LT5528

13

5528f

Application Measurements

The LT5528 is recommended for base-station applications

using various modulation formats. Figure 12 shows a typi-

cal application. The CAL box in Figure 12 allows for LO

feed-through and Image suppression calibration.

Figure 13 shows the ACPR performance for W-CDMA using

one, two or four channel modulation. Figures 14, 15 and 16

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 LT5528’s very high dynamic-range, the

test equipment can limit the accuracy of the ACPR mea-

surement. Consult the factory for advice on the ACPR

measurement, if needed.

The ACPR performance is sensitive to the amplitude match

of the BBIP and BBIM (or BBQP and BBQM) inputs. This

is because a difference in AC current 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

is important to keep the currents in those pins exactly the

same (but of opposite sign). The current will enter the

LT5528’s common-base stage, and will flow to the mixer

upper switches. This can be seen in Figure 1 where the

Figure 12. 1.5GHz to 2.4GHz Direct Conversion Transmitter Application with

LO Feed-Through and Image Calibration Loop

90°

0°

LT5528

BASEBAND

GENERATOR

CAL

LO FEED-THROUGH CAL OUT

IMAGE CAL OUT

PA

VCO/SYNTHESIZER

RF = 1.5GHz

TO 2.4GHz

EN

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

5V

V-I

V-I

I-CHANNEL

Q-CHANNEL

BALUN

14

16

1

7

5

8, 13

11

3

5528 F12

I-DAC

Q-DAC

ADC

Figure 14: 1-Channel W-CDMA Spectrum

RF FREQUENCY (MHz)

2127.5

5528 F14

2142.5

2137.5

2132.5

2147.5

2152.5

–30

–40

–60

–70

–80

–90

–120

–110

–100

–50

SYSTEM

NOISE FLOOR

CORRECTED

SPECTRUM

DOWNLINK TEST

MODEL 64 DPCH

UNCORRECTED

SPECTRUM

Figure 15: 2-Channel W-CDMA Spectrum

RF FREQUENCY (MHz)

2125

5528 F15

2140

2135

2130

2145

2155

2150

–30

–40

–60

–70

–80

–90

–120

–110

–100

–50

UNCOR-

RECTED

SPECTRUM

SYSTEM

NOISE FLOOR

CORRECTED

SPECTRUM

DOWNLINK TEST

MODEL 64

DPCH

Figure 13: W-CDMA APCR, AltCPR and Noise

vs RF Output Power at 2140MHz for 1, 2 and

4 Channels

RF OUTPUT POWER PER CARRIER (dBm)

–38

–42

–55

–60

–65

–70

–75

–80

–140

–150

–145

–155

–165

–160

5528 F13

–14

–18

–22

–26

–30

–34

4-CH ACPR

2-CH ACPR

1-CH ACPR

4-CH AltCPR

2-CH AltCPR

DOWNLINK TEST MODEL 64 DPCH

1-CH AltCPR

4-CH NOISE

1-CH NOISE

Figure 16: 4-Channel W-CDMA Spectrum

DOWNLINK

TEST

MODEL 64

DPCH

RF FREQUENCY (MHz)

2115

5528 F16

2145

2135

2125

2155

2165

–40

–60

–70

–80

–90

–130

–120

–110

–100

–50

UNCOR-

RECTED

SPECTRUM

SYSTEM

NOISE FLOOR

CORRECTED SPECTRUM

CORRECTED

SPECTRUM

APPLICATIO S I FOR ATIO