New generation LCD test equipment often requires simultaneous high-precision, high-voltage, multi-channel measurement capabilities and minimum channel-to-channel variation during measurement.

In LCD test systems, the parametric measurement unit (PMU) is tasked to measure device (DUT) LCD driver parametric information in terms of voltage and current. To measure current, voltage is applied at the DUT pin. To measure voltage, current is applied at the DUT pin. A 4-channel SPST switch can be used to select appropriate signals in the feedback path and measurement path in the two measurement modes. The PMU typically supports a voltage range of -12 V to 35 V and can be any combination of high or low current. An appropriate switch like the TMUX7612 with low on-resistance works well in these applications to increase the capability of higher current and even PMU ganging where multiple PMU channels are connected in parallel, allowing for a higher current output. Figure 8-1 shows a simplified diagram of such an implementation. The extremely flat on-resistance profile reduced the IR drop variation across the switch, enabling a much more streamlined calibration.

For calibration and diagnostics, the LCD test equipment also includes signals routed to the input path to confirm the system is calibrated across the life of a product or after installation. The multiplexer connects the selected signal to the appropriate pin. The TMUX7612 devices with very low RON (1.35 Ω typical) and on-leakage current (1 nA maximum) allows these devices to be used in precision measurement applications providing rail-to-rail operation suitable for high voltage testing.

Figure 8-1 PMU Ganging Multiple Channels in Parallel