CPC5622

12

www.ixysic.com

R03

Where:

sheet.

the application circuits in this data sheet.

sheet.

The recommended components in the application

circuits yield a gain 0.26 dB at 2000 Hz. IXYS

Integrated Circuits Division Application Note AN-117

Customize Caller ID Gain and Ring Detect Voltage Threshold

is a spreadsheet for trying different component values

in this circuit. Changing the CID gain will also change

the ringing detection threshold and the timing of the

polarity reversal detection pulse, if used.

For single-ended receive applications where only one

RX output is used, the snoop circuit gain can be

adjusted back to 0 dB by changing the value of the

snoop series resistors R6, R7, R44 and R45 from

1.8M

 to 715k This change results in negligible

modification to the ringing detect threshold.

3.3 Off-Hook Operation: OH=0

3.3.1 Receive Signal Path

Signals to and from the telephone network appear on

the tip and ring connections of the application circuit.

Receive signals are extracted from transmit signals by

the LITELINK two-wire to four-wire hybrid then

converted to infrared light by the receive path LED.

The intensity of the light is modulated by the receive

signal and coupled across the electrical isolation

barrier by a reflective dome.

On the low voltage side of the barrier, the receive

signal is converted by a photodiode into photocurrent.

The photocurrent, a linear representation of the

receive signal, is amplified and converted to a

differential voltage output on RX+ and RX-.

Variations in gain are controlled to within ±0.4 dB by

factory gain trim, which sets the output to unity gain.

To accommodate single-supply operation, LITELINK

includes a small DC bias on the RX+ and RX- outputs

of 1.0 Vdc. Most applications should AC couple the

receive outputs as shown in Figure 4.

LITELINK may be used for differential or single-ended

output as shown in Figure 4. Single-ended use will

produce 6 dB less signal output amplitude. Do not

exceed 0 dBm referenced to 600

 (2.2 V

output level with the standard application circuits. See

application note AN-157, Increased LITELINK III Transmit

Power for more information.

Figure 4. Differential and Single-ended Receive

Path Connections to LITELINK

3.3.2 Transmit Signal Path

Transmit signals from the CODEC to the TX+ and TX-

pins of LITELINK should be coupled through

capacitors as shown in Figure 5 to minimize dc offset

errors. Differential transmit signals are converted to

single-ended signals within LITELINK then coupled to

the optical transmit amplifier in a manner similar to the

receive path.

The output of the optical amplifier is coupled to a

voltage-to-current converter via a transconductance

stage where the transmit signal modulates the

telephone line loop current. As in the receive path, the

transmit gain is calibrated at the factory, limiting

insertion loss to 0 ±0.4 dB.

Differential and single-ended transmit signals into

LITELINK should not exceed a signal level of 0 dBm

referenced to 600

 (or 2.2 V

levels above 0dBm consult the application note

AN-157, Increased LITELINK III Transmit Power for more

information.



20

TOTAL

+



2

1

fC

SNP



2

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

+

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

log

=

RX+

RX-

RX+

RX+

RX

RX-

0.1μF

0.1μF

0.1μF

LITELINK

Low-Voltage Side CODEC

or Voice Circuit