ADAV400 Analog Devices, ADAV400 Datasheet - Page 22

• Manufacturer Part Number: ADAV400
• Description: Audio Codec
• Manufacturer: Analog Devices

ADAV400
Constant dB and RC Updates (Exponential)
An exponential update is accomplished by shifts and additions
with a range from 6.1 ms to 1.27 sec (−60 dB relative to 0 dB full
scale). When the ramp type is set to 01 (constant dB), each step
size is set to the current value in the slew data. When the ramp
type bits are set to 10 (RC), the step size is equal to the difference
between the values in the target RAM and slew RAM (see
Figure 25, Figure 26, and Figure 27).
–0.2
–0.4
–0.6
–0.8
–1.0
Figure 25. Slew RAM—Constant dB Update Increasing Ramp
–0.2
–0.4
–0.6
–0.8
–1.0
–0.2
–0.4
–0.6
–0.8
–1.0
1.0
0.8
0.6
0.4
0.2
1.0
0.8
0.6
0.4
0.2
1.0
0.8
0.6
0.4
0.2
0
0
0
0
0
0
Figure 26. Slew RAM—RC Update Increasing Ramp
Figure 27. Slew RAM—Constant dB and RC
Updates Decreasing Ramp, Full Scale
5
5
5
10
10
10
15
15
15
TIME (ms)
TIME (ms)
TIME (ms)
20
20
20
25
25
25
30
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Rev. 0 | Page 22 of 36
Constant Time Update
A constant time update is calculated by adding a step value that
is determined after each target is loaded. The equation for this
step size is
Figure 28 shows a plot of the target/slew RAM operating in
constant time mode. For this example, 128 steps are used to
reach the target value. This type of ramping takes a fixed
amount of time for a given number of steps, regardless of the
difference in the initial state and the target value. Figure 29
shows a plot of a constant time ramp from –80 dB to –6 dB (half
scale) using 128 steps; thus, the ramp takes the same amount of
time as the previous ramp from –80 dB to 0 dB. A constant time
decreasing ramp plot is shown in Figure 30.
Figure 29. Slew RAM—Constant Time Update Increasing Ramp, Half Scale
Figure 28. Slew RAM—Constant Time Update Increasing Ramp, Full Scale
Step = (Target Data − Slew Data)/(Number of Steps)
–0.2
–0.4
–0.6
–0.8
–1.0
–0.2
–0.4
–0.6
–0.8
–1.0
1.0
0.8
0.6
0.4
0.2
1.0
0.8
0.6
0.4
0.2
0
0
0
0
5
5
10
10
15
15
TIME (ms)
TIME (ms)
20
20
25
25
30
30
35
35