Agilent Technologies 22D Uživatelská příručka stáhnout pdf (Strana 155)

4-39

MegaZoom Concepts and Oscilloscope Operation

Using Digital Channels to Probe Circuits

High-Frequency Probe Equivalent Circuit

The impedance plots for the two models are shown in these figures. By

comparing the two plots, you can see that both the series tip resistor and the

cable’s characteristic impedance extend the input impedance significantly. The

stray tip capacitance, which is generally small (1 pF), sets the final break point

on the impedance chart.

Impedance versus Frequency for Both Probe Circuit Models

The logic probes are represented by the high-frequency circuit model shown

above. They are designed to provide as much series tip resistance as possible.

Stray tip capacitance to ground is minimized by the proper mechanical design

of the probe tip assembly. This provides the maximum input impedance at high

frequencies.

1 pF

7.5 pF

150

Ω

100 k

Ω

100 k

Ω

10 k

Ω

1 k

Ω

100

Ω

10 kHz 100 kHz 1 MHz 10 MHz 100 MHz 1 GHz

High

Frequency

Model

Typical

Model

Frequency

Impedance

1 2 ... 150 151 152 153 154 155 156 157 158 159 160 ... 275 276

Žádné komentáře

Agilent Technologies 22D Uživatelská příručka Strana 155