Lucent Technologies Inc.
17
Advance Data Sheet
December 2000
T8301 Internet Protocol Telephone
Phone-On-A-Chip
IP Solution DSP
5 Audio Input/Output Circuitry
The discussions in this section pertain to circuitry that is outside of the dotted outline in Figure 3 on page 8.
5.1 Analog Audio Input Channels
The T8301 contains analog interfaces designed to support a 150
handset as well as an additional microphone
and two speakers.
The T8301 integrated circuit contains two audio analog inputs. There is a single-ended input (
AINAN
) to be con-
nected to a standard business telephone handset receiver. There is a differential input (
AINCP
,
AINCN
) to be con-
nected to a microphone. This provides the T8301 with the input circuitry to implement a speakerphone. The
differential input is directly connected to a 30 dB amplifier. The input select multiplexer routes
AINAN
or the output
of the fixed 30 dB amplifier to a programmable gain amplifier (PGA). The programmable gain amplifier is adjustable
from 0 dB to 21 dB in 3 dB steps. The signal output from the programmable gain amplifier is then routed to the
audio codec block to be digitized.
Each of the input signals
AINAN
,
AINCP
, and
AINCN
are ac-coupled to their T8301 inputs by a 0.2
μ
F capacitor.
The maximum signal input to the codec is 2.5 Vp-p. If the user sets the amplification to a value that would produce
a larger signal than 2.5 Vp-p, the audio codec will saturate and clip the input waveform.
The maximum input signal from the handset or from the microphone that can be supported for each gain setting is
listed in Table 7. Since the microphone amplifier has a maximum specified signal of 40 mV, the maximum micro-
phone input is not supported for PGA settings of 0 dB and 3 dB.
5.2 Programmable Gain Amplifier (PGA)
The programmable gain amplifier is using the PGAS[2:0] bits of the
aioc_reg
(see Table 11 on page 21). The set-
table gain values and their tolerances are shown below as well as the maximum allowed input signal voltage from
each of the input signals. Inputs greater than these values will saturate the input codec and produce clipped wave-
forms.
Table 7. Programmable Gain Amplifier Maximum
Bit Code
Gain
Max Input Signal
AINAN
2.500 Vp-p
1.770 Vp-p
1.250 Vp-p
0.844 Vp-p
0.625 Vp-p
0.442 Vp-p
0.313 Vp-p
0.221 Vp-p
AINCN, AINCP
Not supported
Not supported
40.0 mVp-p
28.3 mVp-p
20.0 mVp-p
14.2 mVp-p
10.0 mVp-p
7.1 mVp-p
000
001
010
011
100
101
110
111
0 dB ± 0.5 dB
3 dB ± 0.5 dB
6 dB ± 0.5 dB
9 dB ± 0.5 dB
12 dB ± 0.5 dB
15 dB ± 1.0 dB
18 dB ± 1.0 dB
21 dB ± 1.5 dB