ON-CHIP SAMPLING CIRCUIT AND
CROSS REFERENCE TO RELATED
The present application is a divisional of U.S. application Ser.No. 11/109,535 filed on Apr. 19, 2005 now U.S. Pat. No. 7,251,762, and entitled On-Chip Sampling Circuit and Method.
BACKGROUND OF THE INVENTION
plurality of probe circuits while the other pin is responsive to the other pluralities of probe circuits via a select circuit. Numerous output combinations and permutations are possible.
5 When the probe circuit of the present disclosure is implemented in the context of a solid state memory device, the various decode circuits and output select circuit(s) may be responsive to address signals or some portion of an address signal. A method of operating such a sampling circuit as well
10 as systems embodying sampling circuits are also disclosed.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is directed generally to circuit testing and, more particularly, to the testing of circuits constructed 15 using solid state fabrication techniques.
After the fabrication of a chip containing one or more solid state circuits, it is common in the industry to require that the chip pass certain tests before being identified as a good part. For example, after the fabrication of a memory device, the 20 memory device is connected to a tester which automatically performs a series of preprogrammed tests on the part. See, for example, U.S. Pat. No. 6,483,333 entitled Automated MultiChip Module Handier and Testing System.
Often during the fabrication of parts, particularly new 25 parts, the signals available at the output pins of the part are insufficient to provide the designer with the information necessary to understand how the part is performing. In those situations, diagnostic systems are available such as the system disclosed in U.S. Pat. No. 6,841,991. In such diagnostic 30 systems, probes are brought into contact with various nodes on the circuit to sample and analyze the signals available at those nodes. For that to be performed, the nodes of the circuit must be available to the probe of the diagnostic system. Thus, the part must be tested before fabrication is complete at which 35 time the circuits of the part are accessible only through the part's output pins.
There is a need to be able to access various nodes within a circuit even after a device has been completely fabricated.
According to one embodiment of the present disclosure, a sampling circuit is comprised of a plurality of probe circuits, with each probe circuit connected to a unique node within an 45 encapsulated and/or packaged circuit to be tested. A decode circuit selects one of the probe circuits to enable the signal available at the unique node to which the probe circuit is connected to be transmitted.
According to another embodiment of the present disclo- 50 sure, a sampling circuit is comprised of a first plurality of probe circuits, with each probe circuit connected to a unique node within an encapsulated and/or packaged circuit to be tested. A first decode circuit selects one of the first plurality of probe circuits. A second plurality of probe circuits is provided 55 with each of the probe circuits connected to a unique node within the circuit to be tested. A second decode circuit selects one of the second plurality of probe circuits. An output select circuit is provided for selecting between the first plurality of probe circuits and the second plurality of probe circuits so that 60 a unique signal may be output for review and analysis.
Multiple pluralities of probe circuits and decode circuits may be provided. The manner of signal output may vary depending on the number of pins available. For example, if one pin is available, the multiple pluralities of probe circuits 65 will compete with one another via the output select circuit. If two pins are available, one pin may be responsive to one
For the present invention to be easily understood and readily practiced, the present invention will now be described, for purposes of illustration and not limitation, in conjunction with the following figures, wherein:
FIG. 1 is a block diagram illustrating a first embodiment of a sampling circuit of the present disclosure;
FIG. 2 is a block diagram illustrating another embodiment of a sampling circuit of the present disclosure;
FIG. 3 illustrates one example of a memory device in which the sampling circuit of the present disclosure may be implemented;
FIGS. 4A and 4B illustrate various exemplary circuitry for implementing the block diagram of FIG. 2;
FIG. 5 illustrates another embodiment of the present disclosure;
FIG. 6 illustrates circuits, within a device to be tested, connected to the sampling circuit of the present disclosure; and
FIG. 7 illustrates a system using one or more devices incorporating the sampling circuit of the present disclosure.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram illustrating a first embodiment of a sampling circuit 8 constructed according to the teachings of the present disclosure. A circuit 10 to be tested has discrete nodes or tap points 12,14,16 identified within the circuit 10. The circuit 10 has been, for example, encapsulated such that the circuit 10 communicates via a plurality of pins (not shown). The nodes 12, 14, 16 are identified as points of interest such that the signals available at those nodes will help engineers, designers, etc. to understand how the circuit 10 is functioning. Each of the nodes 12, 14, 16 is connected to a probe circuit 22, 24, 26, respectively. The probe circuits 22, 24, 26 are serially connected. Each of the probe circuits 22, 24,26 is responsive to a decode circuit 28 which is responsive to control signals.
In operation, signals available at nodes 12, 14, 16 are received by their respective probe circuits 22, 24, 26. The decode circuit 28, in response to the control signals, selects one of the probe circuits 22, 24, 26 such that the signal available at the selected probe circuit's node is transmitted as shown by the arrow 30. The transmitted signal may be transmitted to more probe circuits (not shown) or connected to an output pin (not shown). In this example, the signals available at nodes 12, 14, 16 are all capable of being analyzed externally of the circuit 10, although only one at a time. In the embodiment illustrated in FIG. 1, the probe circuits 22,24,26 together with the decode circuit 28 comprise the sampling circuit 8.
FIG. 2 is a block diagram illustrating another embodiment of a sampling circuit of the present disclosure. The upper half of FIG. 2 is identical to FIG. 1. However, in FIG. 2 additional nodes or tap points 12', 14', 16' have been identified within