LT5571

13

5571f

RF OUTPUT POWER PER CARRIER (dBm)

–30

–70

–60

–10

5571 F11

–80

–90

–25

–20

–15

0

–5

–40

–50

–140

–130

–150

–160

–110

–120

DOWNLINK TEST

MODEL 64 DPCH

3-CH ACPR

1-CH

ACPR

3-CH AltCPR

1-CH AltCPR

3-CH NOISE

1-CH NOISE

0

–90

–80

–70

–50

–30

20

10

IR

15

4

3

2

5571 F14

–10

–60

–40

0

–20

25

°C

85

°C

–40

°C

LO FT

APPLICATIONS INFORMATION

Application Measurements

The LT5571 is recommended for base-station applications

using various modulation formats. Figure 10 shows a

typical application.

Figure 11 shows the ACPR performance for CDMA2000

using one and three channel modulation. Figures 12 and 13

illustrate the 1- and 3-channel CDMA2000 measurement.

To calculate ACPR, a correction is made for the spectrum

analyzer’s noise floor (Application Note 99).

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 LT5571’s very high dynamic-range, the test

equipment can limit the accuracy of the ACPR measure-

ment. Consult Design Note 375 or the factory for advice

on ACPR measurement if needed.

VCO/SYNTHESIZER

EN

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

I-CH

Q-CH

BALUN

V-I

BASEBAND

GENERATOR

V-I

LT5571

5V

14

16

1

7

5

8, 13

5571 F10

11

PA

RF = 620MHz

TO 1100MvHz

3

I-DAC

Q-DAC

90

°

0

°

100nF

×2

Figure 10. 620MHz to 1.1GHz Direct Conversion Transmitter Application

Figure 11. CDMA2000 ACPR, ALTCPR and Noise vs

RF Output Power at 900MHz for 1 and 3 Carriers

Figure 12. 1-Channel CDMA2000 Spectrum

Figure 13. 3-Channel CDMA2000 Spectrum

896.25

899.25

902.25

903.75

5571 F12

897.75

900.75

CORRECTED

SPECTRUM

DOWNLINK TEST

MODEL 64 DPCH

SPECTRUM ANALYSER NOISE FLOOR

RF FREQUENCY (MHz)

–130

–120

–110

–90

–80

–70

–30

–100

–60

–50

–40

UNCORRECTED

SPECTRUM

RF FREQUENCY (MHz)

894

–130

–120

–110

–90

–80

–70

902

–30

5571 F13

–100

898

896

904

900

906

–60

–50

–40

UN-

CORRECTED

SPECTRUM

DOWNLINK

TEST MODEL

64 DPCH

CORRECTED SPECTRUM

SPECTRUM

ANALYSER

NOISE

FLOOR

The ACPR performance is sensitive to the amplitude

mismatch 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 is important to keep the amplitudes at the BBIP

and BBIM (or BBQP and BBQM) as equal as possible.

LO feedthrough and image rejection performance may

be improved by means of a calibration procedure. LO

feedthrough is minimized by adjusting the differential DC

offsets at the I and the Q baseband inputs. Image rejection

can be improved by adjusting the amplitude and phase

difference between the I and the Q baseband inputs. The

LO feedthrough and Image Rejection can also change

as a function of the baseband drive level, as depicted in

Figure 14.

Figure 14. Image Rejection and LO Feed-

Through vs Baseband Drive Voltage After

Calibration at 25°C