AD1846: A Low-Cost, Parallel Port, 16-bit Sound Card Stereo Codec

The AD1846 is a single-chip, low-cost, pin- and register-compatible replacement for the AD1848. It is a ΣΔ digital audio stereo codec designed to provide a complete audio solution for commercial and multimedia applications requiring a single +5V power supply.

‌Key Features‌

• ‌Integration:‌ Integrates key audio data conversion and control functions into one chip.
• ‌Interface:‌ Provides a byte-wide parallel interface for ISA and EISA computer buses.
• ‌Data Transfer:‌ Supports DMA request/grant architecture for one or two DMA channels, as well as Programmed I/O (PIO) mode.
• ‌Analog Capabilities:‌
  • ‌Inputs:‌ Accepts stereo line-level or microphone-level inputs from four sources (Line, Mic, Aux1, and post-mix DAC output).
  • ‌Programmable Gain:‌ Independent programmable gain for each ADC input channel (0 to 22.5 dB in 1.5 dB steps).
  • ‌Analog Mixing:‌ AUX1 and AUX2 analog signals can be mixed with the DAC output in the analog domain with independent gain/attenuation per channel.
  • ‌Output:‌ Provides stereo line-level outputs; each channel can be independently muted.
• ‌Digital Capabilities:‌
  • ‌Converters:‌ Contains a pair of stereo ΣΔ ADCs and a pair of stereo ΣΔ DACs.
  • ‌Digital Mixing:‌ The stereo digital output of the ADC can be digitally mixed with the input of the DAC.
  • ‌Data Formats:‌ Supports 16-bit two's complement linear PCM, 8-bit unsigned linear PCM, 8-bit μ-law, and 8-bit A-law companded data. Internally, it always uses 16-bit linear PCM.
  • ‌Attenuation:‌ DAC output has independent per-channel attenuation control (0 dB to –94.5 dB in 1.5 dB steps) with zero-crossing detection to prevent "zipper" noise.
• ‌Sampling & Filtering:‌
  • ‌Sampling Rate:‌ Supports a wide range from 5.5 kHz to 48 kHz, derived from external crystals (16.9344 MHz or 24.576 MHz).
  • ‌On-chip Filters:‌ Includes digital interpolation/decimation filters, anti-imaging DAC output filters, and analog switched-capacitor/continuous-time filters. Requires minimal external components.
• ‌General Specifications:‌
  • ‌Power:‌ Single +5V supply.
  • ‌Package:‌ 68-pin PLCC.
  • ‌Dynamic Range:‌ DAC dynamic range exceeds 80 dB within a 20 kHz bandwidth.

‌Primary Applications‌
The chip is designed for simplified implementation on computer motherboards or add-in cards, targeting applications like the Microsoft Windows Sound System and general multimedia audio systems.