The details of designing a drive circuit for a multiplexed LCD are covered in our App note "Multiplexed Liquid Crystal Displays".  We will only cover the highlights here. We also have a sample drive circuit on in our Application Notes section, entitled "A Sample Multiplex Drive Circuit". There are also numerous design guides available from the many LSI chip vendors, which contain excellent design tips and guidelines.

The above table shows the relationship between the number of driving biases and the display duty cycles needed.

The necessary bias voltages are usually generated by the use of a resistor dividing network, and example of which is shown below. Vcc is usually 5 volts, and the number of resistors in the ladder is determined from the table above.

The values of the resistors is determined mostly by power requirements and waveform distortion. Because an LCD is a capacitive load, the values should be decreased to decrease distortion, however this increases power consumption. These values should therefore be made as large as possible, keeping in mind that very large displays have very large capacitance, and may require lowering the resistor values.