AD8349 Ver la hoja de datos (PDF) - Analog Devices

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AD8349

700 MHz to 2700 MHz Quadrature Modulator

Analog Devices 

Data Sheet

BASIC CONNECTIONS

The basic connections for operating the AD8349 are shown in

Figure 43. A single power supply of between 4.75 V and 5.5 V is

applied to pins VPS1 and VPS2. A pair of ESD protection

diodes connect internally between VPS1 and VPS2, so these

must be tied to the same potential. Both pins should be

individually decoupled using 100 pF and 0.1 μF capacitors to

ground. These capacitors should be located as close as possible

to the device. For normal operation, the output enable pin,

ENOP, must be pulled high. The turn-on threshold for ENOP is

2 V. Pins COM1, COM2, and COM3 should all be tied to the

same ground plane through low impedance paths.

BASEBAND I AND Q INPUTS

The I and Q inputs should be driven differentially. The typical

differential drive level (as used for characterization measure-

ments) for the I and Q baseband signals is 1.2 V p-p, which is

equivalent to 600 mV p-p on each baseband input. The base-

band inputs have to be externally biased to a level between

400 mV and 500 mV. The optimum level for the best perfor-

mance is 400 mV. The recommended drive level of 1.2 V p-p

does not indicate a maximum drive level. If operation closer to

compression is desired, the 1.2 V p-p differential limit can be

exceeded.

For baseband signals with a high peak-to-average ratio (e.g.,

CDDA or WCDMA), the peak signal level will have to be below

the AD8349’s compression level in order to prevent clipping of

the signal peaks. Clipping of signal peaks increases distortion.

In the case of CDMA and WCDMA inputs, clipping results in

an increase of signal leakage into adjacent channels. In general,

the baseband drive should be at a level where the peak signal

AD8349

power of the output signal is at least a crest factor below the

AD8349’s output compression point. Refer to the Applications

section for drive-level considerations in WCDMA and

GSM/EDGE systems.

Reducing the baseband drive level also has the benefit of

increasing the bandwidth of the baseband input. This would

allow the AD8349 to be used in applications requiring a high

modulation bandwidth, e.g., as the IF modulator in high data-

rate microwave radios.

SINGLE-ENDED BASEBAND DRIVE

Where only single-ended I and Q signals are available, a

differential amplifier, such as the AD8132 or AD8138, can be

used to generate the required differential drive signal for the

AD8349.

Figure 44 shows an example of a circuit that converts a ground-

referenced, single-ended signal to a differential signal, and adds

the required 400 mV bias voltage.

The baseband inputs can also be driven with a single-ended

signal biased to 400 mV, with the unused inputs biased to

400 mV dc. This mode of operation is not recommended,

however, because any dc level difference between the bias level

of the drive signal and the dc level on the unused input

(including the effect of temperature drift), can result in

increased LO feedthrough. Additionally, the maximum low

distortion output power will be reduced by 6 dB.

IP

1 IBBP

QBBP 16

QP

2 IBBN

QBBN 15

IN

QN

3 COM1

COM3 14

200Ω

4 COM1

COM3 13

5

1

T1

ETC1-1-13 2

100pF

100pF

AD8349

5 LOIN

VPS2 12

6 LOIP

VOUT 11

100pF

0.1µF

+VS

VOUT

LO

4

3

200Ω

7 VPS1

COM3 10

100pF

8 ENOP

COM2 9

+VS

0.1µF

100pF

Figure 43. Basic Connections

Rev. B | Page 15 of 28

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