(Up to 20 M/bit Real-Time Scope)
Modern bench and portable scopes with 200 MHz or more can trigger and decode low speed serial
data. Specific address or packet data contents can form the triggering for I2C, SPI, CANBUS,
FLEXRAY, or RS-232 signals. Scopes with MSO options can trigger and decode through their digital
inputs. This saves the analog scope channels for more interesting inputs and provide message based
(packet content - address or data) triggering in embedded systems.
(Up to 12.5 G/bit Real-Time Scope)
(Up to 80 G/bit Sampling Scope)
As bit rates increase, the timing budget shrinks as edges must occur with very little variation or
bit errors occur. Real-time scopes can be used up to 12.5 Gbits/s. Faster bit rates require sampling
scopes that can support the BW and the CDR (clock data recovery) for proper triggering. The
real-time scope's BW should be 1.8 times greater than the data rate - for example 18 GHz for 10
Gbits/s.
High speed serial data such as PCI-E (Gen 1 or 2), SAS, XAUI, and Ethernet can be digitized on a single channel using an active differential probe. The transmit side of a SerDes chip is the typical point that is probed. Virtual probing is required to measure the EYE at the input to the equalized receiver.
Then the scope's "Golden PLL" software can extract the clock and overlay all of the data bits to
form a real-time EYE. Note that this can be done from a single shot acquisition or multiple single
shots that accumulate more unit intervals of bits with each new trigger.
New Clock Recovery Application Note
The EYE (a persistence trace overlay of the data bits) shows the envelope of how much variation
there is in the timing of the data bits. Measurements of EYE height and EYE width reveal the
statistical chances of bit errors. Masks can be added and violations mapped to the exact bits that
hit the mask. A new bit error prediction tool that works with EYEs is called "IsoBER" seen in the
screen shot below.
Finally, jitter on the data bits is broken down into Total Jitter (Tj), Random Jitter (Rj), and Deterministic Jitter (Dj) measurements. Good numbers point to a standards compliant link. Bad numbers point to specific areas to troubleshoot. Serial Data Analyzers include appropriate tools to debug the issues that create excessive jitter.
A new scope series has just been announced that combines low speed serial data, high speed serial data, and MSO (logic analyzer like capabilities) in a single platform.
