The concentrated range extender with gain (CREG) provides the subscriber telephone with voice frequency gain, signaling and supervision range extension, and increased loop current so that customer loops beyond the standard central office range can be served. CREG circuits, called 7A REG's, are shared among many customer lines by being connected inside the concentrating portion of an ESS switching machine. Such sharing realizes a typical three-to-one cost advantage over standard per-line treatment. Autonomous operation of the 7A REG minimizes the impact on call processing in the ESS machines, but results in a moderately complex circuit. To satisfy cost and size requirements the 7A REG design uses custom integrated circuits, low profile transformer and relays, and computercontrolled production testing. The 7A REG circuits are configured two on a card. Three hundred twenty 7A REG circuits (160 cards) mount in a standard 7 ft ESS bay together with a control panel, peripheral decoders (in No. 2/2B ESS), and dual -78 V power supplies. A twelve-to-one reduction in effective circuit volume is achieved over earlier nonconcentrated circuits due to the concentration ratio and smaller physical size.

The technique of time-averaging interpolation provides a means for obtaining telephone quality digital-to-analog conversion using conventional digital integrated-circuit processing. This approach has been adopted in a monolithic circuit that decodes the 8-kHz companded PCM commonly used in voiceband communication systems. The circuit, realized in a standard buried collector bipolar technology, contains 300 integrated injection logic(I^{2}L)gates together with a current-driven resistive ladder network. The performance of the decoder exceeds typical toll network objectives.

A novel technique called interpolation has been used to integrate a per-channel PCM encoder in a standard digital circuit technology. This encoder converts voiceband analog signals to both an oversampled 1-bit code and uniform PCM with μ-law companding noise. The circuit comprises approximately 550 integrated injection logic gates together with a resistive digital-to-analog converter, a voltage reference, and a simple differential amplifier. The encoder is part of a full PCM codec chip set suitable for a broad range of voiceband telecommunication applications.

The above paper1 proposed an interpolative encoder for per-channel voiceband application. A description is given here of a very simple bidirectional shift register for use as a digital accumulator in such encoders.