U4080B Datasheet, PDF (12/15 Pages) TEMIC Semiconductors – Voice-Switched Circuit for Handsfree Operation

U4080B
Switching time
The switching times of the speakerphone circuit depend
not only on the various external components, but also on
the operating condition of the circuit at the same time a
change is to take effect. For example, the switching time
from idle to transmit is generally quicker than the
switching time from receive to transmit (or transmit to
receive).
The components which most significantly affect the
timing between the transmit and receive modes are those
at Pin 5 (transmit turn-on), Pin 6 (transmit turn-off), Pin
7 (receive turn-on), and Pin 8 (receive turn-off). These
four timing functions are not independent, but interact
since the T-R comparator operates on a relative T-R com-
parison, rather than on absolute values. The components
at Pins 11, 12, 13 and 23 affect the timing from the trans-
mit to the idle mode. Timing from the idle mode to
transmit mode is relatively quick (due to the quick
charging of the various capacitors), and is not greatly
affected by the component values. Pins 5–8 do not affect
the idle-to-transmit timing since the T-R comparator must
already be in the transmit mode for this to occur.
Additionally, the following should be noted:
1. The RC circuits at Pins 5 and 7 have dual function in
that they affect the sensitivity of the respective log
amplifiers or in other words, how loud the speech
must be in order to gain control of the speakerphone
circuit.
2. The RC circuit at Pin 13 also has a dual function in
that it determines the sensitivity of the transmit detec-
tor circuit.
3. The volume control affects the switching speed and
the relative response to transmit signals in the follow-
ing manner:
When the circuit is in the receive mode, reducing the
volume control setting increases the signal at TO, and
consequently the signal to the TLI pin. Therefore, a
given signal at TI will switch the circuit into the trans-
mit mode quicker at low volume settings.
12 (15)
TELEFUNKEN Semiconductors
Preliminary Information
Rev. A1, 20-May-96