Data Sheet HMC1121
Rev. 0 | Page 11 of 15
THEORY OF OPERATION
The HMC1121 is a three-stage, gallium arsenide (GaAs),
pseudomorphic high electron mobility transfer (pHEMT),
monolithic microwave integrated circuit (MMIC), 4 W power
amplifier consisting of three gain stages in series. A simplified
block diagram is shown in Figure 32. The input signal is divided
evenly into two; each of these two paths are amplified through
three independent gain stages. The amplified signals are then
combined at the output.
13529-032
GG1
,
GG2
RFIN
V
DD2
V
DD1
RFOU
V
GG3
, V
GG4
V
DD4
V
DD3
Figure 32. Simplified Block Diagram
The HMC1121 has single-ended input and output ports whose
impedances are nominally matched to 50 Ω internally over the
5.5 GHz to 8.5 GHz frequency range. Consequently, it can directly
insert into a 50 Ω system without the need for impedance
matching circuitry. In addition, multiple HMC1121 amplifiers
can be cascaded back to back without the need of external
matching circuitry. Similarly, multiple HMC1121 amplifiers
can be used with power dividers at the input and power
combiners at the output to obtain higher output power levels.
The input and output impedances are sufficiently stable vs.
variations in temperature and supply voltage that no impedance
matching compensation is required.
It is critical to supply very low inductance ground connections
to the ground pins as well as to the backside exposed pad to
ensure stable operation.
To ensure the best performance out of the HMC1121, do not
exceed the absolute maximum ratings.
