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FEATURES

LT5528 1.5GHz to 2.4GHz High Linearity Direct Quadrature Modulator DESCRIPTIO
The LT(R)5528 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 configured as an image reject up-converting 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 50 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.
, LTC and LT are registered trademarks of Linear Technology Corporation.

Direct Conversion to 1.5GHz to 2.4GHz High OIP3: 21.8dBm at 2GHz Low Output Noise Floor at 5MHz Offset: No RF: -159.3dBm/Hz POUT = 4dBm: -151.8dBm/Hz 4-Ch W-CDMA ACPR: -66dBc at 2.14GHz Integrated LO Buffer and LO Quadrature Phase Generator 50 AC-Coupled Single-Ended LO and RF Ports 50 DC Interface to Baseband Inputs Low Carrier Leakage: -42dBm at 2GHz High Image Rejection: 45dB at 2GHz 16-Lead QFN 4mm x 4mm Package
APPLICATIO S

Infrastructure Tx for DCS, PCS and UMTS Bands Image Reject Up-Converters for PCS and UMTS Bands Low-Noise Variable Phase-Shifter for 1.5GHz to 2.4GHz Local Oscillator Signals
TYPICAL APPLICATIO
1.5GHz to 2.4GHz Direct Conversion Transmitter Application with LO Feed-Through and Image Calibration Loop
VCC 8, 13 14 I-DAC 16 V-I I-CHANNEL EN 1 Q-CHANNEL V-I CAL BASEBAND DSP 2, 4, 6, 9, 10, 12, 15, 17 3 VCO/SYNTHESIZER 0 90 7 Q-DAC 5 BALUN 11 PA LT5528 5V RF = 1.5GHz TO 2.4GHz
W-CDMA ACPR, AltCPR and Noise vs RF Output Power at 2140MHz for 1, 2 and 4 Channels
-55 DOWNLINK TEST MODEL 64 DPCH -140 NOISE FLOOR AT 30MHz OFFSET (dBm/Hz)
-60 ACPR, AltCPR (dBc) 4-CH ACPR 2-CH AltCPR -70 1-CH AltCPR
-65
LO FEED-THROUGH CAL OUT IMAGE CAL OUT
-75 4-CH NOISE 1-CH NOISE
-38 -34 -30 -26 -22 -18
ADC
5528 TA01a
-80 -42
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-145
2-CH ACPR
-150
4-CH AltCPR 1-CH ACPR -155
-160
-165 -14
RF OUTPUT POWER PER CARRIER (dBm)
5528 TA01b
5528f
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LT5528 ABSOLUTE
(Note 1)
TOP VIEW
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
ORDER PART NUMBER
12 GND 17 11 RF 10 GND 9 5 BBMQ 6 GND 7 BBPQ 8 VCC GND BBMI BBPI GND 16 15 14 13 EN 1 GND 2 LO 3 GND 4 VCC
Supply Voltage .........................................................5.5V Common-Mode Level of BBPI, BBMI and BBPQ, BBMQ .......................................................2.5V Operating Ambient Temperature (Note 2) ...............................................-40C to 85C Storage Temperature Range.................. -65C to 125C Voltage on Any Pin Not to Exceed...................... -500mV to VCC + 500mV
LT5528EUF
UF PART MARKING 5528A
UF PACKAGE 16-LEAD (4mm x 4mm) PLASTIC QFN
TJMAX = 125C, JA = 37C/W EXPOSED PAD IS GROUND (PIN 17) MUST BE SOLDERED TO PCB.
Consult LTC Marketing for parts specified with wider operating temperature ranges.
