10
Biasing and Operation
AMMC-6345 has quite flexible drain biasing conditions.
Recommended quiescent DC bias condition for optimum
power and linearity performances is Vd=5 volts with
Vg set for Id=480 mA. For high gain applications, the
AMMC-6345 can be biased at Vd=3V. Minor improve-
ments in performance are possible depending on the
application. The drain bias voltage range is 3 to 5.5V. A
single DC gate supply connected to Vg will bias all gain
stages. Muting can be accomplished by setting Vg to the
pinch-off voltage Vp.
An optional output power detector network is also
provided. The differential voltage between the Det-Ref
and Det-Out pads can be correlated with the RF power
emerging from the RF output port. The detected voltage
is given by :
ofsref
VVVV −−=
det
where
ref
V
is the voltage at the
RDET _
port,
det
V
is a volt-
age at the
ODET _
port, and
ofs
V
is the zero-input-power
offset voltage. There are three methods to calculate :
1.
ofs
V
can be measured before each detector measure-
ment (by removing or switching off the power source
and measuring ). This method gives an error due to
temperature drift of less than 0.01dB/50°C.
2.
ofs
V
can be measured at a single reference temperature.
The drift error will be less than 0.25dB.
3.
ofs
V
can either be characterized over temperature and
stored in a lookup table, or it can be measured at two
temperatures and a linear fit used to calculate at any
temperature. This method gives an error close to the
method #1.
The RF ports are AC coupled at the RF input to the first
stage and the RF output of the final stage. No ground
wired are needed since ground connections are made
with plated through-holes to the backside of the de-
vice.
Assembly Techniques
The backside of the MMIC chip is RF ground. For mi-
crostrip applications the chip should be attached directly
to the ground plane (e.g. circuit carrier or heatsink) using
electrically conductive epoxy
[1,2]
.
For best performance, the topside of the MMIC should be
brought up to the same height as the circuit surrounding
it. This can be accomplished by mounting a gold plate
metal shim (same length and width as the MMIC) under
the chip which is of correct thickness to make the chip
and adjacent circuit the same height. The amount of
epoxy used for the chip and/or shim attachment should
be just enough to provide a thin fillet around the bottom
perimeter of the chip or shim. The ground plain should
be free of any residue that may jeopardize electrical or
mechanical attachment.
The location of the RF bond pads is shown in Figure
12. Note that all the RF input and output ports are in a
Ground-Signal configuration.
RF connections should be kept as short as reasonable to
minimize performance degradation due to undesirable
series inductance. A single bond wire is normally suf-
ficient for signal connections, however double bonding
with 0.7 mil gold wire or use of gold mesh is recom-
mended for best performance, especially near the high
end of the frequency band.
Notes:
1. Ablebond 84-1 LM1 silver epoxy is recommended.
2. Eutectic attach is not recommended and may jeopardize reliabil-
ity of the device.
