Electrical connectors – Jumper
Reexamination Certificate
2000-12-18
2001-10-30
Sircus, Brian (Department: 2833)
Electrical connectors
Jumper
C361S728000, C330S066000, C333S035000
Reexamination Certificate
active
06309245
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to RF power amplifiers and mounting systems for such amplifiers. More particularly, the present invention relates to RF power amplifiers mounted on pallet structures.
2. Description of Prior Art and Related Information
RF power amplifiers require careful design of all RF signal lines to avoid RF energy loss. In particular, RF signal lines require a consistent connection to ground in order to properly propagate RF signals along the signal line. If the signal line is not properly grounded along the entire signal path, RF signals may reflect, radiate or generate heat. In addition, the distance of the path to ground is important. A longer path to ground distance increases the probability of an RF signal radiating or reflecting as opposed to a shorter path. This consideration becomes more significant at both higher power and frequencies, and in particular the frequency ranges common in modern cellular base station applications.
Conventionally, RF gain blocks are structurally arranged on a pallet which acts as a substrate and heat sink for the associated RF circuitry. These pallets are mounted in a housing base and electrical connections between the RF and DC lines on the pallet and associated traces on the base must be made. The RF connection point is most critical and is typically referred to as the RF launch. The pallet is designed to keep acceptable tolerances of the over hang of the RF gain blocks and the base to provide a consistent ground across the pallet/base connection. A screw at each RF launch is typically employed to mount the pallet to the base and provide a positive ground connection. Despite these efforts to control the pallet/base connection, existing pallet structures, while providing an RF ground, do not provide a fixed and positive RF ground, which is consistent from amplifier to amplifier and over time and temperatures.
One cause of this problem with existing RF pallet structures is that the RF ground is not consistent when moved from a test fixture to a final product. When moving the pallet to a production amplifier assembly, the RF ground changes in distance and location relative to the RF traces and RF launch for various reasons. For example, when the thinned pallet landing is torqued by the machine driving of the screw, the landing may warp. This will change the RF ground location. Also, machine tolerances may be varied in production environments.
Another cause of variations in RF ground is due to changes introduced by temperature variations. Such temperature changes will cause relative movement of the pallet and base since the pallet has the heat generating power transistors mounted thereon. Also, the pallet and base may have different thermal coefficients of expansion. Furthermore, over time thermal cycling may cause the screw at the RF launch to loosen. All these factors cause the specific RF ground location relative to the RF traces at the pallet/base connection to change in an unpredictable way.
Another important consideration in RF power amplifiers is maintaining correct phase relations between RF signal paths. This requires each path to have a consistent known reactance. A problem with existing RF pallet structures is the inherent existence of unpredictable parasitic reactances. The reactances inherent to the conventional structures are introduced because of variables such as junctions of ground contact locations and changes over temperature. The junctions typically are located in phase dependent (high RF power) locations and are susceptible to phase and amplitude errors, return loss changes and possible coupling issues. As a result, immediate negative effects to tuning are created.
Furthermore, some existing RF pallet structures require manual labor in installing pallet to base coupling mechanisms. This leads to increased cost of manufacturing.
Thus, the need exists for an RF amplifier assembly having a reliable RF pallet ground which reduces RF signal losses. A need further exists for an RF pallet design where parasitic reactances are substantially eliminated and the immediate negative effects to tuning can be minimized and compensated over temperature while a need further exists for an RF pallet design compatible with low manufacturing costs.
SUMMARY OF THE INVENTION
In accordance with the teachings of this invention, an RF amplifier assembly is provided which employs a reliable RF pallet ground which reduces RF signal losses. Furthermore, a fixed and positive RF pallet is provided that minimizes inherent parasitic reactances introduced because of ground contact location and changes over temperature. As a result, susceptibility to phase and amplitude errors, return loss changes and possible coupling issues are decreased and, as a result, the immediate negative effects to tuning can be minimized and compensated over a range of operating temperatures.
In one aspect, an RF amplifier assembly is provided. The assembly comprises a base and an RF pallet. The base comprises a recess and a pallet contact portion. The RF pallet is configured in the recess. The pallet has a first end, a second end, and a first overhang disposed at the first end. The overhang comprises a notch and a downwardly protruding ledge. RF amplifier circuitry is configured on the pallet. The pallet contact portion is coupled to the overhang of the pallet. In a preferred embodiment, the RF pallet further comprises a second overhang disposed at the second end. The second overhang is preferably symmetrical to the first overhang.
In a preferred embodiment, the pallet contact portion comprises a shelf adapted to support the overhang of the pallet to provide an RF ground connection. The assembly further comprises an RF connector coupled to the pallet and the pallet contact portion. The RF connector comprises first and second end portions. The first end portion of the RF connector is coupled to a top surface of the pallet, and the second end portion is coupled to a top surface of the pallet contact portion. The RF connector preferably comprises a jumper connector, which may be an omega shaped connector. The pallet further comprises an RF trace extending from the connector and a fastener disposed adjacent to the RF trace to maintain positive contact of the ledge with the pallet contact portion. The fastener may, for example, comprise a screw.
In a preferred embodiment, the assembly further comprises a housing, wherein the housing comprises the base. The housing may be composed of a same material as the pallet; for example, an aluminum alloy. Alternatively, the pallet may be composed of a material with a higher thermal conductivity, such as copper.
In another aspect, a pallet is provided for use in an RF amplifier assembly. The pallet comprises a first end, a second end, a first overhang disposed at the first end, a top major surface, a bottom major surface, and RF amplifier circuitry configured on the top major surface. The first overhang comprises a notch and a downwardly protruding ledge. The ledge comprises a first downward length that is smaller than a second downward length between the top major surface and the bottom major surface. The pallet further comprises a notch surface. The ledge has a bottom ledge surface disposed above the bottom major surface and below the notch surface. The pallet further comprises first and second side edges. The notch and ledge extend from the first side edge to the second side edge.
A method is also provided for making an RF amplifier assembly having a reliable connection of RF ground. The method comprises providing a pallet having a downwardly protruding ledge at one end, providing an RF amplifier module on the pallet, providing a pallet contact portion having a shelf adapted to support the ledge of the pallet, coupling the pallet to the pallet contact portion, and coupling an RF connector to the pallet and the pallet contact portion. The coupling the RF connector to the pallet and the pallet contact portion may comprise fastening one end on top of the pallet and another
Myers Dawes & Andras LLP
Powerwave Technologies Inc.
Sircus Brian
Webb Brian S.
LandOfFree
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