LTC6948IUFD-3TRPBF View Datasheet(PDF) - Linear Technology

Part Name

Description

MFG CO.

LTC6948IUFD-3TRPBF

Ultralow Noise 0.37GHz to 6.39GHz Fractional-N Synthesizer with Integrated VCO

Linear Technology 

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LTC6948

Applications Information

0

68nH, 100pF

–2

180nH, 270pF

–4

–6

–8

–10

–12

–14

–16

01234567

FREQUENCY (GHz)

6947 F17

Figure 17. RF Single-Ended Return Loss

For lower frequencies, transmission line (TL) baluns such as

the M/A-COM MABACT0065 and the TOKO #617DB-1673

provide good results. At higher frequencies, surface mount

(SMT) baluns such as those produced by TDK, Anaren,

and Johanson Technology, can be attractive alternatives.

See Table 19 for recommended balun part numbers versus

frequency range.

The listed SMT baluns contain internal chokes to bias RF±

and also provide input-to-output DC isolation. The pin

denoted as GND or DC FEED should be connected to the

VRF+ voltage. Figure 18 shows a surface mount balun’s

connections with a DC FEED pin.

Table 19. Suggested Baluns

fRF (MHz)

350 to 900

PART NUMBER

#617DB-1673

MANUFACTURER TYPE

TOKO

TL

400 to 600

HHM1589B1

TDK

SMT

600 to 1400 BD0810J50200

Anaren

SMT

600 to 3000

MABACT0065

M/A-COM

TL

1000 to 2000

HHM1518A3

TDK

SMT

1400 to 2000

HHM1541E1

TDK

SMT

1900 to 2300 2450BL15B100E

Johanson

SMT

2000 to 2700

HHM1526

TDK

SMT

3700 to 5100

HHM1583B1

TDK

SMT

4000 to 6000

HHM1570B1

TDK

SMT

The listed TL baluns do not provide input-to-output DC

isolation and must be AC-coupled at the output. Figure 19

displays RF± connections using these baluns.

VRF+

RF+ 12

LTC6948

RF– 11

321

TO 50Ω

LOAD

BALUN

4

5

6

6948 F18

BALUN PIN CONFIGURATION

1 UNBALANCED PORT

2 GND OR DC FEED

3 BALANCED PORT

4 BALANCED PORT

5 GND

6 NC

Figure 18. Example SMT Balun Connection

VRF+

RF+ 12

LTC6948

RF– 11

SEC

TO 50Ω

LOAD

PRI

6948 F19

Figure 19. Example TL Balun Connection

Supply Bypassing and PCB Layout Guidelines

Care must be taken when creating a PCB layout to mini-

mize power supply decoupling and ground inductances.

All power supply V+ pins should be bypassed directly to

the ground plane using a 0.1µF ceramic capacitor as close

to the pin as possible. Multiple vias to the ground plane

should be used for all ground connections, including to

the power supply decoupling capacitors.

6948f

32

For more information www.linear.com/LTC6948

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