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AD1849 データシート(PDF) 9 Page - Analog Devices |
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AD1849 データシート(HTML) 9 Page - Analog Devices |
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9 / 28 page  AD1848K REV. 0 –9– (Continued from page 1) analog signals: line, microphone (“mic”), auxiliary (“aux”) #1, and post-mixed DAC output. The microphone inputs can pass through optional 20 dB gain blocks. A software-controlled pro- grammable gain stage allows independent gain for each channel going into the ADC. The ADCs’ output can be digitally mixed with the DACs’ input. CS A1 A0 WR RD DATA7:0 DBDIR DBEN PDRQ CDRQ PDAK CDAK INT 8 7 4 2 4 5 DIR G AEN SA19:2 SA1 SA0 IOWC IORC DATA7:0 ADDRESS DECODE DRQ<X> DRQ<Y> DAK<X> DAK<Y> IRQ<Z> A B AD1848K ISA BUS 8 18 Figure 1. Interface to ISA Bus The pair of 16-bit outputs from the ADCs is available over a byte-wide bidirectional interface that also supports 16-bit digital input to the DACs and control information. The AD1848K can accept and generate 16-bit twos-complement PCM linear digital data, 8-bit unsigned magnitude PCM linear data, and 8-bit µ-law or A-law companded digital data. The ∑∆ DACs are preceded by a digital interpolation filter. An attenuator provides independent user volume control over each DAC channel. Nyquist images and shaped quantization noise are removed from the DACs’ analog stereo output by on-chip switched-capacitor and continuous-time filters. Two stereo pairs of auxiliary line-level inputs can also be mixed in the analog do- main with the DAC output. AUDIO FUNCTIONAL DESCRIPTION This section overviews the functionality of the AD1848K and is intended as a general introduction to the capabilities of the de- vice. As much as possible, detailed reference information has been placed in “Control Registers” and other sections. The user is not expected to refer repeatedly to this section. Analog Inputs The AD1848K SoundPort Stereo Codec accepts stereo line-level and mic-level inputs. LINE, MIC, and AUX1 inputs and post-mixed DAC output analog stereo signals are multi- plexed to the internal programmable gain amplifier stage (PGA). Each channel of the mic inputs can be amplified by +20 dB prior to the PGA to compensate for the voltage swing difference between line levels and typical condenser micro- phones. Alternatively, the mic inputs can bypass the +20 dB fixed gain block and go straight to the input multiplexer. The PGA following the input multiplexer allows independent se- lectable gains for each channel from 0 to 22.5 dB in +1.5 dB steps. The Codec can operate either in a global stereo mode or in a global mono mode with left channel inputs appearing at both channel outputs. Analog Mixing AUX1 and AUX2 analog stereo signals can be mixed in the ana- log domain with the DAC output. Each channel of each auxil- iary analog input can be independently gained/attenuated from +12 dB to –34.5 dB in –1.5 dB steps or completely muted. The post mixed DAC output is available on OUT externally and as an input to the ADCs. Even if the AD1848K is not playing back data from its DACs, the analog mix function can still be active. Analog-to-Digital Datapath The AD1848K ∑∆ ADCs incorporate a fourth order modulator. A single pole of passive filtering is all that is required for anti-aliasing the analog input due to the ADC’s high 64 times oversampling ratio. The ADCs include linear phase digital deci- mation filters that low-pass filter the input to 0.45 × F S (“FS” is the word rate or “sampling frequency.”) ADC input overrange conditions will cause register bits to be set that can be read. Digital-to-Analog Datapath The ∑∆ DACs contain a programmable attenuator and a low- pass digital interpolation filter. The anti-imaging interpolation filter nominally oversamples by 64 and digitally filters the higher frequency images. The interpolation ratio is increased at low sample rates to ensure that the shaped quantization noise is inaudible. This feature of the AD1848K represents an improve- ment over the earlier AD1848J. The attenuator allows indepen- dent control of each DAC channel from 0 dB to –94.5 dB in 1.5 dB steps plus full mute. The DACs’ ∑∆ noise shapers also oversample by 64 and convert the signal to a single bit stream. The DAC outputs are then filtered in the analog domain by a combination of switched-capacitor and continuous-time filters. They remove the very high frequency components of the DAC bitstream output. No external components are required. Phase linearity at the analog output is achieved by internally compen- sating for the group delay variation of the analog output filters. Changes in DAC output attenuation take effect only on zero crossings of the digital signal, thereby eliminating “zipper” noise. Each channel has its own independent zero-crossing de- tector and attenuator change control circuitry. A timer guarantees that requested volume changes will occur even in the absence of an input signal that changes sign. The time-out period is 8 milli- seconds at a 48 kHz sampling rate and 48 milliseconds at an 8 kHz sampling rate. (Time out [ms] ≈ 384/F S [kHz].) |
同様の部品番号 - AD1849 |
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同様の説明 - AD1849 |
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