adl5386 Analog Devices, Inc., adl5386 Datasheet - Page 20

• Manufacturer Part Number: adl5386
• Description: 50 Mhz To 2200 Mhz Quadrature Modulator With Integrated Detector And Vva
• Manufacturer: Analog Devices, Inc.

ADL5386
LOGARITHMIC DETECTOR
The design of the log detector is similar to that of the
standalone log detector device, where the log function is
generated by a series of limiting amplifiers and detectors. The
output current from this log detector is compared with that
from a voltage-to-current converter connected to the VSET input.
Any net difference between these two currents is pumped into
an on-chip integrating capacitor that is generally augmented by
additional off-chip capacitance. The voltage on the integrating
capacitor is amplified and produces an output error voltage that
is generally used to adjust the attenuation of the voltage variable
attenuator until the VSET current and the current from the log
detector are balanced.
AD8317
Rev. 0 | Page 20 of 36
VOLTAGE VARIABLE ATTENUATOR (VVA)
The VVA is implemented on a GaAs die separate from the
silicon die where the modulator and detector reside. The VVA
is formed by PHEMTs and resistors connected in a PI network
to provide the attenuator function. The gate source bias on the
PHEMTs are controlled by the voltages on the VREF and VDET/
VCTL pins, resulting in different attenuation between ATTI and
ATTO as the voltage at VDET/VCTL is varied. The resistance in
the shunt paths between ATTI and ATTO to ATTCM vary in the
opposite manner as the paths between ATTI and ATTO to
maintain good return loss through different attenuation levels.