CN-0285 [ADI]
Broadband Low Error Vector Magnitude (EVM) Direct Conversion Transmitter; 宽带低误差矢量幅度（ EVM ）直接变频发射机
| 型号： | CN-0285 |
| 厂家： | 
ADI |
| 描述： | Broadband Low Error Vector Magnitude (EVM) Direct Conversion Transmitter |
| 文件： | 总5页 (文件大小：471K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Circuit Note
CN-0285
Devices Connected/Referenced
Circuits from the Lab™ reference circuits are engineered and
tested for quick and easy system integration to help solve today’s
analog, mixed-signal, and RF design challenges. For more
information and/or support, visit www.analog.com/CN0285.
ADF4351
ADL5375
ADP150
Fractional-N PLL IC with Integrated VCO
Wideband Transmit Modulator
Low Noise 3.3 V LDO
ADP3334
Low Noise Adjustable LDO
Broadband Low Error Vector Magnitude (EVM) Direct Conversion Transmitter
EVALUATION AND DESIGN SUPPORT
CIRCUIT FUNCTION AND BENEFITS
Circuit Evaluation Boards
CN-0285 Evaluation Board (EVAL-CN0285-EB1Z)
Design and Integration Files
This circuit is a complete implementation of the analog portion
of a broadband direct conversion transmitter (analog baseband
in, RF out). RF frequencies from 500 MHz to 4.4 GHz are
supported using a phase-locked loop (PLL) with a broadband,
integrated voltage controlled oscillator (VCO). Harmonic filtering
of the local oscillator (LO) from the PLL ensures excellent
quadrature accuracy, sideband suppression, and low EVM.
Schematics, Layout Files, Bill of Materials
ADP150
5.5V
ADP3334
5.5V
1µF
1µF
1µF
1µF
3.3V
5.0V
V
V
DD
VCO
16
I/Q SMA INPUTS
17
26
28
10
AV
4
6
32
VPS1, VPS2
V
PDB
SDV
DV
CE
V
RF
P
VCO
DD
DD
DD
ADL5375
1nF 1nF
IBBP
FREF
REF
CLK
RF
B+ 14
29
51Ω
IN
IN
OUT
V
VCO
Z
IBBN
RF
B–
15
1
2
3
OUT
DATA
LE
Z
BIAS
BIAS
LOIP
12
13
RF
RF
A+
A–
ADF4351
OUT
OUT
V
QUADRATURE
PHASE
RFOUT
LOIN
SPLITTER
22
R
SET
4.7kΩ
20
7
TUNE
1kΩ
QBBP
QBBN
CP
OUT
47nF
2.7nF
680pF
SW
5
360Ω
CP
SD
A
DGND
27
GND
GND AGND
GNDVCO
8
31
9
11 18 21
I/Q SMA INPUTS
Figure 1. Direct Conversion Transmitter (Simplified Schematic: All Connections and Decoupling Not Shown)
Rev. 0
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©2013 Analog Devices, Inc. All rights reserved.
CN-0285
Circuit Note
Figure 2. Evaluation Board for CN-0285 Direct Conversion Transmitter
Low noise, low dropout regulators (LDOs) ensure that the power
management scheme has no adverse impact on phase noise and
EVM. This combination of components represents industry-
leading direct conversion transmitter performance over a
frequency range of 500 MHz to 4.4 GHz
To get the third harmonic below −30 dBc, approximately 20 dB of
attenuation is required.
Table 1. ADF4351 RF Output Harmonic Levels Unfiltered
Harmonic Content Value (dBc) Description
Second
Third
Second
Third
−19
−13
−20
−10
Fundamental VCO output
Fundamental VCO output
Divided VCO output
CIRCUIT DESCRIPTION
The circuit shown in Figure 1 uses the ADF4351, a fully integrated
fractional-N PLL IC, and the ADL5375 wideband transmit
modulator. The ADF4351 provides the LO signal for the ADL5375
transmit quadrature modulator, which upconverts analog I/Q
signals to RF. Taken together, the two devices provide a wideband,
baseband IQ-to-RF transmit solution. The ADF4351 is powered
off the ultralow noise 3.3 V ADP150 regulator for optimal LO
phase noise performance. The ADL5375 is powered off a 5 V
ADP3334 LDO. The ADP150 LDO has an output voltage noise of
only 9 µV rms and helps to optimize VCO phase noise and reduce
the impact of VCO pushing (equivalent to power supply rejection).
Divided VCO output
This circuit gives four different filter options to cover four different
bands. The filters were designed with a 100 Ω differential input
(ADF4351 RF outputs with appropriate matching) and a 50 Ω
differential output (ADL5375 LOIN differential impedance). A
Chebyshev response was used for optimal filter roll-off at the
expense of increased pass-band ripple.
