LT5558

13

5558fa

APPLICATIONS INFORMATION

RF FREQUENCY (MHz)

896.25

–70

–50

–30

902.25

5558 F12

–90

–110

–80

–60

–40

–100

–120

–130

897.75

899.25

900.75

903.75

SPECTRUM ANALYSER NOISE FLOOR

CORRECTED

SPECTRUM

UNCORRECTED

SPECTRUM

DOWNLINK TEST

MODEL 64 DPCH

RF FREQUENCY (MHz)

894

–70

–50

–30

902

5558 F13

–90

–110

–80

–60

–40

–100

–120

–130

896

898

900

904

906

SPECTRUM ANALYSER NOISE FLOOR

CORRECTED SPECTRUM

UNCORRECTED

SPECTRUM

DOWNLINK

TEST

MODEL

64 DPCH

90

°

0

°

LT5558

BASEBAND

GENERATOR

PA

VCO/SYNTHESIZER

RF = 600MHz

TO 1100MHz

EN

2, 4, 6, 9, 10, 12, 15, 17

100nF

×2

5V

V-I

V-I

I-CHANNEL

Q-CHANNEL

BALUN

14

16

1

7

5

8, 13

11

3

5558 F10

I-DAC

Q-DAC

Figure 10. 600MHz to 1.1GHz Direct Conversion Transmitter Application

Example: RFID Application

In Figure 15 the interface between the LTC1565 (U2, U3)

and the LT5558 is designed for RFID applications. The

LTC1565 is a seventh-order, 650kHz, continuous-time,

linear-phase, lowpass filter. The optimum output com-

mon-mode level of the LTC1565 is about 2.5V and the

optimum input common-mode level of the LT5558 is

around 2.1V and is temperature dependent. To adapt the

common-mode level of the LTC1565 to the LT5558, a level

shift network consisting of R1 to R6 and R11 to R16 is

used. The output common-mode level of the LTC1565 can

be adjusted by overriding the internally generated voltage

on pin 3 of the LTC1565.

RF OUTPUT POWER PER CARRIER (dBm)

–30

–90

–80

–70

–60

–50

–40

–160

–150

–140

–130

–120

–110

–25

–20

–15

–10

5558 TA01b

–5

0

3-CH ACPR

1-CH ACPR

3-CH NOISE

3-CH ALTCPR

1-CH ALTCPR

1-CH NOISE

DOWNLINK TEST

MODEL 64 DPCH

Figure 11. ACPR, ALTCPR and Noise for CDMA2000 Modulation

Figure 12. 1-Channel CDMA2000 Spectrum

Figure 13. 3-Channel CDMA2000 Spectrum