AD8348_15 Datasheet, PDF (20/28 Pages) Analog Devices – 50 MHz to 1000 MHz Quadrature Demodulator

AD8348
APPLICATIONS
BASIC CONNECTIONS
Figure 49 shows the basic connections schematic for the AD8348.
J21
LO
C21
1000pF
45
T21
ETC1-1-13
31
R21
60.4Ω
C22
1000pF
AD8348
1 LOIP LOIN 28
+VS
J3I
IOPN
J2I
IOPP
C52
0.1µF
C51
100pF
VREF
2 VPOS1 COM1 27
3 IOPN QOPN 26
4 IOPP QOPP 25
5 VCMO ENVG 24
6 IAIN QAIN 23
IF
+V_S
SW12
MX
7 COM3 COM3 22
C32
1000pF
R31
R32
57.6Ω 174Ω
IFIP
C31
1000pF
+VS
C54
C53
0.1µF
100pF
C0l
0.1µF
C11
4.7µF
8 IMXO QMXO 21
9 COM2 VPOS3 20
10 IFIN
MXIN 19
11 IFIP
MXIP 18
12 VPOS2 VGIN 17
C55 C56
100pF 0.1µF +VS
C43 R42
1000pF 0Ω
C41
T41
1µF
ETK4-2T
VGIN
C42
1000pF
13 IOFS QOFS 16
14 VREF ENBL 15
C0Q
0.1µF
ENBL
+VS
SW11
DENBL
Figure 49. Basic Connections Schematic
J3Q
QOPN
J2Q
QOPP
MXIP
POWER SUPPLY
The voltage supply for the AD8348, between 2.7 V and 5 V, should
be provided to the +VPOSx pins, and ground should be connected
to the COMx pins. Each supply pin should be decoupled separately
using two capacitors whose recommended values are 100 pF and
0.1 μF (values close to these can also be used).
DEVICE ENABLE
To enable the device, the ENBL pin should be driven to VS.
Grounding the ENBL pin disables the device.
VGA ENABLE
Driving the voltage on the ENVG pin to VS enables the VGA. In
this mode, the MX inputs are disabled and the IF inputs are
used. Grounding the ENVG pin disables the VGA and the IF
inputs. When the VGA is disabled, the MX inputs should be used.
GAIN CONTROL
When the VGA is enabled, the voltage applied to the VGIN pin sets
the gain. The gain control voltage range is between 0.2 V and 1.2 V.
This corresponds to a gain range between +25.5 dB and −18.5 dB.
LO INPUTS
For optimum performance, the local oscillator port should be
driven differentially through a balun. The recommended balun
is M/A-COM ETC1-1-13. The LO inputs to the device should
be ac-coupled, unless an ac-coupled transformer is being used.
For a broadband match to a 50 Ω source, a 60.4 Ω resistor
should be placed between the LOIP and LION pins.
LO
1000pF
45
ETC1-1-13
31
60.4Ω
1000pF
1 LOIP
LOIN 28
Figure 50. Differential LO Drive with Balun
Alternatively, the LO port can be driven from a single-ended source
without a balun (Figure 51). The LO signal is ac-coupled directly
into the LOIP pin via an ac-coupling capacitor, and the LOIN pin
is ac-coupled to ground. Driving the LO port from a single-
ended source results in an increase in both quadrature phase
error and LO leakage.
LO
1000pF
60.4Ω
1000pF
1 LOIP
LOIN 28
Figure 51. Single-Ended LO Drive
The recommended LO drive level is between −12 dBm and
0 dBm. The LO frequency at the input to the device should be
twice that of the desired LO frequency at the mixer core. The
applied LO frequency range is between 100 MHz and 2 GHz.
IF INPUTS
The IF inputs have an input impedance of 200 Ω. A broadband
50 Ω match can be presented to the driving source through the use
of a minimum-loss L pad. This minimum-loss pad introduces
an 11.46 dB loss in the input path and must be taken into account
when calculating metrics such as gain and noise figure. Figure 42
shows the S11 of the IF input with and without the L pad.
1000pF
10 IFIN
57.6Ω
174Ω
IFIP
11 IFIP
1000pF
Figure 52. Minimum-Loss L Pad for 50 Ω IF Input
MX INPUTS
The mixer inputs, MXIP and MXIN, have a nominal impedance
of 200 Ω and should be driven differentially. When driven from
a differential source, the input should be ac-coupled to the
source via capacitors, as shown in Figure 53.
Rev. A | Page 20 of 28