0.8 GHz to 2.5 GHz

Quadrature Modulator

AD8346

Rev. A

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FEATURES

High accuracy

1 degree rms quadrature error @ 1.9 GHz

0.2 dB I/Q amplitude balance @ 1.9 GHz

Broad frequency range: 0.8 GHz to 2.5 GHz

Sideband suppression: −46 dBc @ 0.8 GHz

Sideband suppression: −36 dBc @ 1.9 GHz

Modulation bandwidth: dc to 70 MHz

0 dBm output compression level @ 0.8 GHz

Noise floor: −147 dBm/Hz

Single 2.7 V to 5.5 V supply

Quiescent operating current: 45 mA

Standby current: 1 μA

16-lead TSSOP

APPLICATIONS

Digital and spread spectrum communication systems

Cellular/PCS/ISM transceivers

Wireless LAN/wireless local loop

QPSK/GMSK/QAM modulators

Single-sideband (SSB) modulators

Frequency synthesizers

Image reject mixer

FUNCTIONAL BLOCK DIAGRAM

1

2

3

4

5

6

7

8

BIAS

PHASE

SPLITTER

16

15

14

13

12

11

10

9

AD8346

IBBP

IBBN

COM1

COM1

LOIN

LOIP

VPS1

ENBL

QBBP

QBBN

COM4

COM4

VPS2

VOUT

COM3

COM2

Figure 1.

GENERAL DESCRIPTION

The AD8346 is a silicon RFIC I/Q modulator for use from

0.8 GHz to 2.5 GHz. Its excellent phase accuracy and amplitude

balance allow high performance direct modulation to RF.

The differential LO input is applied to a polyphase network

phase splitter that provides accurate phase quadrature from

0.8 GHz to 2.5 GHz. Buffer amplifiers are inserted between

two sections of the phase splitter to improve the signal-to-

noise ratio. The I and Q outputs of the phase splitter drive the

LO inputs of two Gilbert-cell mixers. Two differential V-to-I

converters connected to the baseband inputs provide the

baseband modulation signals for the mixers. The outputs of

the two mixers are summed together at an amplifier which is

designed to drive a 50 Ω load.

This quadrature modulator can be used as the transmit mod-

ulator in digital systems such as PCS, DCS, GSM, CDMA, and

ISM transceivers. The baseband quadrature inputs are directly

modulated by the LO signal to produce various QPSK and

QAM formats at the RF output.

Additionally, this quadrature modulator can be used with direct

digital synthesizers in hybrid phase-locked loops to generate

signals over a wide frequency range with millihertz resolution.

The AD8346 comes in a 16-lead TSSOP package, measuring

6.5 mm × 5.1 mm × 1.1 mm. It is specified to operate over a

−40°C to +85°C temperature range and a 2.7 V to 5.5 V supply

voltage range. The device is fabricated on Analog Devices’ high

performance 25 GHz bipolar silicon process.