SA3291_16 Datasheet, PDF (15/21 Pages) ON Semiconductor – Preconfigured Wireless DSP System

AYRE SA3291
Table 4. DYNAMIC EXAMPLE WITH FOUR VALID PROGRAM MODES (T = momentary switch is toggled; 0 = OPEN; 1 = HIGH)
MS2
0
0
0
1
1
1
0
0
0
1
0
0
0
0
0
0
MS
0
T
T
0
T
T
0
T
T
0
0
T
T
T
T
T
Memory A
B
C
D
D
D
C
A
B
D
B
C
A
B
C
A
Static Switch on MS and MS2
This mode uses two static switches to change program
modes. Table 5 describes which memory is selected
depending on the state of the switches.
In this mode, it is possible to jump from any memory to
any other memory simply by changing the state of both
switches. If both switches are changed simultaneously, then
the transition is smooth. Otherwise, if one switch is changed
and then the other, the part transitions to an intermediate
memory before reaching the final memory. The part starts in
whatever memory the switches are selecting. If a memory is
invalid, the part defaults to memory A.
This mode is set by programming the ‘MSSMode’
parameter to ‘static’ and ‘Donly’ to ‘disabled’.
Table 5. MEMORY SELECTED IN STATIC SWITCH ON
MS and MS2 MODE; Internal Resistors Set to Pull
Down (Example with Four Valid Program Modes)
MS
MS2
Memory
OPEN OPEN
A
HIGH OPEN
B (if valid, otherwise A)
OPEN HIGH
C (if valid, otherwise A)
HIGH
HIGH
D (if valid, otherwise A)
Static Switch on MS, Static Switch on MS2
(Jump to Last Memory)
This mode uses two static switches to change program
modes. Unlike in the previous example, this mode will
switch to the last valid memory when the static switch on
MS2 is HIGH. This means that this mode will only use a
maximum of three program modes (even if four valid
program modes are programmed). Table 6 describes which
memory is selected depending on the state of the switches.
This mode is set by programming the ‘MSSMode’
parameter to ‘static’ and ‘Donly’ to ‘enabled’.
Table 6. MEMORY SELECTED IN STATIC SWITCH ON
MS, Static Switch on MS2 (Jump to Last Memory)
Mode; Internal Resistors Set to Pull Down
MS
MS2
Memory
OPEN OPEN
A
HIGH OPEN
B (if valid, otherwise A)
OPEN HIGH
D
HIGH
HIGH
D
In this mode, it is possible to jump from any memory to
any other memory simply by changing the state of both
switches. If both switches are changed simultaneously, then
the transition is smooth. Otherwise, if one switch is changed
and then the other, the part transitions to an intermediate
memory before reaching the final memory.
When MS2 is set HIGH, the state of the switch on MS is
ignored. This prevents memory select beeps from occurring
if switching MS when MS2 is HIGH. The part starts in
whatever memory the switches are selecting. If a memory is
invalid, the part defaults to memory A.
AGC−O and Peak Clipper
The output compression−limiting block (AGC−O) is an
output limiting circuit whose compression ratio is fixed at
∞: 1. The threshold level is programmable. The AGC−O
module has programmable attack and release time
constants.
The AGC−O on the Ayre SA3291 has optional adaptive
release functionality. When this function is enabled, the
release time varies depending on the environment. In
general terms, the release time becomes faster in
environments where the average level is well below the
threshold and only brief intermittent transients exceed the
threshold.
Conversely, in environments where the average level is
close to the AGC−O threshold, the release time applied to
portions of the signal exceeding the threshold is longer. The
result is an effective low distortion output limiter that clamps
down very quickly on momentary transients but reacts more
smoothly in loud environments to minimize compression
pumping artifacts. The programmed release time is the
longest release time applied, while the fastest release time is
16 times faster. For example, if a release time of 128 ms is
selected, the fastest release time applied by the AGC−O
block is 8 ms.
The Ayre SA3291 also includes the Peak Clipper block for
added flexibility.
Memory Switch Fader
To minimize potential loud transients when switching
between program modes, the Ayre SA3291 uses a memory
switch fader block. When the memory is changed, the audio
signal is faded out, followed by the memory select acoustic
indicators (if enabled), and after switching to the next
memory, the audio signal is faded back in. The memory
switch fader is also used when turning the Tone Generator
on or off, and during SDA programming.
Power Management
Ayre SA3291 has three user−selectable power
management schemes to ensure the hearing aid turns off
gracefully at the end of battery life. Shallow reset, Deep reset
and Advanced Reset mode. It also contains a programmable
power on reset delay function.
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