LVDSEVAL-001 National Semiconductor, LVDSEVAL-001 Datasheet - Page 8

• Manufacturer Part Number: LVDSEVAL-001
• Description: EVALUATION BOARD FOR DS90LV031A
• Manufacturer: National Semiconductor

Specifications of LVDSEVAL-001

• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *LVDSEVAL-001

6.1.6 Probing of High Speed LVDS Signals
Probe specifications for measuring LVDS signals are unique due to the low drive level of LVDS (3 mA
typical). A high impedance probe must be used (100k Ohm or greater). The capacitive loading of the
probe should be kept in the low pF range, and the bandwidth of the probe should be at least 1 Ghz
(4 Ghz preferred) to accurately acquire the waveform under measurement.
National’s Interface Applications group employs a wide range of probes and oscilloscopes. One system
that meets the requirements of LVDS particularly well is a TEK 11801B scope (50 Ghz Bandwidth) and
SD14 probe heads. These probes offer 100k Ohm, 0.4 pF loading and a bandwidth of 4 Ghz. This test
equipment was used to acquire the waveforms shown in figures 4, 5 and 6.
LVDS waveforms may also be measured with lower bandwidth / different loading probes such as common
TEK probes P6135A (150 MHz/1M Ohm / 10.5 pF). These probes were connected to a TEK 602 scope. See
figure 7 for the LVDS waveforms acquired in this set up and compare these to figure 5. The waveform
shows less DC loading (1M Ohm compared to 100k Ohm) and also more capacitive loading and band-
width limiting. Probes with standard 50 Ohm loading should not be since they will load the LVDS signals
too heavily. 50 Ohm probes may be used on the receiver output signal in conjunction the 450 Ohm series
resistor option (see option section below). Note that the scope waveform is an attenuated signal
(50/(450 +50) or 1/10) of the output signal and the receiver output is loaded with 500 Ohm to ground.
Figure 6: LVDS Channel #1 Waveforms - 2m Cable Interconnect
A1
B1
A1-B1
01
LVDS Owner’s Manual
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