Circuit cards having a single ground plane with logic devices connected thereto

#The present invention relates generally to the field of circuit cards and, in particular, to circuit cards having a single ground plane with logic devices connected thereto.

#Three-ground electrical systems, such as many circuit cards deployed in central offices or remote units of telecommunications systems or the like, are often connected to two-ground electrical systems, such as telecommunications systems. For example, some three-ground circuit cards have a logic-ground plane to which ground pins of logic devices of the circuit card are connected, a separate chassis-ground plane, and a battery-return of a power supply of the circuit card, e.g., a DC-to-DC power supply or converter for providing voltages to the logic devices. Telecommunications systems typically have a chassis-ground, e.g., a housing (or rack) of a central office, remote unit, or the like for containing the circuit cards connected to earth ground, and a battery-return connected to the chassis-ground at a single location.

#One method for connecting three-ground circuit cards to two-ground telecommunications systems involves using a circuit card having the logic-ground plane connected to the battery-return of the circuit card and having the logic-ground capacitively coupled to the chassis-ground plane of the circuit card using one or more relatively high-voltage capacitors. The chassis-ground plane is connected to the chassis-ground of the telecommunications system and the battery-return of the circuit card is connected to the battery return of the telecommunications system.

#FIG. 1 is a plan view of a circuit card according to an embodiment of the present invention.

#FIG. 2 is a cross-sectional view of a circuit card according to another embodiment of the present invention.

#FIG. 3 is a block diagram of an electronic system according to another embodiment of the present invention.

#In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific illustrative embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that logical, mechanical and electrical changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense.

#Embodiments of the present invention involve connecting logic components to a single ground plane of a circuit board connectable to a chassis-ground of a housing to ground the logic components to the chassis-ground. Advantageously, this provides a direct, lower impedance path between the logic components and earth ground for ESD and EMI as compared to conventional situations that involve connecting logic devices to one ground plane of a circuit card, connecting the ground plane to a battery-return of the circuit card, and capacitively coupling the ground plane to another separate ground plane connectable to a chassis-ground. This also eliminates one or more relatively high-voltage capacitors that would otherwise be used to couple the separate ground planes together.

#FIG. 1 is a plan view of a circuit card 100, such as a circuit card for a telecommunications system, according to an embodiment of the present invention. Circuit card 100 includes a logic device 102 disposed on a surface 103 of a substrate 101 of circuit card 100. Circuit card 100 includes electrically interconnected conductive layers 1061 to 106N disposed on surface 103. In one embodiment, conductive traces, such as conductive trace 107, electrically interconnect conductive layers 106. Logic device 102 has a ground pin 104 connected to conductive layers 106, such as at conductive layer 1061. In one embodiment, a conductive trace 108 disposed on surface 103 interconnects pin 104 to conductive layer 1061. Conductive layers 106 are connectable to a chassis-ground of an electronic system, such as a housing of a telecommunications system for containing circuit cards. This enables conductive layers 106 to act as a single ground plane of circuit card 100. In one embodiment, the single ground plane comprises one or more of conductive layers 106, conductive trace 107 and conductive trace 108. Connecting ground pin 104 to conductive layers 106 and thus the single ground plane of circuit card 100 provides a direct path between logic device 102 and chassis-ground and thus earth ground for ESD and EMI.