LT5518

13

5518f

Figure 12. Bottom Side Layout of Demo Board

Figure 13. 1.5GHz to 2.4GHz Direct Conversion Transmitter

Application with LO Feedthrough and Image Calibration Loop

90

°

0

°

LT5518

BASEBAND

GENERATOR

CAL

LO FEEDTHROUGH CAL OUT

IMAGE CAL OUT

PA

VCO/SYNTHESIZER

RF = 1.5GHz

TO 2.4GHz

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

5518 F13

I-DAC

Q-DAC

ADC

Application Measurements

The LT5518 is recommended for base-station applications

using various modulation formats. Figure 13 shows a

typical application. The CAL box in Figure 13 allows for

LO feedthrough and Image suppression calibration. Fig-

ure 14 shows the ACPR performance for W-CDMA using

one or four channel modulation. Figures 15, 16 and 17

illustrate the 1, 2 and 4-channel W-CDMA measurement.

To calculate ACPR, a correction is made for the spectrum

analyzer noise floor.

If the output power is high, the ACPR will be limited by the

linearity performance of the part. If the output power is

low, the ACPR will be limited by the noise performance of

the part. In the middle, an optimum ACPR is obtained.

Because of the LT5518’s very high dynamic range, the test

equipment can limit the accuracy of the ACPR measure-

ment. Consult the factory for advice on ACPR measure-

ment, if needed.

The ACPR performance is sensitive to the amplitude match

of the BBIP and BBIM (or BBQP and BBQM) input voltage.

This is because a difference in AC voltage amplitude will

give rise to a difference in amplitude between the even-order

harmonic products generated in the internal V-I converter.

As a result, they will not cancel out entirely. Therefore, it

APPLICATIO S I FOR ATIO

Figure 11. Component Side Layout of Demo Board