VCC = 5V, EN = High, TA = 25C, fLO = 2GHz, fRF = 2.002GHz, PLO = 0dBm. BBPI, BBMI, BBPQ, BBMQ inputs 0.525VDC, Baseband Input Frequency = 2MHz, I&Q 90 shifted (upper sideband selection). PRF, OUT = -10dBm, unless otherwise noted. (Note 3)
SYMBOL RF Output (RF) fRF S22, ON S22, OFF NFloor PARAMETER RF Frequency Range RF Frequency Range RF Output Return Loss RF Output Return Loss RF Output Noise Floor CONDITIONS -3dB Bandwidth -1dB Bandwidth EN = High (Note 6) EN = Low (Note 6) No Input Signal (Note 8) POUT = 4dBm (Note 9) POUT = 4dBm (Note 10) POUT/PIN, I&Q 20 * Log (VOUT, 50/VIN, DIFF, I or Q) 1VP-P DIFF CW Signal, I and Q (Note 17) (Note 7) (Notes 13, 14) (Notes 13, 15) (Note 16) EN = High, PLO = 0dBm (Note 16) EN = Low, PLO = 0dBm (Note 16) MIN TYP 1.5 to 2.4 1.7 to 2.2 -15 -12 -159.3 -151.8 -151.8 -6.5 -6 -2.1 -28 7.9 49 21.8 -45 -42 -57.8 1.5 to 2.4 0 -17 -5.5 14.4 20.4 -10 MAX UNITS GHz GHz dB dB dBm/Hz dBm/Hz dBm/Hz dB dB dBm dB dBm dBm dBm dBc dBm dBm GHz dBm dB dB dB dB dBm
ELECTRICAL CHARACTERISTICS
GP GV POUT G3LO vs LO OP1dB OIP2 OIP3 IR LOFT LO Input (LO) fLO PLO S11, ON S11, OFF NFLO GLO IIP3LO
Conversion Power Gain Conversion Voltage Gain Absolute Output Power 3 * LO Conversion Gain Difference Output 1dB Compression Output 2nd Order Intercept Output 3rd Order Intercept Image Rejection Carrier Leakage (LO Feed-Through) LO Frequency Range LO Input Power LO Input Return Loss LO Input Return Loss LO Input Referred Noise Figure LO to RF Small Signal Gain LO Input 3rd Order Intercept
-10 EN = High (Note 6) EN = Low (Note 6) (Note 5) at 2GHz (Note 5) at 2GHz (Note 5) at 2GHz
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LT5528 ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER Baseband Inputs (BBPI, BBMI, BBPQ, BBMQ) BWBB Baseband Bandwidth VCMBB RIN, SE PLO2BB IP1dB GI/Q I/Q Power Supply (VCC) VCC ICC, ON DC Common Mode Voltage Single-Ended Input Resistance Carrier Feed-Through on BB Input 1dB Compression Point I/Q Absolute Gain Imbalance I/Q Absolute Phase Imbalance Supply Voltage EN = High EN = 0V EN = Low to High (Note 11) EN = High to Low (Note 12) EN = High EN = 5V EN = Low 1.0 240 0.5
VCC = 5V, EN = High, TA = 25C, fLO = 2GHz, fRF = 2.002GHz, PLO = 0dBm. BBPI, BBMI, BBPQ, BBMQ inputs 0.525VDC, Baseband Input Frequency = 2MHz, I&Q 90 shifted (upper sideband selection). PRF, OUT = -10dBm, unless otherwise noted. (Note 3)
CONDITIONS -3dB Bandwidth (Note 4) (Note 4) POUT = 0 (Note 4) Differential Peak-to-Peak (Note 7) MIN TYP 400 0.525 45 -40 3.2 0.05 0.5 4.5 5 125 0.05 0.25 1.3 5.25 145 50 MAX UNITS MHz V dBm VP-P, DIFF dB Deg V mA A s s V A V
Supply Current ICC, OFF Supply Current, Sleep Mode tON Turn-On Time tOFF Turn-Off Time Enable (EN), Low = Off, High = On Enable Input High Voltage Input High Current Sleep Input Low Voltage
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: Specifications over the -40C to 85C temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: Tests are performed as shown in the configuration 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 final 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 feed-through 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 = 2GHz.
