A continuously variable slope adaptive delta modulation codec system

The author describes a CMOS single-chip monolithic adaptive delta modulation coder/decoder (codec). The codec uses a 56 kHz sample rate and is implemented with novel switched-capacitor circuits. The simplicity and efficiency of the encoding/decoding scheme allows the inclusion of several other functions on the chip, including a dual-tone multifrequency generator and and an 8-step programmable attenuator. These features make it especially suitable for private automatic branch exchange (PABX) applications. Experimental results are presented that show the circuit meets the necessary systems requirement for all usual applications.