3.3 V mixed-mode IC design using switched-current techniques for speech applications

A low-cost, low-voltage, mixed-mode integrated circuit for speech applications is presented. The mixed-mode IC can directly preamplify speech signals with the aid of automatic gain control, convert amplified signals to 1-bit digital codes at 24 kbit/s, store the converted codes in memory, and replay the stored codes through an on-chip current-input voltage-output power amplifier. Switched-current techniques are used to implement a filter with a 3.4 kHz bandwidth and a 96 kHz sampling frequency, and also an adaptive delta modulator (ADM) with a 24 kHz sampling frequency. Measured dynamic range of the SI ADM combined with the SI filter is greater than 40 dB. This mixed-mode IC, operating with a 3.3 V supply voltage, was fabricated by a 1.5-μm single-poly single-metal CMOS process. The whole system has been tested using human voice and results show that it is highly suitable for low-cost speech applications