Motorola suggests this circuit in an 80's documentation. The circuit uses an inverter to produce a higher voltage for 9 V battery charge from a single cell.
The circuit is suitable for calls in a residence and was published in the Radio Electronics...
The input impedance of this circuit is about 700 k ohm and the output impedance is about 1 k ohm....
With the values of the components indicated, the circuit generates a 1 kHz signal. The power...