AD8347ARUZ Analog Devices Inc, AD8347ARUZ Datasheet - Page 21

• Manufacturer Part Number: AD8347ARUZ
• Description: IC QUADRATURE DEMOD 28-TSSOP
• Manufacturer: Analog Devices Inc

Specifications of AD8347ARUZ

• Function: Demodulator
• Lo Frequency: 800MHz ~ 2.7GHz
• Rf Frequency: 800MHz ~ 2.7GHz
• P1db: -30dBm
• Gain: 39.5dB
• Noise Figure: 11dB
• Current - Supply: 80mA
• Voltage - Supply: 2.7 V ~ 5.5 V
• Package / Case: 28-TSSOP
• Frequency Range: 0.8GHz To 2.7GHz
• Rf Type: Quadrature
• Supply Voltage Range: 2.7V To 5.5V
• Rf Ic Case Style: TSSOP
• No. Of Pins: 28
• Operating Temperature Range: -40°C To +85°C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The differential output offset voltages of the baseband amplifiers
are typically ±50 mV. This offset voltage results from both input
and output effects.
The overall signal-to-noise ratio can be improved by increasing
the VGA gain by driving it with an external voltage or by changing
the setpoint of the AGC circuit. See the Changing the AGC
Setpoint section.
DRIVING CAPACITIVE LOADS
In applications where the baseband amplifiers are driving
unbalanced capacitive loads, place some series resistance between
the amplifier and the capacitive load. For example, for a 10 pF load,
use four 200 Ω series resistors, one in each baseband output.
EXTERNAL BASEBAND AMPLIFICATION
Reduce baseband output offset voltage and noise by bypassing the
internal baseband amplifiers and amplifying the mixer output
signal using a high quality differential amplifier. In the example
shown in
to gain up the mixer output signals by 20 dB. In this example, the
setpoint of the AGC circuit was increased to give an approximate
72 mV p-p input to the external amplifiers. This resulted in final
baseband output signals of 720 mV p-p.
The closed-loop bandwidth of the amplifiers in Figure 49 is equal
to approximately 20 MHz. Higher bandwidths are achievable, but
at the cost of lower closed-loop gain. In
common-mode levels at Pin 2 (V
by the AD8347’s VREF (approximately 1 V). The output common-
mode levels can also be externally set, using, for example, the
reference voltage from an ADC.
AD8347
QMXO
VREF
IMXO
VDT2
VDT1
Figure 49, two AD8132 differential amplifiers are used
0.1μF
Figure 49. External Baseband Amplification Example
10k Ω
20k Ω
C16
R25
R23
72mV p-p
72mV p-p
20k Ω
10k Ω
R22
R24
R17A
499 Ω
R18A
499 Ω
R17B
499 Ω
R18B
499 Ω
OCM
4.99k Ω
4.99k Ω
4.99k Ω
4.99k Ω
R20A
R19B
R20B
R19A
2
1
8
pin) of the AD8132s are set
1
8
2
AD8132
Figure 49, the output
AD8132
–5V
+5V
3
6
3
6
0.1 μ F
0.1 μ F
0.1 μ F
0.1 μ F
–5V
+5V
5
4
5
4
720mV p-p
DIFFERENTIAL
V
CM
720mV p-p
DIFFERENTIAL
V
10 μ F
10 μ F
10 μ F
10 μ F
CM
= 1V
= 1V
Rev. A | Page 21 of 28
FILTER DESIGN CONSIDERATIONS
Baseband low-pass or band-pass filtering can be conveniently
performed between the mixer outputs (IMXO and QMXO) and the
input to the baseband amplifiers. Because the output impedance of
the mixer is low (approximately 3 Ω) and the input impedance of
the baseband amplifier is high, it is not practical to design a
filter that is reactively matched to these impedances. An LC
filter can be matched by placing a series resistor at the mixer
output and a shunt resistor (terminated to V
the baseband amplifier.
Because the mixer output drive level is limited to a maximum
current of 1.5 mA, the characteristic impedance of the filter
should be greater than 50 Ω, especially to achieve larger signal
swings.
Figure 50 shows the schematic for a 100 Ω, fourth-order elliptic
low-pass filter with a 3 dB cutoff frequency of 20 MHz. Source
and load impedances of approximately 100 Ω ensure that the
filter sees a matched source and load. This also ensures that the
mixer output is driving an overall load of 200 Ω. Note that the
shunt termination resistor is tied to VREF and not to ground.
The frequency response and group delay of this filter are shown
in
Figure 51 and Figure 52.
AD8347
Figure 51. Frequency Response of 20 MHz Baseband Low-Pass Filter
IMXO
–10
–20
–30
–40
–50
–60
–70
–80
0
1
95.3 Ω
RS
Figure 50. Typical Baseband Low-Pass Filter
0.68 μ H
L
4.7pF
1
C1
2 Ω
R3
FREQUENCY (MHz)
1.2 μ H
150pF
C2
L
3
8.2pF
C3
10
2 Ω
R4
VREF
82pF
C4
C16
0.1μF
VREF
RL
100 Ω
) at the input to
IAIN
AD8347
TEXT)
VDT1
(SEE
100