LT5568EUF#TRPBF - Linear Technology

LT5568

5568f

RF OUTPUT POWER PER CARRIER (dBm)

–30

ACPR, AltCPR (dBc)

NOISE FLOOR AT 30MHz

OFFSET (dBm/Hz)

–70

–60

–10

5568 TA02

–80

–90 –25 –20 –15 –5

–50

–145

–135

–155

–165

–125

DOWNLINK TEST MODEL 64 DPCH

1-CH. NOISE

3-CH. NOISE

1-CH. AltCPR

1-CH.

ACPR

3-CH. ACPR

3-CH. AltCPR

700MHz – 1050MHz High

Linearity Direct Quadrature

Modulator

The LT

5568 is a direct I/Q modulator designed for high

performance wireless applications, including wireless

infrastructure. It allows direct modulation of an RF signal

using differential baseband I and Q signals. It supports

PHS, GSM, EDGE, TD-SCDMA, CDMA, CDMA2000, W-

CDMA, and other systems. It may also be conﬁ gured

as an image reject upconverting mixer, by applying

90° phase-shifted signals to the I and Q inputs. The I/Q

baseband inputs consist of voltage-to-current converters

that in turn drive double-balanced mixers. The outputs of

these mixers are summed and applied to an on-chip RF

transformer, which converts the differential mixer signals

to a 50Ω single-ended output. The four balanced I and Q

baseband input ports are intended for DC coupling from a

source with a common mode voltage level of about 0.5V.

The LO path consists of an LO buffer with single-ended

input, and precision quadrature generators that produce

the LO drive for the mixers. The supply voltage range is

4.5V to 5.25V.

■ Infrastructure Tx for Cellular Bands

■ Image Reject Up-Converters for Cellular Bands

■ Low-Noise Variable Phase-Shifter for 700MHz to

1050MHz Local Oscillator Signals

■ RFID Reader

■ Frequency Range: 700MHz to 1050MHz

■ High OIP3: +22.9dBm at 850MHz

■ Low Output Noise Floor at 5MHz Offset:

No RF: –160.3dBm/Hz

OUT = 4dBm: –154dBm/Hz

■ 3-Ch CDMA2000 ACPR: –71.4dBc at 850MHz

■ Integrated LO Buffer and LO Quadrature Phase

Generator

■ 50Ω AC-Coupled Single-Ended LO and RF Ports

■ 50Ω DC Interface to Baseband Inputs

■ Low Carrier Leakage: –43dBm at 850MHz

■ High Image Rejection: –46dBc at 850MHz

■ 16-Lead 4mm × 4mm QFN Package

700MHz to 1050MHz Direct Conversion Transmitter Application

APPLICATIO S

FEATURES DESCRIPTIO

TYPICAL APPLICATIO

, LTC and LT are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

CDMA2000 ACPR, AltCPR and Noise vs RF

Output Power at 850MHz for 1 and 3 Carriers

90°

0°

LT5568

BASEBAND

GENERATOR

VCO/SYNTHESIZER

RF = 700MHz

TO 1050MHz

100nF

V-I

I-CHANNEL

Q-CHANNEL BALUN

VCC

5568 TA01

I-DAC

Q-DAC

LT5568

5568f

Supply Voltage .........................................................5.5V

Common Mode Level of BBPI, BBMI and

BBPQ, BBMQ .......................................................2.5V

Operating Ambient Temperature

(Note 2) ............................................... –40°C to 85°C

Storage Temperature Range ................... –65°C to 125°C

Voltage on any Pin

Not to Exceed ...................... –500mV to VCC + 500mV

(Note 1)

ABSOLUTE AXI U RATI GS

PACKAGE/ORDER I FOR ATIO

UUW

16 15 14 13

5678

TOP VIEW

1EN

GND

BBMI

GND

BBPI

VCC

BBMQ

GND

BBPQ

VCC

UF PACKAGE

16-LEAD (4mm × 4mm) PLASTIC QFN

TJMAX = 125°C, θJA = 37°C/W

EXPOSED PAD (PIN 17) IS GROUND, MUST BE SOLDERED TO PCB

ORDER PART NUMBER UF PART MARKING

LT5568EUF 5568

Order Options Tape and Reel: Add #TR

Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF

Lead Free Part Marking: http://www.linear.com/leadfree/

Consult LTC Marketing for parts speciﬁ ed with wider operating temperature ranges.

CC = 5V, EN = High, TA = 25°C, fLO = 850MHz, fRF = 852MHz, PLO = 0dBm.

BBPI, BBMI, BBPQ, BBMQ inputs 0.54VDC, Baseband Input Frequency = 2MHz, I&Q 90° shifted (upper side-band selection).

