1. Field of the Invention
The present invention relates generally to electronic circuits. More particularly, the present invention relates to a method of arranging signal and destination pads in electronic circuits to provide multiple signal/destination connection configurations.
2. Disclosure Information
In electronic circuits, components are attached to a substrate and the inputs and outputs of the components are interconnected by wires or, more typically, circuit traces. Circuit traces electrically connect an output terminal, or signal origination, of one component to an input terminal, or signal destination, of another component. An individual circuit trace may consist of a single path having only one origination and one destination, or it may be branched so as to have multiple originations and/or destinations. In either case, each end of a circuit trace usually terminates in a pad, to which a component input or output terminal is attached.
When a circuit is designed, it is generally laid out such that each of the components may be oriented in only one way on the circuit substrate. However, it may sometimes be desired to lay out a circuit such that one or more components may be oriented in more than one way, so that more than one configuration of signal/destination connections can be made using a single circuit trace layout. This idea is illustrated in FIG. 1. Here, a signal circuit trace 20 having two signal pads 21/22, and two destination circuit traces 30/35 each having one destination pad 31/36, respectively, have been laid out on a substrate 50. The signal trace 20 is attached at one end to an output terminal (signal origination) of an electronic component, while the destination traces 30/35 are each attached to an input terminal (signal destination) of another component. Although these components and their terminals are not shown, the signal originations are denoted by single-digit reference numerals 1, 2, 3, and so forth, and the signal destinations are denoted by reference letters A, B, C, and so forth.
Once the circuit traces 20/30/35 have been laid out on the substrate 50 as shown in FIG. 1, the circuit can then be populated with components. At this point, the substrate populator has the option of attaching a jumper 10 (1) between signal pad 21 and destination pad 31, thereby connecting signal 1 with destination A, or (2) between signal pad 22 and destination pad 36 (as indicated by the dashed outline of a jumper 10), thereby connecting signal 1 with destination B. In either combination, a unique circuit is produced. Thus it can be seen that a single circuit trace arrangement may be populated with jumpers 10 in more than one way so as to provide more than one signal/destination connection combination (hereinafter referred to as an "SDCC"). This means that rather than producing two separate circuit trace arrangements--e.g., two unpopulated printed circuit boards (PCBs)--which have similar layouts except for a few signal/destination connections, it is possible to use the foregoing multiconfigurable pad arrangement to produce only one such circuit trace/PCB which has the possibility of producing either of two SDCCs. In short, one circuit/PCB using the foregoing pad arrangement can take the place of two separate but similarly laid out circuits/PCBs.
FIG. 1 illustrates a prior art attempt at providing more than one SDCC for one signal origination 1 and two potential destinations A/B. This arrangement offers two possible SDCCs: 1A (i.e., signal 1 to destination A) and 1B. FIG. 2 illustrates the prior art case for two signals 1/2 and two destinations A/B, which also provides two possible connection combinations: 1A/2B and 1B/2A. FIG. 3 illustrates an arrangement of three signals 1/2/3 and three destinations A/B/C, which once again offers two possible connection combinations: 1A/2B/3C and 1B/2C/3A.
Several things should become apparent from the arrangements presented in FIGS. 1-3. First, the layout of the signals and destinations may be re-arranged in many different ways to achieve the same result. For example, FIG. 4 illustrates one of the many ways in which the three signals 1/2/3 and three destinations A/B/C of FIG. 3 may be re-arranged to produce the same two possible SDCCs as FIG. 3. Second, the signals and destinations may be arranged so as to present different sets of two SDCCs. To illustrate this, note that with three signals and three destinations, 3-factorial, or six, SDCCs are possible in all:
I II III IV V VI 1A 1A 1B 1B 1C 1C 2B 2C 2A 2C 2A 2B 3C 3B 3C 3A 3B 3A
(This assumes, of course, that each signal is connected to one and only one distinct destination, and vice versa.) However, although three inputs and three outputs can be arranged in six different SDCCs, only two may be provided for according to the foregoing pad arrangement without adding additional pads. FIG. 5 illustrates one way of arranging the same three signals 1/2/3 and destination pads A/B/C to provide two different SDCCs: 1B/2A/3C and 1C/2A/3B. Third, it should become apparent that the number of signals does not have to equal the number of destinations. For example, FIG. 1 presents the case of one signal 1 and two destinations A/B. Fourth, note that an arrangement having n signals and at least n destinations requires the use of 4n pads. Thus, in FIG. 1 where n=1, four pads are required. In FIG. 2 where n=2, eight pads are needed, and in FIGS. 3-5 where n=3, twelve pads are needed.
Furthermore, several assumptions underlie the prior art arrangements shown in FIGS. 1-5. First, each signal origination and each signal destination may have multiple pads, but each signal must ultimately connect with one and only one signal destination, regardless of which particular pads are jumpered together; likewise, each signal destination must ultimately connect with one and only one signal origination. Second, each signal pad may be connected to no more than one destination pad, and vice versa. Third, each signal or destination pad can have no more than one jumper attached to it. Fourth, jumpers may not cross one another.
Another prior art approach which is an improvement upon the aforementioned one signal-two destination arrangement of FIG. 1, and which also relies upon the assumptions discussed above, is illustrated in FIG. 6. This approach differs from the one pictured in FIG. 1 in that (1) the two signal pads 21/22 and their associated branches have been combined to form only one signal pad 23 and one branch, and (2) the signal pad 23 has been interposed between the two destination pads 31/36. This combination and interposition allows a jumper 10 to be placed either between signal 1 and destination A, as shown in FIG. 6, or between signal 1 and destination B, as represented by the dashed outline. Thus, this improved approach allows the same connection combinations as allowed by FIG. 1, but with the added benefit of requiring only three pads rather than four, thereby taking up less space on the substrate 50.
Although the foregoing prior art approaches are effective ways of arranging signal and destination pads so as to provide multiple SDCCs, they nonetheless suffer some serious drawbacks. First, the methods illustrated in FIGS. 1-5 take up a lot of space on the substrate. Second, these methods provide an undesirable dangling signal trace for each signal in either of the two possible connection combinations. For example, when the jumpers are positioned as shown in FIG. 2, signal pads 22 and 27 and their associated branches form dangling signal traces for signals 1 and 2, respectively. Likewise, when the alternate, dashed-line connections are made in FIG. 2, pads 21 and 26 and their associated branches form dangling traces. (The arrangements shown in FIGS. 3-5 also leave a dangling trace for each signal 1/2/3.) These dangling traces may act as unwanted RF transmitters or receivers, thus interfering with the electrical function of elements within the circuit or with other circuits and equipment in the surrounding environment. As for the approach shown in FIG. 6, dangling traces have been eliminated and the number of pads reduced, but its application has been limited to cases involving only one signal and two possible destinations.
It is desirable, therefore, to provide a way of arranging signal and destination pads on a substrate for multiple (i.e., two or more) signals and an equal or greater number of destinations so as to provide multiple SDCCs while eliminating dangling traces and reducing the overall number of pads required.