AMMC-5024 Datasheet, PDF (9/11 Pages) AVAGO TECHNOLOGIES LIMITED – 30 KHz-40GHz Traveling Wave Amplifier

Biasing and Operation
AMMC-5024 is biased with a single
positive drain supply (V_dd) a
negative gate supply (V_g1) and has
a positive control gate supply (V_g2).
For best overall performance the
recommended bias condition for
the AMMC-5024 is V_dd =7V and
I_dd = 200 mA. To achieve this
drain current level, V_g1 is typi-
cally between –2.5 to –3.5V.
Typically, DC current flow for V_g1
is –10 mA. Open circuit is the
default setting for V_g2 when not
utilizing gain control.
Using the simplest form of
assembly (Figure 20), the device
is capable of delivering flat gain
over a 2 – 50 GHz range with a
minimum of gain slope and
ripple. However, this device is
designed with DC coupled RF I/O
ports, and operation may be
extended to lower frequencies
(<2 GHz) through the use of off-
chip low-frequency extension
circuitry and proper external
biasing components. With low
frequency bias extension it may
be used in a variety of time-
domain applications (through
40 Gb/s).
Figure 21 shows a typical assem-
bly configuration.
When bypass capacitors are
connected to the AUX pads, the
low frequency limit is extended
down to the corner frequency
determined by the bypass capaci-
tor and the combination of the
on-chip 50 ohm load and small
de-queing resistor. At this fre-
quency the small signal gain will
increase in magnitude and stay at
this elevated level down to the
point where the C_aux bypass
capacitor acts as an open circuit,
effectively rolling off the gain
completely. The low frequency
limit can be approximated from
the following equation:
f_Caux =
1
2πC_aux(Ro + R_DEQ)
where:
R_o is the 50Ω gate or drain line
termination resistor.
R_DEQ is the small series de-
queing resistor and 10Ω.
C_aux is the capacitance of the
bypass capacitor connected to
the AUX Drain and AUX Gate
pad in farads.
With the external bypass capaci-
tors connected to the AUX gate
and AUX drain pads, gain will
show a slight increase between
1.0 and 1.5 GHz. This is due to a
series combination of C_aux and
the on chip resistance but is
exaggerated by the parasitic
inductance (L_c) of the bypass
capacitor and the inductance of
the bond wire (L_d). Therefore the
bond wire from the Aux pads to
the bypass capacitors should be
made as short as possible.
Input and output RF ports are
DC coupled; therefore, DC
decoupling capacitors are
required if there are DC paths.
(Do not attempt to apply bias to
these pads.)
RF bond connections should be
kept as short as possible to
reduce RF lead inductance which
will degrade performance above
20 GHz.
An optional output power
detector network is also pro-
vided. Detector sensitivity is
optimized by biasing the diodes
with typical drain voltage V_dd =
7 volts. Simply connecting
Det-Bias to the V_dd supply is a
convenient method of biasing
this detector network. The
differential voltage between the
Det-Ref and Det-Out pads can be
correlated with the RF power
emerging from the RF output
port. A >0.5 µF capacitor is
required for the Det_Out pad to
expand power detection perfor-
mance below 100 MHz.
Ground connections are made
with plated through-holes to the
backside of the device; therefore,
ground wires are not needed.
Assembly Techniques
The chip should be attached
directly to the ground plane
using either a fluxless AuSn
solder preform or electrically
conductive epoxy^[1]. For conduc-
tive epoxy, the amount should be
just enough to provide a thin
fillet around the bottom perim-
eter of the die. The ground plane
should be free of any residue that
may jeopardize electrical or
mechanical attachment. Caution
should be taken to not exceed the
Absolute Maximum Rating for
assembly temperature and time.
Thermosonic wedge bonding is
the preferred method for wire
attachment to the bond pads.
The RF connections should be
kept as short as possible to
minimize inductance. Gold
mesh^[2] or double-bonding with
0.7 mil gold wire is recom-
mended.
Mesh can be attached using a
2 mil round tracking tool and a
tool force of approximately
22 grams with an ultrasonic
power of roughly 55 dB for a
duration of 76 ± 8 mS. A guided
wedge at an ultrasonic power
level of 64 dB can be used for the
0.7 mil wire. The recommended
wire bond stage temperature is
150 ± 2° C.
8