E5052B Signal Source Analyzer

A voltage controlled oscillator (VCO) is one of the most critical electronic components in today’s world of advanced wireless communication and broadcasting. Frequency tuning charac­teristics (tuning voltage versus output signal frequency) and phase noise characteristics (offset frequency versus phase noise power ratio) of a free-running VCO are fundamental parameters that specify the performance of the VCO. Although VCO’s are conceptually easy to understand and describe, actual measure­ments of frequency tuning and phase noise are very difficult and time-consuming. Particularly for the phase noise measurement, a conventional direct method by using a spectrum analyzer can not achieve an accurate measurement and often results in disconti­nuity due to frequency drift or wander (slow jitter) of the free-run­ning VCO shown in Figure 1.

In order to avoid this difficulty an automatic measurement system using phase tracking technique is constructed with a spectrum analyzer as shown in Figure 2*. However, this approach is com­plicated to configure and measurement results heavily depend on noise level of each component.

The Keysight E5052B has dramatically improved phase noise

measurements of a free‑running VCO. As shown in Figure 3,

the measurement configuration is quite simple. All necessary DC voltage sources with sufficient low-noise are equipped in the

instrument, and phase noise measurements from 1 Hz to 100 MHz (in Normal capture mode) or 40 MHz (in Wide capture mode) offset frequency can be done within 13 seconds. The measurement speed is exceptionally fast such as 0.45 seconds if offset frequency is set at a range between 1 kHz and 100 MHz/40 MHz.

Figure 4 and Figure 5 are measured results of 835 MHz free‑running VCO by the E5052B in phase noise (PN) and amplitude noise (AM). Figure 4 shows two results in parallel and Figure 5 shows a user display window with two traces in the same vertical scale.

Typically spectrum analyzer’s measured results show only the sum of PN and AM noise, so that the both can not be identified sepa­rately. However, the E5052B provides both results independently.

An example of VCO parameter measurements is shown in Figure 6 in which four measured parameters at 401 points of tuning voltage (Vc) are displayed simultaneously within 10 seconds.