AN2834 Freescale Semiconductor / Motorola, AN2834 Datasheet - Page 5

• Manufacturer Part Number: AN2834
• Description: AN2834, Packet Telephony Automatic Level Control on the StarCore SC140 Core
• Manufacturer: Freescale Semiconductor / Motorola

Figure 1 shows the resulting top-level structure of the ALC device. The send-in x(n) and receive-in z(n) signals are
processed and generate a send-out y(n) signal. The receive-in signal is employed to adjust the ALC functionality in
the presence of echo. The total ALC gain signal g
Typical ALC control parameters for a 16-bit fixed-point implementation are:
Freescale Semiconductor
x(n)
z(n)
7.
8.
9.
10.
11.
•
•
•
•
•
Use the control signal e
Compute the total gain signal: g
Generate the output signal: y(n) = min{max{g
Estimate the ALC output signal level: P
Repeat steps 1–10 for new samples of x(n).
g
G
g
g
y
min
s
min
max
max
= 2
= –1
= 2
= G
= 1 / g
7
Packet Telephony Automatic Level Control on the StarCore SC140 Core, Rev. 1
–15
1 – az
max
1 – a
s
Figure 1. Top-Level Architecture of the Proposed ALC Device
= 2
–1
10
–7
10/20
1 – az
~ 810
1
z
1 – a
(n): g(n) = [g(n –1) – g
g(n)
–
–1
P
min
2
z
t
–15
(n) = g
–1
(that is, 10 dB)
–
P
t
g
(n) = g
s
min
s
y
g(n).
(n).
MAX
g
s
t
min
(n)x(n),y
g(n) is the linear gain adjusting the send-in signal.
4
MAX
(n)]e
y
min
z
(n) + g
min
}y
max
4
g
MIN
k = 0
(n).
}.
max
N
z
MIN
–k
y
max
(1 – a)z
1 – az
G
MIN
max
–
–1
–1
P
ref
Architecture
y(n)
5