Agilent Technologies 4294A Specifications download pdf (Page 94)

5-8. Resonator measurement

The resonator is the key component in an oscillator circuit. Crystal and ceramic resonators are

commonly used in the kHz and MHz range. Figure 5-29 (a) and (b) show typical equivalent circuit

and frequency response for a resonator. A resonator has 4 primary elements; C, L, R, and Co. C

and L determine the series resonant frequency, fr, and Co and L determine the parallel resonant fre-

quency, fa. Qm (Mechanical Q) is another measurement parameter used to describe the perfor-

mance of resonators. An impedance analyzer or network analyzer is used to measure the resonator

characteristics.

In the following methods note the impedance analyzer has an advantage in the accuracy of the mea-

surement results.

Impedance analyzer advantages

• The impedance value at resonant frequency can be read directly.

(Network analyzers generally read in units of dB.)

• Measurement accuracy for low impedance at series resonance and for high impedance at paral-

lel resonance are better than in network analysis.

• Measurement is made by simply connecting the resonator to the test fixture, and residuals can

be removed using the compensation function.

(Network analyzers require a π network circuit to be connected and cannot compensate for all

the residuals.)

• By using the equivalent circuit analysis function, all resonator parameters are easilly known.

(Network analyzers require complicated calculation or special analysis software to be used.)

Network analyzer advantages

• Faster measurement speed

• Higher measurement frequency range

Agilent’s impedance analyzers are suitable for testing resonators. With its equivalent circuit analy-

sis function, each resonator parameter can be determined individually. Also, I-Basic programming

function facilitates calculation of Qm and the extraction of other parameters. Figure 5-30 shows a

resonator measurement setup using an auto balancing bridge instrument for frequency range up to

approximately 100 MHz. For higher frequency measurement, the same setup can be used with RF I-

V measurement instrument. Take the following precautions to ensure accurate measurements.

1. It is often assumed that the series resonant frequency fr is coincident with minimum impedance

point. This is practical for an approximate measurement, but it is not the true value of fr. The

true value of fr is given at θ= 0 and is typically 1 to 2 Hz above the minimum impedance point.

Search the 0°-phase angle point for fr measurement.

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Agilent Technologies 4294A Specifications Page 94