AD8347-EVAL Analog Devices Inc, AD8347-EVAL Datasheet - Page 20

• Manufacturer Part Number: AD8347-EVAL
• Description: BOARD EVAL FOR AD8347
• Manufacturer: Analog Devices Inc

Specifications of AD8347-EVAL

• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

AD8347
CHANGING THE AGC SETPOINT
The AGC circuit can be easily set up to level at voltages higher
than the nominal 24 mV p-p, as shown in Figure 48. The
voltages on Pin IMXO and Pin QMXO are attenuated before
being applied to the detector inputs. In the example shown, an
attenuation factor of 0.2 (−14 dB) between IMXO and QMXO
and the detector inputs causes the VGA to level at approximately
120 mV p-p (note that the resistor divider network must be
referenced to V
swing at the baseband amplifier outputs of 3.8 V differential,
that is, 1.6 V to 3.4 V on each side. Note that V
increased to 2.5 V to avoid signal clipping at the baseband
outputs. Due to the attenuation between the mixer output and
the detector input, the variation in the settled mixer output level
vs. RF input power will be greater than the variation shown in
Figure 34. The variation will be greater by a factor equal to the
inverse of the attenuation factor.
BASEBAND AMPLIFIERS
The final baseband amplifier stage takes the signals from IMXO
and QMXO and amplifies them by 30 dB, or a factor of 31.6.
This results in a maximum system gain of 69.5 dB. When the
VGA is in AGC mode, the baseband I and Q outputs (IOPN,
RF
INPUT
100pF
R1
200 Ω
100pF
C1
C2
VREF
0.1 μ F
C6
). This results in a peak-to-peak output
ENBL
VGIN
RFIN
RFIP
100pF
VPS1
C5
15
10
11
17
2
0.1 μ F
C7
INTERFACE
CONTROL
VPS2
GAIN
100pF
AD8347
C8
+V
CELL
BIAS
S
12
Figure 48. Adjusting AGC Level to Increase Baseband Amplifier Output Swing
+5V
0.1 μ F
VDT1
C9
DET 1
VPS3
100pF
20
C10
VAGC
VCMO
21
19
VREF
VDT2
has been
DET 2
14
18
VREF
C16
0.1μF
QMXO
IMXO
4kΩ
1kΩ
R21
R22
Rev. A | Page 20 of 28
22
8
R19
1k Ω
R20
4k Ω
120mV p-p
1V BIAS
120mV p-p
13
16
1V BIAS
IOFS
QOFS
C14
0.1 μ F
VREF
VREF
C13
0.1 μ F
SPLITTER
IOPP, QOPN, and QOPP) deliver a differential voltage of
approximately 760 mV p-p (380 mV p-p on each side).
The single-ended input signal to the baseband amplifiers is
applied at IAIN and QAIN, the high impedance inputs. As
shown in Figure 46, the baseband amplifier operates internally
as a differential amplifier, with the second input driven by V
Therefore, bias the input signal to the baseband amplifier at V
The output common-mode level of the baseband amplifiers is
set by the voltage on Pin 5, VCMO. Connect this pin to VREF
(Pin 14) or to an external reference voltage from a device such
as an analog-to-digital converter (ADC). V
range from 0.5 V to 2.5 V. However, since the baseband amplifiers
can only swing down to 0.4 V, higher values of V
ally required to avoid low end signal clipping. Alternatively, the
positive swing at each output is limited to 1.3 V below the
supply voltage; therefore, the maximum p-p swing is given by
2 × (V
For example, for the baseband output amplifier to deliver an
output swing of 2 V p-p (1 V p-p on each side), V
in a range from 0.9 V to 2.5 V.
PHASE
IAIN
2
24
6
VCMO
QAIN
PS
− 1.3 − 0.4) V differentially.
IOPP
25
4
QOPP
VCMO
SPLITTER
PHASE
1
26
3
QOPN
IOPN
28
27
23
5
1
7
9
LOIN
LOIP
VCMO
COM3
COM2
COM3
COM1
2.5V
100pF
100pF
C3
C4
R17
200 Ω
VCMO
ETC 1-1-13
(M/A-COM)
3
1
T1
3.8V p-p
DIFFERENTIAL
V
0.8GHz–2.7GHz
3.8V p-p
DIFFERENTIAL
V
has a nominal
CM
CM
VCMO
4
5
LO INPUT
VCMO
–8dBm
= 2.5V
= 2.5V
QOPN
QOPP
IOPP
IOPN
are gener-
must be
VREF
VREF
.
.