RHYTHM R3110
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6
FUNCTIONAL BLOCK DESCRIPTION
Analog Input and Output Stages
R3110 provides two analog inputs: Microphone 1 (MIC),
and Telecoil (TC−IN). The following input modes can be
selected:
1. Simple Mode, which features two channels of
compression. This mode is ideally suited for
analog replacement hearing aids and for quiet
listening environments.
2. Advanced Mode, where the addition of Adaptive
Noise Reduction and Adaptive Feedback
Cancellation offers the user better listening comfort
in noisier listening environments.
NOTE: You can set Advanced Mode as the default
by tying the MS pin to the VB pin.
3. Telecoil Mode (TCM), where R3110 is not
processing any microphone signal and is only
sampling the signal coming from a telecoil device
present on the TC−IN pin.
Important Note
: All input transducers (microphones and
telecoil) shall use the VREG pin for power and the MGND
pin for ground. All unused analog inputs shall be connected
to MGND. The MGND pin shall not be connected to the
main ground pin (GND)
R3110 includes two 2nd−order sigma−delta analog to
digital converters that are used to sample the relevant analog
inputs, according to the selected input mode in which the
device is operating. The inputs are preconditioned with
anti−alias filtering and amplification before being supplied
to the Digital Signal Processing engine (DSP).
After processing by the DSP, a digital to analog converter
comprised of a 3rd−order sigma−delta modulator and an
H−bridge will render the processed signal into the analog
domain. The modulator accepts digital audio data from the
DSP path and converts it into a 64−times oversampled, 1−bit
PDM data stream, which is then supplied to the H−bridge.
The H−bridge is a specialized CMOS output driver used to
convert the 1−bit data stream into a low−impedance,
differential output voltage waveform suitable for driving
zero−biased hearing aid receivers.
Microphone and Receiver Selection
R3110 supports multiple types of three−terminal hearing
aid microphones operating from a regulated voltage of
0.9 V. Acoustic−referred threshold values for the Wide
Dynamic Range Compressor (WDRC) engine and acoustic
indicators are also determined by the microphone sensitivity
and frequency response. The adaptive feedback suppression
and adaptive noise reduction automatically adjust their
behavior according to the properties of the selected
microphone.
Similarly to the microphone selection, R3110 is designed
to support a variety of zero−bias hearing aid receivers. For
high power devices, a first order RC filter is recommended
to ensure a clean power supply to R3110, despite the large
current required by the receiver. Refer to Figure 3 for a
recommended high−power output filter.
Figure 3. Typical High−Power Filter
Telecoil Support
R3110 is designed to support multiple uses of a telecoil
device. It allows transitioning into telecoil mode upon the
closing of a switch connected to the TC−EN pin (#10). A
static 2−pole switch can be used to initiate such a transition.
Alternatively, with a magnetic sensitive switch (such as a GMR
or Reed switch) connected to TC−EN, the static magnetic
field of a telephone handset will close the switch whenever
the handset is brought close to the hearing aid, resulting in
R3110 changing to telecoil mode (TCM). When this
functionality is used, the MS pin (#9) shall be left floating.
For both cases, static and automatic telecoil control, a
debouncing algorithm is used to prevent undesired
switching in and out of telecoil mode due to mechanical
switch bounces. Upon detecting a close to open switch
transition, the debounce algorithm monitors the switch
status and switches R3110 out of telecoil mode and back to
the initial mode, only once the switch signal has been
continuously sampled open over a 1.5 seconds period.
A third option allows R3110 to enter the telecoil mode
when only a momentary push button is used on the mode
select pin (MS) and no switch is present on TC−EN. Please
refer to the Push Button Support section for additional details.