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VCC = 5V, EN = High, TA = 25C, fLO = 2.14GHz, PLO = 0dBm. BBPI, BBMI, BBPQ, BBMQ inputs 0.525VDC, 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 and Output 1dB Compression vs LO Frequency and Supply Voltage
10 5 GAIN (dB), OP1dB (dBm) 0 -5 -10 GAIN -15 -20 1.3 4.5V 5V 5.5V 1.5 1.7 1.9 2.1 2.3 LO FREQUENCY (GHz) 2.5 2.7
TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Supply Voltage
140 85C 5 25C 120 -40C 110 GAIN (dB), OP1dB (dBm) SUPPLY CURRENT (mA) 130 0 -5 -10 10
100 4.5
5.0 SUPPLY VOLTAGE (V)
Output IP3 and Noise Floor vs LO Frequency and Temperature
26 24 22 20 OIP3 (dBm) 18 16 14 12 10 8 6 1.3 1.5 1.7 1.9 2.1 2.3 LO FREQUENCY (GHz) 2.5 NOISE FLOOR NO BASEBAND SIGNAL 20MHz OFFSET NOISE OIP3 fBB, 1 = 2MHz fBB, 2 = 2.1MHz -142 -40C 25C -144 85C -146 NOISE FLOOR (dBm/Hz) -148 -150 -152 -154 -156 -158 -160 -162 2.7 26 24 22 20 OIP3 (dBm) 18 16 14 12 10 8
-150 -152 -154
OIP2 (dBm)
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5.5
5528 G01 5528 G04
Gain and Output 1dB Compression vs LO Frequency and Temperature
OP1dB
OP1dB
GAIN -15 -20 1.3 -40C 25C 85C 1.5 1.7 1.9 2.1 2.3 LO FREQUENCY (GHz) 2.5 2.7
5528 G02
5528 G03
Output IP3 and Noise Floor vs LO Frequency and Supply Voltage
-142 4.5V 5V -144 5.5V -146 NOISE FLOOR (dBm/Hz) OIP3 fBB, 1 = 2MHz fBB, 2 = 2.1MHz -148 65 60 55 50 45 40
Output IP2 vs LO Frequency
NOISE FLOOR NO BASEBAND SIGNAL 20MHz OFFSET NOISE
-156 -158 -160
6 1.3
1.5
1.7 1.9 2.1 2.3 LO FREQUENCY (GHz)
2.5
-162 2.7
35 1.3
4.5V, 25C 5V, -40C 5V, 25C 5V, 85C 5.5V, 25C 1.5 1.7 1.9 2.1 2.3 LO FREQUENCY (GHz) 2.5 2.7
5528 G05
fIM2 = fBB,1 + fBB,2 + fLO fBB, 1 = 2MHz
fBB, 2 = 2.1MHz
5528 G06
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LT5528 TYPICAL PERFOR A CE CHARACTERISTICS
VCC = 5V, EN = High, TA = 25C, fLO = 2.14GHz, PLO = 0dBm. BBPI, BBMI, BBPQ, BBMQ inputs 0.525VDC, 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)
2 * LO Leakage to RF Output vs 2 * LO Frequency
-25 -30 P(2 * LO) (dBm) P(3 * LO) (dBm) -35 -40 -45 -50 -55 2.6 -30 -35 -40 -45 -50 -55 -60 -65
4.5V, 25C 5V, -40C 5V, 25C 5V, 85C 5.5V, 25C 3.0 3.4 3.8 4.2 4.6 5.0 2 * LO FREQUENCY (GHz) 5.4
-70 3.9
4.5V, 25C 5V, -40C 5V, 25C 5V, 85C 5.5V, 25C 4.5 5.1 5.7 6.3 6.9 7.5 3 * LO FREQUENCY (GHz) 8.1
LOFT (dBm)
Image Rejection vs LO Frequency
-26 -30 IMAGE REJECTION (dBc) -32 -34 -36 -38 -40 -42 -44 -46 -48 1.3 1.5 1.7 1.9 2.1 2.3 LO FREQUENCY (GHz) 2.5 2.7 ABSOLUTE I/Q GAIN IMBALANCE (dB) -28 4.5V, 25C 5V, -40C 5V, 25C 5V, 85C 5.5V, 25C 0.3
ABSOLUTE I/Q PHASE IMBALANCE (DEG)
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3 * LO Leakage to RF Output vs 3 * LO Frequency
-36 -38 -40 -42 -44 -46 -48 -50 -52
LO to RF Output Feed-Through vs LO Frequency
4.5V, 25C 5V, -40C 5V, 25C 5V, 85C 5.5V, 25C
-54 1.3
1.5
1.7 1.9 2.1 2.3 LO FREQUENCY (GHz)
2.5
2.7
5528 G07
5528 G08
5528 G09
Absolute I/Q Gain Imbalance vs LO Frequency
4.5V, 25C 5V, -40C 5V, 25C 5V, 85C 5.5V, 25C 5
Absolute I/Q Phase Imbalance vs LO Frequency
4.5V, 25C 5V, -40C 5V, 25C 5V, 85C 5.5V, 25C
4
0.2
3
2
0.1
1
0 1.3
1.5
1.7 1.9 2.1 2.3 LO FREQUENCY (GHz)
2.5
2.7
0 1.3
1.5
1.7 1.9 2.1 2.3 LO FREQUENCY (GHz)
2.5
2.7
5528 G10
