LVDS47/48EVK National Semiconductor, LVDS47/48EVK Datasheet - Page 9

• 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

Figure 8: LVDS Channel #3 Waveforms - 10m Cable Interconnect
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). Either
a high impedance probe (100k Ohm or greater) or the TEK P6247 differential probe (>1GHz bandwidth) must be used.
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 TDS 684B Digital Real Time scope (>1GHz bandwidth) and TEK
P6247 differential probe heads. These probes offer 200k , 1pF loading and a bandwidth of 1GHz. This test equipment
was used to acquire the waveforms shown in Figures 5, 6, 7, 8 and 9.
The TEK P6247 differential probes may be used to measure the differential LVDS signal or each signal of the
differential pair single-ended. This test equipment was used to acquire the waveforms differentially as well as single-
endedly with the differential signal calculated by (D
) – (D
) shown in Figure 9. You can see that both of the
OUT+
OUT-
differential signals look identical. The method in which you acquire the single-ended signals is important (such as
matching probe types and lengths) if you intend to calculate the differential signal from the two single-ended signals.