Adjacent to the RF layers, a digitization layer includes an analog-to-
digital converter (ADC) and a digital-to-analog converter (DAC). Using our
extensive experience in mixed-signal products, this layer connects the RF
front-end to the SiP processor. In the custom SiP, we apply our experience
with digital packaging, stacked memory and field-programmable gate
array (FPGA) technology to create a compact, multifunction capability.
Densely Integrated RF Circuitry
Minimizing the size and weight of the assembly requires more than just
a focus on a modular framework, it also requires densely integrated
components and interconnects. While this is critical for achieving the
primary goal of a complex sub-assembly that is no larger than a stack of
quarters, it presents additional challenges such as maintaining sufficient
electrical isolation.
The RF circuity is often the most sensitive to noise and radiated
signals. To isolate this circuitry and provide environmental protection,
it is packaged in a hermetic ceramic or metal housing. This housing
allows the use of bare die, which require significantly less space than
individually packaged devices. Inside the hermetic package, metal
internal walls enhance the channel-to-channel isolation and reduce
unwanted electromagnetic cavity effects.
While hermetic RF modules have existed for decades,
few suppliers have the ability to produce a complex
RF assembly packaged in a single 1-inch diameter
hermetic module.
The key to this high-precision engineering is both advanced design and
manufacturing. Optimizing the size of the circuity while meeting the
electrical specifications requires not only skilled engineers, but also the
capability to perform both non-linear and electromagnetic modeling.
Since any variation in die placement can result in major impacts to the
electrical performance, Mercury uses automated assembly to reduce
variation.
Figure 6. Interior detail of the hermetic RF module layer
3
Figure 5. Simplified block diagram of ultra-compact transceiver implemented with Mercury's Spectrum Series Multiband Platform.
