Si3056
Si3018/19/10
There are two selections that are useful for satisfying setting the RPOL bit (Register 14, bit 1). This pin is a
non-standard ac termination requirements. The 350 Ω + standard CMOS output. If multiple RGDT pins are
(1000 Ω || 210 nF) impedance selection is the ANSI/ connected to a single input, the combined pullup or
EIA/TIA 464 compromise impedance network for trunks. pulldown resistance should equal 4.7 kΩ.
The last ac termination selection, ACIM[3:0] = 1111, is
designed to satisfy minimum return loss requirements
for every country in the world that requires a complex
termination. For any of the ac termination settings, the
programmable hybrid can be used to further reduce
near-end echo. See “5.13.Transhybrid Balance” for
more details.
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.
5.13. Transhybrid Balance
The Si3056 contains an on-chip analog hybrid that
performs the 2- to 4-wire conversion and near-end echo
cancellation. This hybrid circuit is adjusted for each ac
termination setting selected.
The Si3056 also offers a digital filter stage for additional
near-end echo cancellation. For each ac termination
setting selected, the eight programmable hybrid
registers (Registers 45-52) can be programmed with
coefficients to provide increased cancellation of real-
world line anomalies. This digital filter can produce
10 dB or greater of near-end echo cancellation in
addition to the echo cancellation provided by the analog
hybrid circuitry.
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
5.14. Ring Detection
The ring signal is resistively coupled from TIP and RING
to the RNG1 and RNG2 pins. The Si3056 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 “5.21.Caller ID” on
page 32. The ring detection threshold is programmable
with the RT bit (Register 16, bit 0). 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.
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. 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
communications link 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.
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 When RFWE is 0, DTX is –32768 (0x8000) while the
voltage less than the negative ring threshold across RNG1-RNG2 voltage is between the thresholds. When
RNG1-RNG2. When the RFWE bit is 1, the ring detector a ring is detected, DTX transitions to +32767 when the
operates in full-wave rectifier mode. In this mode, both ring signal is positive, then goes back to –32768 when
positive and negative ring signals are detected.
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.
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 When RFWE is 1, DTX sits at approximately +1228
Rev. 1.05
29
SILICON [ SILICON ]
