ADF4113BCP datasheet(22/24 Pages) AD

22 / 24 page

REV. 0

ADF4110/ADF4111/ADF4112/ADF4113

–22–

RSET

ADF4113

100pF

REFIN

100pF

RFINA

RFINB

SERIAL

DIGITAL

NTERFACE

TCXO

OSC 3B1-13M0

100pF

620pF

3.9k

3.3k

9.1nF

4.7k

100pF

RFOUT

POWER SUPPLY CONNECTIONS AND DECOUPLING

CAPACITORS ARE OMITTED FROM DIAGRAM FOR CLARITY.

AD9761

TxDAC

REFIO

FS ADJ

MODULATED

DIGITAL

DATA

QOUTB

IOUTA

IOUTB

QOUTA

AD8346

LOIN

LOIP

VOUT

100pF

910pF

VCO190-1960T

IBBP

IBBN

QBBP

QBBN

LOW-PASS

FILTER

LOW-PASS

FILTER

Figure 33. Direct Conversion Transmitter Solution

DIRECT CONVERSION MODULATOR

In some applications a direct conversion architecture can be used

in base station transmitters. Figure 33 shows the combination

available from ADI to implement this solution.

The circuit diagram shows the AD9761 being used with the

AD8346. The use of dual integrated DACs such as the AD9761

with specified

±0.02 dB and ±0.004 dB gain and offset match-

ing characteristics ensures minimum error contribution (over

temperature) from this portion of the signal chain.

The Local Oscillator (LO) is implemented using the ADF4113.

In this case, the OSC 3B1-13M0 provides the stable 13 MHz

reference frequency. The system is designed for a 200 kHz

channel spacing and an output center frequency of 1960 MHz.

The target application is a WCDMA base station transmitter.

Typical phase noise performance from this LO is –85 dBc/Hz at

a 1 kHz offset.

The LO port of the AD8346 is driven in single-ended fashion.

LOIN is ac-coupled to ground with the 100 pF capacitor and

LOIP is driven through the ac coupling capacitor from a 50

Ω

source. An LO drive level of between –6 dBm and –12 dBm is

required. The circuit of Figure 33 gives a typical level of –8 dBm.

The RF output is designed to drive a 50

Ω load but must be

ac-coupled as shown in Figure 33. If the I and Q inputs are

driven in quadrature by 2 V p-p signals, the resulting output

power will be around –10 dBm.

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