5528 G11
5528 G12
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LT5528
VCC = 5V, EN = High, TA = 25C, fLO = 2.14GHz, PLO = 0dBm. BBPI, BBMI, BBPQ, BBMQ inputs 0.525VDC, 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) RF Output Power, HD2 and HD3 at 2140MHz vs Baseband Voltage and Temperature
-10 RF -20 HD3 HD2, HD3 (dBc) -30 -40 HD2 -50 -60 -70 -30 -40C -40 25C 85C -50 1 2 3 4 5 I AND Q BASEBAND VOLTAGE (VP-P, DIFF) -10 -20 0 RF OUTPUT POWER (dBm) 10
TYPICAL PERFOR A CE CHARACTERISTICS
Gain vs LO Power
-4 -6 -8 OIP3 (dBm) 4.5V, 25C 5V, -40C 5V, 25C 5V, 85C 5.5V, 25C -16 -12 -8 -4 0 LO POWER (dBm) 4 8
5528 G13
GAIN (dB)
-10 -12 -14 -16 -18 -20 -20
RF Output Power, HD2 and HD3 at 2140MHz vs Baseband Voltage and Supply Voltage
-10 RF -20 HD3 HD2, HD3 (dBc) -30 -40 HD2 -50 -60 -70 -30 4.5V -40 5V 5.5V -50 1 2 3 4 5 I AND Q BASEBAND VOLTAGE (VP-P, DIFF) -10 -20 0 RF OUTPUT POWER (dBm) LOFT (dBm), IR (dBc) -30 10 -25
0
fBBI = 2MHz, 0 fBBQ = 2MHz, 90 HD2 = MAX POWER AT fLO + 2 * fBB OR fLO - 2 * fBB HD3 = MAX POWER AT fLO + 3 * fBB OR fLO - 3 * fBB
5528 G16
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Output IP3 vs LO Power
22 20 18 16 14 12 10 8 6 4 2 0 -20 -16 -12 -8 -4 0 LO POWER (dBm) 4.5V, 25C 5V, -40C 5V, 25C 5V, 85C 5.5V, 25C 4 8
0
fBB, 1 = 2MHz fBB, 2 = 2.1MHz
5528 G14
fBBI = 2MHz, 0 fBBQ = 2MHz, 90 HD2 = MAX POWER AT fLO + 2 * fBB OR fLO - 2 * fBB HD3 = MAX POWER AT fLO + 3 * fBB OR fLO - 3 * fBB
5528 G15
LO Feed-Through and Image Rejection at 2140MHz vs Baseband Voltage and Temperature
-40C 25C 85C
LOFT
-35
-40 IR -45
-50
0
1 2 3 4 5 I AND Q BASEBAND VOLTAGE (VP-P, DIFF)
fBBI = 2MHz, 0 fBBQ = 2MHz, 90
5528 G17
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LT5528 TYPICAL PERFOR A CE CHARACTERISTICS
LO Feed-Through and Image Rejection at 2140MHz vs Baseband Voltage and Supply Voltage
-25 4.5V 5V 5.5V 0
VCC = 5V, EN = High, TA = 25C, fLO = 2.14GHz, PLO = 0dBm. BBPI, BBMI, BBPQ, BBMQ inputs 0.525VDC, 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) LO and RF Port Return Loss vs RF Frequency
LO PORT, EN = LOW RF OUTPUT POWER (dBm) 0 -2 LOFT -10 -4 -6 -8 4.5V, 25C 5V, -40C 5V, 25C 5V, 85C 5.5V, 25C
-30 LOFT (dBm), IR (dBc)
S11 (dB)
-35
-40 IR -45
-50
0
1 2 3 4 5 I AND Q BASEBAND VOLTAGE (VP-P, DIFF)
fBBI = 2MHz, 0 fBBQ = 2MHz, 90
PI FU CTIO S
EN (Pin 1): Enable Input. When the EN 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 internally. 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 singleended input with approximately 50 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-channel, each 45 input impedance. Internally biased at about 0.525V. Applied voltage must stay below 2.5V. VCC (Pins 8, 13): Power Supply. Pins 8 and 13 are connected to each other internally. It is recommended to use 0.1F 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 50 output 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. BBPI, BBMI (Pins 14, 16): Baseband Inputs for the I-channel, each with 45 input impedance. These pins are internally biased at about 0.525V. Applied voltage must stay below 2.5V. Exposed Pad (Pin 17): Ground. This pin must be soldered to the printed circuit board ground plane.
