LTC5505 LINER [Linear Technology], LTC5505 Datasheet - Page 14

• Manufacturer Part Number: LTC5505
• Description: 800MHz to 2.7GHz High Linearity Direct Conversion Quadrature Demodulator
• Manufacturer: LINER [Linear Technology]

LT5575
APPLICATIONS INFORMATION
Care should be taken when the demodulator’s outputs are
DC-coupled to the external load to make sure that the I/Q
mixers are biased properly. If the current drain from the
outputs exceeds 6mA, there can be signifi cant degrada-
tion of the linearity performance. Each output can sink no
more than 16.8mA when the outputs are connected to an
external load with a DC voltage higher than V
The I/Q output equivalent circuit is shown in Figure 8.
In order to achieve best IIP2 performance, it is important
to minimize high frequency coupling among the baseband
outputs, RF port and LO port. For a multilayer PCB layout
design, the metal lines of the baseband outputs should be
placed on the backside of the PCB as shown in Figures 2
and 3. Typically, output shunt capacitors C1-C4 are not
required for the application near 1900MHz. However, for
other frequency bands, these capacitors can be optimized
for best IIP2 performance. For example, when the oper-
ating frequency is 900MHz, the IIP2 can be improved to
54dBm or better when 10pF shunt capacitors are placed
at each output.
14
Figure 9. Enable Pin Simplifi ed Circuit
5
CC
EN
– 1.1V.
V
CC
60k
Enable Interface
A simplifi ed schematic of the EN pin is shown in Fig-
ure 9. The enable voltage necessary to turn on the LT5575
is 2V. To disable or turn off the chip, this voltage should
be below 1V. If the EN pin is not connected, the chip is
disabled. However, it is not recommended that the pin be
left fl oating for normal operation.
It is important that the voltage applied to the EN pin
should never exceed V
the supply current may be sourced through the upper
ESD protection diode connected at the EN pin. Under no
circumstances should voltage be applied to the EN pin
before the supply voltage is applied to the V
occurs, damage to the IC may result.
LT5575
5575 F09
60k
CC
by more than 0.3V. Otherwise,
CC
pin. If this
5575f