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Logic analyzers can have a large number of probes that need connecting to a variety of points on the circuit under test to be able to monitor the required number of lines.
In view of the number of lines and the small size required for the probes, they can be difficult to design. As with many things, the cost of the probe increases with the level of performance. Low cost logic analyzer probes may just be sufficient for basic test applications, but for more exacting requirements, more expensive logic analyzer probes are needed.
Logic analyzer probes
With the large number of signals required to be monitored, often from a small area on a board and possibly even from one integrated circuit, the design of the probes can be a critical issue.
The logic analyzer probes contain an internal comparator where the voltage of the waveform on the board is compared against the threshold voltage. This can be set using the main instrument to a variety of levels so that signals from a variety of logic families can be monitored.
Logic analyzer probes can take a variety of physical forms, but generally fall into one of three categories:
- Multichannel probes that use a dedicated connector on the circuit board. These probes enable a large number of points to be accessed using a high density connector. This facility has to be designed on to the board and may only be retained for the development phase where access for a logic analyzer is required.
- High density compression probes. These probes use a compression contact that does not have a dedicated connector. Contacts on the board are required for this type of connection.
- Flying lead probes. As the name implies, these probes are on a flying lead that is connected to a small electronic unit that contains the electronics for detecting the high and low levels. However these flying lead probes are used to monitor points that may not be included on any of the other access points.
Logic analyzer probe quality
There are many different logic analyzer probes that are available to buy. There are many low cost logic analyzer probes, some available with the low cost logic analyzers that are available. The probes like these are normally not robust. The clips and the connections may break or become unreliable.
High quality probes will provide a much better connection. The clips will be much better and the electrical performance. These probes and their clips naturally come at an additional cost.