MC34118DWR2 Freescale Semiconductor, MC34118DWR2 Datasheet - Page 14

• Manufacturer Part Number: MC34118DWR2
• Description: IC VOICE SWITCH SPKPHONE 28-SOIC
• Manufacturer: Freescale Semiconductor

Specifications of MC34118DWR2

• Function: Voice-Switched Speakerphone
• Number Of Circuits: 1
• Voltage - Supply: 3.5 V ~ 6.5 V
• Current - Supply: 5.5mA
• Operating Temperature: -20°C ~ 60°C
• Mounting Type: Surface Mount
• Package / Case: *
• Includes: Background Noise Monitor, Chip Disable, Dial Tone Detector, Driver Amplifiers, Level Detectors, Microphone Amplifier, MUTE
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power (watts): -
• Interface: -
• Other names: MC34118DWTR

SWITCHING TIME
the components at C
ondarily by the capacitors at the level detector outputs
(RLO1, RLO2, TLO1, TLO2).
termined by the capacitor at C
current sources (refer to Figure 6). The switching time is:
is 5.0 µF, ∆T = 20 ms. If the circuit switches directly from re-
ceive to transmit (or vice--versa), the total switching time
would be 40 ms.
depends on which type of idle mode is in effect. If the circuit
is going to “fast idle,” the time constant is determined by the
C
C
time to idle of ≈30 ms (for 95% change). Fast idle is an infre-
quent occurrence, however, occurring when both speakers
are talking and competing for control of the circuit. The
switching time from idle back to either transmit or receive is
described above.
determined by the C
(see Figure 6). With C
time constant is ≈ 600 ms, giving a switching time of
≈1.8 seconds (for a 95% change). The switching period to
slow idle begins when both speakers have stopped talking.
The switching time back to the original mode will depend on
how soon that speaker begins speaking again. The sooner
the speaking starts during the 1.8 second period, the quicker
the switching time since a smaller voltage excursion is re-
quired. That switching time is determined by the internal cur-
rent sources as described above.
detectors have detected the appropriate signal levels, since
their outputs operate the Attenuator Control Block. Referring
to Figure 4, the rise time of the level detectors’ outputs to
new speech is quick by comparison (≈1.0 ms), determined
by the internal 350 Ω resistor and the external capacitor (typi-
cally 2.0 µF). The output’s decay time is determined by the
external capacitor, and an internal 4.0 µA current source giv-
ing a decay rate of ≈60 ms for a 120 mV excursion at RLO
or TLO. However, the overall response time of the circuit is
not a constant since it depends on the relative strength of the
signals at the different level detectors, as well as the timing of
the signals with respect to each other. The capacitors at the
four outputs (RLO1, RLO2, TLO1, TLO2) must be equal
value (± 10%) to prevent problems in timing and level re-
sponse.
MC34118
14
T
T
The switching time of the MC34118 circuit is dominated by
The time to switch to receive or to transmit from idle is de-
For the typical case where ∆V = 240 mV, I = 60 µA, and C
The switching time from either receive or transmit to idle
If the circuit is switching to “slow idle,” the time constant is
The above switching times occur, however, after the level
capacitor, and the internal 2.0 kΩ resistor (Figure 6). With
= 5.0 µF, the time constant is ≈10 ms, giving a switching
DESIGN GUIDELINES
T
T
∆T =
capacitor and R
(Pin 14, refer to Figure 6), and sec-
T
= 5.0 µF, and R
∆V x C
T
I
, together with the internal
T
T
, the external resistor
T
= 120 kΩ, the
T
cant since it is so short. The decay time, however, provides a
significant part of the “hold time” necessary to hold the circuit
during the normal pauses in speech.
RLI2, TLI1, TLI2) do not affect the switching time, but rather
affect the relative signal levels required to switch the circuit,
as well as the frequency response of the detectors.
omitted for simplicity), and the circuit of Figure 23, the follow-
ing definitions will be used (all measurements are at
1.0 kHz):
— G
— G
— G
— G
— G
— G
— G
— G
— G
— G
I) Transmit Gain
and Ring, is determined by the output characteristics of the
microphone, and the desired transmit level. For example, a
typical electret microphone will produce ≈0.35 mVrms un-
der normal speech conditions. To achieve 100 mVrms at Tip/
Ring, an overall gain of 285 V/V is necessary. The gain of the
transmit attenuator is fixed at 2.0 (+ 6.0 dB), and the gain
through the hybrid of Figure 23 (G
(-- 8.0 dB). Therefore a gain of 357 V/V is required of the
microphone and hybrid amplifiers. It is desirable to have the
majority of that gain in the microphone amplifier for three rea-
sons: 1) the low level signals from the microphone should be
The rise time of the level detector’s outputs is not signifi-
The components at the inputs of the level detectors (RLI1,
Referring to Figure 24 (the coupling capacitors have been
The transmit gain, from the microphone output (V
from the microphone output to TXI (typically 35 V/V, or
31 dB);
TXI to TXO;
to the HTO--/HTO+ differential output (typically 10.2 V/V,
or 20.1 dB);
signals, and includes the balance network (measured at
0.4 V/V, or -- 8.0 dB);
the filter input (measured at 0.18 V/V, or --15 dB);
signals (measured at 0.833 V/V or -- 1.6 dB);
put of the filter to RXI, typically 0 dB at 1.0 kHz;
RXI to RXO;
RXO to the differential output of the MC34119 (typically
22 V/V or 26.8 dB);
differential voltage to the microphone output voltage.
MA
TX
HA
HT
ST
HR
FO
RX
SA
AC
is the gain of the transmit attenuator, measured from
is the gain from HTO--/HTO+ to Tip/Ring for transmit
is the sidetone gain, measured from HTO--/HTO+ to
is the gain of hybrid amplifiers, measured from TXO
is the gain of the speaker amplifier, measured from
is the acoustic coupling, measured from the speaker
is the gain from Tip/Ring to the filter input for receive
is the gain of the filter stage, measured from the in-
is the gain of the receive attenuator measured from
is the gain of the microphone amplifier measured
DESIGN EQUATIONS
HT
) is nominally 0.4
MOTOROLA
M
) to Tip