SI3232 datasheet(39/128 Pages) SILABS

39 / 128 page

Si3232

Preliminary Rev. 0.96

In addition to the variable frequency and amplitude,

there is a selectable dc offset (VOFF) that can be added

to the waveform. The dc offset is defined in the RINGOF

RAM location. The ringing generator has two timers

which 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. Once this is done, the TAEN and TIEN bits are

set as desired. Ringing state is invoked by a write to the

linefeed register. At the expiration of RINGTA, the

Si3232 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.

4.6.2. Internal Trapezoidal Ringing

In addition to the traditional sinusoidal ringing

waveform, the Si3232 can generate a trapezoidal

ringing waveform similar to the one illustrated in

Figure 19.

The

RINGFREQ,

RINGAMP,

and

RINGPHAS RAM locations are used for programming

the ringing wave shape as follows:

RINGPHAS = 4 x Period x 8000

RINGAMP = (Desired V/160.8 V) x (215)

RINGFREQ = (2 x RINGAMP) / (tRISE x 8000)

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.

where

So, for a 90 VPK, 20 Hz trapezoidal waveform with a

crest factor of 1.3, the period is 0.05 s, and the rise time

requirement is 0.015 s.

RINGPHAS = 4 x 0.05 x 8000 = 1600 (0x0640)

RINGAMP = 90/160.8 x (215) = 18340 (0x47A5)

RINGFREQ = (2 x RINGAMP) (0.0153 x 8000) =

300 (0x012C)

The time registers and interrupts described in the

sinusoidal ring description also apply to the trapezoidal

ring waveform.

4.7. Internal Unbalanced Ringing

The Si3232 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 18

illustrates the internal unbalanced ringing waveform.

Figure 18. Internal Unbalanced Ringing

To enable unbalanced ringing, set the RINGUNB bit of

the RINGCON register. As is the case with internal

balanced ringing, the unbalanced ringing waveform is

generated by using the on-chip ringing tone generator.

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

RINGAMP

--- .00789

1.99211

---------------------

()

160.173

---------------------

273

0x111

tRISE

---T1

-----------

–

⎝⎠

⎛⎞

TPeriod

fRING

--------------

desired crest factor

RING

TIP

VRING

Si3232

DC Offset

GND

VTIP

VRING

VBATR

-80V

VOVRING

DC Offset

VOFF

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