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Application Notes
Introduction
The Keysight Technologies, Inc. E5052B Signal Source Analyzer (SSA) is designed to help R&D and manufacturing engineers across a wide range of electronic industries perform signal source tests more accurately, at higher throughput and lower cost, with unprecedented simplicity.
The SSA provides a complete set of measurement functions for the full characterization of signal sources in microwaves and RF. The SSA has six basic independent functions such as phase noise measurement, spectrum monitoring, frequency and power measurement (VCO test), transient measurement, AM noise measurement, and baseband (LF) noise measurement. Each of the SSA’s measurement functions delivers a performance that is comparable to or exceeds that of conventional dedicated test instruments and systems.
This document describes two major advanced techniques of the SSA in phase noise measurement and transient measurement.
Table of contents
1. Phase Noise Measurement
1.1 Problems with conventional test solutions
1.2 For low phase noise measurement, the most commonly used method is a PLL method (Reference source / PLL technique) shown in Figure 1. This traditional method is widely used and works very well in general. However, it has several drawbacks in order to cover a wider range of phase noise levels.
The measurement process of the PLL method is relatively complicated. In order to configure the test system, an external reference source or local oscillator (LO) must be configured according to measurement needs so that it has sufficiently low phase noise compared to the signal source under test. It is not easy to configure a very low noise reference source for testing quiet oscillators, such as crystal oscillators and SAW resonator oscillators. In addition to this challenge, after the system is configured, a time-consuming set-up and calibration must be performed for accurate measurements.
The minimum sensitivity of the PLL method is determined by the noise floor of the reference source and the scaling amplifier. And the PLL method fails to measure phase noise of relatively drifty and noisy signal sources due to its measurement principle. When the signal source under test is fairly noisy, phase-locking problems (PLL tracking failure) often occur, and it takes a long time to re-adjust the PLL’s loop-bandwidth or loop-gain and re-calibrate the measurement system. Another common method of conventional phase noise measurements is the discriminator method (analog delay line technique) shown in Figure 2. This method provides very high sensitivity far from carrier offset frequencies. It satisfies, for example, the test requirement for GSM. In addition, it can measure wider phase noise ranges for somewhat drifty sources, but the discriminator method has several disadvantages also.
The discriminator method is a fairly complex process. It is necessary to use several different analog delay lines according to the carrier frequency under test. Actually, it is almost impossible to prepare appropriate delay lines at arbitrary test frequencies. In addition, a complicated calibration must be performed for each delay line.
Phase noise measurement at close-to-carrier offset frequencies by the discriminator method is not practical or accurate because a discriminator coefficient (shown in Figure 5b) limits a practical dynamic range at lower offset frequencies. To reduce the discriminator coefficient’s effect, longer delay lines are required at lower offset frequencies. It is difficult to measure signal sources having low RF output power since the discriminator (phase detector) may not work properly due to insufficient driving power of the signal under the test
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