Si3220/Si3225
Internal Sinusoidal Ringing
Internal Trapezoidal Ringing
A sinusoidal ringing waveform is generated by the on- In addition to the traditional sinusoidal ringing
chip digital tone generator. The tone generator used to waveform, the Dual ProSLIC can generate a trapezoidal
generate ringing tones is a two-pole resonator with a ringing waveform similar to the one illustrated in
programmable frequency and amplitude. Since ringing Figure 26 on page 49. The RINGFREQ, RINGAMP, and
frequencies are low compared to the audio band RINGPHAS RAM addresses are used for programming
signaling frequencies, the sinusoid is generated at a the ringing wave shape as follows:
1 kHz rate. The ringing generator is programmed via the
RINGFREQ, RINGAMP, and RINGPHAS registers. The
equations are as follows:
RINGPHAS = 4 x Period x 8000
RINGAMP = (Desired V/160.8 V) x (2 )
RINGFREQ = (2 x RINGAMP)/(t x 8000)
15
RISE
2πf
RINGFREQ is a value that is added or subtracted from
the waveform to ramp the signal up or down in a linear
fashion. This value is a function of rise time, period, and
amplitude, where rise time and period are related
through the following equation for the crest factor of a
trapezoidal waveform.
--------------------
coeff = cos
1000Hz
RINGFREQ = coeff × 223
DesiredVPK
---------------------------------
160.173V
1
15
1 – coeff
--
RINGAMP =
----------------------- × (2 ) ×
1 + coeff
4
3
1
--
----------
tRISE
=
T 1 –
CF2
RINGPHAS = 0
4
For example, to generate a 60 V
(87 V ), 20 Hz
PK
rms
ringing signal, the equations are as follows:
where
1
--------------
T = Period =
2π20
fRING
--------------------
coeff = cos
= 0.9921
1000Hz
CF = desired crest factor
RINGFREQ = 0.9921 × (223) = 8322461 =
0x7EFD9D
So, for a 90 V , 20 Hz trapezoidal waveform with a
PK
crest factor of 1.3, the period is 0.05 s, and the rise time
requirement is 0.015 s.
1
15
85
RINGPHAS = 4 x 0.05 x 8000 = 1600 (0x0640)
RINGAMP = 90/160.8 x (2 ) = 18340 (0x47A5)
00789
--
---------------------
RINGAMP =
--------------------- × (2 ) ×
= 273= 0x111
4
160.173
15
1.99211
In addition to the variable frequency and amplitude, a
RINGFREQ = (2 x RINGAMP)/(0.0153 x 8000) = 300
selectable dc offset (V
), which can be added to the
(0x012C)
OFF
waveform, is included. The dc offset is defined in the
The time registers and interrupts described in the
sinusoidal ring description also apply to the trapezoidal
ring waveform:
RINGOF RAM location.
As with the tone generators, the ringing generator has
two timers which function as described above. They
allow on/off cadence settings up to 8 s on/8 s off. In
addition to controlling ringing cadence, these timers
control the transition into and out of the ringing state.
To initiate ringing, the user must program the
RINGFREQ, RINGAMP, and RINGPHAS RAM
addresses as well as the RINGTA and RINGTI registers
and select the ringing waveshape and dc offset. After
this is done, TAEN and TIEN bits are set as desired.
The ringing state is invoked by a write to the linefeed
register. At the expiration of RINGTA, the Dual ProSLIC
turns off the ringing waveform and goes to the on-hook
transmission state. At the expiration of RINGTI, ringing
is initiated again. This process continues as long as the
two timers are enabled and the linefeed register
remains in the ringing state.
Internal Unbalanced Ringing
The Si3220 also provides the ability to generate a
traditional battery-backed unbalanced ringing waveform
for ringing terminating devices that require a high dc
content or for use in ground-start systems that cannot
tolerate a ringing waveform on both the TIP and RING
leads. The unbalanced ringing scheme applies the
ringing signal to the RING lead; the TIP lead remains at
the programmed VCM voltage that is very close to
ground. A programmable dc offset can be preset to
provide dc current for ring trip detection. Figure 25
illustrates the internal unbalanced ringing waveform.
48
Rev. 1.0
SILICONIMAGE [ Silicon image ]
