LVDS47/48EVK National Semiconductor, LVDS47/48EVK Datasheet - Page 7

• Manufacturer Part Number: LVDS47/48EVK
• Description: EVALUATION BOARD FOR LVDS47/48
• Manufacturer: National Semiconductor

Specifications of LVDS47/48EVK

• Main Purpose: Interface, Digital Cable Driver
• Utilized Ic / Part: DS90LV047A, DS90LV048A
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Secondary Attributes: -
• Embedded: -
• Primary Attributes: -
• Other names: *LVDS47/48EVK; *LVDS47/48EVK/NOPB; LVDS47/48EVK/NOPB

The PCB interconnect signal (LVDS Channel #2) can be measured at the receiver inputs (test points J6-1 and J6-3). Due
to the short interconnect path via the PCB little distortion to the waveform is caused by the interconnect. See Figure 5.
Note that the data rate is 100 Mbps and the differential waveform (V
= D
- D
) shows fast transition times
DIFF
OUT2+
OUT2-
with little distortion.
In Figure 5, 6, 7 and 8, the top two waveforms are the single-ended outputs (between the driver and receiver), the middle
waveform is the calculated differential output signal from the two single-ended signals and the bottom waveform is the
output TTL signal from the receiver.
Figure 5: LVDS Channel #2 Waveforms — PCB Interconnect
The cable interconnect signal is also measured at the receiver inputs (test points J7-1 & J7-3 and J8-1 & J8-3). Due to
the characteristics of the cable some waveform distortion has occurred. Depending upon the cable length and quality, the
transition time of the signal at the end of the cable will be slower than the signal at the driver’s outputs. This effect can
be measured by taking rise and fall measurements and increasing the cable length. A ratio of transition time to unit
interval (minimum bit width) is a common gauge of signal quality. Depending upon the application ratios of 30% to
50% are common. These measurements tend to be more conservative than jitter measurements. The waveforms
acquired with an RJ45 cable of 1 meter, 5 meters and 10 meters in length are shown in Figure 6, 7 and 8. Note the
additional transition time slowing due to the cable’s filter effects on the 5 meter and 10 meter test case.