PRF, OUT = –10dBm, unless otherwise noted. (Note 3)

ELECTRICAL CHARACTERISTICS

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

RF Output (RF)

fRF RF Frequency Range

RF Frequency Range

–3dB Bandwidth

–1dB Bandwidth

0.6 to 1.2

0.7 to 1.05

GHz

S22, ON RF Output Return Loss EN = High (Note 6) –14 dB

S22, OFF RF Output Return Loss EN = Low (Note 6) –12 dB

NFloor RF Output Noise Floor No Input Signal (Note 8)

POUT = 4dBm (Note 9)

POUT = 4dBm (Note 10)

–160.3

–154

dBm/Hz

GPConversion Power Gain POUT/PIN, I&Q –9 –6.8 –3 dB

GVConversion Voltage Gain 20 • Log (VOUT, 50Ω/VIN, DIFF, I or Q) –6.8 dB

POUT Absolute Output Power 1VP-P DIFF CW Signal, I and Q –2.8 dBm

G3LO vs LO 3 • LO Conversion Gain Difference (Note 17) –23 dB

OP1dB Output 1dB Compression (Note 7) 8.3 dBm

OIP2 Output 2nd Order Intercept (Notes 13, 14) 63 dBm

OIP3 Output 3rd Order Intercept (Notes 13, 15) 22.9 dBm

IR Image Rejection (Note 16) –46 dBc

LOFT Carrier Leakage

(LO Feedthrough)

EN = High, PLO = 0dBm (Note 16)

EN = Low, PLO = 0dBm (Note 16)

–43

–65

dBm

LT5568

5568f

CC = 5V, EN = High, TA = 25°C, fLO = 850MHz, fRF = 852MHz, PLO = 0dBm.

BBPI, BBMI, BBPQ, BBMQ inputs 0.54VDC, Baseband Input Frequency = 2MHz, I&Q 90° shifted (upper side-band selection).

PRF, OUT = –10dBm, unless otherwise noted. (Note 3)

Note 1: Absolute Maximum Ratings are those values beyond which the life

of a device may be impaired.

Note 2: Speciﬁ cations over the –40°C to 85°C temperature range are

assured by design, characterization and correlation with statistical process

controls.

Note 3: Tests are performed as shown in the conﬁ guration of Figure 7.

Note 4: On each of the four baseband inputs BBPI, BBMI, BBPQ and

BBMQ.

Note 5: V(BBPI) – V(BBMI) = 1VDC, V(BBPQ) – V(BBMQ) = 1VDC.

Note 6: Maximum value within –1dB bandwidth.

Note 7: An external coupling capacitor is used in the RF output line.

Note 8: At 20MHz offset from the LO signal frequency.

Note 9: At 20MHz offset from the CW signal frequency.

Note 10: At 5MHz offset from the CW signal frequency.

Note 11: RF power is within 10% of ﬁ nal value.

Note 12: RF power is at least 30dB lower than in the ON state.

Note 13: Baseband is driven by 2MHz and 2.1MHz tones. Drive level is set

in such a way that the two resulting RF tones are –10dBm each.

Note 14: IM2 measured at LO frequency + 4.1MHz.

Note 15: IM3 measured at LO frequency + 1.9MHz and LO frequency +

2.2MHz.

Note 16: Amplitude average of the characterization data set without image

or LO feedthrough nulling (unadjusted).

Note 17: The difference in conversion gain between the spurious signal at

f = 3 • LO – BB versus the conversion gain at the desired signal at f = LO +

BB for BB = 2MHz and LO = 850MHz.

Note 18: The input voltage corresponding to the output P1dB.

ELECTRICAL CHARACTERISTICS

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

LO Input (LO)

fLO LO Frequency Range 0.6 to 1.2 GHz

PLO LO Input Power –10 0 5 dBm

S11, ON LO Input Return Loss EN = High (Note 6) –11.4 dB

S11, OFF LO Input Return Loss EN = Low (Note 6) –2.7 dB

NFLO LO Input Referred Noise Figure (Note 5) at 850MHz 12.7 dB

GLO LO to RF Small Signal Gain (Note 5) at 850MHz 23.8 dB

IIP3LO LO Input 3rd Order Intercept (Note 5) at 850MHz –11.5 dBm

Baseband Inputs (BBPI, BBMI, BBPQ, BBMQ)

BWBB Baseband Bandwidth –3dB Bandwidth 380 MHz

VCMBB DC Common Mode Voltage (Note 4) 0.54 V

RIN, SE Single-Ended Input Resistance (Note 4) 48 Ω

PLO2BB Carrier Feedthrough on BB POUT = 0 (Note 4) –38 dBm

IP1dB Input 1dB Compression Point Differential Peak-to-Peak (Notes 7, 18) 4.3 VP-P, DIFF

ΔGI/Q I/Q Absolute Gain Imbalance 0.07 dB

ΔϕI/Q I/Q Absolute Phase Imbalance 0.45 Deg

Power Supply (VCC)

VCC Supply Voltage 4.5 5 5.25 V

ICC, ON Supply Current EN = High 80 117 165 mA

ICC, OFF Supply Current, Sleep Mode EN = 0V 50 μA

tON Turn-On Time EN = Low to High (Note 11) 0.3 μs

tOFF Turn-Off Time EN = High to Low (Note 12) 1.4 μs

Enable (EN), Low = Off, High = On

Enable Input High Voltage

Input High Current

EN = High

EN = 5V

1.0

230

μA

Sleep Input Low Voltage

Input Low Current

EN = Low

EN = 0V 0

0.5 V

μA

LT5568

5568f

SUPPLY VOLTAGE (V)

