Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1997-09-17
2001-07-03
Hunter, Daniel (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S078000, C455S082000, C333S103000
Reexamination Certificate
active
06256495
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of RF transmission, and more particularly to semiconductor switching and radio frequency signal transport within a multi-layered printed circuit board configuration.
BACKGROUND OF THE INVENTION
Mobile Cellular and Personal Communication Service (PCS) devices typically provide for transmission and reception of signals through one of two antenna configuration options. One option is to transmit and receive through an internal antenna, permanently attached to the device itself, and provided so that the device always remains portable and mobile. The second option is to use an external antenna, often a car mounted antenna and usually connected via an accessory transmission cable from an adapter on the device to a connector configured to deliver and receive transmissions over the external antenna. Selection between the two antennas is accomplished utilizing a switch. Implementation of an antenna selection and porting switch in practice mandates a low loss switch implementation, thereby minimizing the degradation of received signal strength and preserving transmitted power.
Additionally, most mobile handsets position the internal antenna port, and consequently the internal antenna, at the top portion of the handset, while placing the external antenna port at the bottom of the handset. Such a configuration, although ergonomically convenient for the end user, mandates the incorporation of an internal radio frequency (RF) transmission medium from the top end of the handset to the bottom end. The RF signal transmission path must be selectable via the aforementioned switch. A common prior art implementation for providing a transmission path for the RF signal from switch to external antenna port is via incorporation of a low loss RF coaxial cable from the top of the handset to the bottom external antenna port. However, this method is a costly manufacturing technique.
Furthermore, the advent of allocation of a PCS communications bandwidth has motivated many communication system manufacturers and designers to investigate methods of incorporating both PCS band transmission and cellular band transmission within one communications device. Incorporating both bands within one device provides the motivation for designers to minimize replicated components in each RF band, thereby reducing the overall complexity and cost of the new dual band devices. In consideration of the above engineering and economic restrictions, use of a common switching device, which would direct either PCS or cellular communications over either the internal or external antenna, would be most advantageous. A variety of switch types, including mechanical coxial or waveguide four-way porting switches and diversity switches, are available to accomplish the task. Mechanical coaxial or waveguide four-way porting switches, however, tend to be relatively large and extremely costly. Semiconductor diversity switches are inherently less expensive to produce and offer increased reliability as compared to mechanical type switches, but diversity switches have a drawback in that a signal must pass through two junctions within a diversity switch configuration, and therefore received and transmitted signals experience the attenuation associated with passing through two semiconductor junctions.
SUMMARY OF THE INVENTION
The present invention is a multiport, multiband semiconductor switching and transmission circuit. Although the present invention is particularly well suited for use within a dual band cellular/PCS phone, it may be utilized whenever port switching for an alternating current (AC) signal is required. Another function of the present invention is to provide an inexpensive, low-loss radio frequency (RF) transmission medium within a multi-layer printed circuit board. Switching is provided by semiconductor switches located in a plurality of switching legs from a common transmission or reception node. Semiconductor switches are biased on and off with a DC biasing signal, thus allowing an RF signal to pass through an appropriately biased switching leg. An exemplary embodiment of the present invention forward biases a diode by applying a DC current through a first inductor prior to passing through the diode. The DC current then passes through a second inductor and returns to ground. The inductor values are chosen so that the inductors act as a virtual open to high frequency AC (RF) signals while simultaneously acting as a short to the DC biasing signal. An RF signal applied on either side of the forward biased switch, passes through the switch from a first port to a second port. Capacitors are provided, as needed within a specific application, to allow high frequency RF signals to pass unimpeded while blocking the DC biasing current from passing through undesired circuit paths.
In a dual band cellular/PCS device having an internal antenna and an external antenna port, switching of transmitted and received cellular and PCS signals to either the internal antenna or the external antenna port is accomplished by linking the cellular transmitter/receiver to the internal antenna via a first semiconductor switching leg, linking the cellular transmitter/receiver to the external antenna port via a second semiconductor switching leg, linking the PCS transmitter/receiver to the internal antenna via a third semiconductor switching leg, and linking the PCS transmitter/receiver to the external antenna port via a fourth semiconductor switching leg. In effect, each of a plurality of ports is linked by a semiconductor switching leg to form a semiconductor bridge switching circuit. Each semiconductor switching leg is individually operable by applying an appropriate DC biasing signal. A DC biasing signal may also be applied to more than one switching leg to allow any combination of switching legs to operate in unison.
Advantageously, implementation of the semiconductor switching circuits within a multi-layer printed circuit board is less expensive and less prone to failure than mechanical switches. Furthermore switched signals must pass through only one semiconductor junction to arrive at the desired port, thereby minimizing the signal attenuation associated with the utilization of semiconductor diversity switches.
In one embodiment of the present invention, the semiconductor device incorporated within an individual switching leg is a diode. In another embodiment of the present invention, the circuit is implemented utilizing diode-connected bipolar transistors. Other choices for semiconductor devices are also contemplated, as would be apparent to those skilled in the art.
In yet another embodiment of the present invention as incorporated within a dual band, antenna selectable transmitting/receiving device, transport of a transmitted and/or received RF signal is provided between the previously described semiconductor switching circuit and a selected antenna over a stripline fabricated within the intermediate layers of the multi-layer printed circuit board. Via arrays are utilized, in lieu of continuous metallic side walls within the multi-layer printed circuit board, to reduce crosstalk with other stripline/microstrip incorporated within the printed circuit board and additionally to minimize electromagnetic/electrostatic disturbances with incorporated components. Advantageously, fabricating stripline within multi-layer printed circuit boards is relatively inexpensive compared to other means of RF signal transport.
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patent: 5
Francisco Mark
Kim Myung-Kul
Agere Systems Guardian Corp.
Armstrong Darnell R.
Gibbons Del Deo Dolan Griffinger & Vecchione
Hunter Daniel
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