User`s guide

Agilent Technologies E5500 Phase Noise Measurement System 6-9
Absolute Measurement Fundamentals
Selecting a Reference
Using a Signal
Generator
When using a signal generator as a reference source, it is important that the
generator’s noise characteristics are adequate for measuring your device.
Tuning Requirements Often the reference source you select will also serve as the VCO source for
the PLL measurement. (The VCO source can be either the unit-under-test
(UUT) or the reference source.) To configure a PLL measurement, you will
need to know the following tuning information about the VCO source you
are using:
• Tuning Constant (Hz/V) (within a factor of 2)
• Tuning Voltage Range (V)
• Center Voltage of Tuning Range (V)
• Input Resistance of Tuning Port (ohms)
The primary consideration when evaluating a potential VCO source for your
measurement is whether it will provide the test system with sufficient
capture and drift tracking ranges to maintain lock throughout the
measurement. To make this determination, you must estimate what the drift
range of the sources you are using will be over the measurement period
(thirty minutes maximum). (Details on the relationship between the capture
and drift tracking ranges and the tuning range of the VCO source are
provided in Table 6-1. This information will help you evaluate your VCO
source based on the estimated drift of your sources.)
Table 6-1 lists the tuning parameters for several VCO options.
Table 6-1 Tuning Characteristics of Various VCO Source Options
VCO Source
Carrier
Freq.
Tuning Constant
(Hz/V)
Center
Voltage
(V)
Voltage Tuning
Range (
± V)
Input
Resistance
(
Ω)
Tuning
Calibration
Method
Agilent/HP 8662/3A
EFC
DCFM
υ
0
5E–9xυ
0
FM Deviation
0
0
10
10
1E + 6
1 k (8662)
600 (8663)
Measure
Calculate
Calculate
Agilent/HP 8642A/B FM Deviation 0 10 600 Calculate
Agilent/HP 8644B FM Deviation 0 10 600 Calculate
Other Signal
Generator
DCFM Calibrated for
±1V
FM Deviation 0 10 R
in
Calculate
OtherUserVCO
Source
Estimated within a
factor of 2
–10 to
+10
See Figure 6-7 on
page 6-10
1 E + 6 Measure