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RF Output Power vs RF Frequency at 1VP-P Differential Baseband Drive
-20
-30
RF PORT, EN = HIGH, PLO = OFF RF PORT, EN = HIGH, PLO = 0dBm
LO PORT, EN = HIGH
-10 -12
-40
RF PORT, EN = LOW
-50 1.3
1.5
1.7 1.9 2.1 2.3 RF FREQUENCY (GHz)
2.5
2.7
VBBI = 1VP-P, DIFF VBBQ = 1VP-P, DIFF -14 1.3 1.5 1.7 1.9 2.1 2.3 RF FREQUENCY (GHz)
2.5
2.7
5528 G19
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5528 G18
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LT5528 BLOCK DIAGRA W
VCC 8 BBPI 14 BBMI 16 V-I 11 RF 0 90 BBPQ 7 BBMQ 5 V-I BALUN 1 EN 13 LT5528 2 4 GND 6 9 3 LO 10 12 15 17
5528 BD
GND
APPLICATIO S I FOR ATIO
The LT5528 consists of I and Q input differential voltageto-current converters, I and Q up-conversion mixers, an RF output balun, an LO quadrature phase generator and LO buffers.
RF VCC = 5V C BALUN FROM Q LOMI LOPI LT5528
R1A 20 BBPI 12pF
R1B 23 CM R3 VREF = 0.52V
R2B 23
R4
BBMI
5528 F01
GND
Figure 1. Simplified Circuit Schematic of the LT5528 (Only I-Half is Drawn)
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External I and Q baseband signals are applied to the differential 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 50. 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 inphase 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, 50-matched and AC coupled. Baseband Interface The baseband inputs (BBPI, BBMI), (BBPQ, BBMQ) present a differential input impedance of about 90. At each of the four baseband inputs, a first-order low-pass filter using 20
12pF
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LT5528 APPLICATIO S I FOR ATIO
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 0.52V and is approximately constant over temperature. It is important that the applied common-mode voltage level of the I and Q inputs is about 0.52V in order to properly bias the LT5528. 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 0.26V to match the LT5528 internal bias, because for DC signals, there is no -6dB source-load voltage division (see Figure 2).
50 0.26VDC 0.52VDC GENERATOR 50 50 0.52VDC 0.52VDC GENERATOR 0.52VDC LT5528
5528 F02
+ -
+ -
Figure 2. DC Voltage Levels for a Generator Programmed at 0.26VDC for a 50 Load and the LT5528 as a Load
0.5V 0mA TO 20mA DAC 0mA TO 20mA GND R5, 50 C1 R6, 50 0.5V
L1A
C2 L1B
Figure 3. LT5528 5th Order Filtered Baseband Interface with Common DAC (Only I-Channel is Shown)
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It is recommended that the part be driven differentially; otherwise, the even-order distortion products will degrade the overall linearity severely. Typically, a DAC will be the signal source for the LT5528. To prevent aliasing, a filter should be placed between the DAC output and the LT5528's baseband inputs. In Figure 3, an example interface schematic shows a commonly used DAC output interface followed by a passive 5th order ladder filter. 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 feed-through. Optionally, transformer T1 can be inserted to improve the current balance in the BBPI and BBMI pins. This will improve the second-order distortion performance (OIP2). The maximum single sideband CW RF output power at 2GHz using 20mA drive to both I and Q channels with the configuration shown in Figure 3 is about -2.5dBm. The maximum CW output power can be increased by connecting resistors R5 and R6 to -5V instead of GND, and changing their values to 550. In that case, the maximum single sideband CW RF output power at 2GHz will be about 2.3dBm. In addition, the ladder filter component values require adjustment for a higher source impedance.
VCC = 5V RF = -2.5dBm, MAX C LOMI LOPI BALUN LT5528
+ -
L2A
OPTIONAL T1 1:1
BBPI
R1 45 CM R3 VREF = 0.52V
R2 45
*
C3
R4
*
L2B
BBMI
5528 F03
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LT5528 APPLICATIO S I FOR ATIO
LO Section The internal LO input amplifier performs single-ended to differential conversion of the LO input signal. Figure 4 shows the equivalent circuit schematic of the LO input.
