Each of these designs use a TC4667 charge pump to create a negative voltage from a +9VDC supply. DC offset adjustment of the AC output signal is attained via the +/- voltage divider OFFSET potentiometer. This is summed along with the generated waveform. The amplitude of the output waveform is determined by the feedback network on the non-inverting leg of the last op amp, controlled by the GAIN potentiometer. You can use a dual supply with the hex inverter IC to attain offset above/below ground.