The filter schematic is shown in Figure 3. This topology allows
the use of either a fully differential filter to minimize component
count, a single-ended filter for each output, or a combination of
the two. It was determined that for higher frequencies (>2 GHz)
two single-ended filters gave the best performance because the
series inductor values are twice the value compared to a fully
differential filter and, hence, the impact of component parasitics is
reduced. For lower frequencies (<2 GHz), a fully differential
filter provides adequate results.
Filtering is required on the ADF4351 RF outputs to attenuate
harmonic levels to minimize errors in the quadrature generation
block of the ADL5375. From measurement and simulation, the
odd-order harmonics contribute more than even-order harmonics
to quadrature error and, if attenuated to below −30 dBc, results
in sideband suppression performance of −40 dBc or better. The
second harmonic (2H) and third harmonic (3H) levels of the
ADF4351 are as given in the data sheet and shown in Table 1.
Table 2. ADF4351 RF Output Filter Component Values (DNI = Do Not Insert)
L1
(nH)
L2
(nH)
C1a
(pF)
C1c
(pF)
C2a
(pF)
C2c
(pF)
C3a
(pF)
C3c
(pF)
Frequency Range (MHz)
500 to 1300 (Filter Type A)
850 to 2450 (Filter Type B)
1250 to 2800 (Filter Type C)
2800 to 4400 (Filter Type D)
ZBIAS
27 nH||50 Ω
19 nH||(100 Ω in Position C1c)
50 Ω
3.9 nH
3.9
2.7
0 Ω
0 Ω
3.9
2.7
3.6
0 Ω
DNI
3.3
DNI
DNI
4.7
DNI
4.7
2.2
5.6
DNI
3.3
1.5
3.3
100 Ω
DNI
DNI
DNI
DNI
DNI
DNI
DNI
DNI
DNI
DNI
Rev. 0 | Page 2 of 5
Circuit Note
CN-0285
Q
The ADF4351 output match consists of the ZBIAS pull-up and, to
a lesser extent, the decoupling capacitors on the supply node. To
get a broadband match, it is recommended to use either a resistive
load (ZBIAS = 50 Ω) or a resistive in parallel with a reactive load for
ZBIAS. The latter gives slightly higher output power, depending on
the inductor chosen. Note that it is possible to place the parallel
resistor as a differential component (that is, 100 Ω) in Position
C1c to minimize board space (see Filter Type B, Table 2).
MAGNITUDE ERROR
(I/Q ERROR PHASE)
ERROR
VECTOR
MEASURED
SIGNAL
PHASE ERROR
(I/Q ERROR PHASE)
Design the filter with a cutoff approximately 1.2 times to 1.5 times
the highest frequency in the band of interest. This cutoff allows
margin in the design, because typically the cutoff is lower than
designed due to parasitics. The effect of printed circuit board
(PCB) parasitics can be simulated in an electromagnetic (EM)
simulation tool for improved accuracy.
0
IDEAL SIGNAL
(REFERENCE)
I
Figure 5. EVM Plot
3.3V
A sweep of sideband suppression vs. frequency is shown in Figure 4
for the circuit using Filter Type B (800 MHz to 2400 MHz). In
this sweep, the test conditions were the following:
120pF
120pF
0.1µF
C1a
L1
C2a
L2
C3a
1nF
Z
BIAS
•
Baseband I/Q amplitude = 1 V p-p differential sine waves
in quadrature with a 500 mV (ADL5375-05) dc bias
Baseband I/Q frequency (fBB) = 1 MHz.
12
13
3
4
LOIP
RF
RF
A+
A–
OUT
•
C1c
L1
C2c
L2
C3c
1nF
Z
BIAS
EVM is a measure of the quality of the performance of a digital
transmitter or receiver and is a measure of the deviation of the
actual constellation points from their ideal locations, due to
both magnitude and phase errors (see Figure 5).
LOIN
OUT
C1a
C2a
C3a
ADF4351
ADL5375
Figure 3. ADF4351 RF Output Filter Schematic
EVM measurements are given in Table 3 comparing the results
with and without the filter. In this case, the baseband I/Q signals
were generated using 3GPP Test Model 4 using a Rohde & Schwarz
AMIQ I/Q modulation generator with differential I and Q analog
outputs. Filter Type B was also used. A block diagram of the test
setup for the EVM is shown in Figure 6. For comparative purposes,
the ADF4350 is also measured. Lower EVM due to in-band PLL
noise improvements on the ADF4351 can be seen in Table 3. Other
contributing factors to the EVM improvement are the lower
phase frequency detector (PFD) spurious levels on the ADF4351.
As can be seen from Table 2, at frequencies lower than 1250 MHz,
a fifth-order filter is required. For 1.25 GHz to2.8 GHz, third-order
filtering is sufficient. For frequencies more than 2.8 GHz, filtering
is not required because the harmonic levels are sufficiently low
to meet the sideband suppression specifications.
