Test generation techniques of analogue circuits have been studied for more
than two decades
followed by the development of the
corresponding design-for-testability (DFT) techniques.
The requirements for fast, efficient and low-cost testing impose solutions
suitable for specific classes of circuits. Hence general test strategies
are usually further developed to achieve partial solutions suitable
for specific classes of circuits.
An oscillation-based test approach has recently been applied to
testing integrated operational amplifiers
and digitally-programmable switched-current biquadratic filters.
In oscillation-based testing,
the unit-under-test is converted to an oscillating circuit and the frequency
of oscillation is measured.
Changes of the frequency of oscillation from its nominal value indicate
possible faults in the
unit-under-test. The method of putting the unit-under-test in the oscillation
mode and the choice of the actual frequency of oscillation are specific
for the fault detection procedure employed.
In this paper we propose an oscillation-based test structure for testing
active RC filters. For this class of circuits, different DFT methodologies
have been reported after the initial work of M.Soma.
Our approach can be
regarded as complementary to the existing methodologies since it is primarily
used as an effective go no-go test that verifies if the filter-stage-under-test
conforms with the required specifications.
The proposed test structure uses an all-pass equalizer
in order to fulfil the conditions for oscillation at the frequency of the pole of the
filter stage-under-test.
Examples of testing a bandpass resonator active filter
and a low-pass filter stage with a frequency
dependent negative resistor (FDNR) are presented to illustrate the approach.