Large LCD devices of 1" or more exhibit a large driving capacitance to the driver circuits. To solve this problem, the drive circuit shown (see the figure) introduces a buffer amplifier for each of the three common lines. Each amplifier can be programmed independently for a quiescent current of 10, 100, or 1000uA. In this application, the bias network applies a voltage that sets the three quiescent currents to 100uA.
The display driver and triple op amp operate between 5V and ground, and the COM signals range from 5V to approximately 1V. To ensure that these signals remain within the amplifiers' common-mode range, the signals are attenuated by one-half and the buffers operate at a gain of two. The circuit drives eight 1-inch displays, and is suitable for ambient temperature variations of 15 degrees F or less. At the highest expected temperature, R1 should be adjusted so that no "off" segments are visible.