Half wave voltage is nothing but the switching voltage which decides the slope of the transfer function of the modulator.
To bias the modulator in quadrature, keep the switching voltage at 4volts (for example) and the bias voltage (either 1 or 2) at 2 volts. The modulator will generate double sideband full carrier signal when the phase shift between the two is 180 degrees. Let me know if you need furthur help.