Digital Signal Processing Reference
In-Depth Information
1. A multifrequency signal source is used to speed up the whole measurement
process by avoiding a repetition of the measurement process step by step for
each separate frequency.
2. A spectrum analyser rather than a vector voltmeter is used for high-speed
estimation of the frequency response of the electronic device being tested by
processing a single shot of the output signal.
3. The multifrequency signal source generates the test signal using specified
parameters, including the phase angles for all frequency components, leading
to the possibility of using a single rather than two spectrum analysers and thus
reducing the complexity and production costs of the system.
4. Pseudo-randomized sampling techniques are used to achieve and provide for a
high-resolution vector spectrum analysis of wideband signals in the frequency
range up to a few GHz.
While all the elements of the system determine its performance, the multifre-
quency test signal generator plays a special role. In an ideal case, the generated
excitation signal contains discrete frequencies covering the required density for
the whole frequency range within which the object behaviour is to be observed.
It is not easy to cover all of it at one go if this frequency range is indeed wide. It
is more realistic to generate multifrequency test signals covering some part of the
whole frequency range of interest. Then the test measurement procedure has to
be repeated several times. Obviously, much depends on the frequency band that
could be covered by a single realization of the test signal.
There is some risk when just one channel spectrum analysis is used. Then most
of the responsibility for phase-locking of the generated frequency components of
the excitation signal in the predetermined positions is put on the excitation signal
synthesizer. There may also be some hidden problems as various impedances
may impact on the measurement accuracy. It is necessary to check whether this
effect can be kept under control and whether one spectrum analyser measurement
scheme can be applied in all cases.
All these considerations show that the performance of the whole test system
depends to a large degree on the capabilities of the multifrequency test signal
synthesizer. An approach to such signal synthesis, based on exploitation of the
alias-free signal sampling techniques, is discussed in the next section.
19.2
Test Signal Synthesis from a Sparsely Periodically
Sampled Basis Function
The task of analog signal synthesis from discrete data comes up frequently and the
ways used to resolve it by using a DAC are well known. However, that is true only if
