ADRF6821 datasheet(29/61 Pages) AD

29 / 61 page

Data Sheet

ADRF6821

Rev. A | Page 29 of 61

I/Q OUTPUT LOADING

By design, the ADRF6821 has an I/Q output impedance of 10 Ω

and it is optimized to perform with an external 25 Ω in each

differential leg. External resistors increase the output impedance

and with the external 25 Ω, the total differential output

impedance equals 60 Ω. When terminated with a 100 Ω differential

load, the return loss is less than −10 dB for a wide range of IF

frequencies.

25Ω

I/Q OUTPUTS

25Ω

ZLOAD

10Ω

ADRF6821

Figure 51. IF Output Schematic

Different application circuits can require various loading

conditions for the I and Q outputs. Therefore, it is important

to understand the effect of I and Q output loading on the

performance characteristics, such as output IF gain, output IP3,

output IP2, HD2 and HD3. Figure 53 to Figure 55 illustrates the

effect of output loading on these characteristics.

100

200

300

400

500

IF FREQUENCY (MHz)

200Ω

100Ω

Figure 52. Gain vs. IF Frequency for Different Loads

500

960

1420

1880

2340

2800

LO FREQUENCY (MHz)

200Ω

100Ω

Figure 53. Output IP3 (OIP3) vs. LO Frequency for Different Loads

500

960

1420

1880

2340

2800

LO FREQUENCY (MHz)

200Ω

100Ω

Figure 54. Output IP2 (OIP2) vs. LO Frequency for Different Loads

–100

–60

–140

–130

–120

–110

–100

–90

–80

–70

–90

–80

–70

–60

–50

–40

–30

–20

–10

100

150

200

250

IF FREQUENCY (MHz)

200Ω

100Ω

Figure 55. HD2 and HD3 vs. IF Frequency for Different Loads

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