ADL5353 データシートの表示（PDF） - Analog Devices
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ADL5353 Datasheet PDF : 24 Pages
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ADL5353
CIRCUIT DESCRIPTION
The ADL5353 consists of two primary components: the radio
frequency (RF) subsystem and the local oscillator (LO) subsystem.
The combination of design, process, and packaging technology
allows the functions of these subsystems to be integrated into a
single die, using mature packaging and interconnection technolo-
gies to provide a high performance, low cost design with excellent
electrical, mechanical, and thermal properties. In addition, the
need for external components is minimized, thereby optimizing
cost and size.
The RF subsystem consists of an integrated, low loss RF balun,
passive MOSFET mixer, sum termination network, and IF
amplifier.
The LO subsystem consists of an SPDT-terminated FET switch
and a three stage, limiting LO amplifier. The purpose of the LO
subsystem is to provide a large, fixed amplitude, balanced signal
to drive the mixer independent of the level of the LO input. A
block diagram of the device is shown in Figure 50.
IFGM
20
IFOP
19
IFON
18
PWDN
17
LEXT
16
VPIF 1
ADL5353
15 LOI2
RFIN 2
14 VPSW
RFCT 3
COMM 4
BIAS
GENERATOR
13 VGS1
12 VGS0
COMM 5
11 LOI1
6
7
8
9
10
VLO3
LGM3
VLO2
LOSW
NC
NC = NO CONNECT
Figure 50. Simplified Schematic
RF SUBSYSTEM
The single-ended, 50 Ω RF input is internally transformed to a
balanced signal using a low loss (<1 dB) unbalanced-to-balanced
(balun) transformer. This transformer is made possible by an
extremely low loss metal stack, which provides both excellent
balance and dc isolation for the RF port. Although the port can
be dc connected, it is recommended that a blocking capacitor be
used to avoid running excessive dc current through the part.
The RF balun can easily support an RF input frequency range
of 2200 MHz to 2700 MHz.
The resulting balanced RF signal is applied to a passive mixer
that commutates the RF input with the output of the LO subsystem.
The passive mixer is essentially a balanced, low loss switch that
adds minimum noise to the frequency translation. The only
noise contribution from the mixer is due to the resistive loss
of the switches, which is in the order of a few ohms.
Because the mixer is inherently broadband and bidirectional, it
is necessary to properly terminate all the idler (M × N product)
frequencies generated by the mixing process. Terminating the
mixer avoids the generation of unwanted intermodulation pro-
ducts and reduces the level of unwanted signals at the input of
the IF amplifier, where high peak signal levels can compromise the
compression and intermodulation performance of the system. This
termination is accomplished by the addition of a sum network
between the IF amplifier and the mixer and also in the feedback
elements in the IF amplifier.
The IF amplifier is a balanced feedback design that simultaneously
provides the desired gain, noise figure, and input impedance that
are required to achieve the overall performance. The balanced
open-collector output of the IF amplifier, with impedance mod-
ified by the feedback within the amplifier, permits the output to be
connected directly to a high impedance filter, differential amplifier,
or to an analog-to-digital input while providing optimum second-
order intermodulation suppression. The differential output
impedance of the IF amplifier is approximately 200 Ω. If operation
in a 50 Ω system is desired, the output can be transformed to
50 Ω by using a 4:1 transformer.
The intermodulation performance of the design is generally
limited by the IF amplifier. The Input IP3 performance can be
optimized by adjusting the IF current with an external resistor.
Figure 41, Figure 42, and Figure 43 illustrate how various IF and
LO bias resistors affect the performance with a 5 V supply. Addi-
tionally, dc current can be saved by increasing either or both
resistors. It is permissible to reduce the dc supply voltage to as
low as 3.3 V, further reducing the dissipated power of the part.
(Note that no performance enhancement is obtained by reducing
the value of these resistors, and excessive dc power dissipation
may result.)
LO SUBSYSTEM
The ADL5353 has two LO inputs permitting multiple synthe-
sizers to be rapidly switched with extremely short switching
times (<40 ns) for frequency agile applications. The two inputs
are applied to a high isolation SPDT switch that provides a
constant input impedance, regardless of whether the port is
selected, to avoid pulling the LO sources. This multiple section
switch also ensures high isolation to the off input, minimizing
any leakage from the unwanted LO input that may result in
undesired IF responses.
The single-ended LO input is converted to a fixed amplitude
differential signal using a multistage, limiting LO amplifier.
This results in consistent performance over a range of LO input
power. Optimum performance is achieved from −6 dBm to
+10 dBm, but the circuit continues to function at considerably
lower levels of LO input power.
Rev. 0 | Page 16 of 24
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