SI3225-FQ Datasheet, PDF (49/108 Pages) Silicon image – DUAL PROSLIC® PROGRAMMABLE CMOS SLIC/CODEC

Si3220/Si3225
Si3220
V_RING
RING
DC Offset
TIP
GND
V_TIP
V_CM
DC Offset
-80V
V_OFF
V_RING
V_BATR
V_OVRING
Figure 25. Internal Unbalanced Ringing
To enable unbalanced ringing, set the RINGUNB bit of
the RINGCON register. As with internal balanced
ringing, the unbalanced ringing waveform is generated
by using one of the two on-chip tone generators
provided in the Si3220. The tone generator used to
generate ringing tones is a two-pole resonator with
programmable frequency and amplitude. Since ringing
frequencies are low compared to the audio band
signaling frequencies, the ringing waveform is
generated at a 1 kHz rate.
The ringing generator is programmed via the RINGAMP,
RINGFREQ, and RINGPHAS registers. The RINGOF
register is used in to set the dc offset position around
which the RING lead will oscillate. The dc offset is set at
a dc point equal to VCM – (–80 V + VOFF), where
VOFF is the value that is input into the RINGOF RAM
location. Positive VOFF values will cause the dc offset
point to move closer to ground (lower dc offset), and
negative VOFF values will have the opposite effect. The
dc offset can be set to any value; however, the ringing
signal will be clipped digitally if the dc offset is set to a
value that is less than half the ringing amplitude. In
general, the following equation must hold true to ensure
the battery voltage is sufficient to provide the desired
ringing amplitude:
|V_BATR| > |V_RING,PK + (–80 V + V_OFF) + V_OVRING|
It is possible to create reverse polarity unbalanced
ringing waveforms (the TIP lead oscillates while the
RING lead stays constant) by setting the UNBPOLR bit
of the RINGCON register. In this mode, the polarity of
VOFF must also be reversed (in normal ringing polarity
VOFF is subtracted from –80 V, and in reverse polarity,
ringing VOFF is added to –80 V).
Ringing Coefficients
The ringing coefficients are calculated in decimals for
sinusoidal and trapezoidal waveforms. The RINGPHAS
and RINGAMP hex values are decimal to hex
conversions in 16-bit 2’s complement representations
for their respective RAM locations.
To obtain sinusoidal RINGFREQ RAM values, the
RINGFREQ decimal number is converted to a 24-bit 2’s
complement value. The lower 12 bits are placed in
RINGFRLO bits 14:3. RINGFRLO bits 15 and 2:0 are
cleared to 0. The upper 12 bits are set in a similar
manner in RINGFRHI, bits 13:3. RINGFRHI bit 14 is the
sign bit, and RINGFRHI bits 2:0 are cleared to 0.
For example, the register values for
RINGFREQ = 0x7EFD9D are as follows:
RINGFRHI = 0x3F78
RINGFRLO = 0x6CE8
To obtain trapezoidal RINGFREQ RAM values, the
RINGFREQ decimal number is converted to an 8-bit, 2’s
complement value. This value is loaded into RINGFRHI.
RINGFRLO is not used.
V_TIP-RING
V_OFF
T = 1/freq
t_RISE
time
Figure 26. Trapezoidal Ringing Waveform
Ringing DC Offset Voltage
A dc offset voltage can be added to the Si3220’s ac
ringing waveform by programming the RINGOF RAM
location to the appropriate setting. The value of
RINGOF is calculated as follows:
RINGOF = -^V----^O----^F---^F-- × 2¹⁵
160.8
Rev. 1.0
49