4.5

SUPPLY CURRENT (mA)

140

130

120

110

100

5568 G01

55.5

85°C

25°C

–40°C

LO FREQUENCY (MHz)

–10

RF OUTPUT POWER (dBm)

–6

–8

–4

–2

5568 G02

5.5V, 25°C

4.5V, 25°C

5V, 85°C

5V, 25°C

5V, –40°C

550 650 750 850 950 1050 1150 1250

LO FREQUENCY (MHz)

–14

VOLTAGE GAIN (dB)

–10

–12

–8

–6

–4

5568 G03

5.5V, 25°C

4.5V, 25°C

5V, 85°C

5V, 25°C

5V, –40°C

550 650 750 850 950 1050 1150 1250

LO FREQUENCY (MHz)

OIP3 (dBm)

5568 G04

5.5V, 25°C

4.5V, 25°C

5V, 85°C

5V, 25°C

5V, –40°C

550 650 750 850 950 1050 1150 1250

fBB, 1 = 2MHz

fBB, 2 = 2.1MHz

LO FREQUENCY (MHz)

550

OIP2 (dBm)

650 750 850 950

5568 G05

1050 1150 1250

5.5V, 25°C

4.5V, 25°C

5V, 85°C

5V, 25°C

5V, –40°C

fIM2 = fBB, 1 + fBB, 2 + fLO

fBB, 1 = 2MHz

fBB, 2 = 2.1MHz

LO FREQUENCY (MHz)

550

OP1dB (dBm)

650 750 850 950

5568 G06

1050 1150 1250

5.5V, 25°C

4.5V, 25°C

5V, 85°C

5V, 25°C

5V, –40°C

LO FREQUENCY (MHz)

550

–48

LOFT (dBm)

–44

–46

–42

–40

650 750 850 950

5568 G07

1050 1150 1250

5.5V, 25°C

4.5V, 25°C

5V, 85°C

5V, 25°C

5V, –40°C

2 • LO FREQUENCY (GHz)

1.1

–60

P(2 • LO) (dBm)

–50

–55

–45

–40

1.3 1.5 1.7 1.9

5568 G08

2.1 2.3 2.5

5.5V, 25°C

4.5V, 25°C

5V, 85°C

5V, 25°C

5V, –40°C

3 • LO FREQUENCY (GHz)

1.65

–65

–60

P(3 • LO) (dBm)

–50

–55

–45

–40

1.95 2.25 2.55 2.85

5568 G09

3.15 3.45 3.75

5.5V, 25°C

4.5V, 25°C

5V, 85°C

5V, 25°C

5V, –40°C

VCC = 5V, EN = High, TA = 25°C, fLO = 850MHz,

PLO = 0dBm. BBPI, BBMI, BBPQ, BBMQ inputs 0.54VDC, Baseband Input Frequency fBB = 2MHz, I&Q 90° shifted. fRF = fBB + fLO (upper

sideband selection). PRF, OUT = –10dBm (–10dBm/tone for 2-tone measurements), unless otherwise noted. (Note 3)

Supply Current vs Supply Voltage

RF Output Power vs LO Frequency

at 1VP-P Differential Baseband Drive

Voltage Gain vs LO Frequency

Output IP3 vs LO Frequency

Output IP2 vs LO Frequency

Output 1dB Compression

vs LO Frequency

TYPICAL PERFOR A CE CHARACTERISTICS

LO Feedthrough to RF Output

vs LO Frequency

2 • LO Leakage to RF Output

vs 2 • LO Frequency

3 • LO Leakage to RF Output

vs 3 • LO Frequency

LT5568

5568f

RF FREQUENCY (MHz)

550

–164

NOISE FLOOR (dBm/Hz)

–162

–163

–161

–160

650 750 850 950

5568 G10

1050 1150 1250

5.5V, 25°C

4.5V, 25°C

5V, 85°C

5V, 25°C

5V, –40°C

fLO = 850MHz

(FIXED)

LO FREQUENCY (MHz)

550

–50

IMAGE REJECTION (dBc)

–40

–45

–35

–30

650 750 850 950

5568 G11

1050 1150 1250

5.5V, 25°C

4.5V, 25°C

5V, 85°C

5V, 25°C

5V, –40°C

RF FREQUENCY (MHz)

550

–40

S11 (dB)

–20

–30

–10

650 750 850 950

5568 G12

1050 1150 1250

LO PORT, EN = LOW

LO PORT, EN = HIGH,

PLO = 0dBm

RF PORT,

EN = LOW

RF PORT, EN = HIGH, PLO = 0dBm

RF PORT, EN = HIGH, No LO

LO PORT,

EN = HIGH,

PLO = –10dBm

LO FREQUENCY (MHz)

550

ABSOLUTE I/Q GAIN IMBALANCE (dB)

