參數(shù)資料
型號(hào)： AM79C32A
廠商： Advanced Micro Devices, Inc.
英文描述： Digital Subscriber Controller⑩ (DSC⑩) Circuit
中文描述： 數(shù)字用戶控制器⑩法（DSC⑩）電路
文件頁(yè)數(shù)： 25/101頁(yè)
文件大?。?/td> 1607K
代理商： AM79C32A
Am79C30A/32A Data Sheet
25
Programmable Analog Preamplifier
A programmable analog preamplifier GA is included in
front of the A/D converter and is adjustable in 6-dB in-
crements from 0 dB to +24 dB. The existing GX gain
stage in the transmit path may be used for finer adjust-
ment of transmit gain. This preamplifier eliminates the
need for an external operational amplifier when inter-
facing electret-type handsets to the DSC circuit.
Analog Sidetone
Analog sidetone takes the analog input to the transmit-
ter ADC and sums it into the single-ended input of the
EAR output buffer. The summing point is after the out-
put selection switch. The analog sidetone path has pro-
grammable attenuation between –6 and –27 dB, plus
infinity (off). Default is infinity. Programming is via four
bits in the Extended FIFO Control Register, EFCR.6–3.
The programming values are given in Table 20.
Signal Processing
Transmitter
The transmitter performs a series of operations as de-
scribed below.
1. An ADC converts the incoming analog signal at a
sampling rate of 512 kHz.
2. The Band Pass filter and a series of decimators re-
ject DC and 50- to 60-Hz line frequencies while re-
ducing the sampling rate to 8 kHz.
3. The X filter is an 8-tap user-programmable filter for
tuning the microphone. The default is flat with unity
gain.
4. The GX filter is a programmable gain filter that al-
lows the user to program a gain of 0 to +12 dB in
0.5-dB steps. The default value is 0 dB.
5. The
μ
-law or A-law digital compression algorithm
converts the linear output of the GX filter to
μ
- or
A-law code. The default algorithm is
μ
-law code.
The MSB (sign bit) is transferred first to (or from) the
MUX.
Receiver
The receiver performs a series of operations described
as follows:
1. An expander converts the input A- or
μ
-law data to
digital linear data. The most significant bit is trans-
ferred from the MUX first. The default value is μ-law.
2. The GR filter is a programmable gain filter that al-
lows the user to program a gain of –12 to 0 dB in
0.5-dB steps. The default value of GR is 0 dB.
3. The GER and Sidetone Gain (STG) are program-
mable constant multipliers which allow the user to
program a gain of –10 to +18 dB in 0.5-dB steps
(default value 0 dB) and –18 to 0 dB in 0.5-dB steps
(default value –18 dB) respectively. The GER pro-
vides volume control (for the hearing impaired) and
should be programmed to 0 dB for normal opera-
tion. The sidetone gain path provides feedback from
the transmitter.
4. The R filter is provided to correct for speaker atten-
uation distortion and is a user-programmable filter
similar to the X filter in the transmitter.
5. A series of interpolators increases the sampling
frequency.
6. A DAC converts the digital signal to the analog
audio output signal.
PEAK Hold Registers
Logic in the form of two microprocessor accessible
peak hold registers will be provided to allow for support
of a software based speaker phone solution. These
registers, one in the transmit path (PEAKX) and one in
the receive path (PEAKR), will provide the compressed
maximum (peak) absolute value of the data in the path
since the register was last read. With appropriate soft-
ware, this can be used to implement a hands-free func-
tion. Refer to the MAP block diagram for the location of
these registers in the processing path.
The following assumptions are made:
1. The GX and GR blocks are used as gain/attenua-
tors, without modification to their range or resolu-
tion.
2. The data is presented in compressed A-law format,
without the alternate bit inversion. The sign bit is not
presented.
3. The data extraction point for the transmit path is
after the X filter.
4. The data extraction point for the receive path is im-
mediately following the expander.
5. The compressed data from the transmit and receive
paths is presented using the same compression
algorithm.
Table 20.
Analog Sidetone
0000 =
∞
0001 = –27.0 dB
0100 = –22.5 dB
0101 = –21.0 dB
0010 = –25.5 dB
0110 = –19.5 dB
0011 = –24.0 dB
0111 = –18.0 dB
1000 = –16.5 dB
1100 = –10.5 dB
1001 = –15.0 dB
1101 = –9.0 dB
1010 = –13.5 dB
1110 = –7.5 dB
1011 = –12.0 dB
1111 = –6.0 dB
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