1 and R7) is increased to 121

Ω.

Enable Interface

Figure 14 shows a simplified schematic of the EN pin

interface. The voltage necessary to turn on the LT5521 is

2.9V. To disable the chip, the enable voltage must be below

0.2V. If the EN pin is not connected, the chip is disabled.

It is not recommended, however, that any pins be left

floating for normal operation.

It is important that the voltage at the EN pin never exceed

VCC, the power supply voltage, by more than 0.2V. If this

should occur, the supply current could be sourced through

the EN pin ESD protection diodes, potentially damaging

the IC. The resistor R8 (Figure 1) in series with the EN pin

on the demo board is populated with a 10k

Ω resistor to

protect the EN pin to avoid inadvertant damage to the IC.

For timing measurements, this resistor is replaced with a

Figure 13. LO Port Return Loss

Figure 14. Enable Input Circuit

FREQUENCY (MHz)

–15

–10

–5

3000

5521 F13

–20

–25

1000

2000

500

3500

1500

2500

4000

–30

–35

C1 = 6.8pF

C1 = 2.7pF

VCC

5521 F14

LT5521

Ω resistor. If the shutdown function is not required, then

the EN pin should be wired directly to the VCC power supply

on the PCB.

Supply Decoupling

The power supply decoupling shown in the schematic of

Figure 1 is recommended to minimize spurious signal

coupling into the output through the power supply.

ACPR Performance

Because of its high linearity and low noise, the LT5521 offers

outstanding ACPR performance in a variety of applications.

For example, Figures 15 and 16 show ACPR and Alternate

Channel measurements for single channel and 4-channel

64 DPCH W-CDMA signals at 1.95GHz output frequency.

OUTPUT CHANNEL POWER (dBm)

–40

–50

–40

–30

5521 F15

–60

ACPR

–70

–30

–20

–10

–80

–90

–100

–140

–135

–130

–145

–150

–155

–160

–165

TA = 25°C

fRF = 1.95GHz

fIF = 70MHz

fLO = 1.88GHz

30MHz OFFSET NOISE

OUTPUT CHANNEL POWER, EACH CHANNEL (dBm)

–40

–80

–75

–70

–65

–60

–50

–35

–30

–25

–20

1635 G24

–15

–55

–165

–160

–155

–150

–145

–135

–140

ACPR

AltCPR

30MHz OFFSET NOISE

TA = 25°C

fRF = 1.95GHz

fIF = 70MHz

fLO = 1.88GHz

Figure 15. Single Channel W-CDMA ACPR

and 30MHz Offset Noise Performance

Figure 16. 4-Channel W-CDMA ACPR,

AltCPR and 30MHz Offset Noise Floor

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