LT5568-2EUF#PBF Datasheet LT5568-2EUF#PBF, LT5568EUF#PBF, LT5568-2EUF#TRPBF | P7-P9

LT5568

5568f

EN (Pin 1): Enable Input. When the enable pin voltage is

higher than 1V, the IC is turned on. When the input voltage

is less than 0.5V, the IC is turned off.

GND (Pins 2, 4, 6, 9, 10, 12, 15): Ground. Pins 6, 9, 15

and 17 (exposed pad) are connected to each other inter-

nally. Pins 2 and 4 are connected to each other internally

and function as the ground return for the LO signal. Pins

10 and 12 are connected to each other internally and

function as the ground return for the on-chip RF balun.

For best RF performance, pins 2, 4, 6, 9, 10, 12, 15 and

the Exposed Pad 17 should be connected to the printed

circuit board ground plane.

LO (Pin 3): LO Input. The LO input is an AC-coupled single-

ended input with approximately 50Ω input impedance at

RF frequencies. Externally applied DC voltage should be

within the range –0.5V to V

+ 0.5V in order to avoid

turning on ESD protection diodes.

BBPQ, BBMQ (Pins 7, 5): Baseband Inputs for the Q-chan-

nel, each 50Ω input impedance. Internally biased at about

0.54V. Applied voltage must stay below 2.5V.

(Pins 8, 13): Power Supply. Pins 8 and 13 are con-

nected to each other internally. It is recommended to use

0.1μF capacitors for decoupling to ground on each of

these pins.

RF (Pin 11): RF Output. The RF output is an AC-coupled

single-ended output with approximately 50Ω output im-

pedance at RF frequencies. Externally applied DC voltage

should be within the range –0.5V to V

+ 0.5V in order

to avoid turning on ESD protection diodes.

BBPI, BBMI (Pins 14, 16): Baseband Inputs for the

I-channel, each with 50Ω input impedance. Internally biased

at about 0.54V. Applied voltage must stay below 2.5V.

Exposed Pad (Pin 17): Ground. This pin must be soldered

to the printed circuit board ground plane.

PI FU CTIO S

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LT5568

5568f

The LT5568 consists of I and Q input differential voltage-

to-current converters, I and Q up-conversion mixers, an

RF output balun, an LO quadrature phase generator and

LO buffers.

Figure 1. Simpliﬁ ed Circuit Schematic of the LT5568

(Only I-Half is Drawn)

External I and Q baseband signals are applied to the dif-

ferential baseband input pins, BBPI, BBMI, and BBPQ,

BBMQ. These voltage signals are converted to currents and

translated to RF frequency by means of double-balanced

up-converting mixers. The mixer outputs are combined

in an RF output balun, which also transforms the output

impedance to 50Ω. The center frequency of the resulting

RF signal is equal to the LO signal frequency. The LO input

drives a phase shifter which splits the LO signal into in-

phase and quadrature LO signals. These LO signals are then

applied to on-chip buffers which drive the up-conversion

mixers. Both the LO input and RF output are single-ended,

50Ω-matched and AC coupled.

Baseband Interface

The baseband inputs (BBPI, BBMI), (BBPQ, BBMQ) present

a differential input impedance of about 100Ω. At each of the

four baseband inputs, a ﬁ rst-order lowpass ﬁ lter using 25Ω

APPLICATIO S I FOR ATIO

WUU

BLOCK DIAGRA

90°

0°

LT5568

V-I

BALUN

5568 BD

396

GND

8 13

BBPI

BBMI

BBPQ

BBMQ

1715

GND

1210

= 5V

BBPI

BBMI

GND

LOMI LOPI

FROM

5568 F01

BALUN

REF

= 540mV

R1B

23Ω

R1A

25Ω

12pF

R2A

25Ω

R2B

23Ω

12pF

LT5568

5568f

APPLICATIO S I FOR ATIO

WUU

Figure 3. LT5568 5

Order Filtered Baseband Interface with Common DAC (Only I-Channel is Shown)

Figure 2. DC Voltage Levels for a Generator Programmed at

0.27V

for a 50Ω Load and the LT5568 as a Load

The baseband inputs should be driven differentially; other-

wise, the even-order distortion products will degrade the

overall linearity severely. Typically, a DAC will be the signal

source for the LT5568. Reconstruction ﬁ lters should be

placed between the DAC output and the LT5568’s baseband

inputs. In Figure 3, an example interface schematic shows a

commonly used DAC output interface followed by a passive

order ladder ﬁ lter. The DAC in this example sources

a current from 0mA to 20mA. The interface may be DC

coupled. This allows adjustment of the DAC’s differential

output current to minimize the LO feedthrough. Optionally,

transformer T1 can be inserted to improve the current

balance in the BBPI and BBMI pins. This will improve the

2nd order distortion performance (OIP2).

The maximum single sideband CW RF output power at

850MHz using both I and Q channels with the conﬁ gura-

tion shown in Figure 3 is about –3dBm. The maximum

CW output power can be increased by connecting load

resistors R5 and R6 to –5V instead of GND, and changing

their values to 550Ω. In that case, the maximum single

sideband CW RF output power at 850MHz will be about

+2dBm. In addition, the ladder ﬁ lter component values

require adjustment for a higher source impedance.

and 12pF to ground is incorporated (see Figure 1), which

limits the baseband bandwidth to approximately 330MHz

(–1dB point). The common mode voltage is about 0.54V

and is approximately constant over temperature.

It is important that the applied common mode voltage level

of the I and Q inputs is about 0.54V in order to properly

bias the LT5568. Some I/Q test generators allow setting

the common mode voltage independently. In this case, the

common mode voltage of those generators must be set

to 0.27V to match the LT5568 internal bias, because for

DC signals, there is no –6dB source-load voltage division

(see Figure 2).

5568 F02

48Ω50Ω

LT5568GENERATOR

0.54V

–

50Ω

GENERATOR

0.54V

0.27V

–

••

RF = –3dBm, MAX

= 5V

GND

LOMI LOPI

15mA

5568 F03

LT5568

GND

REF

= 500mV

1:1

BBPI

BBMI

L1A

L1B

C1 C3

0.5V

R5, 50Ω

0.5V

R6, 50Ω

DAC

0mA to 20mA

L2A

L2B

BALUN

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P16

LT5568-2EUF#PBF

Mfr. #:

Buy LT5568-2EUF#PBF

Manufacturer:

Analog Devices Inc.

Description:

Modulator / Demodulator 900MHz Direct I/Q Modulator for GSM/EDGE

Lifecycle:

New from this manufacturer.

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LT5568-2EUF#PBF

LT5568-2EUF#PBF

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