VCC 20pF LO INPUT ZIN 57
5528 F04
Figure 4. Equivalent Circuit Schematic of the LO Input
The internal, differential LO signal is then split into inphase 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 fixed, and is independent of start-up conditions. The phase shifters are designed to deliver accurate quadrature signals for an LO frequency near 2GHz. For frequencies significantly below 1.8GHz or above 2.4GHz, the quadrature accuracy will diminish, causing the image rejection to degrade. The LO pin input impedance is about 50, and the recommended LO input power is 0dBm. For lower LO input power, the gain, OIP2, OIP3 and dynamicrange will degrade, especially below -5dBm and at TA = 85C. For high LO input power (e.g. 5dBm), the LO feedthrough will increase with no improvement in linearity or gain. 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 4GHz) and third harmonics (at 6GHz) at -20dBc level, the introduced signal at the image frequency is about -56dBc or lower, corresponding to an excess phase shift much below 1 degree. For the second and third 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 17dB over the 1.7GHz to 2.3GHz range. Table 1 shows the LO port input impedance vs. frequency.
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Table 1. LO Port Input Impedance vs Frequency for EN = High
Frequency MHz 1000 1400 1600 1800 2000 2200 2400 2600 Input Impedance 49.9 + j18.5 68.1 + j8.8 71.0 + j2.0 70.0 - j8.6 62.0 - j12.8 53.8 - j13.6 47.3 - j12.4 41.1 - j12.0 S11 Mag 0.182 0.171 0.175 0.182 0.156 0.135 0.128 0.161 Angle 80 22 4.8 -6.6 -40 -66 -95 -119
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If the part is in shut-down 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
Frequency MHz 1000 1400 1600 1800 2000 2200 2400 2600 Input Impedance 46.6 + j47.6 136 + j44.5 157 - j24.5 114 - j70.6 70.7 - j72.1 45.3 - j59.0 31.2 - j45.2 22.8 - j34.2 S11 Mag 0.443 0.507 0.526 0.533 0.533 0.528 0.527 0.543 Angle 67.8 13.8 -6.2 -24.6 -43.2 -62.8 -83.5 -103
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 50. 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 MHz 1000 1400 1600 1800 2000 2200 2400 2600 Output Impedance 23.1 + j7.9 34.4 + j20.7 45.8 + j22.3 54.5 + j12.4 48.7 + j1.7 39.1 + j1.0 32.9 + j4.4 29.7 + j7.4 S22 Mag 0.382 0.298 0.231 0.125 0.022 0.123 0.213 0.269 Angle 158 113 87.6 63.2 127 174 163 155
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LT5528 APPLICATIO S I FOR ATIO
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 MHz 1000 1400 1600 1800 2000 2200 2400 2600 Output Impedance 23.7 + j8.1 37.7 + j18.5 47.0 + j14.3 46.0 + j5.5 39.2 + j3.7 34.2 + j6.2 31.0 + j9.4 29.6 + j11.6 S22 Mag 0.371 0.248 0.149 0.071 0.127 0.201 0.260 0.292 Angle 157 112 93.6 123 159 154 147 142
For EN = Low the S22 is given in Table 5.
Table 5. RF Port Output Impedance vs Frequency for EN = Low
Frequency MHz 1000 1400 1600 1800 2000 2200 2400 2600 Output Impedance 22.8 + j7.7 32.4 + j20.8 42.4 + j25.1 54.6 + j20.1 55.3 + j6.0 44.7 + j0.0 36.0 + j1.9 31.3 + j4.8 S22 Mag 0.386 0.321 0.274 0.193 0.076 0.056 0.164 0.237 Angle 158 116 91.7 66.2 45.3 180 171 162
To improve S22 for lower frequencies, a shunt capacitor can be added to the output. At higher frequencies, a shunt inductor can improve the S22. Figure 5 shows the equivalent circuit schematic of the RF output. 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 50 termination impedance is connected directly to ground. To prevent this, a
VCC 20pF RF OUTPUT 3nH 21pF
5528 F05
52.5
Figure 5. Equivalent Circuit Schematic of the RF Output
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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 simplified schematic of the EN pin interface. The voltage necessary to turn on the LT5528 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 guaranteed 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.
VCC EN 75k 25k
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Figure 6. EN Pin Interface
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.
