TWL1102 Datasheet, PDF (4/29 Pages) Texas Instruments – VOICE-BAND AUDIO PROCESSOR VBAPE

TWL1102
VOICE-BAND AUDIO PROCESSOR (VBAP™)
SLVS264 – NOVEMBER 1999
functional description (continued)
sidetone
A portion of the transmitted audio is attenuated and fed back to the receive channel through the sidetone path.
The sidetone path defaults to –12 dB. The sidetone path can be enabled by writing to the power control register.
receive volume control
The receive volume control block acts as an attenuator with a range of –18 dB to 0 dB in 2 dB steps for control
of the receive channel volume. The receive volume control gain defaults to 0 dB.
receive filter and PGA
The receive filter is a digital filter that meets CCITT G.714 requirements with a high-pass filter that is selectable
through the I²C interface. The device operates in either the 15-bit linear or 8-bit µ-law or A-law companded
mode, which is selectable through the I²C interface. The gain defaults to –1 dB representing a 3 dBm0 level
for a 32 Ω load impedance and the corresponding digital full scale PCMI code. The gain may be set to –2 dB
for the respective 3 dBm0 level for a 16-Ω load impedance.
digital modulator and filter
The second-order digital modulator and filter convert the received digital PCM data to the analog output required
by the earphone interface.
earphone amplifiers
The analog signal can be routed to either of two earphone amplifiers, one with differential output (EAR1ON and
EAR1OP) and one with single-ended output (EAR2O). Clicks and pops are suppressed for EAR1 differential
output only.
tone generator
The tone generator provides generation of standard DTMF tones and single tone frequencies which are output
to the following: 1) The buzzer driver, as a pulse density modulation (PDM) signal. 2) The receive path
digital/analog converter (D/A), for outputting through the earphone. There are 255 possible single tones. The
tone integer value is determined by the following formula Round (Tone Freq (Hz)/7.8135 Hz). The value is
loaded into one of two 8-bit registers, the high tone register [04}or the low tone register {05}. The tone output
is 2 dB higher when applied to the high tone register {04}. When generating DTMF tones the high DTMF tone
must be applied to the high tone register, and the low frequency tone to the low tone register.
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