BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a perspective view of a feedthrough capacitor that may be used in accordance with the process of this invention.
FIG. 2 is a graphical symbol for the feedthrough capacitor shown in FIG. 1.
FIG. 3 is a block/circuit diagram illustrating a circuit having a transparent-to-test capacitor. In this example component 28 and 30 is transparent-to-test because of the low capacitance value. In-Circuit tester has limitation to measure capacitance below certain value (say 15 pF).
FIG. 4 is block/circuit diagram illustrating another electric circuit having a transparent-to-test capacitor. In this example component 48 and 46 are connected in parallel. So if one of the capacitor has very high value compared to the other capacitor, the lower value capacitor become transparent-to-test part.
FIG. 5 is a block/circuit diagram illustrating a circuit that is equivalent to the circuit shown in FIG. 3, which in accordance with the process of this invention uses a feedthrough capacitor in place of a conventional two-terminal capacitor.
FIG. 6 is a block/circuit diagram illustrating a circuit that is equivalent to the circuit shown in FIG. 4, which in accordance with the process of this invention uses a feedthrough capacitor in place of a conventional two-terminal capacitor which is identified as transparent-to-test.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In accordance with the process of this invention, difficulties associated with detecting the presence of a conventional two-terminal capacitor that is transparent to standard in-circuit testing techniques are overcome by replacing a conventional two-terminal capacitor with a feedthrough capacitor having internally electrically connected terminals, and testing for electrical continuity between a test point electrically connected to one of the internally connected terminals of the feedthrough capacitor, and a test point electrically connected to the other internally connected terminal of the capacitor. This is a very simple test to determine whether there is electrical continuity or an open circuit, thereby indicating whether the capacitor is properly positioned and electrically connected or completely missing or improperly positioned. The process of this invention is easily and inexpensively automated using conventional component indexing and in-circuit testing techniques, eliminating complicated pad designs such as the split-pad technique discussed above, and avoids the need for expensive equipment and/or high labor costs.
In FIG. 1, there is shown a perspective view of a feedthrough capacitor 10 having terminals 12, 13, 14 and 15. Terminals 12 and 13 are internally connected, i.e., an electrical conductor passes through the dielectric core material of the capacitor electrically connecting terminals 12 and 13. Electrical capacitance is present between either of the internally electrically connected terminals 12, 13 and either of the remaining terminals 14, 15. Feedthrough capacitor 10 is represented symbolically in FIG. 2.
FIG. 3 is a block/circuit diagram illustrating an electric circuit 20 having electrically conductive pathways or circuit traces 22 connecting the various components as illustrated, including an oscillator 24 (e.g. 8 MHz), a resistor 26, and capacitors 28 and 30 to each of the crystal terminals. In such an arrangement, capacitors 28 and 30, depending on the values of their capacitance, can be extremely difficult, if not impossible to detect using standard in-circuit testing techniques.
FIG. 4 is a block circuit diagram illustrating an electronic circuit 40 having a power input 42, a resistor 44 (e.g., 10 microhenrys), and two capacitors 46 and 48, which are in parallel. In this illustrated circuit arrangement, when one of the capacitors has a much higher capacitance than the other capacitor, the capacitor with the lower capacitance cannot be tested using standard in-circuit testing techniques. For example, with a 3.3 volt 2.52 MHz power source, a 10 microhenry inductor 44, and a 10 microfarad (+/−10/%) capacitor 48, a 0.047 microfarad capacitor (+/−10%) 46 could not be tested using standard in-circuit testing techniques.
FIG. 5 shows an equivalent circuit 20′ to that shown in FIG. 3, in which the conventional two-terminal capacitors 28, 30 are replaced with feedthrough capacitors 28′ and 30′. With this arrangement, the presence of capacitor 28′ in the circuit can be verified by determining that there is electrical continuity between, for example, test points 50 and 55. Similarly, the proper placement of capacitor 30′ in the circuit can be verified by determining that there is electrical continuity between test points 56 and 58.
FIG. 6 shows a circuit 60 that is equivalent to circuit 40 shown in FIG. 4. However, rather than using a conventional 0.047 microfarad capacitor 46 having two-terminals as shown in FIG. 4, circuit 60 utilizes a feedthrough capacitor 46′, which allows verification of proper placement and electrical connection of capacitor 46′ by simply testing for electrical continuity between, for example, test points 62 and 64.
It will be understood by those who practice the invention and those skilled in the art that various modifications and improvements may be made to the invention without departing from the spirit of the disclosed concept. The scope of protection afforded is to be determined by the claims and by the breadth of interpretation allowed by law.
Patent Application
20080088318
