Approaches to dramatic test time reductions

The Aeroflex 3000 series solution incorporates all of the following features
to reduce test time.

The transfer of low level time series sample data between the test
instrument and the test system PC maximizes the flexibility in what
measurements can be performed. This also enables different sets of
measurements to be performed on one set of captured data which minimizes
test time when the time to capture data is determined by the unit under test
e.g. slot time for GSM.

Once it has been decided to take this approach then data transfer time
between the test instruments and the test system PC becomes an important
factor. In this respect the PCI bus is significantly faster than GPIB,
Ethernet or VXI. PCI offers peak transfer rates of 132 Mbyte/sec, over 100
times faster than GPIB.

The provision of a local bus between PXI modules can be used to provide
direct communication between compatible instruments and in doing so reduce
the communication loading to the system controller.

A further contribution to measurement speed is any data reduction that can
take place prior to data transfer. Aeroflex PXI modules therefore include a
large FPGA for signal processing. This FPGA is currently used for
programmable decimation prior to data transfer to maximize speed, retain
flexibility and maximize signal to noise ratio. Test time improvements are
specific to the particular tests being carried out and the particular test
configuration but as an example, we have had reported to us a 5 times speed
improvement over a GPIB instrument for power measurement.

There are further opportunities to improve speed by synchronizing stimulus
and data capture using the dedicated PXI trigger bus.

For measurement applications requiring relatively long time records e.g for
averaging, it is important that measurement processing can be performed in
parallel with the acquisition of the next data sample.

For example, for TDMA systems the provision of ‘gated’ capture where the
gate source is either internally or externally derived enables the test
system to acquire only the active burst(s) within a TDMA frame. The sample
record would then be a non-continuous time record of contiguous bursts
represented as a much shorter data set thus minimizing the transfer time
required. The test system may then be set up to capture a block of
contiguous bursts which are each transferred for analysis during which time
the next block of data is being acquired. This minimizes the time required
to perform multiple burst averaging.

The use of register based hardware control is used to speed up response
times. This together with the use of synthesizer designs with fast frequency
switching times (typically less than 250us when optioned) and fast, reliable
and repeatable electronic attenuator designs is exploited to speed up
measurements made over a range of carrier frequencies and signal levels.

Unlike integrated instruments, PXI systems based upon capture, transfer and
remote analysis of sampled data permit easier migration to new CPU
technology. Faster processing directly accelerates test time and requires
only the interchange of the system controller and no re-engineering — unlike
integrated instruments. A product whose life expectancy is 5 years or more
can therefore provide cutting edge performance throughout its period of
deployment.

The provision within Aeroflex 3030 RF Digitizers for real time data output
through the ‘front’ panel provides expansion capability to perform real time
measurement processing in a commercially available third party DSP module.

The Aeroflex measurement Active X controls employ efficient proprietary
measurement algorithms.

Benchmarking has revealed that without optimization a complete single
burst/slot analysis for power, modulation error, frequency error,
spectrum/ACLR is achieved faster than with dedicated GPIB instruments.

The measurement results are calculated in underlying OCX controls, which in
turn call DLLs. A summary of the times taken for these measurements is given below:

*Capture times need to be added to all these numbers. Ffor GSM/EDGE an
asynchronous capture and transfer of a single slot adds approx. 1.5 ms to 2
ms based on a decimated sample rate of 1.92 MHz and a sample size of 11k
covering 9 timeslot periods. Times are based upon a MXI-3 interface to a 2.4
GHz Pentium PC.

The PXI architecture from Aeroflex includes open, documented ActiveX
component interfaces optimized for the chief objectives of cost and test
time reduction, and also provides the required flexibility needed for today's mobile manufacturing.

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