电源纹波 噪声 专业测试方法

Introduction

A common question from SynQor customers is, “Why do I see large high frequency noise spikes on my oscillo-

scope when testing the output ripple of a SynQor converter?” Customers often worry that these large spikes will

cause their digital circuitry to malfunction, either because of absolute voltage deviation or because of noise cou-

pling to adjacent circuitry. Fortunately this noise spike is largely a measurement artifact and does not reflect the

actual voltage deviation between the power planes. With some simple test set-up changes, a much more accu-

rate measurement is possible.

Measuring Output Voltage Ripple

ed at the scope end of the cable, with amplitudes larger than those present on the circuit side of the cable.

small amount of high frequency differential mode noise. This high frequency noise resonates and reflects from

one end of the cable to the other. The high Q of the cable actually makes the peak noise higher than the actu-

al noise source. To eliminate reflections, the transmission line must be terminated either with a 50 ohm resistor

from signal to ground at the scope (referred to as parallel or end termination), or with a 50 ohm resistor in series

with the signal on the eval board end (referred to as source termination). A diagram showing proper evalua-

tion test set-up and termination is shown in Figure 6 on page 3.

and have a scale of 20mV per division.

SynQor -

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888-567-9596

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www.synqor.com

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