0.1

0.2

650 750 850 950

5568 G13

1050 1150 1250

5.5V, 25°C

4.5V, 25°C

5V, 85°C

5V, 25°C

5V, –40°C

LO FREQUENCY (MHz)

550

ABSOLUTE I/Q PHASE IMBALANCE (DEG)

650 750 850 950

5568 G14

1050 1150 1250

5.5V, 25°C

4.5V, 25°C

5V, 85°C

5V, 25°C

5V, –40°C

LO INPUT POWER (dBm)

–16

–14

VOLTAGE GAIN (dB)

–10

–12

–8

–6

–4

5568 G15

5.5V, 25°C

4.5V, 25°C

5V, 85°C

5V, 25°C

5V, –40°C

–20 –16 –12 –8 –4 0 4 8

LO INPUT POWER (dBm)

0IP3 (dBm)

5568 G16

5.5V, 25°C

4.5V, 25°C

5V, 85°C

5V, 25°C

5V, –40°C

–20 –16 –12 –8 –4 0 4 8

fBB, 1 = 2MHz

fBB, 2 = 2.1MHz

I AND Q BASEBAND VOLTAGE (VP–P, DIFF)

–80

HD2, HD3 (dBc)

RF CW OUTPUT POWER (dBm)

–40

–60

–20

–10

1234

5568 G17

–50

–70

–30

–60

–20

–40

–30

–50

–10

HD2 = MAX POWER AT fLO + 2 • fBB OR fLO – 2 • fBB

HD3 = MAX POWER AT fLO + 3 • fBB OR fLO – 3 • fBB

–40°C

25°C

HD3

85°C

RF –40°C

85°C

HD2

25°C

–40°C

25°C

85°C

TYPICAL PERFOR A CE CHARACTERISTICS

VCC = 5V, EN = High, TA = 25°C, fLO = 850MHz,

PLO = 0dBm. BBPI, BBMI, BBPQ, BBMQ inputs 0.54VDC, Baseband Input Frequency fBB = 2MHz, I&Q 90° shifted. fRF = fBB + fLO (upper

sideband selection). PRF, OUT = –10dBm (–10dBm/tone for 2-tone measurements), unless otherwise noted. (Note 3)

Noise Floor vs RF Frequency

Image Rejection vs LO Frequency

LO and RF Port Return Loss

vs RF Frequency

Absolute I/Q Gain Imbalance

vs LO Frequency

Absolute I/Q Phase Imbalance

vs LO Frequency

Voltage Gain vs LO Power

Output IP3 vs LO Power

RF CW Output Power, HD2 and HD3 vs

CW Baseband Voltage and Temperature

LT5568

5568f

I AND Q BASEBAND VOLTAGE (VP–P, DIFF)

–44

LOFT (dBm)

–40

–42

–38

–36

1234

5568 G19

5.5V, 25°C

4.5V, 25°C

5V, 85°C

5V, 25°C

5V, –40°C

I AND Q BASEBAND VOLTAGE (VP–P, DIFF)

–55

IR (dBc)

–45

–50

–40

–35

1234

5568 G20

5.5V, 25°C

4.5V, 25°C

5V, 85°C

5V, 25°C

5V, –40°C

I AND Q BASEBAND VOLTAGE (VP–P, DIFF, EACH TONE)

0.1

–80

PRF,TONE (dBm), IM2, IM3 (dBc)

–40

–60

–20

–10

5568 G21

–50

–70

–30

IM2 = POWER AT fLO + 4.1MHz

IM3 = MAX POWER AT fLO + 1.9MHz OR fLO + 2.2MHz

IM3

IM2

85°C

–40°C

85°C

–40°C

25°C

85°C

25°C

fBBI = 2MHz, 2.1MHz, 0°

fBBQ = 2MHz, 2.1MHz, 90°

25°C

I AND Q BASEBAND VOLTAGE (VP–P, DIFF, EACH TONE)

0.1

–80

PRF,TONE (dBm), IM2, IM3 (dBc)

–40

–60

–20

–10

5568 G22

–50

–70

–30

IM2 = POWER AT fLO + 4.1MHz

IM3 = MAX POWER AT fLO + 1.9MHz OR fLO + 2.2MHz

IM3

IM2

fBBI = 2MHz, 2.1MHz, 0°

fBBQ = 2MHz, 2.1MHz, 90°

4.5V

5V, 5.5V

4.5V

5.5V

I AND Q BASEBAND VOLTAGE (VP–P, DIFF)

–80

HD2, HD3 (dBc)

RF CW OUTPUT POWER (dBm)

