U4082B-DEV-BOARD Atmel, U4082B-DEV-BOARD Datasheet - Page 25

• Manufacturer Part Number: U4082B-DEV-BOARD
• Description: WiFi / 802.11 Modules & Development Tools Voice Switched Circuit
• Manufacturer: Atmel

8.2.4
4743D–CORD–03/06
Switching Thresholds
An acoustic loss of at least 23 dB is necessary to prevent instability and oscillations, commonly
referred to as “singing”. However, the following equations show that greater acoustic loss is nec-
essary to obtain proper level detection and switching.
To switch comparator C1, currents I
page
according to the following equation:
where the terms in the brackets are the V/V gain terms. The speaker amplifier gain is divided by
two since GSA is the differential gain of the amplifier, and V
output. The current I
where V
ing the above two equations yields:
This is the general equation defining the microphone voltage necessary to switch comparator C1
when a receive signal V
maximum gain (+6.0 dB). Using the typical numbers for equation 6 yields:
V
To switch comparator C2, currents I
microphone, a voltage V
Since G
V
Setting I
I
I
V
I
I
V
3
1
2
4
M
2
M
L
=
=
=
=
applied to R
= 0.52 × V
=
=
V
------ -
R
V
-------------------------- -
V
------- -
V
------ - G
R
R
23, with a receive signal V
V
V
L
M
M
L
3
4
2
M
L
HA
M
4
R
= I
1
HR
G
is the microphone voltage. Since the switching threshold occurs when I
is the differential gain of the hybrid amplifiers, it is divided by two to obtain the voltage
G
R
------ -
R
R
------ -
R
G
MA
2
HR
1
3
4
2
MA
, and combining the above equations results in:
L
G
2
-------------------------------------------------------------------- -
. Comparator C2 switches when I
------------------------------------------------- -
FO
G
G
G
G
G
HR
MA
FO
HR
T
(5)
1
, coming from the microphone circuit, is defined by:
G
---------- -
G
G
G
G
G
2
M
HA
L
FO
T
R
MA
FO
(9)
is present. The highest V
is created by the microphone, resulting in a current I
G
G
---------- -
G
HA
2
2
2
SA
R
L
(8)
applied to Tip/Ring, a current I
G
SA
1
2
and I
and I
(10)
(4)
3
4
need to be determined. Referring to
need to be determined. With sound applied to the
(6)
4
= I
M
2
. I
occurs when the receive attenuator is at
(7)
4
is defined by:
3
is obtained from one side of that
3
will flow through R
2
into TLI1:
U4082B
1
Figure 8-3 on
= I
3
3
, combin-
into RLI2
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