AD8348 Analog Devices, AD8348 Datasheet - Page 8

• Manufacturer Part Number: AD8348
• Description: 50-1000 MHz Quadrature Demodulator
• Manufacturer: Analog Devices

Applications
Basic Connections
The basic connections described here refer to the AD8348
evaluation board. The schematic for the evaluation board is
shown in Figure 1.
Power Supply
The voltage supply for the AD8348, between 2.7V and 5V,
should be connected to the +Vs test point and ground should
be connected to one of the GND test points.
Device Enable
To enable the device, the pin ENBL should be driven to +Vs.
Grounding the same pin will disable the device. On the
evaluation board this can be achieved by moving SW11 to the
ENBL and DENBL positions respectively.
VGA Enable
The VGA can be enabled by driving the voltage on the pin
ENVG to +Vs. In this mode, the MX inputs are disabled and
the IF inputs should be utilized. Grounding the pin will
disable the VGA and the IF inputs. When the VGA is
disabled the MX inputs should be used. On the evaluation
board, SW12 should be positioned in either the IF or MX
positions.
Gain Control
When the VGA is enabled, the gain can be controlled by the
voltage on pin VGIN. The gain control voltage range is
between 0.2 V and 1.2 V. This corresponds to a gain range
between 25.6 dB and –18.3 dB. For convenience, a
potentiometer R15 is provided to allow for changes in gain
without the need for an additional DC voltage source. To use
the potentiometer, the switch SW13 must be set to the POT
position. Alternatively, an external voltage applied to either
the testpoint or SMA connector labeled VGIN can set the
gain. SW13 must be set to the EXT position when an external
gain control voltage is used.
AD8348
PRELIMINARY TECHNICAL DATA
- 8 -
LO Input
The local oscillator signal should be fed to the SMA connector
J21. This port is terminated in 50 Ohms. The recommended
LO drive level is between –10 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 Input
The IF input should be fed into the SMA connector IFIP. The
VGA must be enabled when this port is used (SW12 in the IF
position).
MX Input
The input to the mixer input can be either single-ended or
differential. The evaluation board is, by default, set for
single-ended MX drive. To change to a differential drive, T41
should be removed along with resistor R42. DC blocking
capacitors (C42, C43) should be installed in place of T41.
This will present a nominal differential impedance of 200
Ohms (100 Ohms each side). The differential inputs should
then be fed into SMA connectors MXIP and MXIN.
Baseband Outputs
The baseband outputs are at the IOPP, IOPN, QOPP and
QOPN testpoints and SMA connectors. These outputs are not
designed to drive 50 Ohm loads directly and should be
presented with loads of at least 2k Ohms.
Output DC Bias Level
The DC bias level of the baseband amplifier outputs are by
default tied to Vref through LK11. If desired, the DC bias
level can be changed by removing LK11 and driving a DC
voltage onto either the VCMO testpoint.
Rev. PrF
2/11/03