–40

–60

–20

–10

1234

5568 G18

–50

–70

–30

–60

–20

–40

–30

–50

–10

HD2 = MAX POWER AT fLO + 2 • fBB OR fLO – 2 • fBB

HD3 = MAX POWER AT fLO + 3 • fBB OR fLO – 3 • fBB

HD2 4.5V

4.5V

5.5V

HD3

RF CW Output Power, HD2 and

HD3 vs CW Baseband Voltage

and Supply Voltage

LO Feedthrough to RF Output

vs CW Baseband Voltage

Image Rejection

vs CW Baseband Voltage

RF Two-Tone Power (Each Tone),

IM2 and IM3 vs Baseband Voltage

and Temperature

RF Two-Tone Power (Each Tone),

IM2 and IM3 vs Baseband Voltage

and Supply Voltage

TYPICAL PERFOR A CE CHARACTERISTICS

VCC = 5V, EN = High, TA = 25°C, fLO = 850MHz,

PLO = 0dBm. BBPI, BBMI, BBPQ, BBMQ inputs 0.54VDC, Baseband Input Frequency fBB = 2MHz, I&Q 90° shifted. fRF = fBB + fLO (upper

sideband selection). PRF, OUT = –10dBm (–10dBm/tone for 2-tone measurements), unless otherwise noted. (Note 3)

GAIN (dB)

–8

PERCENTAGE (%)

–7

5568 G23

–7.5 –6.5 –6

–40°C

25°C

85°C

NOISE FLOOR (dBm/Hz)

–160.8

PERCENTAGE (%)

–160

5568 G24

–160.4 –159.6 –159.2

–40°C

25°C

85°C

fNOISE = 870MHz

LO LEAKAGE (dBm)

–54

PERCENTAGE (%)

–46

5568 G25

–50 –42 –38 –34

PLO = –10dBm

NO BASEBAND

APPLIED

–40°C

25°C

85°C

IMAGE REJECTION (dBc)

< –60

PERCENTAGE (%)

–52

5568 G26

–56 –48 –44

VBB = 800mVP-P,DIFF

–40°C

25°C

85°C

Noise Floor Distribution LO Leakage Distribution Image Rejection Distribution

Gain Distribution

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 VCC + 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.

VCC (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 VCC + 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

UUU

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

WUUU

BLOCK DIAGRA

90°

0°

LT5568

V-I

BALUN

VCC

5568 BD

396

GND

8 13

BBPI

BBMI

BBPQ

BBMQ

1715

GND

1210

VCC = 5V

BBPI

BBMI

GND

LOMI LOPI

FROM

5568 F01

BALUN

VREF = 540mV

R1B

23Ω

R1A

25Ω

12pF

R2A

25Ω

R2B

23Ω

12pF

LT5568

5568f

APPLICATIO S I FOR ATIO

WUUU

Figure 3. LT5568 5th Order Filtered Baseband Interface with Common DAC (Only I-Channel is Shown)

Figure 2. DC Voltage Levels for a Generator Programmed at

0.27VDC 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

5th 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

0.54VDC

0.54VDC +

–

50Ω

GENERATOR

0.54VDC

0.27VDC

–

••

RF = –3dBm, MAX

VCC = 5V

GND

LOMI LOPI

33Ω

15mA

5568 F03

LT5568

GND

VREF = 500mV

33Ω

45Ω

1:1

BBPI

BBMI

L1A

L1B

C1 C3

45Ω

0.5V

R5, 50Ω

0.5V

R6, 50Ω

DAC

0mA to 20mA

L2A

L2B

BALUN

LT5568

5568f

APPLICATIO S I FOR ATIO

WUUU

LO Section

The internal LO input ampliﬁ er performs single-ended to

differential conversion of the LO input signal. Figure 4

shows the equivalent circuit schematic of the LO input.

Table 1. LO Port Input Impedance vs Frequency for EN = High

and PLO = 0dBm

Frequency Input Impedance S11

MHz ΩMag Angle

500 47.5 + j12.1 0.126 95.0

600 59.4 + j8.4 0.115 37.8

700 66.2 – j1.14 0.140 –3.41

800 67.2 – j13.4 0.185 –31.7

900 61.1 – j23.9 0.232 –53.2

1000 53.3 – j26.8 0.252 –68.7

1100 48.2 – j26.1 0.258 –79.4

1200 42.0 – j27.4 0.297 –90.0

If the part is in shutdown mode, the input impedance of

the LO port will be different. The LO input impedance for

EN = Low is given in Table 2.

Table 2. LO Port Input Impedance vs Frequency for EN = Low and

PLO = 0dBm

Frequency Input Impedance S11

MHz ΩMag Angle

500 33.6 + j41.3 0.477 85.4

600 59.8 + j69.1 0.539 49.8

700 140 + j89.8 0.606 19.6

800 225 – j62.6 0.659 –6.8

900 92.9 – j128 0.704 –29.6

1000 39.8 – j95.9 0.735 –45.5

1100 22.8 – j72.7 0.755 –65.6

1200 16.0 – j57.3 0.763 –79.7

RF Section

After up-conversion, the RF outputs of the I and Q mixers are

combined. An on-chip balun performs internal differential

to single-ended output conversion, while transforming the

output signal impedance to 50Ω. Table 3 shows the RF

port output impedance vs frequency.

