PICO PicoConnect 900 Guia Del Usuario página 9

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User's Guide

PicoConnect 900 Series Probes

Choosing the best PicoConnect probe for a given application is generally a compromise

between minimal probe loading (highest probe impedance) and smallest division

ratio (for best signal level at the measurement instrument), while ensuring sufficient

bandwidth in the measurement. Uniquely you can also select AC or DC coupling.

For signals such as HDMI, LVDS and (P)ECL, or when probing for decouple issues on

supply or control lines, all with a DC bias, an AC-coupled probe does not source or

sink a disturbing current at the test node. If you have a selection of probe heads, we

recommend the use of an AC-coupled probe with the highest impedance (and division

ratio) that meets the needs of the measurement.

A final and secondary consideration may be the quality of input match of the

connected measurement instrument. Poor match (typically > –20 dB) may cause an

unwanted reflection aberration or rippled frequency response. The PicoConnect 921,

922, 923 and 924 probes present the best match at the sending end and minimize

such errors.

Getting started

PicoConnect passive probes are suited to use with any instrument, or connectorized

accessory or cable, having a 50 Ω input and adequate bandwidth. Inter-series

adaptors are available, and supplied with some kits, for N(f) and BNC(f) connector

interfacing. Where necessary, make sure that the measuring instrument is set to 50 Ω

input coupling. Note that an external 50 Ω through-terminator cannot be used for

applications above a few hundred megahertz.

These very low-capacitance probes can be used with either one or two ground

contacts, with a slightly better response when using both. All probe tips are removable

using tweezers and gentle force. Note the grip points on the sprung ground probe tips

in the diagram below. Spare probe tips are supplied with your probe(s) and more can

be ordered (order code TA315).

Solder-in connection is an important option, especially for very fine-geometry test

nodes. Prepare the PicoConnect probe by removing the test pins and inserting

short lengths of the supplied gold-plated copper wire. Use Ø 0.6 mm 23 SWG for

the grounds and where possible for the signal connection. For very fine-geometry

connection or fragile test nodes use Ø 0.3 mm 30 SWG. Trim and form the wires

as required, keeping their length as short as convenient connection will allow. The

0.3 mm wire can be bent double at the probe end to achieve a tight fit. However, for a

fragile node, a loose fit may be preferred. Pre-tin the wire ends. Solder first to secure

ground node(s)—the use of both grounds will improve mechanical stability as well

as response—then solder the signal connection. Take care on very short connection

lengths to prevent solder flow back to the probe sockets.

The very light and flexible unsleeved 085 coaxial cables (TA263 and TA264) are highly

suited to solder-in applications. Take care however that the cable route does not risk

shorting to adjacent circuitry.

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