ILA1062 Datasheet, PDF (4/9 Pages) Integral Corp. – TELEPHONE SPEECH NETWORK WITH DIALER INTERFACE

ILA1062/ILA1062A
filter. The value of C8 is 10 times the value of C6. The cut-off frequency corresponds to the time constant R7
x C6.
Input MUTE (ILA1062)
When MUTE is LOW or open-circuit, the DTMF input is enable and the microphone and receiving amplifier
inputs are inhibited. The reverse is true when MUTE is HIGH.
MUTE switching causes only negligible clicking on the line and earpiece output. If the number of parallel sets
in use causes a drop in line current to below 6 mA the DTMF amplifier becomes active independent to the
DC level applied to the MUTE input.
Dual-tone multi-frequency input DTMF
When the DTMF input is enable dialing tones may be sent on to the line. The voltage gain from DTMF to LN
is typically 25.5 dB (when R7=68k?) and varies with R7 in the same way as the microphone gain. The
signalling tones can be heard in the earpiece at a low level (confidence tone).
Receiving amplifier IR, QR and GAR
The receiving amplifier has one input (IR) and a non-inverting output (QR). The IR to QR gain is typically
31dB (when R4 = 100k?). It can be adjusted between 20 and 31dB to match the sensitivity of the transducer
in use. The gain is set with the value of R4 which is connected between GAR and QR. The overall receive
gain, between LN and QR, is calculated by subtracting the anti-sidetone network attenuation (32dB) from the
amplifier gain. Two external capacitors, C4 and C7, ensure stability. C4 is normally 100pF and C7 is 10
times the value of C4. The value of C4 may be increased to obtain a first-order low-pass filter. The cut-off
frequency will depend on the time constant R4 x C4.
The output voltage of the receiving amplifier is specified for continuous-wave drive. The maximum output
voltage will be higher under speech conditions where the peak to RMS ratio is higher.
Automatic gain control input AGC
Automatic line loss compensation is achieved by connecting a resistor (R6) between AGC and V_EE.
The automatic gain control varies the gain of the microphone amplifier and the receiving amplifier in
accordance with the DC line current. The control range is 5.8 dB which corresponds to a line length of 5 km
for a
0.5mm diameter twisted-pair copper cable with a DC resistance of 176 ?/km and average attenuation of
1.2dB/km. Resistor R6 should be chosen in accordance with the exchange supply voltage and its feeding
bridge resistance. The ratio of start and stop currents of the AGC curve is independent of the value of R6. If
no automatic
line-loss compensation is required the AGC pin may be left open-circuit. The amplifiers, in this condition, will
give their maximum specified gain.
Sidetone suppression
The anti-sidetone network, R1//Z_line, R2, R3, R8, R9 and Z_bal suppresses the transmitted signal in the
earpiece. Maximum compensation is obtained when the following conditions are fulfilled:
 ^{R 8 x}  ^Zbal
R9 x R2 = R1 x R 3 + _{ R 8 + Zbal }
(1)
Zbal
Zline
=
(2)
Zbal + R 8 Zline+ R 1
If fixed values are chosen for R1, R2, R3 and R9, then condition (1) will always be fulfilled when
To obtain optimum sidetone suppression, condition (2) has to be fulfilled which results in:
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