Table 3. RF Port Output Impedance vs Frequency for EN = High

and PLO = 0dBm

Frequency Input Impedance S22

MHz ΩMag Angle

500 22.0 + j5.7 0.395 164.2

600 28.2 + j12.5 0.317 141.3

700 38.8 + j14.8 0.206 117.5

800 49.4 + j7.2 0.072 90.6

900 49.3 – j5.1 0.051 –94.7

1000 42.5 – j11.1 0.143 –117.0

1100 36.7 – j11.7 0.202 –130.7

1200 33.0 – j10.3 0.238 –141.6

INPUT

20pF

51Ω

5568 F04

VCC

The internal, differential LO signal is then split into in-phase

and quadrature (90° phase shifted) signals that drive LO

buffer sections. These buffers drive the double balanced

I and Q mixers. The phase relationship between the LO

input and the internal in-phase LO and quadrature LO

signals is ﬁ xed, and is independent of start-up conditions.

The internal phase shifters are designed to deliver accu-

rate quadrature signals. For LO frequencies signiﬁ cantly

below 600MHz or above 1GHz, however, the quadrature

accuracy will diminish, causing the image rejection to

degrade. The LO pin input impedance is about 50Ω, and

the recommended LO input power is 0dBm. For lower

LO input power, the gain, OIP2, OIP3 and noise ﬂ oor at

PRF = 4dBm will degrade, especially below –5dBm and at

TA = 85°C. For high LO input power (e.g., +5dBm), the LO

feedthrough will increase with no improvement in linearity

or gain. For lower LO input power, e.g., PLO = –5dBm, the

image rejection improves (especially around 950MHz) at

the cost of 1.5dB degradation of the noise ﬂ oor at PRF =

4dBm. Harmonics present on the LO signal can degrade the

image rejection because they can introduce a small excess

phase shift in the internal phase splitter. For the second (at

1.7GHz) and third harmonics (at 2.55GHz) at –20dBc, the

resulting signal at the image frequency is about –56dBc

or lower, corresponding to an excess phase shift of much

less than 1 degree. For the second and third LO harmonics

at –10dBc, the introduced signal at the image frequency is

about –47dBc. Higher harmonics than the third will have

less impact. The LO return loss typically will be better than

11dB over the 700MHz to 1.05GHz range. Table 1 shows

the LO port input impedance vs frequency.

Figure 4. Equivalent Circuit Schematic of the LO Input

LT5568

5568f

APPLICATIO S I FOR ATIO

WUUU

The RF output S22 with no LO power applied is given in

Table 4.

Table 4. RF Port Output Impedance vs Frequency for EN = High

and No LO Power Applied

Frequency Input Impedance S22

MHz ΩMag Angle

500 22.7 + j5.6 0.381 164.0

600 29.7 + j11.6 0.290 142.0

700 40.5 + j11.6 0.164 121.9

800 47.3 + j2.2 0.037 139.6

900 44.1 – j6.7 0.094 –126.9

1000 38.2 – j9.8 0.171 –133.9

1100 34.0 – j9.4 0.218 –143.1

1200 31.5 – j7.8 0.245 –151.6

For EN = Low the S22 is given in Table 5.

Table 5. RF Port Output Impedance vs Frequency for EN = Low

Frequency Input Impedance S22

MHz ΩMag Angle

500 21.2 + j5.4 0.409 164.9

600 26.6 + j12.5 0.340 142.5

700 36.6 + j16.6 0.241 118.1

800 49.2 + j11.6 0.116 87.4

900 52.9 – j2.0 0.034 –33.1

1000 46.4 – j11.2 0.121 –101.1

1100 39.3 – j13.2 0.188 –120.6

1200 34.4 – j12.1 0.231 –133.8

Note that an ESD diode is connected internally from

the RF output to ground. For strong output RF signal

levels (higher than 3dBm), this ESD diode can degrade

the linearity performance if the 50Ω termination imped-

ance is connected directly to ground. To prevent this, a

coupling capacitor can be inserted in the RF output line.

This is strongly recommended during a 1dB compression

measurement.

Enable Interface

Figure 6 shows a simpliﬁ ed schematic of the EN pin in-

terface. The voltage necessary to turn on the LT5568 is

1V. To disable (shut down) the chip, the enable voltage

must be below 0.5V. If the EN pin is not connected, the

chip is disabled. This EN = Low condition is assured by

the 75k on-chip pull-down resistor. It is important that

the voltage at the EN pin does not exceed VCC by more

than 0.5V. If this should occur, the supply current could

be sourced through the EN pin ESD protection diodes,

which are not designed to carry the full supply current,

and damage may result.

Figure 5. Equivalent Circuit Schematic of the RF Output Figure 6. EN Pin Interface

75k

5568 F06

VCC

25k

21pF

1pF7nH 51Ω

5568 F05

VCC

OUTPUT

LT5568

5568f

Evaluation Board

Figure 7 shows the evaluation board schematic. A good

ground connection is required for the exposed pad. If this

is not done properly, the RF performance will degrade. Ad-

ditionally, the exposed pad provides heat sinking for the part

and minimizes the possibility of the chip overheating.

