LM4546AVH NSC [National Semiconductor], LM4546AVH Datasheet - Page 15

• Manufacturer Part Number: LM4546AVH
• Description: AC 97 Rev 2 Multi-Channel Audio Codec with Sample Rate Conversion and National 3D Sound
• Manufacturer: NSC [National Semiconductor]

Functional Description
GENERAL
The LM4546A codec can mix, process and convert among
analog (stereo and mono) and digital (AC Link format) inputs
and outputs. There are two stereo and four mono analog in-
puts and one stereo and one mono analog outputs. A single
codec supports data streaming on two input and two output
channels of the AC Link digital interface simultaneously.
ADC INPUTS AND OUTPUTS
Both stereo analog inputs and three of the mono analog inputs
can be selected for conversion by the 18-bit stereo ADC. Dig-
ital output from the left and right channel ADCs is always
located in AC Link Input Frame slots 3 and 4 respectively.
Input level to either ADC channel can be muted or adjusted
from the Record Gain register, 1Ch. Adjustments are in 1.5
dB steps over a gain range of 0 dB to +22.5 dB and both
channels mute together (D15). Input selection for the ADC is
through the Record Select Mux controlled from the Record
Select register, 1Ah, together with microphone selection con-
trolled by the MS bit (D8) in the General Purpose register, 20h.
The stereo input, CD_IN, uses a quasi-differential 3-pin inter-
face where both stereo channel inputs are referenced to the
third pin, CD_GND. CD_GND should be AC coupled to the
source ground and provides common-mode feedback to can-
cel ground noise. It is not a DC ground. The other stereo input,
LINE_IN, is a 2-pin interface, single-ended for each stereo
channel with analog ground (AV
Either of the two mono microphone inputs can be muxed to a
programmable boost amplifier before selection for either
channel of the ADC. The Microphone Mux is controlled by the
Microphone Selection (MS) bit (D8) in the General Purpose
register 20h and the 20 dB programmable boost is enabled
by the 20dB bit (D6) in register 0Eh. The other selectable
mono input, coupled directly to the Record Select Mux, is
PHONE.
ANALOG MIXING: MIX1
Three analog inputs are available for mixing at the stereo
mixer, MIX1 – both stereo and one mono, namely the micro-
phone input selected by MS (D8, reg 20h). Digital input to the
codec can be directed to either MIX1 or to MIX2 after con-
version by the 18-bit stereo DAC and level adjustment by the
PCM Out Volume control register (18h). Each input to MIX1
may be muted or level adjusted using the appropriate Mixer
Input Volume Register: Mic Volume (0Eh), Line_In Volume
(10h), CD Volume (12h) and PCM Out Volume (18h). The
mono microphone input is mixed equally into left and right
stereo channels but stereo mixing is orthogonal, i.e. left chan-
nels are only mixed with other left channels and right with
right. The left and right amplitudes of any stereo input may be
adjusted independently however mute for a stereo input acts
on both left and right channels.
DAC MIXING AND 3D PROCESSING
Control of routing the DAC output to MIX1 or MIX2 is by the
POP bit (D15) in the General Purpose register, 20h. If MIX1
is selected (default, POP=0) then the DAC output is available
for processing by the National 3D Sound circuitry. If MIX2 is
selected, the DAC output will bypass the 3D processing. This
allows analog inputs to be enhanced by the analog 3D Sound
circuitry prior to mixing with digital audio. The digital audio
may then use alternative digital 3D enhancements. National
3D Sound circuitry is enabled by the 3D bit (D13) in the Gen-
SS
) as the signals' reference.
200308 Version 5 Revision 1
Print Date/Time: 2009/07/15 15:26:52
15
eral Purpose register, 20h, and is a fixed depth implementa-
tion. The 3D Control register, 22h, is therefore not pro-
grammable (read-only). The 3D Sound circuitry defaults to
disabled after reset.
ANALOG MIXING: MIX2
MIX2 combines the output of MIX1 (Stereo Mix 3D) with the
two mono analog inputs, PHONE and PC_BEEP, these each
level-adjusted by the input control registers Phone Volume
(0Ch) and PC_Beep Volume (0Ah) respectively. If selected
by the POP bit (D15, reg 20h), the DAC output is also summed
into MIX2.
STEREO MIX
The output of MIX2 is the signal, Stereo Mix. Stereo Mix is
used to drive the Line output (LINE_OUT) and can also be
selected as the input to the ADC by the Record Select Mux.
In addition, the two channels of Stereo Mix are summed to
form a mono signal (Mono Mix) also selectable by the Record
Select Mux as an input to either channel of the ADC.
STEREO OUTPUT
The output volume from LINE_OUT can be muted or adjusted
by 0 dB to 45 dB in nominal 3 dB steps under the control of
the Master Volume register, 02h. As with the input volume
registers, adjustments to the levels of the two stereo channels
can be made independently but both left and right channels
share a mute bit (D15).
MONO OUTPUT
The mono output (MONO_OUT) is driven by one of two sig-
nals selected by the MIX bit (D9) in the General Purpose
register, 20h. The signal selected by default (MIX = 0) is the
mono summation of the two channels of Stereo Mix 3D, the
stereo output of the mixer MIX1. Setting the control bit MIX =
1, selects a microphone input, MIC1 or MIC2. The choice of
microphone is controlled by the Microphone Select (MS) bit
(D8) also in the General Purpose register, 20h.
ANALOG LOOPTHROUGH AND DIGITAL LOOPBACK
Analog Loopthrough refers to an all-analog signal path from
an analog input through the mixers to an analog output. Digital
Loopback refers to a mixed-mode analog and digital signal
path from an analog input through the ADC, looped-back (LP-
BK bit – D7, 20h) through the DAC and mixers to an analog
output.
RESETS
COLD RESET is performed when RESET# (pin 11) is pulled
low for > 1 µs. It is a complete reset. All registers and internal
circuits are reset to their default state. It is the only reset which
clears the ATE and Vendor Test Modes.
WARM RESET is performed when SYNC (pin 10) is held high
for > 1 µs and the codec AC Link digital interface is in pow-
erdown (PR4 = 1, Powerdown Control / Status register, 26h).
It is used to clear PR4 and power up the AC Link digital in-
terface but otherwise does not change the contents of any
registers nor reset any internal circuitry.
REGISTER RESET is performed when any value is written to
the RESET register, 00h. It resets all registers to their default
state and will modify circuit configurations accordingly but
does not reset any other internal circuits.
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