Circuit Note

CN-0311

Circuits from the Lab™ reference circuits are engineered and

tested for quick and easysystemintegrationto helpsolve today’s

analog, mixed-signal, and RF design challenges. For more

informationand/orsupport, visitwww.analog.com/CN0311.

Devices Connected/Referenced

ADF4351

Fractional-N PLL IC with Integrated VCO

ADL5385

Wideband Transmit Modulator

ADP150

Low Noise 3.3 V LDO

ADP3334

Low Noise Adjustable LDO

Broadband, Low Error Vector Magnitude (EVM) Direct Conversion Transmitter Using

LO Divide-by-2 Modulator

Rev. 0

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EVALUATION AND DESIGN SUPPORT

Circuit Evaluation Boards

ADF4351 Evaluation Board (EVAL-ADF4351EB1Z)

ADL5385 Evaluation Board (ADL5385-EVALZ)

Design and Integration Files

Schematics, Layout Files, Bill of Materials

CIRCUIT FUNCTION AND BENEFITS

This circuit is a complete implementation of the analog portion of a

broadband direct conversion transmitter (analog baseband in, RF

out). RF frequencies from 30 MHz to 2.2 GHz are supported by

using a phase-locked loop (PLL) with a broadband integrated

voltage controlled oscillator (VCO). Unlike modulators that use a

divide-by-1 local oscillator (LO) stage (as described in CN-0285),

harmonic filtering of the LO is not required.

Figure 1. Direct Conversion Transmitter (Simplified Schematic: All Connections and Decoupling Not Shown)

22nF

10nF

330nF

180

Ω

82

Ω

IBBP

IBBN

LOIP

QBBP

QBBN

ADF4351

3.3V

AGND

DGND

1nF

1nF

4.7k

Ω

LE

DATA

CLK

10

28

16

29

1

2

3

22

8

31

9

11

18

21

27

51

Ω

14

15

17

20

7

26

6

32

5

SW

4

ADL5385

RFOUT

13

12

I/Q SMA INPUTS

I/Q SMA INPUTS

ADP150

1µF

1µF

5.5V

5.0V

VPS1, VPS2

ADP3334

1µF

1µF

5.5V

DIVIDE-BY-2

QUADRATURE

PHASE

SPLITTER

LOIN

1nF

1nF