A BiCMOS Speech Circuit with only Two External Components

This paper reports on a telephone chip that performs all the basic functions of a speech circuit using only two external components. Precision filtering using 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. Better than 30 dB matching is achieved without any external trimming. The TX linearity is better than 50 dB up to 4.4 Vpp on the line. The chip has an active area of approximately 4,000 mils² and draws 1.5 mA from the supply.