R1 (optional) limits the EN pin current in the event that

the EN pin is pulled high while the VCC inputs are low. In

Figures 8 and 9 the silk screens and the PCB board layout

are shown.

Figure 8. Component Side of Evaluation Board

Figure 9. Bottom Side of Evaluation Board

APPLICATIO S I FOR ATIO

WUUU

Figure 7. Evaluation Circuit Schematic

BBIPBBIM

16 15 14 13

VCC

VCC EN

5678

5568 F07

BBQM

BBQP

BOARD NUMBER: DC966A

100nF J6

OUT

GND

100nF

BBMI

LT5568

BBPI VCC

BBMQ GND

GND

BBPQ VCC

GND

100Ω

LT5568

5568f

RF OUTPUT POWER PER CARRIER (dBm)

–30

ACPR, AltCPR (dBc)

NOISE FLOOR AT 30MHz

OFFSET (dBm/Hz)

–70

–60

–10

5568 F11

–80

–90 –25 –20 –15 –5

–50

–145

–135

–155

–165

–125

DOWNLINK TEST MODEL 64 DPCH

1-CH. NOISE

3-CH. NOISE

1-CH. AltCPR

1-CH.

ACPR

3-CH. ACPR

3-CH. AltCPR

RF FREQUENCY (MHz)

846.25

POWER IN 30kHz BW (dBm)

–70

–50

–30

852.25

5568 F12

–90

–110

–80

–60

–40

–100

–120

–130 847.75 849.25 850.75 853.75

SPECTRUM ANALYSER NOISE FLOOR

CORRECTED

SPECTRUM

UNCORRECTED

SPECTRUM

DOWNLINK TEST

MODEL 64 DPCH

RF FREQUENCY (MHz)

844

POWER IN 30kHz BW (dBm)

–70

–50

–30

852 852

5568 F13

–90

–110

–80

–60

–40

–100

–120

–130 846 848 850 856

CORRECTED

SPECTRUM

UNCORRECTED

SPECTRUM

DOWNLINK

TEST

MODEL 64

DPCH

SPECTRUM ANALYSER

NOISE FLOOR

APPLICATIO S I FOR ATIO

WUUU

Application Measurements

The LT5568 is recommended for base-station applications

using various modulation formats. Figure 10 shows a typi-

cal application. Figure 11 shows the ACPR performance

for CDMA2000 using 1- and 3-carrier modulation. Figures

12 and 13 illustrate the 1- and 3-carrier CDMA2000 RF

spectrum. To calculate ACPR, a correction is made for the

spectrum analyzer noise ﬂ oor. If the output power is high,

the ACPR will be limited by the linearity performance of the

part. If the output power is low, the ACPR will be limited

by the noise performance of the part. In the middle, an

optimum ACPR is observed.

Because of the LT5568’s very high dynamic range, the test

equipment can limit the accuracy of the ACPR measure-

ment. See Application Note 99. Consult the factory for

advice on the ACPR measurement, if needed.

The ACPR performance is sensitive to the amplitude match

of the BBIP and BBIM (or BBQP and BBQM) inputs. This

is because a difference in AC current amplitude will give

rise to a difference in amplitude between the even-order

harmonic products generated in the internal V-I converter.

As a result, they will not cancel out entirely. Therefore, it

is important to keep the currents in those pins exactly the

same (but of opposite sign). The current will enter the

LT5568’s common-base stage, and will ﬂ ow to the mixer

upper switches. This can be seen in Figure 1 where the

internal circuit of the LT5568 is drawn. For best results,

a high ohmic source is recommended; for example, the

Figure 10. 700MHz to 1050MHz Direct

Conversion Transmitter Application

90°

0°

L5568

BASEBAND

GENERATOR

VCO/SYNTHESIZER

2, 4, 6, 9, 10, 12, 15, 17

V-I

I-CHANNEL

Q-CHANNEL BALUN

8, 13

VCC

35568 F10

I-DAC

Q-DAC

RF = 700MHz

TO 1050MHz

100nF

Figure 12. 1-Carrier CDMA2000 Spectrum Figure 13. 3-Carrier CDMA2000 Spectrum

Figure 11. APCR, AltCPR and Noise

CDMA2000 Modulation

LT5568

5568f

TEMPERATURE (°C)

–40 –20

–90

LOFT (dBm), IR (dBc)

–70

–40

040 80

5568 F14

–80

–50

–60

20 60

VCC = 5V

fBBI = 2MHz, 0°

fBBQ = 2MHz, 90° + ϕ

fLO = 850MHz

fRF = fBB + fLO

PLO = 0dBm

EN = High

IMAGE REJECTION

LO FEED-

THROUGH

CALIBRATED WITH PRF = –10dBm

I AND Q BASEBAND VOLTAGE (VP-P, DIFF)

PRF, LOFT (dBm), IR (dBc)

–30

–10

5568 F15

–50

–70

–40

–20

–60

–80

–90 1235

VCC = 5V

EN = High

fLO = 850MHz

fBB, 1 = 2MHz, 0°

fBB, 0 = 2MHz, 90°

fRF = fBB + fLO

PLO = 0dBm

–40°C

–40°C–40°C

85°C

LOFT

PRF

25°C

APPLICATIO S I FOR ATIO

WUUU

interface circuit drawn in Figure 3, modiﬁ ed by pulling

resistors R5 and R6 to a –5V supply and adjusting their

values to 550Ω, with T1 omitted.

