Abstract: An ADPCM transcoder (60) includes an integral tone generator (65) which inserts a linear tone signal, such as a conventional DTMF tone signal, into either the transmit or receive data stream, or both. A digital PCM input signal is first converted to a first linear signal. If tone generation is enabled for transmission, then the linear tone signal is substituted for or added to the first linear signal and provided to an ADPCM encoder (63), which provides an ADPCM output signal in response. An ADPCM decoder (66) receives an ADPCM input signal and provides a second linear input signal in response. If tone generation is enabled for reception, then the linear tone signal is substituted for or added to the second linear input signal, and converted to a digital PCM output signal. The ADPCM transcoder (60) may also be integrated with other components of a signal processing system.

Abstract: A charge pump circuit and associated method is provided for outputting either a positive or a negative output voltage, or both, which each may have a predetermined magnitude which is an integer multiple of the magnitude of a power supply voltage used to power the circuit. In one form, a first capacitor is charged to the power supply voltage. The first capacitor is coupled to the power supply voltage to develop a double voltage transfer supply with the supply voltage. Second and third capacitors are charged by the double voltage transfer supply. The second capacitor is used to store the charge from the first capacitor for a continuous output voltage having a magnitude which is twice the magnitude of the power supply. The third capacitor may be reconfigured to generate a negative transfer voltage. The negative transfer voltage is used to charge a fourth capacitor which provides a negative output voltage with twice the magnitude of the power supply voltage.