ia3222 integration, ia3222 Datasheet - Page 34

• Manufacturer Part Number: ia3222
• Description: Ia3222/ia3223 Ez Daa? Chipset With Analog Interface
• Manufacturer: integration

Measuring Loop-Current Changes through the Received Audio signal
The Line Side senses line-current information and encodes it for the System Side as a DC offset superimposed onto the received
audio data. Since modem DSP algorithms routinely remove low-frequency components from the incoming data stream, DC offset is
not a problem, but it needs to be taken into account in headroom calculations.
The current sensor has considerable DC offset, which needs to be calibrated to obtain good current-sensor performance. This is
achieved by adding a DC component to the transmitted data proportional to the received DC offset using the following algorithm:
• Disable the current sensor by setting bit LP1 in the Line-Side LSB programming register. This cancels the DC component due to
• Add a small amount (20 to 50mV) of DC offset to the outgoing data and note the amount of change in DC offset in the incoming
• Add a DC offset to all transmitted data equal to the received DC offset divided by the DC-offset correction factor, based on the
• Enable the current sensor. The loop current can now be read as incoming-data DC offset from the DC reference voltage. The
the loop current itself and leaves the current sensor’s offset component as DC offset in the received data stream.
data. The ratio of incoming to outgoing DC offset changes is the DC-offset correction factor, for which the sign must be retained.
desired DC reference for the received signal. This is normally the same voltage as that of the ACREF pin.
sensitivity of the current sensor is approximately 1.25 mV of DC offset for every 1 mA of loop current. Note that both the DC-offset
correction factor and the gain change with the Line-Side termination impedance setting.
IA3222/IA3223
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