Compaq M-LVDS manual Test Results, 4. Point-to-Point Parallel Simplex Typical Eye Pattern Data

Test Results

2.2 Test Results

The test configurations described in Section 2.1 were used to simulate point- to-point simplex, parallel-terminated point-to-point simplex, and two-node multipoint. The test results are shown in the following figures. A Tektronix HFS9003 was used to generate input signals, and a Tektronix TDS784D was used to collect the output data.

The EVM was populated with a SN65MLVD207D and SN65MLVD201D for U1 and U2 respectively. The eye patterns were measured with the source (Tektronix HFS9003) generating 215−1 PRBS NRZ data. In all cases, the length of the transmission line is approximately 21 inches (53 cm), and adds to the propagation delay in the device. This can be seen in the figures below as a time delay from input to output

Figure 2−4 shows the point-to-point simplex transmission eye patterns. Trace 1 is the driver input signal applied to J2. The output signal is shown below measured on both J1 (Figure 2−4 left picture), and TP1 (Figure 2−4 right picture). The receiver output in both figures shows the offset zero crossing, which is due to the Type-2 receiver incorporated into the SN65MLVD207 device. The reduced offset from a Type-1 receiver can be seen in Figure 2−6, receiver number 2 output.

Measuring the output signal on J1 with a 50-Ωcable terminated into 50-Ωat the scope will attenuate the signal due to the 453-Ωresistor in series with the receiver output. The resistor is installed as a current limit for termination into a 50-Ωload. As can be seen in the traces below the magnitude of trace 2 on the left is one-tenth of trace 2 on the right. Measuring the signal with a high-impedance probe on TP1 requires replacing R2, the 453-Ωresistor, with a short to reduce signal roll-off. Measuring the output on TP1 allows the user to see absolute signal levels out of the device.

Figure 2−4. Point-to-Point Parallel Simplex Typical Eye Pattern Data

Driver

Input

Receiver

Output

Differential

Bus

Voltage

50-Ohm Output Termination	High Impedance Output Termination, R2 Shorted
Receiver Output Scaled 10:1

The eye patterns in Figure 2−5 are parallel-terminated point-to-point simplex data where trace 1 is the input signal applied to J2, and trace 2 is the output

Test Setup 2-5