RPT-85

The RPT-85 has the following features including Automatic ALBO Function;Low-Power Operation (100mW);Wide Data Rate Range <100 kbit/s to >3 Mbit/s;Compatible with T1, CEPT/E1, and T1C Systems;Pin Compatible with XR-T445.

The RPT-85 is an integrated circuit that performs the active functions required for regenerative PCM repeaters. It can operate from less than 100kHz to greater than 3MHz. In PCM systerms, information is transmitted by the presence or absence of bipolar pulses in specified time slots. The RPT-85 repeater automatically adjusts gain to optimize signal levels, determines if a pulse is present or not, and retransmits the reconstructed pulses.Bipolar-pulse transmission, the transmission of alternately positive and negative pulses, is used on repeater lines to remove the DC component present in unipolar PCM pulse trains.This also places the principal energy components in the 0-1.544MHz band, as opposed to the 0-3.088MHz band for unipolar pulse trains. The absence of a DC component in bipolar pulse trains permits the repeater to be transformer-coupled to the repeater line and helps prevent time-shifting of the regenerator firing levels with variations in input pulse density (see Figure 1).

The preamplifierstage amplifies the inputsignal and applies it to the three comparators labeled data detector, clock detector,and peak detector, respectively. Each comparator provides an output whenever the signal exceeds the trip point on both positive and negative pulses. Each comparator trips at a different threshold. The data detector is set to trip at the 540/ point; the clock detector trips at the 73% point; and the peak detector trips at peak amplitude. Thresholds and waveforms are shown in Figure 3.The clock detector output locks the oscillator to the input frequency. The following amplifier stages shape the oscillator output and shift it in time. The phase-shift capacitor is selected to provide additional phase-shift so that the strobe pulses will occur at the center of the incoming pulses. This provides optimum timing for determining if a "1" or a "0" is present. A 0-to-30pF capacitor (10pF is typical at 1.544MHz) will optimize the performance of the complete repeater.