The AD1890 and AD1891 SamplePorts™ are fully digital, stereo Asynchronous Sample Rate Converters (ASRCs) that solve sample rate interfacing and compatibility problems in digital audio equipment.Conceptually, these converters interpolate the input data up to a very high internal sample rate with a time resolution of 300 ps, then decimate down to the desired output sample rate. The AD1890 is intended for 18- and 20-bit professional applications,and the AD1891 is intended for 16-bit lower cost applications where large dynamic sample-rate changes are not encountered.These devices are asynchronous because the frequency and phase relationships between the input and output sample clocks (both are inputs to the AD1890/AD1891 ASRCs) are arbitrary and need not be related by a simple integer ratio. There is no need to explicitly select or program the input and output sample clock frequencies, as the AD1890/AD1891 automatically sense the relationship betweenthe two clocks. The input and output sample clock frequencies can nominally range from 8 kHz to 56 kHz, and the ratio between them can vary from 1:2 to 2:1.
The AD1890/AD1891 use multirate digital signal processing techniques to construct an output sample stream from the input sample stream. The input word width is 4 to 20 bits for the AD1890 or 4 to 16 bits for the AD1891. Shorter input words are automatically zero-filled in the LSBs. The output word width for both devices is 24 bits. The user can receive as many of the output bits as desired. Internal arithmetic is performed with 22-bit coefficients and 27-bit accumulation. The digital samples are processed with unity gain.
The input and output control signals allow for considerable flexibility for interfacing to a variety of DSP chips, AES/EBU receivers and transmitters and for I2S compatible devices. Input and output data can be independently justified to the left/right clock edge, or d
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