–20
5dBm
–25
FILTER B: 850MHz TO 2450MHz
–30
–35
–40
–45
–50
–55
–60
–65
–70
800
1000
1200
1400
1600
1800
2000
2200
2400
CARRIER FREQUENCY (MHz)
Figure 4. Sideband Suppression for Filter Type B, 850 MHz to 2450 MHz
Rev. 0 | Page 3 of 5
CN-0285
Circuit Note
Table 3. Single-Carrier W-CDMA Composite EVM Results Comparing Filter vs. No Filter on ADF4351 RF Outputs (Measured As
Per 3GPP Specification Test Model 4)
ADF4350 Composite
EVM No LO Filtering
ADF4350 Composite
EVM with LO Filtering, Filter B
ADF4351 Composite
EVM with LO Filtering, Filter B
Frequency (MHz)
2140
1800
900
3.27%
1.46%
10.01%
1.31%
1.13%
1.03%
1.02%
0.95%
0.96%
COMMON VARIATIONS
R&S AMIQ GEN.
It is possible to use the auxiliary outputs on the ADF4351 to
switch between two filter types where wideband operation beyond
that possible with one single filter is required (see Figure 8).
An RF double-pole, 4-throw switch (DP4T) is used to select
the differential outputs of either Filter 1 or Filter 2.
SPECTRUM ANALYZER
[R&S FSQ 8]
I+
I–
Q+
Q–
CN-0285
EVALUATION
BOARD
RF OUT
1nF
12
3
LOIP
LOIN
RF
A+
OUT
OUT
5.5V
FILTER 1
1nF
RF
A–
13
4
DP4T
SWITCH
RF
RF
B+ 14
B– 15
OUT
FILTER 2
POWER SUPPLY
OUT
Figure 6. EVM Measurement Setup (Simplified Diagram)
ADF4351
ADL5375
In addition to the improvement in sideband suppression and EVM,
there is also a performance benefit to driving the ADL5375
LO inputs differentially. This benefit improves modulator output
IP2 performance by 2 dB to 5 dB, compared with single-ended
LO drive. Note that most external VCOs only come with a single-
ended output, so using the differential outputs on the ADF4351
provides a benefit over an external VCO in this case.
Figure 8. Application Diagram Showing Possibility of Filter Switching Using
the ADF4351 Main and Auxiliary Outputs
CIRCUIT EVALUATION AND TEST
The EVAL-CN0285-EB1Z evaluation board contains the circuit
described in CN-0285, allowing for the quick setup and evaluation
of the performance of the circuit. The control software for the
EVAL-CN0285-EB1Z uses the standard ADF4351 programming
software located on the CD that accompanies the evaluation board.
Figure 7 shows sideband suppression results using an 850 MHz
to 2450 MHz filter (Filter Type B).
–20
Equipment Needed
The following equipment is needed:
–30
–40
–50
•
A standard PC running Windows® XP, Windows Vista (32-
bit), or Windows 7 with a USB port
•
•
•
•
•
The EVAL-CN0285-EB1Z circuit evaluation board
The ADF435x programming software
5.5 V power supplies
An I-Q signal source, such as the Rohde & Schwarz AMIQ
A spectrum analyzer, such as the Rohde & Schwarz FSQ8
–60
–4dBm
–1dBm
+2dBm
+5dBm
–70
–80
–90
For additional details, see the UG-521 User Guide, the ADF4351
data sheet, and the ADL5375 data sheet.
800
1000
1200
1400
1600
1800
2000
2200
2400
CARRIER FREQUENCY (MHz)
Figure 7. Sideband Suppression Results for 850 MHz to 2450 MHz Filter Type B
A complete design support package for this circuit note can be
found at http://www.analog.com/CN0285-DesignSupport.
Rev. 0 | Page 4 of 5
Circuit Note
CN-0285
Getting Started
Data Sheets and Evaluation Boards
ADF4351 Data Sheet
See the UG-521 User Guide for software installation and test setup.
The user guide also includes the block diagram, the application
schematic, the bill of materials, and the layout and assembly
information. In addition, see the ADF4351 data sheet and the
ADL5375 data sheet for additional details.
ADF4351 Evaluation Board
ADL5375 Data Sheet
ADL5375 Evaluation Board
ADP150 Data Sheet
Functional Block Diagram
See Figure 1 and Figure 6 in this document, and also see the
UG-521 User Guide.
ADP3334 Data Sheet
REVISION HISTORY
Setup and Test
2/13—Revision 0: Initial Version
After setting up the equipment, use standard RF test methods to
measure the sideband suppression of the circuit.
LEARN MORE
CN0285 Design Support Package:
http://www.analog.com/CN0285-DesignSupport
ADIsimPLL Design Tool
ADIsimPower Design Tool
ADIsimRF Design Tool
AN-0996 Application Note. The Advantages of Using a
Quadrature Digital Upconverter (QDUC) in Point-to-Point
Microwave Transmit Systems. Analog Devices.
AN-1039 Application Note. Correcting Imperfections in IQ
Modulators to Improve RF Signal Fidelity. Analog Devices.
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CN10921-0-2/13(0)
Rev. 0 | Page 5 of 5
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