SA3229 Datasheet, PDF (11/16 Pages) ON Semiconductor – Preconfigured DSP System

RHYTHM SA3229
In Momentary Memory Select mode, the rocker switch
allows cycling through the memory profiles in both
directions. An “up” switch closure indicates a program
advance to the next higher numbered memory and “down”
switch closures indicates a program retreat to the next lower
numbered memory. In this mode, volume control is only
available through software control.
In Mixed Mode, operation of the switch as a volume
control or memory select is governed by the time duration
of the switch closure: either short or long. The
discrimination of short and long pulses is set by
a programmable, time−threshold value, from 1 s to 5 s in 1 s
increments. An additional programmable parameter
determines whether the short pulses refer to volume−control
operation or memory−select operation.
If long pulses control memory select operation, the
memory change is initiated once the switch is held for the
long pulse period without requiring the switch to be
released. In Digital VC mode or Momentary Memory Select
mode, the action takes place after the switch is released.
AGC−O
The AGC−O module is an output limiting circuit with
a fixed compression ratio of ∞ : 1. The limiting level is
programmable as a level measured in dB from full scale. The
maximum output of the device is 0 dBFS.
The AGC−O module has its own level detector, with
programmable attack and release time constants.
Graphic Equalizer
SA3229 has a 8−band graphic equalizer. Each band
provides up to 24 dB of gain adjustment in 1 dB increments.
Biquadratic Filters
Additional frequency shaping can be achieved by
configuring generic biquad filters. The transfer function for
each of the biquad filters is as follows:
H(z)
+
b0 ) b1
1 ) a1
z^*1 ) b2
z^*1 ) a2
z^*2
z^*2
NOTE:
The a0 coefficient is hard−wired to always be
‘1’. The coefficients are each 16 bits in length
and formatted as one sign bit, one integer bit and
14 fractional bits. This maps onto a decimal
range of −2.0 to 2.0 before quantization (−32767
to 32767 after quantization).
Thus, before quantization, the floating−point coefficients
must be in the range −2.0 ≤ x < 2.0 and quantized with the
function:
round(x 2¹⁴)
After designing a filter, the quantized coefficients can be
entered into the PreBiquads or PostBiquads tab in the
Interactive Data Sheet. The coefficients b0, b1, b2, a1, and
a2 are as defined in the transfer function above. The
parameters meta0 and meta1 do not have any effect on the
signal processing, but can be used to store additional
information related to the associated biquad.
The underlying code in the product components
automatically checks all of the filters in the system for
stability (i.e., the poles have to be within the unit circle)
before updating the graphs on the screen or programming
the coefficients into the hybrid. If the Interactive Data Sheet
receives an exception from the underlying stability checking
code, it automatically disables the biquad being modified
and displays a warning message. When the filter is made
stable again, it can be re−enabled.
Also note that in some configurations, some of these
filters may be used by the product component for
microphone/telecoil compensation, low−frequency EQ, etc.
If this is the case, the coefficients entered by the user into
IDS are ignored and the filter designed by the software is
programmed instead. For more information on filter design
refer to the Biquad Filters In PARAGON Digital Hybrid
information note.
Tinnitus Treatment Noise
The Tinnitus Treatment noise is generated using white
noise generator hardware and shaping the generated noise
using four 2^nd order biquadratic filters. The filter parameters
are the same coefficients as those presented in the
Biquadratic Filters section.
The Tinnitus Treatment noise can be added into the signal
path at two possible locations: before the VC (before the
AGC−O, but compensated for the Wideband Gain) or after
the VC (between the last generic biquad and the Cross
Fader).
If the noise is injected before the VC then the level of the
noise will change along with the rest of the audio through the
device when the VC is adjusted. If the noise is injected after
the VC it is not affected by VC changes.
EVOKE Lite Acoustic Indicators
Ten Acoustic Indicators are available for indicating
events. Each indicator is fixed to a particular event. Any
event can have its assigned indicator enabled or disabled
although not always independently. Individual enable/
disable control is provided for the following event or group
of events:
• Power on reset (POR)
• Four memory selects
• Volume Up and Volume Down
• Volume Max and Volume Min
• Low Battery
Each Acoustic Indicator is made up of up to four faded
tones. A faded tone exhibits a 64 ms fade−in and fade−out
transition time. The duration of an Acoustic Indicator is
configurable, with a maximum value of 6.35 seconds.
Power Management
SA3229 has three user−selectable power management
schemes to ensure the hearing aid dies gracefully at the end
of battery life. Shallow reset, Deep reset and Advanced
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