AD1843JS datasheet(13/64 Pages) AD

13 / 64 page

AD1843

REV. 0

–13–

On-chip bit and baud clock generation circuitry allows either

synchronous or asynchronous operation of the transmit (DAC)

and receive (ADC) paths. Each path features independent

phase advance and retard adjustments via software control. The

AD1843 can also synchronize modem operation to an external

terminal band clock. Because the device has multiple input and

output channels and converters, it is well suited for telephony

applications requiring multiple channels for voice and modem.

A detailed block diagram of the AD1843 is shown in Figure 2.

DETAILED PRODUCT DESCRIPTION

The Serial-Port AD1843 SoundComm Codec integrates the key

audio and PSTN data conversion and control functions into a

single integrated circuit. The AD1843 is intended to provide a

complete, single-chip audio and fax/modem solution for PC

multimedia applications.

External circuit requirements are limited to a minimal number

of low cost support components. Dynamic range exceeds 80 dB

over the 20 kHz audio band. Sample rates from 4 kHz to

54 kHz with 1 Hz resolution are supported from a single exter-

nal crystal or clock source.

The AD1843 SoundComm Codec is intended to be interfaced

through a DSP chip or an ASIC to a host bus such as ISA,

EISA or PCI. A general system architecture is shown in

Figure 3.

ASIC

ADSP-21xx

ANALOG I/O

AD1843

Figure 3. AD1843 System Diagram

The SoundComm codec includes a stereo pair of

∑∆ analog-to-

digital converters and two stereo pairs of

∑∆ digital-to-analog

converters. Inputs to the ADC can be selected from eight

sources of analog signals: stereo line (LIN), stereo microphone

(MIC), stereo auxiliary line #1 (AUX1), stereo auxiliary line #2

(AUX2), stereo auxiliary line #3 (AUX3), mono line (MIN),

mixer output, and DAC2 output. A mono output and a stereo

headphone driver are included on-chip. A stereo line level input

(SUM) can be mixed into the output summer. A software-con-

trolled programmable gain stage allows independent gain for

each ADC channel. The ADCs’ output can be digitally mixed

with both the DAC1 and DAC2 inputs. The left and right

ADC channels can be configured for different sample rates and

digital filter function (audio, modem or resampling).

The pair of 16-bit outputs from the ADCs is available over a se-

rial interface that also supports 16-bit digital input to the DACs

and control/status information. The AD1843 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 data format is defined indepen-

dently for each conversion resource on the AD1843.

The

∑∆ DACs are preceded by a four sample deep FIFO buffer

and a digital interpolation filter. The DAC1 and DAC2 outputs

can be mixed in the digital domain. Digital and analog attenua-

tors provide independent user volume control (plus mute) over

each DAC channel. Nyquist images and shaped quantized

noise are removed from the DACs’ analog stereo output by on-

chip switched-capacitor and continuous-time filters. All of the

analog inputs (except the stereo line input) can be mixed with

the DAC1 output in the analog domain. The DAC2 output can

also be mixed with the DAC1 output in the analog domain.

The DAC1 and DAC2 digital data can be fed back to the digital

half of the ADC to enable digital resampling operation. DAC1

and DAC2 can be run at different sample rates and with differ-

ent digital filter functions, without any beat frequency problems.

FUNCTIONAL DESCRIPTION

This section overviews the functionality of the AD1843 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 AD1843 SoundComm Codec accepts stereo line-level and

mic-level inputs. The mono MIN analog signal input, and LIN

(differential), MIC, AUX1, AUX2, AUX3 and post-mixed

DAC output analog stereo signals are multiplexed to the inter-

nal programmable gain amplifier stage (PGA).

The PGA following the input multiplexer allows left and right

independent selectable gains for each channel from 0 dB 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

The MIN analog mono signal, and the MIC, AUX1, AUX2,

AUX3 and SUM analog stereo signals can be mixed in the ana-

log domain with the DAC1 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

mixer output is available on LOUT1 externally and as an input

to the ADCs. Even if the AD1843 is not playing back data from

its DACs, the analog mix function can still be active.

MIN allows the analog signal intended for the PC speaker to be

passed through, attenuated or mixed in the AD1843’s analog

domain. MIN can be used to accept other mono input sources.

A digital control signal pin PDMNFT (Power Down Mono

Feed Through) enables the mono input signal to be fed through

to the mono output when the AD1843 mixer is powered down.

Analog-to-Digital Datapath

The AD1843

∑∆ ADCs incorporate a fourth-order modulator.

A single pole of passive filtering is all that is required for

antialiasing the analog input because of the ADC’s high over-

sampling ratio. The ADCs include linear-phase digital decima-

tion filters that low-pass filter the input. ADC input overrange

conditions will cause bits to be set that can be read.

Each channel of the mic inputs can be amplified in the analog

domain by +20 dB to compensate for the voltage swing differ-

ence between line levels and typical condenser microphone levels.

Digital-to-Analog Datapath

The

∑∆ DACs are preceded by a programmable attenuator and

a low-pass digital interpolation filter. The anti-imaging interpo-

lation filter oversamples and digitally filters the higher frequency

images. The attenuator allows independent control of each

DAC channel from +12.0 dB to –82.5 dB in 1.5 dB steps plus

full mute. The DACs’

∑∆ noise shapers oversample and con-

vert the signal to a single-bit stream. The DAC outputs are then

AD1843JS Datasheet(PDF) 13 Page - Analog Devices

AD1843JS Datasheet(HTML) 13 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64

Datasheet Download

Link URL