METHOD AND APPARATUS FOR TESTING ANALOG AND DIGITAL CIRCUITRY WITHIN A LARGER CIRCUIT

摘要

The present invention relates to a circuit comprising an analog circuit element, a digital circuit element separated from the analog circuit element and a boundary scan cell chain distributed along the boundary between the analog and digital circuit elements. During the test, the chain can be controlled to separate the analog circuitry from the digital circuitry and provide the selected test signals to nodes distributed along the boundary between the analog and digital circuitry. Typically, the circuit is an integrated circuit that directly applies a signal to each of an analog circuit element, a digital circuit element and a boundary scan cell chain, and has external pins for receiving the signal directly from each. Preferably, each cell of the chain has a first multiplexer, a flip-flop (an input connected to the output of the flip-flip, another input and an analog circuit element and a digital circuit element connected to one of the analog circuit elements and the digital circuit element). And a second multiplexer having an output connected to another one of the two. The cells can be connected together in series so that the chain can be controlled to operate in any of four modes: non-test mode in which the chain is transparent to analog and digital circuit elements; A serial shift mode in which data values are shifted in or out of the chain sequentially (where the chain is transparent to analog and digital circuit elements); A parallel load mode in which data values are sequentially shifted in a chain and these data values are also sequentially shifted into analog circuit elements and digital circuit elements; And a test mode in which data values (pre-chained) are applied simultaneously to analog and digital circuit elements. Other embodiments include a boundary scan cell chain of the type used in such a circuit, one of the cells used in such a chain, and a method of testing such a circuit.