ADL5812-EVALZ AD [Analog Devices], ADL5812-EVALZ Datasheet - Page 21

• Manufacturer Part Number: ADL5812-EVALZ
• Description: Dual High IP3, 700 MHz to 2800 MHz, Double Balanced, Passive Mixer, IF Amplifier, and Wideband LO Amplifier
• Manufacturer: AD [Analog Devices]

LO SUBSYSTEM
The LO amplifier is designed to provide a large signal level to
the mixer to obtain optimum intermodulation and compression
performance. The resulting LO amplifier provides very high
performance over a wide range of LO input frequencies.
The ideal waveshape for switching the passive mixer is a square
wave at the LO frequency to cause the mixer to switch through
its resistive region (from on to off and off to on) as rapidly as
possible. While it has always been possible to generate such a
square wave, the amount of dc current required to generate a
large amplitude square wave at high frequencies has made it
impractical to create such a mixer. Novel circuitry within the
ADL5812
at frequencies up to 2800 MHz with dc current that compares
favorably with that employed by narrow-band passive mixers.
The input stages of the LO amplifier provide common-mode
rejection, permitting the LO input to be driven either single ended
or balanced. For a single-ended input, either LOIP or LOIN can
be grounded. It is desirable to dc block the LO inputs to avoid
damaging the part by the accidental application of a large dc
voltage to the part. In addition, the LO inputs are internally dc
blocked.
Because the LO amplifier is inherently wideband, the
can be driven with either high-side or low-side LO by simply
setting the optimum RF balun and LPF inputs to the SPI.
The LO amplifier converts a variable level, single or balanced input
signal (−6 dBm to +10 dBm) to a hard voltage limited, balanced
signal internally to drive the mixer. Excellent performance can be
obtained with a 0 dBm input level; however, the circuit continues to
function at considerably lower levels of LO input power.
permits the generation of a near-square wave output
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Rev. 0 | Page 21 of 28
The performance of this amplifier is critical in achieving a high
intercept passive mixer without degrading the noise floor of the
system. This is a critical requirement in an interferer rich
environment, such as cellular infrastructure, where blocking
interferers can limit mixer performance. Blocking dynamic
range can benefit from a higher level of LO drive, which pushes
the LO amplifier stages harder into compression and causes them
to switch harder and to limit the small signal gain of the chain.
Both of these conditions are beneficial to low noise figure under
blocking. NF under blocking can be improved several decibels
for LO input power levels above 0 dBm.
The LO amplifier topology inherently minimizes the dc current
based on the LO operating voltage and the LO operating frequency.
It is permissible to reduce the LO supply voltage down as low as
3.6 V, which drops the dc current rapidly. The mixer dynamic
range varies accordingly with the LO supply voltage. No external
biasing resistor is required for optimizing the LO amplifier.
In addition, the
down mode can be used with any supply voltage applied to the part.
All of the SPI inputs are designed to work with any logic family that
provides a Logic 0 input level of less than 0.4 V and a Logic 1 input
level that exceeds 1.4 V.
All pins, including the RF pins, are ESD protected and have been
tested up to a level of 2000 V HBM and 1250 V CDM.
ADL5812
has a power-down mode. This power-
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