STLC3040

The subscriber line codec-filter, STLC3040, is fabricated in BiCMOS (12V bipolar / 5V CMOS) technology. It uses Digital-Signal-Processing( DSP) to implement central-office telephone interface features: DC-feed, Supervision, PCMCodec- Filter, Ring, Teletax metering (TTX) and

Test functions. The STLC3040 is fully programmable and needs few external resistors and capacitors. The STLC3040 interfaces the subscriber's line via the High-Voltage (HV) (L3000N, L3000S, STLC3170) device and the central-office back- plane via a GCI compatible interface (see fig.2). The GCI handles all STLC3040 control and voice channel.

The STLC3040 processes the transversal linecurrent sensed by the ST HV (L3000N, L3000S, STLC3170) Line Driver Circuit and generates voltage-drive to the line via the HV (L3000N, L3000S, STLC3170), thus synthetizing the impedances required by various world administrations .

Line impedances as well as the two-to-four wire conversion synthesis are software programmable. Also Transmit (Tx) and Receive(Rx) AC frequency response, determined by DSP-filters, guarantee voice-band flat-response. Tx and Rx Gains are programmable as well. Digitized voice can be encoded on A-law or u-law.

The DC characteristic is obtained by selecting limit-current value, DC-feed resistance (2 X 50W steps) and Drop-voltage. It also permits On-hook transmission and TTX pulse injection with filtering and shaping. TTX metering pulse generation (12 or 16kHz) has programmable amplitude up to 10 Vrms.

Off-hook detection with programmable thresholds is possible in all operating modes as described in section 4.

Ring-signal with zero-crossing start/stop injection is generated on chip with programmable frequency and amplitude. In addition, when Ringtrip is detected, the Ring-signal is automatically disconnected at the next zero-crossing.

Power consumption is kept low by providing a "Power-Down" mode where the HV-SLIC is switched off (Power Denial). A set of internal resistors connected to the line allows Off-hook detection in this mode. Overall power dissipation is around 50mW (max.) in Power Down mode.

Several testing features are included in the STLC3040, both for self-test and to test line leakage, capacitance ..etc, thus saving on test equipment and relays. Measured DC quantities are digitized and sent via the B1 voice channel to the backplane. With proper software selection each signal can be modulated by a 1KHz carrier before being sent to B1 voice channel. Programmable linear code, software selectable, boosts the calculation resolution.

Sigma-Delta converters (ASD: Analog, DSD: Digital) make the conversion independent of technology parameters (fig. 3).