From simple crystal oscillators to YIG-tuned resonators and frequency synthesizers, RF and microwave signal sources require an extensive battery of tests to fully assess their performance. And with the existing 3G and emerging 4G wireless standards, the complexity of testing and evaluating such signal sources is further convoluted. As a result, this entails several instruments, either singly or networked to form an automated system to perform the requisite tests. Either way, it is an expensive and elaborate proposition. That problem is now addressed by Agilent Technologies' new signal source analyzer (SSA), the E5052A. The SSA performs all of the necessary tests in a single instrument and even includes two clean dc sources for power and tuning voltage control. In addition, the new SSA speeds measurement times by a factor of 10. Although the standard measurement range for the newest analyzer is 10 MHz to 7 GHz, it can be increased to 110 GHz with currently available downconverters.

Developed to perform tests like phase noise, transient response (frequency, power, and phase vs. time), power, frequency, and dc current consumption. The E5052A offers a spectrum monitor function with a 15 MHz span for checking synthesizer reference leakage. Phase noise offset range is 1 Hz to 40 MHz. For transient measurements, the frequency resolution ranges from 5 Hz to 7 kHz with sampling resolution of 10 ns to 160 ms in heterodyne (narrowband) mode. In direct wideband mode, maximum frequency span is 4.8 GHz and selectable between 1.6 MHz and 25.6 MHz in heterodyne mode.

Thanks to a proprietary cross-correlation technique, the performance of the E5052A is comparable to instruments dedicated to a single measurement, such as phase noise or transients, according to Agilent. Its high phase-noise performance is achieved through use of cross-correlation and digital signal processing (DSP) that together can lower measurement of phase noise sensitivity by up to 20 dB (see the figure). It can also maintain it at any offset from the carrier frequency.

Cross correlation, which was developed in the 1960s, has always shown promise, but its use has been stymied because it requires long measurement times to produce results of data capture and computation. To eliminate this problem, the E5052A uses a 100 MHz (10 ns) analog-to-digital converter (ADC) with a stepped Fast Fourier Transform (FFT) implemented using a DSP. The result is a phase noise sensitivity of more than -178 dBc/Hz and an order of magnitude increase in measurement speed.

Essentially, cross correlation cancels noise by employing two channels that have independent reference sources. When the 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, ADCs 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.

Two internal low-noise dc sources for device-under-test (DUT) power and control voltages are optimized for use with signal sources, which are 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 large (10.7-inch) TFT LCD. In particular, the dc control voltage source supplies an ultralow noise dc signal (1 nV/✓Hz at 10 kHz offset) to free running VCOs. This enables a user to make measurements without a low-pass filter. Other features include GPIB, USB and Ethernet connectivity, programming via SCPI commands and Microsoft Visual Basic for Applications (VBA), which makes creation of test routines simple. Up to four windows plus one user window allows a user to view multiple results simultaneously. The E5052A is priced from $75,000 and is available next quarter.
Agilent Technologies
(800) 829-4444
ext. 7799
www.agilent.com

RSS    Save to Del.icio.us  Digg This