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ADL5375-05ACPZ-WP Datasheet(PDF) 19 Page - Analog Devices
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ADL5375-05ACPZ-WP Datasheet(HTML) 19 Page - Analog Devices
/ 36 page
Rev. C | Page 19 of 36
THEORY OF OPERATION
The ADL5375 can be divided into five circuit blocks: the LO
interface, the baseband voltage-to-current (V-to-I) converter,
the mixers, the differential-to-single-ended (D-to-S) stage,
and the bias circuit. A block diagram of the device is shown in
Figure 53. Block Diagram
The LO interface generates two LO signals in quadrature.
These signals are used to drive the mixers. The I/Q baseband
input signals are converted to currents by the V-to-I stages,
which then drive the two mixers. The outputs of these mixers
combine to feed the output balun, which provides a single-
ended output. The bias cell generates reference currents for
the V-to-I stage.
The LO interface consists of a polyphase quadrature splitter
and a limiting amplifier. The LO input impedance is set by
the polyphase splitter. Each quadrature LO signal then passes
through a limiting amplifier that provides the mixer with a
limited drive signal.
The LO input can be driven single-ended or differentially.
For applications above 3 GHz, improved OIP2 and LO leakage
may result from driving the LO input differentially.
The differential baseband inputs (QBBP, QBBN, IBBN, and
IBBP) present a high impedance. The voltages applied to these
pins drive the V-to-I stage that converts baseband voltages into
currents. The differential output currents of the V-to-I stages
feed each of their respective mixers. The dc common-mode
voltage at the baseband inputs sets the currents in the two
mixer cores. Varying the baseband common-mode voltage
influences the current in the mixer and affects overall modula-
tor performance. The recommended dc voltage for the baseband
common-mode voltage is 500 mV dc for the ADL5375-05 and
1500 mV for the ADL5375-15.
The ADL5375 has two double-balanced mixers: one for the
in-phase channel (I channel) and one for the quadrature chan-
nel (Q-channel). The output currents from the two mixers sum
together into an internal load. The signal developed across this
load is used to drive the D-to-S stage.
The output D-to-S stage consists of an on-chip active balun
that converts the differential signal to a single-ended signal.
The balun presents 50 Ω impedance to the output (VOUT).
Therefore, no matching network is needed at the RF output
for optimal power transfer in a 50 Ω environment.
An on-chip band gap reference circuit is used to generate a
proportional-to-absolute temperature (PTAT) reference current
for the V-to-I stage.
The DSOP pin can be used to disable the output stage of the
modulator. If the DSOP pin is connected to ground or left
unconnected, the part operates normally. If the DSOP pin is
connected to the positive voltage supply, the output stage is
disabled and the LO leakage is also reduced.
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