DA9191A.000
July 31, 1997
FUNCTIONS
◆ RX Audio
The RX audio block starts with switch S1. The switch
is controlled by bit S1 of register 0EHEX. The input
ALP is used for enabling the audio loopback mode.
In normal operation RX is used. Behind the switch is
amplifier GC1 with adjustable gain from -3dB to
+3dB. The gain is controlled with bits 0..3 in register
0EHEX.The amplifier output is connected to the
second order lowpass filter F1. The cutoff frequency
of the filter is 50 kHz and the gain at 1kHz is 0dB.
The filter output is connected to data comparator C1
and to the SAT bandpass filter F2 and to the rest of
the RX audio block. The polarity of the received data
can be inverted with bit INVRX, which is located in
register 13HEX. The data comparator output is
connected to the DPLL and Manchester decoder
blocks. The filter F2 is a 6kHz bandpass filter for
supervisory audio tone. The filter is a second order
SC filter. The filter output is connected to SAT
comparator C2 and the SAT detection block.
the data is received on the voice channel the
lowpass filter F3 input is grounded automatically with
this switch. With switches S6 and S7 the received
audio and transmitted audio can be summed. The
control bits of the switches are located in register
03HEX. This signal is fed to F4 and to the DTMF
receiver. The function of the DTMF receiver is
described in the next section RX de-emphasis filter
F4 has a -6dB/octave (±1dB) frequency response in
the range 300Hz ... 3kHz. The filter can be bypassed
with S2-RXTST0-RXTST1. Switch S2-RXTST0-
RXTST1 is connected to the DEOUT pin. The
performance of C1, C2 and F2 can be monitored with
switch S2-RXTST0-RXTST1. Bits 5 and 6 in register
02HEX and bit 5 in register 0EHEX control this switch.
An external capacitor is needed between DEOUT
and RBPFIN. The RBPFIN input is connected to filter
F5, which is a 6th order bandpass filter. The gain of
this filter is 0dB at 1kHz. The filter can be bypassed
with switch S4. After S4 the signal is connected to
the RBPFOUT pin. An external capacitor is used to
connect the signal to the EXPIN input.
The signal from F1 is connected to filter F3 through a
switch which is used by the internal logic when the
AUMUT bit of register 13HEX is active. In this case if
C1 C2 F2
MICOUT
RX data, SAT
S2
RXTST0
RXTST1
S7
GC1
S4
F1
F5
F3
S1
RXMUTE
F4
ALP
RX
S6
+
DTMF
Receiver
S9
A2
SIDETONE
SIDEFB
A3
BUZOUT
BUZFB
EARP2
EXPANDER
1:2
GC2
F6
M1
S5
+
+
A4
A5
S8
S10
F7
EARP1
EXTERP
S11
Audio Receive Path
17
MAS [ MICRO ANALOG SYSTEMS ]