Another method to reduce current mismatch between

the currents ﬂ owing in the BBIP and BBIM pins (or the

BBQP and BBQM pins) is to use a 1:1 transformer with

the two windings in the DC path (T1 in Figure 3). For DC,

the transformer forms a short, and for AC, the transformer

will reduce the common mode current component, which

forces the two currents to be better matched. Alternatively,

a transformer with 1:2 impedance ratio can be used, which

gives a convenient DC separation between primary and

secondary in combination with the required impedance

match. The secondary center tap should not be connected,

which allows some voltage swing if there is a single-ended

input impedance difference at the baseband pins. As a

result, both currents will be equal. The disadvantage is that

there is no DC coupling, so the LO feedthrough calibration

cannot be performed via the BB connections. After calibra-

tion when the temperature changes, the LO feedthrough

and the image rejection performance will change. This is

illustrated in Figure 14. The LO feedthrough and image

rejection can also change as a function of the baseband

drive level, as is depicted in Figure 15. In Figures 16 and

17 the LO feedthrough and image rejection vs LO power

are shown.

Figure 15. LO Feedthrough and Image Rejection

vs Baseband Drive Voltage after Calibration at 25°C

Figure 14. LO Feedthrough and Image Rejection

vs Temperature after Calibration at 25°C

Figure 16. LO Feedthrough vs LO Power

LO INPUT POWER (dBm)

–20

–50

LO FEEDTHROUGH (dBm)

–46

–48

–44

–42

–16 –12 –8 –4

5568 G16

048

5.5V, 25°C

4.5V, 25°C

5V, 85°C

5V, 25°C

5V, –40°C

fLO = 850MHz

LO INPUT POWER (dBm)

–20

–55

IMAGE REJECTION (dBc)

–45

–50

–40

–25

–30

–35

–16 –12 –8 –4

5568 G17

048

5.5V, 25°C

4.5V, 25°C

5V, 85°C

5V, 25°C

5V, –40°C

fLO = 850MHz

PRF = –10dBm

Figure 17. Image Rejection vs LO Power

LT5568

5568f

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However,

no responsibility is assumed for its use. Linear Technology Corporation makes no representation that

the interconnection of its circuits as described herein will not infringe on existing patent rights.

PACKAGE DESCRIPTIO

UF Package

16-Lead Plastic QFN (4mm × 4mm)

(Reference LTC DWG # 05-08-1692)

4.00 ± 0.10

(4 SIDES)

NOTE:

1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WGGC)

2. DRAWING NOT TO SCALE

3. ALL DIMENSIONS ARE IN MILLIMETERS

4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE

MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE

5. EXPOSED PAD SHALL BE SOLDER PLATED

6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION

ON THE TOP AND BOTTOM OF PACKAGE

PIN 1

TOP MARK

(NOTE 6)

0.55 ± 0.20

1615

BOTTOM VIEW—EXPOSED PAD

2.15 ± 0.10

(4-SIDES)

0.75 ± 0.05 R = 0.115

TYP

0.30 ± 0.05

0.65 BSC

0.200 REF

0.00 – 0.05

(UF16) QFN 10-04

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

0.72 ±0.05

0.30 ±0.05

0.65 BSC

2.15 ± 0.05

(4 SIDES)

2.90 ± 0.05

4.35 ± 0.05

PACKAGE OUTLINE

PIN 1 NOTCH R = 0.20 TYP

OR 0.35 × 45° CHAMFER

LT5568

5568f

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com

LT/TP 1005 500 • PRINTED IN USA

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PART NUMBER DESCRIPTION COMMENTS

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24.2dBm IIP3 at 1.95GHz, NF = 12.5dB, 3.15V to 5.25V Supply, Single-Ended LO

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LT5522 600MHz to 2.7GHz High Signal Level

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4.5V to 5.25V Supply, 25dBm IIP3 at 900MHz, NF = 12.5dB, 50Ω Single-Ended RF

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450MHz Bandwidth, 40dBm OIP3, 4.5dB to 27dB Gain Control

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–65dBm LO-RF Leakage

LT5527 400MHz to 3.7GHz High Signal Level

Downconverting Mixer

IIP3 = 23.5dBm and NF = 12.5dB at 1900MHz, 4.5V to 5.25V Supply, ICC = 78mA

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21.8dBm OIP3 at 2GHz, –159.3dBm/Hz Noise Floor, 50Ω, 0.5VDC Baseband Interface,

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300MHz to 3GHz, Temperature Compensated, 2.7V to 6V Supply

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LT5534 50MHz to 3GHz Loq RF Power Detector with

60dB Dynamic Range

±1dB Output Variation over Temperature, 38ns Response Time

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