ts34118 Taiwan Semiconductor Company, Ltd. (TSC), ts34118 Datasheet - Page 16

• Manufacturer Part Number: ts34118
• Description: Voice Switched Speakerphone Circuit
• Manufacturer: Taiwan Semiconductor Company, Ltd. (TSC)

TS34118
Design Equations
This is the general equation defining the microphone voltage necessary to switch comparator C1 when a received
signal V
numbers for Equation 6 yields:
To switch comparator C2, currents I2 and I4 need to be determined. With sound applied to the
microphone, a voltage V
Since G
Comparator C2 switches when I4=I2. I4 is defined by:
Setting I4=I2, and combining the above equations results in:
This equation defines the line voltage at Tip/Ring necessary to switch comparator C2 in the presence of a microphone
voltage. The highest V
Equation 10 yields:
At idle, where the gain of the two attenuators is –20dB (0.1V/V), Equations 6 and 10 yield the same result:
Equations 7, 11 and 12 define the thresholds for switching, and are represented in the following graph:
V
I2 =
I4 =
V
V
V
M
L
L
M
L
HA
=840V
=0.024V
= V
= 0.52V
is present. The highest V
is the differential gain of the hybrid amplifiers, it is divided by two to obtain the voltage V2 applied to R2.
V
V
R4
R2
M
M
L
×
M
(or V
L
L
>
R4
R2
ª
« ¬
G
G
HR
MA
u
M
(Equation 7)
(Equation 12)
L
=0.0019 V
u
M
>
occurs when the circuit is in the transmit mode (G
G
u
is creased by the microphone, resulting in a current I2 into TLI1:
G
>
G
G
MA
FO
Figure 10. Basic Block Diagram For Design Purpos
HR
TX
u
@
u
u
G
L
)
M
G
G
TX
occurs when the receive attenuator is at maximum gain (+6.0dB). Using the typical
2
FO
HA
u
u
º
» ¼
G
2
HA
@
@
16-20
(Equation 11)
(Equation 8)
(Equation 9)
(Equation 10)
TX
= +6.0dB). Using the typical numbers for
2004/09 rev. B