J1 BBIM J2 BBIP VCC 16 VCC EN LO IN R1 100 1 2 J4 3 4 EN GND LO GND LT5528 15 14 13 GND RF GND GND 12 11 10 9 17 J3 RF OUT C2 100nF
BBMI GND BBPI VCC
GND BBMQ GND BBPQ VCC 5 J5 BBQM GND 6 7 8
C1 100nF
J6 BBQP
BOARD NUMBER: DC729A
5528 F07
Figure 7. Evaluation Circuit Schematic
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LT5528 APPLICATIO S I FOR ATIO
Additionally, the exposed pad provides heat sinking for the part and minimizes the possibility of the chip overheating. If improved LO and Image suppression are required, an LO feed-through calibration and an Image suppression calibration can be performed. The evaluation board schematic of the calibration hardware, the calibration procedure and
Figure 8. Component Side Silk Screen of Evaluation Board
Figure 10. Bottom Side Silk Screen of Evaluation Board
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the results are described in an application note. R1 (optional) limits the Enable pin current in the event that the Enable pin is pulled high while the VCC inputs are low. In Figures 8, 9, 10 and 11, the silk screens and the PCB board layout are shown.
Figure 9. Component Side Layout of Evaluation Board Figure 11. Bottom Side Layout of Evaluation Board
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LT5528 APPLICATIO S I FOR ATIO
Application Measurements The LT5528 is recommended for base-station applications using various modulation formats. Figure 12 shows a typical application. The CAL box in Figure 12 allows for LO feed-through and Image suppression calibration. Figure 13 shows the ACPR performance for W-CDMA using one, two or four channel modulation. Figures 14, 15 and 16 illustrate the 1-, 2- and 4-channel W-CDMA measurement. To calculate ACPR, a correction is made for the spectrum analyzer noise floor. 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 obtained.
VCC 8, 13 14 I-DAC 16 V-I I-CHANNEL EN 1 Q-CHANNEL V-I CAL BASEBAND GENERATOR 2, 4, 6, 9, 10, 12, 15, 17 3 VCO/SYNTHESIZER 0 90 7 Q-DAC 5 BALUN 11 PA LT5528 5V RF = 1.5GHz TO 2.4GHz -55 DOWNLINK TEST MODEL 64 DPCH -140 NOISE FLOOR AT 30MHz OFFSET (dBm/Hz)
ACPR, AltCPR (dBc)
ADC
5528 F12
Figure 12. 1.5GHz to 2.4GHz Direct Conversion Transmitter Application with LO Feed-Through and Image Calibration Loop
-30 -40 POWER IN 30kHz BW (dBm) -50 -60 -70 -80 -90 -100 -110 -120 2127.5 UNCORRECTED SPECTRUM
DOWNLINK TEST MODEL 64 DPCH POWER IN 30kHz BW (dBm)
-30
-60 -70 -80 -90 -100 -110 SYSTEM NOISE FLOOR 2130 2135 2140 2145 2150 RF FREQUENCY (MHz) 2155
5528 F15
POWER IN 30kHz BW (dBm)
DOWNLINK TEST -40 MODEL 64 DPCH -50
CORRECTED SPECTRUM
SYSTEM NOISE FLOOR 2132.5 2137.5 2142.5 2147.5 RF FREQUENCY (MHz) 2152.5
5528 F14
-120 2125
Figure 14: 1-Channel W-CDMA Spectrum
Figure 15: 2-Channel W-CDMA Spectrum
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Because of the LT5528's very high dynamic-range, the test equipment can limit the accuracy of the ACPR measurement. 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 LT5528's common-base stage, and will flow to the mixer upper switches. This can be seen in Figure 1 where the
-60 4-CH ACPR 2-CH AltCPR -70 1-CH AltCPR -145 -65 2-CH ACPR -150 LO FEED-THROUGH CAL OUT IMAGE CAL OUT 4-CH AltCPR 1-CH ACPR -155 -75 4-CH NOISE 1-CH NOISE -160 -80 -42 -165 -26 -22 -18 -14 RF OUTPUT POWER PER CARRIER (dBm)
-38 -34 -30
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Figure 13: W-CDMA APCR, AltCPR and Noise vs RF Output Power at 2140MHz for 1, 2 and 4 Channels
-40
DOWNLINK -50 TEST MODEL 64 -60 DPCH -70 -80 -90 -100 -110 -120 SYSTEM NOISE FLOOR CORRECTED SPECTRUM 2125 2135 2145 2155 RF FREQUENCY (MHz) 2165
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UNCORRECTED SPECTRUM
CORRECTED SPECTRUM
UNCORRECTED SPECTRUM
CORRECTED SPECTRUM
-130 2115
Figure 16: 4-Channel W-CDMA Spectrum
