AMMC-5024 Datasheet, PDF (8/10 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 typically
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 assembly 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 capacitor and the
combination of the on-chip 50 ohm load and small de-
queing resistor. At this frequency 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 connect-
ed to the AUX Drain and AUX Gate pad in farads.
With the external bypass capacitors 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 combina-
tion 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 perfor-
mance 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 con-
necting 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 ex-
pand power detection performance 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 conductive epoxy, the amount
should be just enough to provide a thin fillet around the
bottom perimeter 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 induc-
tance. Gold mesh^[2] or double-bonding with 0.7 mil gold
wire is recommended.
Mesh can be attached using a 2 mil round tracking tool
and a tool force of approximately 22 grams with an ultra-
sonic 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.