Si3050 datasheet(33/128 Pages) SILABS

33 / 128 page

Si3050 + Si3011/18/19

Rev. 1.5

5.18. Ring Detection

The ring signal is resistively coupled from TIP and RING

to the RNG1 and RNG2 pins. The Si3050 supports

either full- or half-wave ring detection. With full-wave

ring detection, the designer can detect a polarity

reversal of the ring signal. See “5.25.Caller ID” on

page 36. The ring detection threshold is programmable

with the RT bit (Register 16, bit 0) and RT2 bit

(Register 17, bit 4). The ring detector output can be

monitored in three ways. The first method uses the

RGDT pin. The second method uses the register bits,

RDTP, RDTN, and RDT (Register 5). The final method

uses the DTX output.

The ring detector mode is controlled by the RFWE bit

(Register 18, bit 1). When the RFWE bit is 0 (default

mode), the ring detector operates in half-wave rectifier

mode. In this mode, only positive ring signals are

detected. A positive ring signal is defined as a voltage

greater than the ring threshold across RNG1-RNG2.

Conversely, a negative ring signal is defined as a

voltage less than the negative ring threshold across

RNG1-RNG2. When the RFWE bit is 1, the ring detector

operates in full-wave rectifier mode. In this mode, both

positive and negative ring signals are detected.

The first method to monitor ring detection output uses

the RGDT pin. When the RGDT pin is used, it defaults

to active low, but can be changed to active high by

setting the RPOL bit (Register 14, bit 1). This pin is an

open-drain output, and requires a 4.7 k pullup or

pulldown for correct operation. If multiple RGDT pins

are connected to a single input, the combined pullup or

pulldown resistance should equal 4.7 k

When the RFWE bit is 0, the RGDT pin is asserted

when the ring signal is positive, which results in an

output signal frequency equal to the actual ring

frequency. When the RFWE bit is 1, the RGDT pin is

asserted when the ring signal is positive or negative.

The output then appears to be twice the frequency of

the ring waveform.

The second method to monitor ring detection uses the

ring detect bits (RDTP, RDTN, and RDT). The RDTP

and RDTN behavior is based on the RNG1-RNG2

voltage. When the signal on RNG1-RNG2 is above the

positive ring threshold, the RDTP bit is set. When the

signal on RNG1-RNG2 is below the negative ring

threshold, the RDTN bit is set. When the signal on

RNG1-RNG2 is between these thresholds, neither bit is

set.

The RDT behavior is also based on the RNG1-RNG2

voltage. When the RFWE bit is 0, a positive ring signal

sets the RDT bit for a period of time. When the RFWE

bit is 1, a positive or negative ring signal sets the RDT

bit.

The RDT bit acts like a one shot. When a new ring

signal is detected, the one shot is reset. If no new ring

signals are detected prior to the one shot counter

reaching 0, then the RDT bit clears. The length of this

count is approximately 5 seconds. The RDT bit is reset

to 0 by an off-hook event. If the RDTM bit

(Register 3, bit 7) is set, a hardware interrupt occurs on

the AOUT/INT pin when RDT is triggered. This interrupt

can be cleared by writing to the RDTI bit

(Register 4, bit 7). When the RDI bit (Register 2, bit 2) is

set, an interrupt occurs on both the beginning and end

of the ring pulse as defined by the RTO bits

(Register 23, bits 6:3). Ring validation may be enabled

when using the RDI bit.

The third method to monitor detection uses the DTX

data samples to transmit ring data. If the ISOcap is

active (PDL=0) and the device is not off-hook or in

on-hook line monitor mode, the ring data is presented

on DTX. The waveform on DTX depends on the state of

the RFWE bit.

When RFWE is 0, DTX is –32768 (0x8000) while the

RNG1-RNG2 voltage is between the thresholds. When

a ring is detected, DTX transitions to +32767 when the

ring signal is positive, then goes back to –32768 when

the ring is near 0 and negative. Thus a near square

wave is presented on DTX that swings from –32768 to

+32767 in cadence with the ring signal.

When RFWE is 1, DTX sits at approximately +1228

while the RNG1-RNG2 voltage is between the

thresholds. When the ring becomes positive, DTX

transitions to +32767. When the ring signal goes near 0,

DTX remains near 1228. As the ring becomes negative,

the DTX transitions to –32768. This repeats in cadence

with the ring signal.

To observe the ring signal on DTX, watch the MSB of

the data. The MSB toggles at the same frequency as

the ring signal independent of the ring detector mode.

This method is adequate for determining the ring

frequency.

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