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LT5528 APPLICATIO S I FOR ATIO
internal circuit of the LT5528 is drawn. For best results, a high ohmic source is recommended; for example, the interface circuit drawn in Figure 3, modified by pulling resistors R5 and R6 to a -5V supply and adjusting their values to 550, with T1 omitted. Another method to reduce current mismatch between the currents flowing 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
-50 -55 LOFT (dBm), IR (dB) -60 -65 -70 IMAGE REJECTION -75 -80 -85 -40 CALIBRATED WITH PRF = -10dBm -20 0 20 40 TEMPERATURE (C) fLO = 2.14GHz fRF = fBB + fLO PLO = 0dBm
5528 F18
LO FEED-THROUGH LOFT (dBm), IR (dBc)
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80
EN = HIGH VCC = 5V fBBI = 2MHz, 0 fBBQ = 2MHz, 90
Figure 17: LO Feed-Through and Image Rejection vs Temperature after Calibration at 25C
10 PRF, EACH TONE (dBm), IM2, IM3 (dBm) 0 -10 -20 -30 -40 -50 -60 -70 -80
-90 1 0.1 10 I AND Q BASEBAND VOLTAGE (VP-P, DIFF EACH TONE) EN = HIGH fLO = 2.14GHz VCC = 5V fRF = fBB + fLO PLO = 0dBm fBBI = 2MHz, 2.1MHz, 0 fBBQ = 2MHz, 2.1MHz, 90 IM2 = POWER AT fLO + 4.1MHz IM3 = MAX POWER AT fLO + 1.9MHz OR fLO + 2.2MHz
Figure 19: RF Two-Tone Power, IM2 and IM3 at 2140MHz vs Baseband Voltage
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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 singleended 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 feed-through calibration cannot be performed via the BB connections. After calibration when the temperature changes, the LO feed-through and the Image Rejection performance will change. This is illustrated in Figure 17. The LO feed-through and Image Rejection can also change as a function of the baseband drive level, as is depicted in Figure 18. The RF output power, IM2 and IM3 vs a two-tone baseband drive are given in Figure 19.
-20 -30 -40 -50 -60 -70 -80 -90 IR LOFT PRF 10 0 -10 PRF (dBm) -20 -30 -40 -40C -50 25C 85C -60 1 2 3 4 5 I AND Q BASEBAND VOLTAGE (VP-P, DIFF) fLO = 2.14GHz fRF = fBB + fLO PLO = 0dBm
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EN = HIGH VCC = 5V fBBI = 2MHz, 0 fBBQ = 2MHz, 90
Figure 18: LO Feed-Through and Image Rejection vs Baseband Drive Voltage after Calibration at 25C
PRF
IM3
IM2
-40C 25C 85C
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LT5528 PACKAGE DESCRIPTIO U
UF Package 16-Lead Plastic QFN (4mm x 4mm)
(Reference LTC DWG # 05-08-1692)
0.72 0.05 PACKAGE OUTLINE 0.30 0.05 0.65 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS BOTTOM VIEW--EXPOSED PAD 4.00 0.10 (4 SIDES) PIN 1 TOP MARK (NOTE 6) 2.15 0.10 (4-SIDES) 0.75 0.05 R = 0.115 TYP 0.55 0.20 15 16 1 2
(UF) QFN 1103
4.35 0.05 2.15 0.05 2.90 0.05 (4 SIDES)
0.200 REF 0.00 - 0.05 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
0.30 0.05 0.65 BSC
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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.
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RF Power Detectors LT5504 LTC5505 LTC5507 LTC5508 LTC5509 LTC5530 LTC5531 LTC5532 LT5534
Low Voltage RF Building Blocks LT5500 LT5502 LT5503 LT5506 LT5546 1.8V to 5.25V Supply, Dual-Gain LNA, Mixer, LO Buffer 1.8V to 5.25V Supply, 70MHz to 400MHz IF, 84dB Limiting Gain, 90dB RSSI Range 1.8V to 5.25V Supply, Four-Step RF Power Control, 120MHz Modulation Bandwidth 1.8V to 5.25V Supply, 40MHz to 500MHz IF, -4dB to 57dB Linear Power Gain, 8.8MHz Baseband Bandwidth
500MHz Quadrature Demodulator with VGA and 17MHz Baseband Bandwidth, 40MHz to 500MHz IF, 1.8V to 5.25V Supply, -7dB to 17MHz Baseband Bandwidth 56dB Linear Power Gain 12-Bit, 80Msps 14-Bit, 80Msps 500MHz BW S/H, 71.8dB SNR 500MHz BW S/H, 75.5dB SNR
5528f LT/TP 1104 1K * PRINTED IN USA
Wide Bandwidth ADCs LTC1749 LTC1750
16 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2004

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