ADL5380ACPZ-R7 datasheet(25/36 Pages) AD

25 / 36 page

ADL5380

Rev. 0 | Page 25 of 36

Figure 83 shows the zero-IF EVM performance of a 10 MHz

IEEE 802.16e WiMAX signal through the ADL5380. The

differential dc offsets on the ADL5380 are in the order of a few

millivolts. However, ac coupling the baseband outputs with 10 μF

capacitors eliminates dc offsets and enhances EVM performance.

With a 10 MHz BW signal, 10 μF ac coupling capacitors with

the 500 Ω differential load results in a high-pass corner frequency

of ~64 Hz, which absorbs an insignificant amount of modulated

signal energy from the baseband signal. By using ac coupling

capacitors at the baseband outputs, the dc offset effects, which

can limit dynamic range at low input power levels, can be

eliminated.

Figure 84 exhibits multiple W-CDMA low-IF EVM performance

curves over a wide RF input power range into the ADL5380. In

the case of zero-IF, the noise contribution by the vector signal

analyzer becomes predominant at lower power levels, making it

difficult to measure SNR accurately.

–45

–40

–35

–30

–25

–20

–15

–10

–80

–70

–60

–50

–40

–30

–20

–10

RF INPUT POWER (dBm)

0Hz IF

5MHz LOW-IF

7.5MHz LOW-IF

2.5MHz LOW-IF

–60

–50

–40

–30

–20

–10

–75

–65

–55

–45

–35

–25

–15

–5

RF INPUT POWER (dBm)

5.8GHz

3.5GHz

2.6GHz

Figure 84. EVM, RF = 1900 MHz, IF = 0 Hz, IF = 2.5 MHz, IF = 5 MHz, and IF =

7.5 MHz vs. RF Input Power for a W-CDMA Signal (AC-Coupled Baseband Outputs)

LOW IF IMAGE REJECTION

The image rejection ratio is the ratio of the intermediate frequency

(IF) signal level produced by the desired input frequency to that

produced by the image frequency. The image rejection ratio is

expressed in decibels. Appropriate image rejection is critical

because the image power can be much higher than that of the

desired signal, thereby plaguing the down-conversion process.

Figure 85 illustrates the image problem. If the upper sideband

(lower sideband) is the desired band, a 90° shift to the Q channel

(I channel) cancels the image at the lower sideband (upper sideband).

Phase and gain balance between I and Q channels are critical

for high levels of image rejection.

Figure 83. EVM, RF = 2.6 GHz, RF = 3.5 GHz, and RF = 5.8 GHz, IF = 0 Hz vs.

RF Input Power for a 16 QAM 10 MHz Bandwidth Mobile WiMAX Signal

(AC-Coupled Baseband Outputs)

0°

SIN

ωLOt

COS

ωLOt

ωIF

ωLSB

ωUSB

–

ωIF

–

ωIF

ωLO

–90°

+90°

Figure 85. Illustration of the Image Problem

ADL5380ACPZ-R7 数据表(PDF) 25 Page - Analog Devices

ADL5380ACPZ-R7 数据表(HTML) 25 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

数据表下载