AD8349AREZ Analog Devices Inc, AD8349AREZ Datasheet - Page 18

• Manufacturer Part Number: AD8349AREZ
• Description: IC QUADRATURE MOD 700MHZ 16TSSOP
• Manufacturer: Analog Devices Inc

Specifications of AD8349AREZ

• Function: Modulator
• Lo Frequency: 700MHz ~ 2.7GHz
• Rf Frequency: 700MHz ~ 2.7GHz
• P1db: 5.6dBm
• Noise Floor: -156dBm/Hz
• Output Power: 5.1dBm
• Current - Supply: 150mA
• Voltage - Supply: 4.75 V ~ 5.5 V
• Test Frequency: 2.14GHz
• Package / Case: 16-TSSOP Exposed Pad, 16-eTSSOP, 16-HTSSOP
• Frequency Range: 700MHz To 2700MHz
• Rf Type: Quadrature
• Supply Voltage Range: 4.75V To 5.5V
• Rf Ic Case Style: TSSOP
• No. Of Pins: 16
• Operating Temperature Range: -40°C To +85°C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD8349
BASEBAND DAC INTERFACE
The recommended baseband input swing and bias levels of the
AD8349’s differential baseband inputs allow for direct
connection to most baseband DACs without the need for any
external active components. Typically these DACs have a
differential full-scale output current from 0 mA to 20 mA on
each differential output. These currents can be easily converted
to voltages using ground-referenced shunt resistors. Most
baseband DACs for transmit chains are designed with two
DACs in a single package.
AD9777 INTERFACE
The AD977x family of dual DACs is well suited to driving the
baseband inputs of the AD8349. The AD9777 is a dual 16-bit
DAC that can generate either a baseband output or a complex
IF using the device’s complex modulator.
The basic interface between the AD9777’s I
AD8349’s differential baseband inputs is shown in Figure 51.
The Resistors R1 and R2 set the dc bias level, and R3 sets the
amplitude of the baseband input voltage swing.
AD9777
–2
–4
–6
–8
8
6
4
2
0
I
I
I
I
OUTA1
OUTB1
OUTA2
OUTB2
0
73
72
69
68
Figure 51. Basic AD9777 to AD8349 Interface
Figure 50. ENOP Disable Time, 900 MHz
20
R1Q
R2Q
R1I
R2I
40
LOW-PASS
OPTIONAL
LOW-PASS
OPTIONAL
TIME (ns)
FILTER
FILTER
60
R3Q
R3I
OUT
80
outputs and the
16
15
1
2
IBBP
IBBN
QBBP
QBBN
AD8349
100
800
600
400
200
0
–200
–400
–600
–800
Rev. A | Page 18 of 28
BIASING AND FILTERING
A value of 40 Ω on R1 and R2 in Figure 51 will generate the
required 400 mV dc bias. Note that this is independent of the
value of R3. Figure 52 shows the relationship between the value
of R3 and the peak baseband input voltage with the 40 Ω
resistors in place. From Figure 52, it can be seen that a value of
240 Ω will provide a peak-to-peak swing of approximately
1.2 V p-p differential into the AD8349’s baseband inputs.
The closest available resistor values are 40.2 Ω and 240 Ω, and
these values were used in the characterization of the AD8349
when the DAC was used as a signal source.
When using a DAC, low-pass image reject filters are typically
used to eliminate images that are produced by the DAC. They
provide the added benefit of eliminating broadband noise that
might feed into the modulator from the DAC.
Figure 53 shows a single sideband spectrum at 2140 MHz. The
baseband sine and cosine signals come from the digital output
of a Rohde & Schwarz AMIQ arbitrary waveform generator.
These signals drive the AD9777 dual DAC, which in turn drives
the AD8349’s baseband inputs. Note that the AD9777’s complex
modulator is not being used.
Due to offset voltages, internal device mismatch, and imperfect
quadrature over the AD8349’s operating range, the SSB
spectrum has a number of undesirable components such as LO
feedthrough and undesired sideband leakage. When the
AD8349 is driven by a modulated baseband signal, (e.g. 8-PSK,
GMSK, QPSK, or QAM), these nonidealities will manifest
themselves as degraded error vector magnitude (EVM) and
degraded spectral purity.
1.50
1.35
1.20
1.05
0.90
0.75
0.60
0.45
0.30
0.15
10
Figure 52. Relationship Between R3 in Figure 51 and Peak
Baseband Input Voltage
R3 (Ω)
100
1.10
3