TLC320AD80 Datasheet, PDF (19/37 Pages) Texas Instruments – Audio Processor Subsystem

A typical set-top-box application would connect AUDIO MONO output to one of the inputs of the wideband
multiplexer after applying external 75 µs pre-emphasis. If selected by the wideband multiplexer, the
monaural audio output would then be processed by the channel 3/4 RF modulator and then connected to
an external TV or VCR receiver (with a coaxial cable). The full-scale analog output is typically 2.8 V
peak-to-peak. This analog output (AUDIO MONO) can drive load impedances as low as 10 kΩ and is short
circuit protected to 7 mA.
2.2.2 External Stereo Audio Output
The external stereo output (EXT OUTL, EXT OUTR) provides the output of the analog multiplexer
(connected to the analog inputs, the DAC, and the monaural decoder). A typical connection would ac couple
this output to the volume and balance external inputs. Alternate connections may include external analog
functions located before the volume and balance input.
The selected audio input is output at a fixed volume of 0 dB on the external stereo audio output (EXT OUTL,
EXT OUTR). The full-scale analog output of each channel is typically 2.8 V peak-to-peak. The analog
outputs can drive load impedances as low as 10 kΩ and are short circuit protected to 7 mA.
2.2.3 Wideband Multiplexer Output
The wideband multiplexer output is a single-ended output provided by the wide-band multiplexer. The inputs
and output of this multiplexer are provided by external terminals. A typical application would use this function
to provide source selection for a channel 3/4 RF modulator. The modulator would then be connected to a
TV or VCR by means of a coaxial cable.
The wideband multiplexer can output one of two inputs (MUX IN1 AND MUX IN2) or perform an audio mute.
A typical connection would connect one input to the composite TV baseband audio signal. The other input
would connect to the AUDIO MONO output of the TLC320AD80 with external 75 µs pre-emphasis. This
feature allows remodulating an analog audio program which was broadcast in stereo without sacrificing the
stereo content.
The wideband multiplexer has a 3-dB bandwidth greater than 90 kHz to provide a flat response for the SAP
channel of a TV aural baseband signal. The volume control mute does not have any effect on the wideband
multiplexer output. The wideband multiplexer has an independent mute control located at bit D5 of control
register 02h. The full-scale analog output is typically 2.8 V peak-to-peak. The analog output can drive load
impedances as low as 600 Ω and is short circuit protected to 10 mA.
2.3 Volume/Balance/Mute Control
The inputs and outputs of the volume and balance control are provided by external terminals. The inputs
to this block (EXT INL, EXT INR) are typically ac-coupled to the EXT OUTL and EXT OUTR outputs. The
outputs consist of a stereo pair (AUDIO LEFT, AUDIO RIGHT) and a mono output (AUDIO MONO). The
volume of the left and right audio channels can be controlled independently for stereo balance control. The
lowest volume control setting corresponds to audio mute.
2.3.1 Volume Control
The TLC320AD80 provides a volume control range from 6 dB to –62 dB in 1 dB increments. Volume changes
can be executed in each channel (left or right) independently or in ganged mode. All volume transitions take
effect at zero-crossing to avoid clicks during volume transitions.
Volume control changes are programmed by means of control registers 03h and 04h (see Appendix A,
Register Set). These changes will take effect during zero crossing of the data on a given channel. A zero
crossing is defined by when the relative magnitude of the signal is zero (i.e., equal to the V_ref voltage level).
However, if no zero crossing occurs within 4096 LRCLK periods, the gain is forced to change. Independent
left channel and right channel zero crossing detectors are provided to minimize pops or clicks on stereo
signals.
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