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AD1881AJST Datenblatt(PDF) 10 Page - Analog Devices |
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AD1881AJST Datenblatt(HTML) 10 Page - Analog Devices |
10 / 26 page AD1881A –10– REV. 0 PRODUCT OVERVIEW The AD1881A meets the Audio Codec ’97 2.0 and 2.1 Extensions. In addition, the AD1881A SoundMAX Codec is designed to meet all requirements of the Audio Codec ’97, Component Specification, Revi- sion 1.03, © 1996, Intel Corporation, found at www.Intel.com. The AD1881A also includes some other Codec enhanced fea- tures such as the built-in PHAT Stereo 3D enhancement. The AD1881A is an analog front end for high performance PC audio applications. The AC’97 architecture defines a 2-chip audio solution comprising a digital audio controller, plus a high quality analog component that includes Digital-to-Analog Converters (DACs), Analog-to-Digital Converters (ADCs), mixer and I/O. The main architectural features of the AD1881A are the high quality analog mixer section, two channels of Σ∆ ADC conversion, two channels of Σ∆ DAC conversion with Data Direct Scram- bling (D 2S) rate generators. The AD1881A’s left channel ADC and DAC are compatible for modem applications supporting irra- tional sample rates and modem filtering requirements. FUNCTIONAL DESCRIPTION This section overviews the functionality of the AD1881A and is intended as a general introduction to the capabilities of the device. Detailed reference information may be found in the descriptions of the Indexed Control Registers. Analog Inputs The Codec contains a stereo pair of Σ∆ ADCs. Inputs to the ADC may be selected from the following analog signals: tele- phony (PHONE_IN), mono microphone (MIC1 or MIC2), stereo line (LINE_IN), auxiliary line input (AUX), stereo CD ROM (CD), stereo audio from a video source (VIDEO) and post-mixed stereo or mono line output (LINE_OUT). Analog Mixing PHONE_IN, MIC1 or MIC2, LINE_IN, AUX, CD and VIDEO can be mixed in the analog domain with the stereo output from the DACs. Each channel of the stereo analog inputs may be inde- pendently gained or attenuated from +12 dB to –34.5 dB in 1.5 dB steps. The summing path for the mono inputs (PHONE_IN, MIC1, and MIC2 to LINE_OUT) duplicates mono channel data on both the left and right LINE_OUT. Additionally, the PC attention sig- nal (PC_BEEP) may be mixed with the line output. A switch allows the output of the DACs to bypass the PHAT Stereo 3D enhancement. Digital Audio Mode The AD1881A is designed with a Digital Audio Mode (DAM) that allows mixing of all analog inputs independent of the DAC output signal path. Mixed analog input signals may be sent to the ADCs for processing by the controller or the host, and may be used during simultaneous capture and playback at different sample rates. Analog-to-Digital Signal Path The selector sends left and right channel information to the programmable gain amplifier (PGA). The PGA following the selector allows independent gain control for each channel entering the ADC from 0 dB to +22.5 dB in 1.5 dB steps. Each channel of the ADC is independent, and can process left and right chan- nel data at different sample rates. Sample Rates and D 2S The AD1881A default mode sets the Codec to operate at 48 kHz sample rates. The converter pairs may process left and right channel data at different sample rates. The AD1881A sample rate generator allows the Codec to instantaneously change and process sample rates from 8 kHz to 48 kHz with a resolution of 1 Hz. The in-band integrated noise and distortion artifacts introduced by rate conversions are below –90 dB. The AD1881A uses a 4-bit D/A structure and Data Directed Scrambling (D 2S) to enhance noise immunity on motherboards and in PC enclo- sures, and to suppress idle tones below the device’s quantization noise floor. The D 2S process pushes noise and distortion artifacts caused by errors in the multibit DAC to frequencies beyond the auditory response of the human ear and then filters them. Digital-to-Analog Signal Path The analog output of the DAC may be gained or attenuated from +12 dB to –34.5 dB in 1.5 dB steps, and summed with any of the analog input signals. The summed analog signal enters the Master Volume stage where each channel of the mixer output may be attenuated from 0 dB to –94.5 dB in 1.5 dB steps or muted. Line-Level Outputs The AD1881A offers a true line-level output for notebook dock- ing station and home theater applications. The line-level output does not change with master volume settings. Host-Based Echo Cancellation Support The AD1881A supports time correlated I/O data format by pre- senting MIC data on the left channel of the ADC and the mono summation of left and right output on the right channel. The ADC is splittable; left and right ADC data can be sampled at different rates. Power Management Modes The AD1881A is designed to meet ACPI power consumption requirements through flexible power management control of all internal resources. |
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