Abstract: A telephone line transformer having less iron in its core can be achieved by providing the transformer with a third winding to balance out the DC magnetization produced by the tip and ring windings. This winding must be bypassed by a capacitor of fairly large size to provide sufficiently low impedance at voice frequencies to prevent voice currents from flowing through the balancing winding. A capacitor of large enough size, however, may prevent the development of sufficient voltage change during dial pulsing for reliable dial pulse detection. This problem is solved by providing a dynamic capacitor bypass arrangement which includes a negative feedback operational amplifier together with a balancing winding bypass capacitor of reasonable size. The dynamic circuit magnifies the bypass capacitance with respect to voice frequency signals but saturates during dial pulsing and thus leaves the capacitance temporarily unamplified. The arrangement thus yields an effective bypass capacitance of approximately 35,000.mu.

Abstract: A PCM coder/decoder circuit is disclosed employing a counter that counts clock pulses until a transmitting ramp voltage equals that of an outgoing speech sample. The encoded count is transmitted in complemented form to the distant station where it is eventually entered into a counter similar to that of the transmitting station. Clock pulses are then applied to the receiving counter until a carry is generated at which time a receiving ramp waveform is disconnected from a decoding capacitor. The counter at the receiving station is enabled prematurely to generate the count so that the "reaction time" of the physical circuit components is compensated for. Compensation of this reaction time is important in reducing the nonlinear distortion that would otherwise be introduced when the ramp waveforms that are employed are of the companded type. The circuit operates in an overlap fashion, encoding and receiving in one field and decoding and transmitting in another field.