A BiCMOS speech circuit with only two external components

A telephone chip that performs all the basic functions of a speech circuit using only two external components is reported. Precision filtering based on switched-capacitor (SC) techniques is used to implement on-chip impedance termination, hybrid with sidetone cancellation, and DC characteristics starting from a single 1% external resistor. A new low-drop on-chip voltage supply generator derived from the line using an external storage capacitor is also realized. Better than 33-dB impedance matching and more than 30-dB sidetone cancellation is achieved without any external trimming. The TX linearity is better than 50 dB up to 4.4 V_p-p on the line. The chip has an active area of approximately 2.6 mm² and draws 1.5 mA of quiescent current