ADL5350ACPZ-R7 datasheet(22/24 Pages) AD

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ADL5350

Preliminary Technical Data

Rev. PrC | Page 22 of 24

HIGH FREQUENCY APPLICATIONS

The ADL5350 can be used at extended frequencies with some

careful attention to board and component parasitics. Figure 61

is an example of a 2.3 GHz to 2.5 GHz down-conversion using a

low-side LO. The performance of this circuit is depicted in

Figure 62. Note that the inductor and capacitor values are very

small, especially for the RF and IF ports. Above 2.5 GHz, it is

necessary to consider alternate solutions to avoid unreasonably

small inductor and capacitor values.

RF/IF

GND2

LOIN

GND1

RF/IF

VPOS

2.1nH

100pF

4.7µF

0.7pF

1.5nH

1nF

1pF

0.67nH

GND1

ADL5350

3.0nH

100pF

ALL INDUCTORS

ARE 0302CS

SERIES FROM

COILCRAFT

Figure 61. 2.3 GHz to 2.5 GHz Down-Conversion Schematic

–5

–10

–9

–6

–3

–12

2200

2250

2300

2350

2400

2450

2500

GAIN

IP1dB

IIP3

RF FREQUENCY (MHz)

Figure 62. Measured Performance for Circuit in Figure 61

Using Low-Side LO Injection and 374 MHz IF

The typical networks used for cellular applications below

2.5 GHz utilize band-select and band-reject networks on the RF

and IF ports. At higher RF frequencies, these networks are not

easily realized using lumped element components (discrete Ls

and Cs). As a result, it is necessary to consider alternate filter

network topologies to allow more reasonable values of

inductors and capacitors.

Figure 63 depicts a cross-over filter network approach to

provide isolation between the RF and IF ports for a down-

converting application. The cross-over network essentially

provides a high-pass filter to allow the RF signal to pass to the

RF/IF node (Pin 1 and Pin 8), while presenting a low-pass filter,

(which is actually band-pass when considering the DC blocking

capacitor, CAC). This allows the difference component (fRF – fLO)

to be passed to the desired IF load.

RF/IF

GND2

LOIN

GND1

RF/IF

VPOS

3.8nH

100pF

1.8pF

1.5nH

CAC

100pF

1.2pF

100pF

3.5nH

GND1

ADL5350

3.5nH

4.7µF

ALL

INDUCTORS

ARE 0302CS

SERIES FROM

COILCRAFT

Figure 63. 3.3 GHz to 3.8 GHz Down-Conversion Schematic

When designing the RF and IF port networks, it is important to

remember that the networks share a common node (the RF/IF

pins). In addition, the opposing network presents some loading

impedance to the target network being designed. Classic audio

crossover filter design techniques can be applied to help derive

component values. However, some caution must be applied

when selecting component values. At high RF frequencies, the

board parasitics may significantly influence the final optimum

inductor and capacitor component selections. Some empirical

testing may be necessary to optimize the RF and IF port filter

networks. The performance of the circuit depicted in Figure 63

is provided in Figure 64.

–2

IIP3

–10

–9

–8

–7

–6

–5

–4

–3

3300 3350 3400 3450 3500 3550 3600 3650 3700 3750 3800

RF FREQUENCY (MHz)

IP1dB

GAIN

Figure 64. Measured Performance for Circuit in Figure 63

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