June 2004
The complexity of testing and evaluating
signal sources is increasing with the emergence of 3G and 4G
wireless standards. Until now, there was no single instrument
that could thoroughly characterize a wide variety of signal
sources ranging from crystal oscillators to dielectric resonator
oscillators (DROs), surface acoustic wave (SAW) oscillators,
voltage-controlled oscillators (VCOs), IG-tuned oscillators,
PLL and fractional-N frequency synthesizers, and RF and microwave
integrated circuits (ICs).
The Agilent E5052A Signal Source Analyzer
(SSA) is a new class of instrument that can evaluate the critical
performance characteristics of nearly all types of RF and microwave
signal sources. Agilent's goal in creating the SSA was to offer
a single instrument that would significantly speed measurement
times, and help R&D and manufacturing engineers in the wireless
communications, broadband optical, aerospace/defense and electronics
industries perform tests more accurately, and with unprecedented
simplicity. The SSA also significantly lowers cost by eliminating
the need to purchase multiple standalone instruments.
While the SSA follows the tradition
of Agilent's popular 4352S VCO/PLL Signal Test System, which
is designed to characterize voltage-controlled oscillators (VCOs)
and PLL synthesizers, it addresses the limitations of the 4352S
and offers new test capabilities that enable evaluation of a
much broader range of signal source types.
Comprehensive Capabilities
The Agilent E5052A SSA makes four types of
measurements:
- Frequency, power and DC current
- Transient measurements (frequency, phase and power versus
time)
- Spectrum monitor
- Phase noise
The SSA has been designed to meet or exceed
current and anticipated requirements for each measurement type.
Frequency, power and DC current tests are facilitated by simultaneously
measuring frequency, RF power and DC current consumption. DC
tuning (control) voltage and DC power sweeps enable a variety
of measurements, including:
- Tuning sensitivity (frequency versus DC tuning voltage)
- Frequency pushing (frequency versus DC power voltage)
- RF power versus either DC tuning voltage or DC power voltage
- DC current consumption versus either DC tuning voltage or
DC power voltage
Two internal DC sources for device-under-test
(DUT) power and control voltages are optimized for use with
signal sources, which are very sensitive to noise on either
tuning voltage or power voltage lines. Either DC control or
power voltage can be swept with the result displayed on the
instrument's LCD. There is no need to control the voltages with
an external PC.
For versatile transient measurements that
are necessary for characterizing PLL synthesizers and transmitters,
the SSA employs frequency and phase demodulation as well as
power measurements. Frequency, phase and power transients are
simultaneously measured in heterodyne (narrowband) mode and
direct (wideband) mode. Wideband mode is also available for
wide frequency transient to enable designers to see more overall
transient phenomenon. An external hardware trigger is accommodated
by a rear-panel interface, and video and pre-trigger events
can be observed before and after an event. Fine resolution is
maintained even at the instrument's highest sample rate of 10
ns. The instrument's spectrum monitor function facilitates measurement
of reference signal leakage (spurious) around the carrier and
is useful because the signal source does not need to be reconnected.
Phase Noise Measurement Breakthrough
The E5052A SSA uses Agilent's proprietary
cross correlation technique, which allows very low phase noise
levels to be measured at all offsets from the carrier frequency
without reducing measurement speed or compromising phase measurement
performance. Cross correlation can remove the limitation posed
by the noise floor of the reference source, while also lowering
the usable noise floor by up to 20 dB. Cross correlation reduces
the dependency of the measurement on low input power versus
the available noise floor.
The cross correlation technique essentially
cancels noise by employing two channels that have independent
reference sources and through digital signal processing (DSP).
If two signals are correlated and vector summed, the vector
(amplitude and phase) of the two signals is emphasized. However,
if two signals are uncorrelated, their vector sum is canceled,
so the internal noise from references such as sources, analog-to-digital
converters and mixers can be canceled. The amount of noise cancellation
depends on the "number" of correlation and is based
on root N (the number of correlation). Correlation of 10 times
produces a 5 dB noise floor improvement, and 100 times correlation
produces a 10 dB improvement.
The cross correlation technique traditionally
has suffered from one primary limitation. It increased measurement
time for data capture and computation, which itself depends
on the difference between the phase noise of the DUT and that
of the internal reference source. The SSA has solved this problem
so that engineers can take advantage of the benefits of the
technique. The instrument reduces measurement time by using
a high-performance, 100 MHz (10 ns) digital-to-analog converter
with a stepped Fast Fourier Transform (FFT) implemented with
DSP.
Reducing Costs with a Single Instrument
Engineers duplicating the tests performed
by the SSA would need a modulation domain analyzer, DC power
supply (for the DUT), digital multimeter, frequency counter,
RF power meter, signal generator, and phase noise analyzer and
test set. Purchased new, this set of equipment would cost more
than $100,000. In addition, the equipment would be dedicated
to signal source analysis testing and thus unavailable for use
elsewhere. It would also require considerable test routine development
and cabling, and it would require several orders of magnitude
of additional space than the Agilent E5052A SSA. Very little
would be gained in terms of additional features with this approach
since all but a few major tests important for signal sources
can be performed by the SSA as a stand-alone instrument.
A Complete Measurement Solution
The Agilent E5052A Signal Source Analyzer
is a complete measurement solution for all types of signal sources.
The SSA reduces the limitations of earlier multifunction instruments
or "rack-and-stack" assemblages of instruments, and
offers the advantage of not being limited to measuring only
current devices. To achieve this, all major tests are performed
at the highest achievable levels of performance, and the DUT
is provided with a clean DC source. The SSA also works with
external down converters that currently extend the top frequency
range to 110 GHz. This feature helps ensure the SSA will not
be limited by frequency in the future.
Key E5052A Specifications
Carrier frequency range: 10 MHz to
7 GHz (110 GHz with down converters)
Tests performed: Phase noise, frequency,
power, DC current, spectrum monitor and frequency/power/phase
transients
Phase noise test:
- Offset frequencies: 1 Hz to 40 MHz
- Phase noise sensitivity: >-178 dBc/Hz
- Noise floor lowering method: Two-channel
cross correlation
Frequency and power test:
- Parameters: Frequency and power
- Sweep type: DC power voltage or DC control
voltage
Transient tests:
- Parameters: Frequency, phase, and power
versus time
- Frequency resolution: 5 Hz to 7 kHz (Heterodyne
mode)
- Time resolution: 10 nanoseconds to 160
microseconds
- Frequency transient range: (Heterodyne
mode) 1.6 to 25.6 MHz
- Pretrigger capability: Direct mode: 4.8
GHz max; -80% of time span or
+1 s
DC tests:
- Parameters: DC current (DUT power only)
- Voltage/current range: Control: -15 to
+35 VDC, 20 mA max; DUT power: 0 to +16 VDC, 80 mA max
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